Effects of a low-fat, high-carbohydrate diet on VLDL-triglyceride assembly, production, and clearance

Bifidobacterium lactis IDCC 4301 (B. lactis Fit™) supplementation effects on body fat, serum triglyceride, and adipokine ratio in obese women: a randomized clinical trial

Obesity is a common metabolic disease characterized by abnormal fat accumulation. It contributes to health issues, such as type 2 diabetes, cardiovascular disease, and dyslipidemia, necessitating continuous management through diet and physical activity. Probiotics, particularly Bifidobacterium lactis IDCC 4301 (B. lactis Fit™), have shown promise in positively regulating the gut microbiota. Therefore, this study aimed to evaluate the anti-obesity effect of B. lactis IDCC 4301 (B. lactis Fit™) in obese women. A randomized, double-blind, placebo-controlled, parallel-arm study was performed in 99 volunteers with a body mass index (BMI) of 25-30 kg m-2. The participants were randomly assigned to probiotics (n = 49, >5.0 × 109 CFU day-1) or placebo (n = 50) groups. Body fat, lipid profiles, and adipokine levels were assessed at baseline and at 12 weeks. After 12 weeks, changes in total fat (placebo -0.16 ± 0.83 kg; probiotics -0.45 ± 0.83 kg; p = 0.0407), trunk fat (placebo -0.03 ± 0.50 kg; probiotics -0.22 ± 0.51 kg; p = 0.0200), and serum triglyceride concentration (placebo 13 ± 60 mg dL-1; probiotics -15 ± 62 mg dL-1; p = 0.0088) were significantly different between the groups. The difference in total fat mass change between groups among postmenopausal women was greater than that of all women. A significant positive correlation was found between the change in total fat mass and log leptin/adiponectin ratio (R = 0.371, p = 0.0112) in the probiotics group. In addition, BMI (26.6 ± 1.9 kg m-2 to 26.4 ± 2.0 kg m-2, p = 0.0009) and leg fat (42 ± 5% to 41 ± 5%, p = 0.0006) significantly decreased in the probiotics group after 12 weeks, but there was no difference in the placebo group. In conclusion, B. lactis IDCC 4301 (B. lactis Fit™) may be associated with body fat loss through changes in metabolic health parameters, such as serum triglyceride and adipokine levels. The clinical trial registry number is KCT0007425 (https://cris.nih.go.kr).

Effect of daily avocado consumption for 6 mo compared with habitual diet on red blood cell fatty acid profiles and association with cardiometabolic risk factors in individuals with abdominal obesity: a randomized trial

BACKGROUND

Avocado intake improves dietary fat quality, but the subsequent impact on red blood cell (RBC) saturated (SFA), monounsaturated (MUFA), polyunsaturated (PUFA), and trans-fatty acid (TFA) composition and association with cardiometabolic health, has not been elucidated.

OBJECTIVES

To compare the effect of consuming 1 avocado/d relative to habitual diet (HAB) on RBC-FA profiles, and their association with visceral adiposity and cardiometabolic risk factors (CMRFs) in individuals with abdominal obesity.

METHODS

RBC-FA profiling at baseline, 3- and 6 mo was conducted in participants (n = 994) from the Habitual Diet and Avocado Trial (HAT). HAT was a multisite, free-living, parallel-arm intervention study in which participants were randomly assigned to either the avocado-supplemented group (AVO, usual diet with 1 avocado/d) or the HAB group (usual diet with limited avocado intake) for 6 mo. Changes in RBC-FA profiles, a secondary outcome measure, were determined within and between groups using linear regression and mixed effect models, adjusting for age, sex, BMI, clinical site, smoking status, and percentage of energy intake from fat at baseline. The association between changes in RBC-FAs with visceral adiposity measures and CMRFs was assessed after covariate and False Discovery Rate (FDR <0.05) adjustment.

RESULTS

No major differences in RBC-FA profiles were observed between groups, with the exception of MUFA cis-vaccenic [18:1n-7c], which was significantly higher in AVO (β: 0.11 [0.05, 0.17]) compared with the HAB (β: 0.03 [-0.03, 0.08]) participants. In the HAB but not AVO group, increases in MUFA cis (18:1n-7c, oleic [18;1n-9c], erucic [22:1n-9c]) and MUFA trans (palmitelaidic [16:1n-7t], vaccenic [18:1n-7t], elaidic [18:1n-9t], and petroselaidic [18;1n-10-12t), as well as PUFA γ-linolenic [18:3n-6], dihomo-γ-linolenic [20:3n-6], arachidonic [20:4n-6], and α-linolenic [18:3n-3] were associated with unfavorable changes in visceral adiposity measures, lipid profiles, glucose, insulin and high sensitivity C-reactive protein concentrations.

CONCLUSIONS

Daily avocado intake over 6-mo modified RBC-MUFA composition, notably 18:1n-7c, and potentially mitigated some of the unfavorable individual RBC-FA-CMRF associations observed over time in the HAB group. This trial was registered at https://clinicaltrials.gov/study as NCT03528031.

Hepatic fatty acid and glucose handling in metabolic disease: Potential impact on cardiovascular disease risk

The prevalence of metabolic diseases, including type 2 diabetes mellitus (T2DM) and metabolic dysfunction-associated steatotic liver disease (MASLD) is increasing. Although invariably associated with obesity, the importance of fat deposition in non-adipose tissue organs has yet to be fully explored. Pathological ectopic fat deposition within the liver (known as (MASLD)) has been suggested to underlie the development of T2DM and is now emerging as an independent risk factor for cardiovascular disease (CVD). The process of hepatic de novo lipogenesis (DNL), that is the synthesis of fatty acids from non-lipid precursors (e.g. glucose), has received much attention as it sits at the intersect of hepatic glucose and fatty acid handling. An upregulation of the DNL pathway has been suggested to be central in the development of metabolic diseases (including MASLD, insulin resistance, and T2DM). Here we review the evidence to determine if hepatic DNL may play a role in the development of MASLD and T2DM and therefore underlie an increased risk of CVD.

Adipose tissue in cortisol excess: What Cushing's syndrome can teach us?

Endogenous Cushing's syndrome (CS) is a rare condition due to prolonged exposure to elevated circulating cortisol levels that features its typical phenotype characterised by moon face, proximal myopathy, easy bruising, hirsutism in females and a centripetal distribution of body fat. Given the direct and indirect effects of hypercortisolism, CS is a severe disease burdened by increased cardio-metabolic morbidity and mortality in which visceral adiposity plays a leading role. Although not commonly found in clinical setting, endogenous CS is definitely underestimated leading to delayed diagnosis with consequent increased rate of complications and reduced likelihood of their reversal after disease control. Most of all, CS is a unique model for systemic impairment induced by exogenous glucocorticoid therapy that is commonly prescribed for a number of chronic conditions in a relevant proportion of the worldwide population. In this review we aim to summarise on one side, the mechanisms behind visceral adiposity and lipid metabolism impairment in CS during active disease and after remission and on the other explore the potential role of cortisol in promoting adipose tissue accumulation.

Modelling remission from overweight type 2 diabetes reveals how altering advice may counter relapse

The development or remission of diet-induced overweight type 2 diabetes involves many biological changes which occur over very different timescales. Remission, defined by HbA1c<6.5%, or fasting plasma glucose concentration G<126 mg/dl, may be achieved rapidly by following weight loss guidelines. However, remission is often short-term, followed by relapse. Mathematical modelling provides a way of investigating a typical situation, in which patients are advised to lose weight and then maintain fat mass, a slow variable. Remission followed by relapse, in a modelling sense, is equivalent to changing from a remission trajectory with steady state G<126 mg/dl, to a relapse trajectory with steady state G≥126 mg/dl. Modelling predicts that a trajectory which maintains weight will be a relapse trajectory, if the fat mass chosen is too high, the threshold being dependent on the lipid to carbohydrate ratio of the diet. Modelling takes into account the effects of hepatic and pancreatic lipid on hepatic insulin sensitivity and β-cell function, respectively. This study leads to the suggestion that type 2 diabetes remission guidelines be given in terms of model parameters, not variables; that is, the patient should adhere to a given nutrition and exercise plan, rather than achieve a certain subset of variable values. The model predicts that calorie restriction, not weight loss, initiates remission from type 2 diabetes; and that advice of the form 'adhere to the diet and exercise plan' rather than 'achieve a certain weight loss' may help counter relapse.

The effect of orlistat in the treatment of non-alcoholic fatty liver in adolescents with overweight and obese

Nonalcoholic fatty liver disease (NAFLD), which can manifest as nonalcoholic steatohepatitis (NASH) or severe fibrosis, is the most prevalent chronic liver disease in children and adolescents. However, there is no proven cure for it so far. This study was conducted to determine whether adolescents with NAFLD would improve with treatment intervention with orlistat. This study is a randomized controlled trial (RCT). Fifty-three adolescents with overweight/obese as well as with NAFLD randomly allocated to receive orlistat (n = 27) or placebo as control (n = 26) for 12 weeks. In addition, NAFLD activity score, anthropometric factors, biochemical parameters including serum levels of lipid profiles, liver enzyme, and glucose metabolism taken from subjects at baseline and end of the study were investigated. The findings of our article indicated that orlistat improves liver enzymes (alanine transaminase and aspartate transaminase) (P =  < 0.001), steatosis score (P = 0.001), NAFLD activity score (P =  < 0.001), weight (P =  < 0.001), body mass index (BMI) (P =  < 0.001), waist circumferences (WC) (P =  < 0.001), BMI-Z score (P =  < 0.001), glucose metabolism (P = 0.001), total cholesterol (TC) (P = 0.009), low density lipoprotein-cholesterol (LDL) (P =  < 0.001), and high density lipoprotein-cholesterol HDL levels (P = 0.014) compared to the control group after adjusting for possible confounders for 12 weeks. However, no significant changes were observed on triglyceride (TG) following intake of orlistat compared to placebo after adjusting for confounders.

CONCLUSION

The findings of our study reported that orlistat improved NAFLD-related factors and metabolic syndrome-related factors compared to placebo for 12 weeks.

TRIAL REGISTRATION

(Clinical trial registry number: IRCT20220409054467N2, with a registration date of 2022-05-13).

WHAT IS KNOWN

• Among the interventions of interest for the management of pediatric NAFLD, we can mention lifestyle and pharmaceutical measures.

WHAT IS NEW

• This study was conducted to determine whether adolescents with NAFLD would improve with treatment intervention with orlistat. • The findings of our study reported that orlistat improved NAFLD-related factors and metabolic syndrome-related factors compared to placebo for 12 weeks.

Food Intake Suppresses ApoB Secretion and Fractional Catabolic Rates in Humans

BACKGROUND

Humans spend much of the day in the postprandial state. However, most research and clinical guidelines on plasma lipids pertain to blood drawn after a 12-hour fast. We aimed to study the metabolic differences of apoB lipoproteins between the fasting and postprandial states.

METHODS

We investigated plasma apoB metabolism using stable isotope tracers in 12 adult volunteers under fasting and continuous postprandial conditions in a randomized crossover study. We determined the metabolism of apoB in multiple lipoprotein subfractions, including light and dense VLDLs (very-low-density lipoproteins), IDLs (intermediate-density lipoproteins), and light and dense LDLs (low-density lipoproteins) that do or do not contain apoE or apoC3.

RESULTS

A major feature of the postprandial state is 50% lower secretion rate of triglyceride-rich lipoproteins and concurrent slowdown of their catabolism in circulation, as shown by 34% to 55% lower rate constants for the metabolic pathways of conversion by lipolysis from larger to smaller lipoproteins and direct clearance of lipoproteins from the circulation. In addition, the secretion pattern of apoB lipoprotein phenotypes was shifted from particles containing apoE and apoC3 in the fasting state to those without either protein in the postprandial state.

CONCLUSIONS

Overall, during the fasting state, hepatic apoB lipoprotein metabolism is activated, characterized by increased production, transport, and clearance. After food intake, endogenous apoB lipoprotein metabolism is globally reduced as appropriate to balance dietary input to maintain the supply of energy to peripheral tissues.

Dietary Regulation of Hepatic Triacylglycerol Content-the Role of Eucaloric Carbohydrate Restriction with Fat or Protein Replacement

Accumulation of hepatic triacylglycerol (TG) is highly associated with impaired whole-body insulin-glucose homeostasis and dyslipidemia. The summarized findings from human intervention studies investigating the effect of reduced dietary carbohydrate and increased fat intake (and in studies also increased protein) while maintaining energy intake at eucaloric requirements reveal a beneficial effect of carbohydrate reduction on hepatic TG content in obese individuals with steatosis and indices of insulin resistance. Evidence suggests that the reduction of hepatic TG content after reduced intake of carbohydrates and increased fat/protein intake in humans, results from regulation of fatty acid (FA) metabolism within the liver, with an increase in hepatic FA oxidation and ketogenesis, together with a concomitant downregulation of FA synthesis from de novo lipogenesis. The adaptations in hepatic metabolism may result from reduced intrahepatic monosaccharide and insulin availability, reduced glycolysis and increased FA availability when carbohydrate intake is reduced.

Temporal optimization of exercise to lower fasting glucose levels

Exercise stimulates glucose uptake and increases insulin sensitivity acutely. Temporally optimizing exercise timing may minimize the nocturnal rise in glucose levels. This study examined the effect of exercise timing on evening and overnight glucose concentrations in individuals who were non-obese with normal fasting glucose levels (Non-Ob; n = 18) and individuals with obesity (OB) with impaired fasting glucose levels (OB+IFG) and without (n = 16 and n = 18, respectively). Subjects were studied on three occasions (no exercise (NOEX)), morning exercise (AMEX; 0700 h) and evening exercise (PMEX; 2000 h). The evening meal was provided (1800 h) and blood samples were taken from 1740 to 0700 h and morning endogenous glucose production (EGP) was measured. Glucose and insulin concentrations increased with the dinner meal with peak concentrations being higher in OB+IFG than in OB and Non-Ob (P = 0.04). In OB+IFG, evening glucose concentrations rose above baseline levels at about 2300 h, with the glucose concentrations staying somewhat lower with AMEX and PMEX until ∼0500 h than with NOEX. In OB+IFG, insulin concentrations decreased following the dinner meal and waned throughout the night, despite the rising glucose concentrations. In the OB and Non-Ob individuals following the dinner meal, no increase in glucose concentrations occurred in the evening period and insulin levels mirrored this. No difference was observed in the morning fasting glucose levels between study days or between groups. Regardless of time of day, exercise delays the evening rise in glucose concentrations in adults with OB+IFG but does not lower morning fasting glucose levels or improve the synchrony between glucose and insulin concentrations. KEY POINTS: Insulin resistance and type 2 diabetes have been linked to disturbances of the core clock, and glucose tolerance demonstrates a diurnal rhythm in healthy humans with better glucose tolerance in the morning than in the afternoon and evening. Skeletal muscle is a primary site for insulin resistance in people with impaired glucose tolerance. In individuals with obesity and impaired fasting glucose levels (OB+IFG), following a dinner meal, glucose concentrations started to rise and continues throughout the night, resulting in elevated glucose levels, while concomitantly, insulin levels are waning. Exercise, regardless of the time of day, suppressed the rise in glucose levels in OB+IFG for many hours during the night but did not lower morning fasting glucose levels. Morning exercise was not quite as effective as evening exercise.

Short-Term Standard Diet Consumption Prior to the Oral Fat Tolerance Test Modulates the Postprandial Triglyceride Response

We hypothesized that the consumption of a 3-day standard diet (SD) prior to the oral fat tolerance test (OFTT), used to evaluate postprandial lipemia, may counteract the undesirable effects of individual dietary habits on the test results. The OFTT was applied to 22 healthy adults (11 females and 11 males), after their habitual diets (HDs) and following the consumption of a 3-day SD (45-60% energy from carbohydrate, 20-35% from fat, and 10-20% from protein). Plasma triglyceride (TG) concentrations were measured during fasting and at the fourth hour of the OFTT. A 3-day SD significantly reduced fasting and fourth-hour TG concentrations and delta TG values by 10%, 12.8%, and 22.7%, respectively. Decreases were observed in fasting and fourth-hour TG and delta TG values following the 3-day SD compared to the HD in subjects with fasting TG concentrations between 89 and 180 mg/dL (p = 0.062, p = 0.018, and 0.047, respectively). As a result, the consumption of a 3-day standardized diet prior to the OFTT may be useful to eliminate the false positive or negative effects of individual dietary habits on test results and to correctly identify individuals who should be administered the OFTT.

Liver insulinization as a driver of triglyceride dysmetabolism

Metabolic dysfunction-associated fatty liver disease (MAFLD) is an increasingly prevalent fellow traveller with the insulin resistance that underlies type 2 diabetes mellitus. However, the mechanistic connection between MAFLD and impaired insulin action remains unclear. In this Perspective, we review data from humans to elucidate insulin's aetiological role in MAFLD. We focus particularly on the relative preservation of insulin's stimulation of triglyceride (TG) biosynthesis despite its waning ability to curb hepatic glucose production (HGP). To explain this apparent 'selective insulin resistance', we propose that hepatocellular processes that lead to TG accumulation require less insulin signal transduction, or 'insulinization,' than do those that regulate HGP. As such, mounting hyperinsulinaemia that barely compensates for aberrant HGP in insulin-resistant states more than suffices to maintain hepatic TG biosynthesis. Thus, even modestly elevated or context-inappropriate insulin levels, when sustained day and night within a heavily pro-lipogenic metabolic milieu, may translate into substantial cumulative TG biosynthesis in the insulin-resistant state.

Dysregulation of Lipid and Glucose Metabolism in Nonalcoholic Fatty Liver Disease

Non-Alcoholic Fatty Liver Disease (NAFLD) is a highly prevalent condition affecting approximately a quarter of the global population. It is associated with increased morbidity, mortality, economic burden, and healthcare costs. The disease is characterized by the accumulation of lipids in the liver, known as steatosis, which can progress to more severe stages such as steatohepatitis, fibrosis, cirrhosis, and even hepatocellular carcinoma (HCC). This review focuses on the mechanisms that contribute to the development of diet-induced steatosis in an insulin-resistant liver. Specifically, it discusses the existing literature on carbon flux through glycolysis, ketogenesis, TCA (Tricarboxylic Acid Cycle), and fatty acid synthesis pathways in NAFLD, as well as the altered canonical insulin signaling and genetic predispositions that lead to the accumulation of diet-induced hepatic fat. Finally, the review discusses the current therapeutic efforts that aim to ameliorate various pathologies associated with NAFLD.

Mediterranean Diet, Energy Restriction, Physical Activity, and Atherogenicity of Very-Low Density Lipoproteins: Findings from Two Randomized Controlled Trials

SCOPE

Some very-low density lipoprotein (VLDL) properties may render them more pro-atherogenic. We aimed to assess whether a Mediterranean diet (MedDiet) or an energy-reduced MedDiet with increased physical activity improves them.

METHODS AND RESULTS

In a sample of the PREvención con DIeta MEDiterránea (PREDIMED) study, a 1-year intervention with MedDiet with extra-virgin olive oil (n = 89) or nuts (MedDiet-Nuts; n = 79) is compared with a low-fat diet (n = 90). In the PREDIMED-Plus study, a 1-year intervention with energy-reduced MedDiet and physical activity (n = 103) is compared with an ad libitum MedDiet (n = 101). VLDL levels of apolipoprotein C-I, C-III, triglycerides, and cholesterol; the apolipoprotein E-/C-I ratio; and VLDL ex-vivo triglyceride transfer are measured. In PREDIMED participants in both MedDiet groups combined, VLDL apolipoprotein C-III levels are nominally reduced (-0.023 SD units, 95% CI -0.44 to -0.014, p = 0.037). VLDL triglyceride transfer is nominally increased in the MedDiet-Nuts group (+0.39 SD units, 95% CI 0.012-0.78, p = 0.045). In PREDIMED-Plus, no inter-group differences are detected.

CONCLUSIONS

In older adults at high cardiovascular risk, MedDiet is associated with lower VLDL atherogenicity versus a low-fat diet. No differences are seen after an energy-reduced MedDiet with physical activity.

Vegetarianism, Microbiota and Cardiovascular health: Looking back, and forward

Cardiovascular diseases (CVD) are the leading cause of death globally, with over 17.9 million attributed deaths in 2019. Unhealthy diet is an often-overlooked major modifiable risk factor for CVD. Global Burden of Disease (GBD) estimates suggest that unhealthy diets account for nearly 26% of all deaths, of which 84% were attributed to CVD. Plant-based diets (PBDs), which are a diverse group of dietary patterns focused on plant produce, with flexibility for varying levels of vegetarianism, have been suggested to decrease the incidence of various cardiovascular and cardiometabolic diseases. In this review, we aim to delve into the spectrum of PBDs, revisit objective definitions and classifications, and compare them with standard non-vegetarian diets. We examine plausible mechanisms underlying the cardiovascular benefits of PBDs with a particular focus on the dietary manipulation of gut microbiota-host interaction and its effect on energy metabolism, and local and systemic inflammation. In addition, we explore the evidence on the impact of PBDs on cardiovascular disease, examine the challenges and limitations associated with dietary intervention studies, and devise strategies to draw valid conclusions. Dietary interventions, such as PBDs are one of the most powerful, attainable, cost-effective tools for health and environmental protection at the population level. We conclude with a clear appreciation for PBDs in environmental sustainability, climate change, and animal welfare.

Impact of Dietary Palmitic Acid on Lipid Metabolism

Palmitic acid (PA) is ubiquitously present in dietary fat guaranteeing an average intake of about 20 g/d. The relative high requirement and relative content in the human body, which accounts for 20–30% of total fatty acids (FAs), is justified by its relevant nutritional role. In particular physiological conditions, such as in the fetal stage or in the developing brain, the respectively inefficient placental and brain blood–barrier transfer of PA strongly induces its endogenous biosynthesis from glucose via de novo lipogenesis (DNL) to secure a tight homeostatic control of PA tissue concentration required to exert its multiple physiological activities. However, pathophysiological conditions (insulin resistance) are characterized by a sustained DNL in the liver and aimed at preventing the excess accumulation of glucose, which result in increased tissue content of PA and disrupted homeostatic control of its tissue concentration. This leads to an overaccumulation of tissue PA, which results in dyslipidemia, increased ectopic fat accumulation, and inflammatory tone via toll-like receptor 4. Any change in dietary saturated FAs (SFAs) usually reflects a complementary change in polyunsaturated FA (PUFA) intake. Since PUFA particularly n-3 highly PUFA, suppress lipogenic gene expression, their reduction in intake rather than excess of dietary SFA may promote endogenous PA production via DNL. Thereby, the increase in tissue PA and its deleterious consequences from dysregulated DNL can be mistakenly attributed to dietary intake of PA.

De novo lipogenesis in non-alcoholic fatty liver disease: Quantification with stable isotope tracers

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is characterized as an abnormal accumulation of triglyceride in hepatocytes. Hepatic de novo lipogenesis may play an important role in the accumulation of lipids in the liver during NAFLD. Due to the importance of lipid biosynthetic fluxes in NAFLD and T2D, tracer methodologies have been developed for their study and quantification. Here, we address novel approaches to measure and quantify DNL using stable isotope tracers. Deuterated water is a widely used tracer for quantifying DNL rates in both animal models and humans. Enrichment of lipid hydrogens from ² H2O can be resolved and quantified by ² H NMR and MS spectroscopy of isolated lipids. NMR provides a much higher level of positional enrichment information compared with MS which yields a more detailed picture of lipid biosynthetic. It can also be used to quantify low levels of lipid ¹³ C enrichment from a second tracer such as [U-¹³ C]sugar with minimal interference of one tracer with the other.

CONCLUSIONS

Despite the clear association between elevated DNL activity and increased hepatic triglyceride levels, implementation of non-destructive and novel methods to quantify DNL and its contribution to NAFLD are also of huge interest.

Association of adolescent lipoprotein subclass profile with carotid intima-media thickness and comparison to adults: Prospective population-based cohort studies

BACKGROUND AND AIMS

Assessment of comprehensive lipoprotein subclass profiles in adolescents and their relation to vascular disease may enhance our understanding of the development of dyslipidemia in early life and inform early vascular prevention.

METHODS

Nuclear magnetic resonance was used to measure lipoprotein profiles, including lipids (cholesterol, free cholesterol, triglycerides, phospholipids) and apolipoproteins (apoB-100, apoA1, apoA2) of 17 lipoprotein subclasses (from least dense to densest: VLDL-1 to -6, IDL, LDL-1 to -6, HDL-1 to -4) in n = 1776 14- to 19-year olds (56.6% female) and n = 3027 25- to 85-year olds (51.5% female), all community-dwelling. Lipoprotein profiles were related to carotid intima-media thickness (cIMT) as ascertained by sonography.

RESULTS

Adolescents compared to adults had lower triglycerides, total, LDL, and non-HDL cholesterol, and apoB, and higher HDL cholesterol. They showed 26.6-59.8% lower triglyceride content of all lipoprotein subclasses and 21.9-51.4% lower VLDL lipid content. Concentrations of dense LDL-4 to LDL-6 were 36.7-40.2% lower, with also markedly lower levels of LDL-1 to LDL-3, but 24.2% higher HDL-1 ApoA1. In adolescents, only LDL-3 to LDL-5 subclasses were associated with cIMT (range of differences in cIMT for a 1-SD higher concentration, 4.8-5.9 μm). The same associations emerged in adults, with on average 97 ± 42% (mean ± SD) larger effect sizes, in addition to LDL-1 and LDL-6 (range, 6.9-11.3 μm) and HDL-2 to HDL-4, ApoA1, and ApoA2 (range, -7.0 to -17.7 μm).

CONCLUSIONS

Adolescents showed a markedly different and more favorable lipoprotein profile compared to adults. Dense LDL subclasses were the only subclasses associated with cIMT in adolescents, implicating them as the potential preferred therapeutic target for primary prevention of cardiovascular disease at this age. In adults, associations with cIMT were approximately twice as large as in adolescents, and HDL-related measures were additionally associated with cIMT.

Metabolism of Triglyceride-Rich Lipoproteins

Triglycerides are critical lipids as they provide an energy source that is both compact and efficient. Due to its hydrophobic nature triglyceride molecules can pack together densely and so be stored in adipose tissue. To be transported in the aqueous medium of plasma, triglycerides have to be incorporated into lipoprotein particles along with other components such as cholesterol, phospholipid and associated structural and regulatory apolipoproteins. Here we discuss the physiology of normal triglyceride metabolism, and how impaired metabolism induces hypertriglyceridemia and its pathogenic consequences including atherosclerosis. We also discuss established and novel therapies to reduce triglyceride-rich lipoproteins.

The effects of fat consumption on low-density lipoprotein particle size in healthy individuals: a narrative review

Cardiovascular disease (CVD) is the number one contributor to death in the United States and worldwide. A risk factor for CVD is high serum low-density lipoprotein cholesterol (LDL-C) concentrations; however, LDL particles exist in a variety of sizes that may differentially affect the progression of CVD. The small, dense LDL particles, compared to the large, buoyant LDL subclass, are considered to be more atherogenic. It has been suggested that replacing saturated fatty acids with monounsaturated and polyunsaturated fatty acids decreases the risk for CVD. However, certain studies are not in agreement with this recommendation, as saturated fatty acid intake did not increase the risk for CVD, cardiovascular events, and/or mortality. Furthermore, consumption of saturated fat has been demonstrated to increase large, buoyant LDL particles, which may explain, in part, for the differing outcomes regarding fat consumption on CVD risk. Therefore, the objective was to review intervention trials that explored the effects of fat consumption on LDL particle size in healthy individuals. PubMed and Web of Science were utilized during the search process for journal articles. The results of this review provided evidence that fat consumption increases large, buoyant LDL and/or decreases small, dense LDL particles, and therefore, influences CVD risk.

Advantages of Studying the Metabolome in Response to Mixed-Macronutrient Challenges and Suggestions for Future Research Designs

Evaluating the postprandial response to a dietary challenge containing all macronutrients-carbohydrates, lipids, and protein-may provide stronger insights of metabolic health than a fasted measurement. Metabolomic profiling deepens the understanding of the homeostatic and adaptive response to a dietary challenge by classifying multiple metabolic pathways and biomarkers. A total of 26 articles were identified that measure the human blood metabolome or lipidome response to a mixed-macronutrient challenge. Most studies were cross-sectional, exploring the baseline and postprandial response to the dietary challenge. Large variations in study designs were reported, including the macronutrient and caloric composition of the challenge and the delivery of the challenge as a liquid shake or a solid meal. Most studies utilized a targeted metabolomics platform, assessing only a particular metabolic pathway, however, several studies utilized global metabolomics and lipidomics assays demonstrating the expansive postprandial response of the metabolome. The postprandial response of individual amino acids was largely dependent on the amino acid composition of the test meal, with the exception of alanine and proline, 2 nonessential amino acids. Long-chain fatty acids and unsaturated long-chain acylcarnitines rapidly decreased in response to the dietary challenges, representing the switch from fat to carbohydrate oxidation. Studies were reviewed that assessed the metabolome response in the context of obesity and metabolic diseases, providing insight on how weight status and disease influence the ability to cope with a nutrient load and return to homeostasis. Results demonstrate that the flexibility to respond to a substrate load is influenced by obesity and metabolic disease and flexibility alterations will be evident in downstream metabolites of fat, carbohydrate, and protein metabolism. In response, we propose suggestions for standardization between studies with the potential of creating a study exploring the postprandial response to a multitude of challenges with a variety of macronutrients.

Reversal of hypertriglyceridemia in diabetic BTBR ob/ob mice does not prevent nephropathy

The etiology of diabetic nephropathy in type 2 diabetes is multifactorial. Sustained hyperglycemia is a major contributor, but additional contributions come from the hypertension, obesity, and hyperlipidemia that are also commonly present in patients with type 2 diabetes and nephropathy. The leptin deficient BTBR ob/ob mouse is a model of type 2 diabetic nephropathy in which hyperglycemia, obesity, and hyperlipidemia, but not hypertension, are present. We have shown that reversal of the constellation of these metabolic abnormalities with leptin replacement can reverse the morphologic and functional manifestations of diabetic nephropathy. Here we tested the hypothesis that reversal specifically of the hypertriglyceridemia, using an antisense oligonucleotide directed against ApoC-III, an apolipoprotein that regulates the interactions of VLDL (very low density lipoproteins) with the LDL receptor, is sufficient to ameliorate the nephropathy of Type 2 diabetes. Antisense treatment resulted in reduction of circulating ApoC-III protein levels and resulted in substantial lowering of triglycerides to near-normal levels in diabetic mice versus controls. Antisense treatment did not ameliorate proteinuria or pathologic manifestations of diabetic nephropathy, including podocyte loss. These studies indicate that pathologic manifestations of diabetic nephropathy are unlikely to be reduced by lipid-lowering therapeutics alone, but does not preclude a role for such interventions to be used in conjunction with other therapeutics commonly employed in the treatment of diabetes and its complications.

The interaction between the gut microbiota and dietary carbohydrates in nonalcoholic fatty liver disease

Imbalance between fat production and consumption causes various metabolic disorders. Nonalcoholic fatty liver disease (NAFLD), one such pathology, is characterized by abnormally increased fat synthesis and subsequent fat accumulation in hepatocytes1,2. While often comorbid with obesity and insulin resistance, this disease can also be found in lean individuals, suggesting specific metabolic dysfunction2. NAFLD has become one of the most prevalent liver diseases in adults worldwide, but its incidence in both children and adolescents has also markedly increased in developed nations3,4. Progression of this disease into nonalcoholic steatohepatitis (NASH), cirrhosis, liver failure, and hepatocellular carcinoma in combination with its widespread incidence thus makes NAFLD and its related pathologies a significant public health concern. Here, we review our understanding of the roles of dietary carbohydrates (glucose, fructose, and fibers) and the gut microbiota, which provides essential carbon sources for hepatic fat synthesis during the development of NAFLD.

Direct and indirect control of hepatic glucose production by insulin

There is general agreement that the acute suppression of hepatic glucose production by insulin is mediated by both a direct and an indirect effect on the liver. There is, however, no consensus regarding the relative magnitude of these effects under physiological conditions. Extensive research over the past three decades in humans and animal models has provided discordant results between these two modes of insulin action. Here, we review the field to make the case that physiologically direct hepatic insulin action dominates acute suppression of glucose production, but that there is also a delayed, second order regulation of this process via extrahepatic effects. We further provide our views regarding the timing, dominance, and physiological relevance of these effects and discuss novel concepts regarding insulin regulation of adipose tissue fatty acid metabolism and central nervous system (CNS) signaling to the liver, as regulators of insulin's extrahepatic effects on glucose production.

100th anniversary of the discovery of insulin perspective: insulin and adipose tissue fatty acid metabolism

Insulin inhibits systemic nonesterified fatty acid (NEFA) flux to a greater degree than glucose or any other metabolite. This remarkable effect is mainly due to insulin-mediated inhibition of intracellular triglyceride (TG) lipolysis in adipose tissues and is essential to prevent diabetic ketoacidosis, but also to limit the potential lipotoxic effects of NEFA in lean tissues that contribute to the development of diabetes complications. Insulin also regulates adipose tissue fatty acid esterification, glycerol and TG synthesis, lipogenesis, and possibly oxidation, contributing to the trapping of dietary fatty acids in the postprandial state. Excess NEFA flux at a given insulin level has been used to define in vivo adipose tissue insulin resistance. Adipose tissue insulin resistance defined in this fashion has been associated with several dysmetabolic features and complications of diabetes, but the mechanistic significance of this concept is not fully understood. This review focusses on the in vivo regulation of adipose tissue fatty acid metabolism by insulin and the mechanistic significance of the current definition of adipose tissue insulin resistance. One hundred years after the discovery of insulin and despite decades of investigations, much is still to be understood about the multifaceted in vivo actions of this hormone on adipose tissue fatty acid metabolism.

High-throughput LC-MS method to investigate postprandial lipemia: considerations for future precision nutrition research

Elevated postprandial lipemia is an independent risk factor for cardiovascular disease, yet methods to quantitate postmeal handling of dietary lipids in humans are limited. This study tested a new method to track dietary lipid appearance using a stable isotope tracer (²H₁₁-oleate) in liquid meals containing three levels of fat [low fat (LF), 15 g; moderate fat (MF), 30 g; high fat (HF), 60 g]. Meals were fed to 12 healthy men [means ± SD, age 31.3 ± 9.2 yr, body mass index (BMI) 24.5 ± 1.9 kg/m²] during four randomized study visits; the HF meal was administered twice for reproducibility. Blood was collected over 8 h postprandially, triglyceride (TG)-rich lipoproteins (TRL), and particles with a Svedberg flotation rate >400 (S_f > 400, n = 8) were isolated by ultracentrifugation, and labeling of two TG species (54:3 and 52:2) was quantified by LC-MS. Total plasma TRL-TG concentrations were threefold greater than S_f > 400-TG. Both S_f > 400- and TRL-TG 54:3 were present at higher concentrations than 52:2, and singly labeled TG concentrations were higher than doubly labeled. Furthermore, TG 54:3 and the singly labeled molecules demonstrated higher plasma absolute entry rates differing significantly across fat levels within a single TG species (P < 0.01). Calculation of fractional entry showed no significant differences in label handling supporting the utility of either TG species for appearance rate calculations. These data demonstrate the utility of labeling research meals with stable isotopes to investigate human postprandial lipemia while simultaneously highlighting the importance of examining individual responses. Meal type and timing, control of prestudy activities, and effects of sex on outcomes should match the research goals. The method, optimized here, will be beneficial to conduct basic science research in precision nutrition and clinical drug development.NEW & NOTEWORTHY A novel method to test human intestinal lipid handling using stable isotope labeling is presented and, for the first time, plasma appearance and lipid turnover were quantified in 12 healthy men following meals with varying amounts of fat. The method can be applied to studies in precision nutrition characterizing individual response to support basic science research or drug development. This report discusses key questions for consideration in precision nutrition that were highlighted by the data.

Liver fat storage pathways: methodologies and dietary effects

PURPOSE OF REVIEW

Nonalcoholic fatty liver is the result of an imbalance between lipid storage [from meal, de novo lipogenesis (DNL) and fatty acid (FA) uptake] and disposal (oxidation and VLDL output). Knowledge on the contribution of each of these pathways to liver fat content in humans is essential to develop tailored strategies to prevent and treat nonalcoholic fatty liver. Here, we review the techniques available to study the different storage pathways and review dietary modulation of these pathways.

RECENT FINDINGS

The type of carbohydrate and fat could be of importance in modulating DNL, as complex carbohydrates and omega-3 FAs have been shown to reduce DNL. No effects were found on the other pathways, however studies investigating this are scarce.

SUMMARY

Techniques used to assess storage pathways are predominantly stable isotope techniques, which require specific expertise and are costly. Validated biomarkers are often lacking. These methodological limitations also translate into a limited number of studies investigating to what extent storage pathways can be modulated by diet. Further research is needed to elucidate in more detail the impact that fat and carbohydrate type can have on liver fat storage pathways and content.

LZP is required for hepatic triacylglycerol transportation through maintaining apolipoprotein B stability

The conserved zona pellucida (ZP) domain is found in hundreds of extracellular proteins that are expressed in various organs and play a variety of roles as structural components, receptors and tumor suppressors. A liver-specific zona pellucida domain-containing protein (LZP), also named OIT3, has been shown to be mainly expressed in human and mouse hepatocytes; however, the physiological function of LZP in the liver remains unclear. Here, we show that Lzp deletion inhibited very low-density lipoprotein (VLDL) secretion, leading to hepatic TG accumulation and lower serum TG levels in mice. The apolipoprotein B (apoB) levels were significantly decreased in the liver, serum, and VLDL particles of LZP-deficient mice. In the presence of LZP, which is localized to the endoplasmic reticulum (ER) and Golgi apparatus, the ER-associated degradation (ERAD) of apoB was attenuated; in contrast, in the absence of LZP, apoB was ubiquitinated by AMFR, a known E3 ubiquitin ligase specific for apoB, and was subsequently degraded, leading to lower hepatic apoB levels and inhibited VLDL secretion. Interestingly, hepatic LZP levels were elevated in mice challenged with a high-fat diet and humans with simple hepatic steatosis, suggesting that LZP contributes to the physiological regulation of hepatic TG homeostasis. In general, our data establish an essential role for LZP in hepatic TG transportation and VLDL secretion by preventing the AMFR-mediated ubiquitination and degradation of apoB and therefore provide insight into the molecular function of LZP in hepatic lipid metabolism.

Greater Loss of Central Adiposity from Low-Carbohydrate versus Low-Fat Diet in Middle-Aged Adults with Overweight and Obesity

The objective of this study is to determine whether middle-aged adults prescribed a low carbohydrate-high fat (LCHF) or low fat (LF) diet would have greater loss of central fat and to determine whether the insulin resistance (IR) affects intervention response. A total of 50 participants (52.3 ± 10.7 years old; 36.6 ± 7.4 kg/m2 BMI; 82% female) were prescribed either a LCHF diet (n = 32, carbohydrate: protein: fat of 5%:30%:65% without calorie restriction), or LF diet (n = 18, 63%:13–23%: 10–25% with calorie restriction of total energy expenditure—500 kcal) for 15 weeks. Central and regional body composition changes from dual-x-ray absorptiometry and serum measures were compared using paired t-tests and ANCOVA with paired contrasts. IR was defined as homeostatic model assessment (HOMA-IR) > 2.6. Compared to the LF group, the LCHF group lost more android (15.6 ± 11.2% vs. 8.3 ± 8.1%, p < 0.01) and visceral fat (18.5 ± 22.2% vs. 5.1 ± 15.8%, p < 0.05). Those with IR lost more android and visceral fat on the LCHF verses LF group (p < 0.05). Therefore, the clinical prescription to a LCHF diet may be an optimal strategy to reduce disease risk in middle-aged adults, particularly those with IR.

Metabolic Transition of Milk Triacylglycerol Synthesis in Response to Varying Levels of Three 18-Carbon Fatty Acids in Porcine Mammary Epithelial Cells

This study aimed to examine the effects of increasing levels of three 18-carbon fatty acids (stearate, oleate and linoleate) on mammary lipogenesis, and to evaluate their effects on the milk lipogenic pathway in porcine mammary epithelial cells (pMECs). We found that increasing the three of 18-carbon fatty acids enhanced the cellular lipid synthesis in a dose-dependent manner, as reflected by the increased (triacylglycerol) TAG content and cytosolic lipid droplets in pMECs. The increased lipid synthesis by the three 18-carbon fatty acids was probably caused by the up-regulated expression of major genes associated with milk fat biosynthesis, including CD36 (long chain fatty acid uptake); GPAM, AGPAT6, DGAT1 (TAG synthesis); PLIN2 (lipid droplet formation); and PPARγ (regulation of transcription). Western blot analysis of CD36, DGAT1 and PPARγ proteins confirmed this increase with the increasing incubation of 18-carbon fatty acids. Interestingly, the mRNA expressions of ACSL3 and FABP3 (fatty acids intracellular activation and transport) were differentially affected by the three 18-carbon fatty acids. The cellular mRNA expressions of ACSL3 and FABP3 were increased by stearate, but were decreased by oleate or linoleate. However, the genes involved in fatty acid de novo synthesis (ACACA and FASN) and the regulation of transcription (SREBP1) were decreased by incubation with increasing concentrations of 18-carbon fatty acids. In conclusion, our findings provided evidence that 18-carbon fatty acids (stearate, oleate and linoleate) significantly increased cytosolic TAG accumulation in a dose-dependent manner, probably by promoting lipogenic genes and proteins that regulate the channeling of fatty acids towards milk TAG synthesis in pMECs.

Glucose and lipid metabolism of broiler chickens fed diets with graded levels of corn resistant starch

1. The aim of this study was to investigate the effects of graded levels of dietary corn resistant starch (RS) on glucose and lipid metabolism of broilers. 2. A total of 320 male broiler chicks (Arbor Acres, one-day-old) were randomly allocated to five dietary treatments, including a corn-soybean control diet, a corn-soybean based diet containing 20% corn starch, and three diets containing 4%, 8% and 12% RS by replacing corn starch with 6.67%, 13.33% and 20% Hi-Maize® 260 (identified as control, RS1, RS2, RS3 and RS4, respectively). Each treatment contained eight replicates with eight birds, and the experiment lasted 42 days. 3. Birds fed RS diets showed lower (P < 0.05) concentrations of serum low-density lipoprotein cholesterol and non-esterified fatty acid (NEFA) at d 21 and 42 of age, compared to the control. Lower (P < 0.05) hepatic apolipoprotein B concentration and citrate synthase (CS) activity, as well as a higher (P < 0.05) glycogen synthase (GS) concentration were observed in birds fed RS diets than those in the control group at d 21 of age. Consuming RS diets linearly increased (P < 0.01) serum glucose concentration, and linearly decreased (P < 0.01) NEFA concentrations in broilers at d 21 and 42 of age. Liver GS concentration and activities of hexokinase, pyruvate and CS were linearly increased (P < 0.01) in broilers at d 21 of age, but were linearly decreased (P < 0.05) in birds at d 42 of age in response to the increase of dietary RS levels. Feeding RS diets linearly decreased (P < 0.05) mRNA expressions of PC, PPARα and CPT-1 at d 21 of age and the mRNA expressions of SREBP-1 c, ChREBP, ACC and FAS at d 42 of age, and linearly increased (P < 0.05) the mRNA expressions of PEPCK, PC, LKB1, AMPKα1, PPARα, CPT-1 and L-FABP at d 42 of age. 4. Feeding broilers with diets containing higher concentration of RS promoted hepatic lipolysis and gluconeogenesis through activated AMPK signalling pathway and accelerated whole-body energy expenditures in the grower phase.

Fatty Acid Synthase Inhibitor TVB-2640 Reduces Hepatic de Novo Lipogenesis in Males With Metabolic Abnormalities

BACKGROUND AND AIMS

Elevated hepatic de novo lipogenesis (DNL) is a key distinguishing characteristic of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis. In rodent models of NAFLD, treatment with a surrogate of TVB-2640, a pharmacological fatty acid synthase inhibitor, has been shown to reduce hepatic fat and other biomarkers of DNL. The purpose of this phase I clinical study was to test the effect of the TVB-2640 in obese men with certain metabolic abnormalities that put them at risk for NAFLD.

APPROACH AND RESULTS

Twelve subjects (mean ± SEM, 42 ± 2 years, body mass index 37.4 ± 1.2 kg/m² , glucose 103 ± 2 mg/dL, triacylglycerols 196 ± 27 mg/dL, and elevated liver enzymes) underwent 10 days of treatment with TVB-2640 at doses ranging from 50-150 mg/day. Food intake was controlled throughout the study. Hepatic DNL was measured before and after an oral fructose/glucose bolus using isotopic labeling with 1-¹³ C₁ -acetate intravenous infusion, followed by measurement of labeled very low-density lipoprotein palmitate via gas chromatography mass spectometry. Substrate oxidation was measured by indirect calorimetry. Across the range of doses, fasting DNL was reduced by up to 90% (P = 0.003). Increasing plasma concentrations of TVB-2640 were associated with progressive reductions in the percent of fructose-stimulated peak fractional DNL (R²  = -0.749, P = 0.0003) and absolute DNL area under the curve 6 hours following fructose/glucose bolus (R²  = -0.554, P = 0.005). For all subjects combined, alanine aminotransferase was reduced by 15.8 ± 8.4% (P = 0.05). Substrate oxidation was unchanged, and safety monitoring revealed that the drug was well tolerated, without an increase in plasma triglycerides. Alopecia occurred in 2 subjects (reversed after stopping the drug), but otherwise no changes were observed in fasting glucose, insulin, ketones, and renal function.

CONCLUSION

These data support the therapeutic potential of a fatty acid synthase inhibitor, TVB-2640 in particular, in patients with NAFLD and nonalcoholic steatohepatitis.

Influence of total western diet on docosahexaenoic acid suppression of silica-triggered lupus flaring in NZBWF1 mice

Lupus is a debilitating multi-organ autoimmune disease clinically typified by periods of flare and remission. Exposing lupus-prone female NZBWF1 mice to crystalline silica (cSiO2), a known human autoimmune trigger, mimics flaring by inducing interferon-related gene (IRG) expression, inflammation, ectopic lymphoid structure (ELS) development, and autoantibody production in the lung that collectively accelerate glomerulonephritis. cSiO2-triggered flaring in this model can be prevented by supplementing mouse diet with the ω-3 polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA). A limitation of previous studies was the use of purified diet that, although optimized for rodent health, does not reflect the high American intake of saturated fatty acid (SFA), ω-6 PUFAs, and total fat. To address this, we employed here a modified Total Western Diet (mTWD) emulating the 50th percentile U.S. macronutrient distribution to discern how DHA supplementation and/or SFA and ω-6 reduction influences cSiO2-triggered lupus flaring in female NZBWF1 mice. Six-week-old mice were fed isocaloric experimental diets for 2 wks, intranasally instilled with cSiO2 or saline vehicle weekly for 4 wks, and tissues assessed for lupus endpoints 11 wks following cSiO2 instillation. In mice fed basal mTWD, cSiO2 induced robust IRG expression, proinflammatory cytokine and chemokine elevation, leukocyte infiltration, ELS neogenesis, and autoantibody production in the lung, as well as early kidney nephritis onset compared to vehicle-treated mice fed mTWD. Consumption of mTWD containing DHA at the caloric equivalent to a human dose of 5 g/day dramatically suppressed induction of all lupus-associated endpoints. While decreasing SFA and ω-6 in mTWD modestly inhibited some disease markers, DHA addition to this diet was required for maximal protection against lupus development. Taken together, DHA supplementation at a translationally relevant dose was highly effective in preventing cSiO2-triggered lupus flaring in NZBWF1 mice, even against the background of a typical Western diet.

Relationships between Very Low-Density Lipoproteins-Ceramides, -Diacylglycerols, and -Triacylglycerols in Insulin-Resistant Men

This short report describes the relationships between concentrations of ceramides (CER), diacylglycerols (DAG), triacylglycerols (TAG) in very low-density lipoproteins (VLDL) particles, and hepatic lipid accumulation. VLDL particles were isolated from male subjects (n = 12, mean ± SD, age 42.1 ± 5.4 years, BMI 37.4 ± 4.1 kg/m² , ALT 45 ± 21 U/L) and apolipoprotein B100 (apoB100), VLDL-TAG, -CER, and -DAG quantified. The contents of all three lipids were highly correlated with VLDL particle number (r ≥ 0.768, p ≤ 0.003). The molar quantity of VLDL-TAG was 3× that of DAG and 137× that of CER (14,053 ± 5714, 5004 ± 2714, and 105 ± 49 mol/mol apoB100, respectively). Reduced VLDL-CER concentrations were associated with both higher insulin levels (r = -0.645, p = 0.024) and intrahepatic-TAG (r = -0.670, p = 0.017). In fatty liver, the secretion of hepatic TAG, CER, and DAG may be suppressed and contribute to intrahepatic lipotoxicity. The mechanisms by which hepatic-CER and -DAG synthesis and assembly into VLDL is coordinately controlled with TAG will be important in understanding the emerging role of elevated CER contributing to cardiometabolic disease.

Glucocorticoid-Induced Fatty Liver Disease

Glucocorticoids (GCs) are commonly used at high doses and for prolonged periods (weeks to months) in the treatment of a variety of diseases. Among the many side effects are increased insulin resistance with disturbances in glucose/insulin homeostasis and increased deposition of lipids (mostly triglycerides) in the liver. Here, we review the metabolic pathways of lipid deposition and removal from the liver that become altered by excess glucocorticoids. Pathways of lipid deposition stimulated by excess glucocorticoids include 1) increase in appetite and high caloric intake; 2) increased blood glucose levels due to GC-induced stimulation of gluconeogenesis; 3) stimulation of de novo lipogenesis that is augmented by the high glucose and insulin levels and by GC itself; and 4) increased release of free fatty acids from adipose stores and stimulation of their uptake by the liver. Pathways that decrease hepatic lipids affected by glucocorticoids include a modest stimulation of very-low-density lipoprotein synthesis and secretion into the circulation and inhibition of β-oxidation of fatty acids. Role of 11β-hydroxysteroid dehydrogenases-1 and -2 and the reversible conversion of cortisol to cortisone on intracellular levels of cortisol is examined. In addition, GC control of osteocalcin expression and the effect of this bone-derived hormone in increasing insulin sensitivity are discussed. Finally, research focused on gaining a better understanding of the dose and duration of treatment with glucocorticoids, which leads to increased triglyceride deposition in the liver, and the reversibility of the condition is highlighted.

Mathematical model of diabetes and lipid metabolism linked to diet, leptin sensitivity, insulin sensitivity and VLDLTG clearance predicts paths to health and type II diabetes

An original model of diabetes linked to carbohydrate and lipid intake is presented and applied to predict the effects on biomarkers of various diets. The variables (biomarkers) are concentrations of fasting plasma glucose, insulin, leptin, glucagon, non-esterified fatty acids (NEFA) and very low density lipoprotein triglyceride (VLDLTG), as well as muscle lipids, hepatic lipids, pancreatic lipids, fat mass and mass of β-cells. The model predicts isocaloric high carbohydrate low fat (HCLF) diet and low carbohydrate high fat (LCHF) diet trajectories to health which vary in fat mass by at most a few kilograms at steady state. The LCHF trajectories to health are faster than isocaloric HCLF trajectories with respect to fat mass loss, although these trajectories may be slower initially if parameters are adjusting from HCLF values. On LC diets, leptin sensitivity and VLDLTG clearance are thought to increase. Increasing leptin sensitivity and VLDLTG clearance is predicted to lower lipids including fat mass and VLDLTG. The model predicts that changes in VLDLTG due to a change in diet happen rapidly, approaching steady state values after a few weeks, reflecting leptin sensitivity and VLDLTG clearance which are much harder to measure. The model predicts that if only insulin sensitivity increases on a LC diet, steady state fat mass would increase slightly. If leptin and insulin sensitivities increase concurrently, the combined effect could be a decrease in fat mass, consistent with the fact that increasing insulin sensitivity is often associated with fat mass loss in trials. The model predicts trajectories to fat type II diabetes with hypertriglyceridemia due to high carbohydrate moderate fat diets, on which insulin rises before falling, as ectopic fat deposits increase; made fatter and more diabetic by higher lipid consumption. It predicts trajectories to non-diabetic states with raised fat mass, VLDLTG and muscle, hepatic and pancreatic lipids due to moderate carbohydrate high fat diets. The model predicts paths to lean type II diabetes, on a diet of moderate energy but low β-cell replication rate or high death rate.

Honey does not adversely impact blood lipids of adult men and women: a randomized cross-over trial

Consumption of added sugars in the US is estimated to be approximately 1.5 times recommended levels and has been linked to increased risk for developing chronic diseases. We hypothesized that relative to sugar, honey would reduce energy intake and improve serum lipid profiles. To test this, we assessed the short-term (1-week) and relatively long-term (1-month) effects of honey versus sucrose on changes in dietary intake and serum lipid concentrations. Thirty-seven apparently healthy subjects (21 males; 16 females) aged 24-57 years (BMI = 17.6-37.2 kg/m²) completed two 4-week trials in a randomized, cross-over design separated by ≥4-week washout. During each trial, subjects consumed either clover honey or sucrose providing 1.2 g/kg/day of carbohydrate under free-living conditions with instructions to avoid changing their habitual food intake. Serum triglyceride (TG) concentrations were elevated (P < .05) after 1 week for both trials but only remained elevated (P < .05) at the 4-week time-point during sucrose consumption. The elevation after 1 week during the honey trial was concurrent with a transient increase (P < .05) in body weight. No effects on serum concentrations of insulin, total cholesterol, low density lipoprotein-cholesterol, or high density lipoprotein-cholesterol were detected for either trial. Subjects consumed significantly less energy (P < .05), carbohydrate (P < .005), sugars (P < .05), and saturated fat (P < .05) during the honey trial. These data suggest that honey may serve as a favorable substitute for sucrose with regard to reduced energy intake, carbohydrate and sugars, without negatively influencing serum lipid concentrations.

Dietary Impact on Postprandial Lipemia

Abnormalities in postprandial lipemia (PPL), particularly those related to triglyceride-rich lipoproteins, are considered an independent cardiovascular risk factor. As diet is known to be one of the main modulators of PPL, the aim of this review was to summarize and discuss current knowledge on the impact of diet and its components on PPL in humans; specifically, the impact of weight loss, different nutrients (quantity and quality of dietary fats, carbohydrates, and proteins), alcohol and other bioactive dietary components (i.e., polyphenols), as well as the effect of different dietary patterns. The possible mechanisms behind the metabolic effects of each dietary component were also discussed.

Effect of a Family-Based Intervention on Nutrient Biomarkers, Desaturase Enzyme Activities, and Cardiometabolic Risk Factors in Children with Overweight and Obesity

BACKGROUND

Developing dietary strategies to prevent excess weight gain during childhood is critical to stem the current obesity epidemic and associated adverse cardiometabolic consequences.

OBJECTIVES

We aimed to assess how participation in a family-based weight-management intervention affected nutrient biomarkers and cardiometabolic risk factors (CMRFs) in children (7-12 y old; n = 321) with baseline BMI z score (BMIz) ≥85th percentile.

METHODS

This was a secondary analysis from a randomized-controlled, parallel-arm clinical trial. Families of children, recruited from a largely Hispanic population, were assigned to Standard Care (SC; American Academy of Pediatrics overweight/obesity recommendations), or SC + Enhanced Program (SC + EP; 8 skill-building cores, monthly support sessions, targeted diet/physical activity strategies). Nutrient biomarkers (plasma carotenoids, fat-soluble vitamins, RBC fatty acid profiles, desaturase indexes) and CMRFs were measured in archived blood samples collected at baseline and the end of the 1-y intervention.

RESULTS

Children in both groups had significantly lower trans fatty acid and higher pentadecylic acid (15:0), PUFA n-3, and β-carotene concentrations, indicative of decreased hydrogenated fat and increased dairy, vegetable oil, fish, and fruit/vegetable intake, respectively. Similar changes were seen in de novo lipogenesis and desaturase indexes, as well as CMRFs (BMIz, lipid profile, inflammation, adipokines, liver enzymes) in both groups. Using multiple logistic regression, increase in carotenoids and decrease in endogenously synthesized SFA, MUFA, PUFA n-6, and desaturase indexes were associated with improvements in BMIz, blood pressure, lipid profile, glucose metabolism, inflammatory biomarkers, adipokines, and liver enzymes. Trans fatty acids were associated with improvements in BMIz, glucose metabolism, and leptin, with less favorable effects on inflammatory markers and adiponectin.

CONCLUSIONS

Providing targeted family-based behavioral counseling, as part of SC, can help overweight/obese children adopt healthier eating patterns that are associated with modest improvements in BMIz and several CMRFs. Limited additional benefit was observed with SC + EP. These results provide critical data to design subsequent interventions to increase the impact of family-based obesity prevention programs.This trial was registered at clinicaltrials.gov as NCT00851201.

Separation of postprandial lipoproteins: improved purification of chylomicrons using an ApoB100 immunoaffinity method

Elevated levels of triglyceride-rich lipoproteins (TRLs), both fasting and postprandial, are associated with increased risk for atherosclerosis. However, guidelines for treatment are defined solely by fasting lipid levels, even though postprandial lipids may be more informative. In the postprandial state, circulating lipids consist of dietary fat transported from the intestine in chylomicrons (CMs; containing ApoB48) and fat transported from the liver in VLDL (containing ApoB100). Research into the roles of endogenous versus dietary fat has been hindered because of the difficulty in separating these particles by ultracentrifugation. CM fractions have considerable contamination from VLDL (purity, 10%). To separate CMs from VLDL, we produced polyclonal antibodies against ApoB100 and generated immunoaffinity columns. TRLs isolated by ultracentrifugation of plasma were applied to these columns, and highly purified CMs were collected (purity, 90-94%). Overall eight healthy unmedicated adult volunteers (BMI, 27.2 ± 1.4 kg/m²; fasting triacylglycerol, 102.6 ± 19.5 mg/dl) participated in a feeding study, which contained an oral stable-isotope tracer (1-¹³C acetate). We then used this technique on plasma samples freshly collected during an 8 h human feeding study from a subset of four subjects. We analyzed fractionated lipoproteins by Western blot, isolated and derivatized triacylglycerols, and calculated fractional de novo lipogenesis. The results demonstrated effective separation of postprandial lipoproteins and substantially improved purity compared with ultracentrifugation protocols, using the immunoaffinity method. This method can be used to better delineate the role of dietary sugar and fat on postprandial lipids in cardiovascular risk and explore the potential role of CM remnants in atherosclerosis.

Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men: A secondary analysis of energy expenditure and physical activity

BACKGROUND

A previously published pilot study assessed energy expenditure (EE) of participants with overweight and obesity after they were switched from a baseline high-carbohydrate diet (BD) to an isocaloric low-carbohydrate ketogenic diet (KD). EE measured using metabolic chambers increased transiently by what was considered a relatively small extent after the switch to the KD, whereas EE measured using doubly labeled water (EEDLW) increased to a greater degree after the response in the chambers had waned. Using a publicly available dataset, we examined the effect of housing conditions on the magnitude of the increase in EEDLW after the switch to the KD and the role of physical activity in that response.

METHODS

The 14-day EEDLW measurement period included 4 days when subjects were confined to chambers instead of living in wards. To determine the effect on EEDLW only for the days subjects were living in the wards, we calculated non-chamber EE (EEnonchamber). To assess the role of physical activity in the response to the KD, we analyzed chamber and non-chamber accelerometer data for the BD and KD EEDLW measurement periods.

RESULTS

In comparison with the increase in average 14-day EEDLW of 151 kcal/d ± 63 (P = 0.03) after the switch to the KD, EEnonchamber increased by 203 ± 89 kcal/d (P = 0.04) or 283 ± 116 kcal/d (P = 0.03) depending on the analytical approach. Hip accelerometer counts decreased significantly (P = 0.01) after the switch to the KD, whereas wrist and ankle accelerometer counts did not change.

CONCLUSIONS

Switching from the BD to the KD substantially increased EEDLW, but apparently only on days subjects were living in the ward outside the metabolic chamber. Increased physical activity as measured by accelerometry did not appear to account for this effect.

High Protein Diet and Metabolic Plasticity in Non-Alcoholic Fatty Liver Disease: Myths and Truths

Non-alcoholic fatty liver disease (NAFLD) is characterized by lipid accumulation within the liver affecting 1 in 4 people worldwide. As the new silent killer of the twenty-first century, NAFLD impacts on both the request and the availability of new liver donors. The liver is the first line of defense against endogenous and exogenous metabolites and toxins. It also retains the ability to switch between different metabolic pathways according to food type and availability. This ability becomes a disadvantage in obesogenic societies where most people choose a diet based on fats and carbohydrates while ignoring vitamins and fiber. The chronic exposure to fats and carbohydrates induces dramatic changes in the liver zonation and triggers the development of insulin resistance. Common believes on NAFLD and different diets are based either on epidemiological studies, or meta-analysis, which are not controlled evidences; in most of the cases, they are biased on test-subject type and their lifestyles. The highest success in reverting NAFLD can be attributed to diets based on high protein instead of carbohydrates. In this review, we discuss the impact of NAFLD on body metabolic plasticity. We also present a detailed analysis of the most recent studies that evaluate high-protein diets in NAFLD with a special focus on the liver and the skeletal muscle protein metabolisms.

Short-term Dietary Interventions for the Management of Nonalcoholic Fatty Liver

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) affects millions of individuals on a global scale and currently no gold standard treatment exists. The risk of developing NAFLD is considerably higher with increasing body mass index. Consequently, weight loss should be recommended to all overweight patients with fatty liver. However, lifestyle interventions, irrespective of weight status, may also influence the condition. The aim herein is to present examples of short-term interventions which assess direct effects of dietary-related components on hepatic steatosis.

METHODS

This review includes studies with short-term dietary-related interventions of up to 16 weeks that evaluate their efficacy in reducing intrahepatic lipid contents (hepatic steatosis). This review primarily focuses on the three main macronutrients: dietary carbohydrates, fats and proteins.

RESULTS

High saturated fat intake and high consumption of carbohydrates, particularly from simple sugars such as fructose are reported as risk factors for hepatic steatosis. Overall, shortterm hypocaloric diets have shown beneficial effects in reducing intrahepatic lipid contents. Macronutrient manipulations such as carbohydrate restriction as well as the consumption of unsaturated fatty acids are also reported to have efficacious effects.

CONCLUSION

This review highlights the different dietary interventions that can influence hepatic steatosis in the short term, illustrating both pro and anti-steatotic effects.

The regulation of hepatic fatty acid synthesis and partitioning: the effect of nutritional state

Nonalcoholic fatty liver disease (NAFLD) is an increasing global public health burden. NAFLD is strongly associated with type 2 diabetes mellitus, obesity and cardiovascular disease and begins with intrahepatic triacylglycerol accumulation. Under healthy conditions, the liver regulates lipid metabolism to meet systemic energy needs in the fed and fasted states. The processes of fatty acid uptake, fatty acid synthesis and the intracellular partitioning of fatty acids into storage, oxidation and secretion pathways are tightly regulated. When one or more of these processes becomes dysregulated, excess lipid accumulation can occur. Although genetic and environmental factors have been implicated in the development of NAFLD, it remains unclear why an imbalance in these pathways begins. The regulation of fatty acid partitioning occurs at several points, including during triacylglycerol synthesis, lipid droplet formation and lipolysis. These processes are influenced by enzyme function, intake of dietary fats and sugars and whole-body metabolism, and are further affected by the presence of obesity or insulin resistance. Insight into how the liver controls fatty acid metabolism in health and how these processes might be affected in disease would offer the potential for new therapeutic treatments for NAFLD to be developed.

Hepatic lipid metabolism is affected by a daily 3-meal pattern with varying dietary crude protein with a pig model

The present study was conducted to evaluate the effects of 3 meals administered daily with varying dietary crude protein (CP) contents on hepatic lipid metabolism with a pig model. Pigs were divided into 3 groups according to the following feeding patterns: feeding a basal CP diet 3 times daily (3C); feeding a high CP diet for breakfast, the basal CP diet for lunch, and a low CP diet for dinner (HCL); and feeding the low CP diet for breakfast, the basal CP diet for lunch, and the high protein diet for dinner (LCH). Three groups took equivalent diet per meal ensuring that every pig was fed with similar dietary formulae daily. Results showed that HCL feeding pattern reduced the relative kidney weight (P < 0.05), and LCH feeding pattern increased the relative liver weight of pigs (P < 0.05) when compared with those in the 3C group. Plasma urea nitrogen (P < 0.01) and lipase (P < 0.05) decreased in the HCL group but increased in the LCH group. Both HCL and LCH feeding patterns reduced plasma triglycerides (P < 0.01), non-esterified fatty acids (NEFA) (P < 0.01), and hepatic crude fat (0.05 < P < 0.10) of pigs. Real-time quantitative PCR (RT-qPCR) results showed that dynamic feeding patterns down-regulated (P < 0.05) the mRNA level of lipid metabolism related genes, including adipose triglyceride lipase (ATGL), acetyl-CoA carboxylase (ACCα), liver X receptor (LXRα) in the liver, and negatively regulate elements of circadian clock, including period 1 (Per1), period 2 (Per2), cryptochrome (Cry2), which in turn, upregulated (P < 0.05) the protein expression of positive regulate element brain and muscle Arnt-like 1 (BMAL1) when compared with 3C group. Overall, our findings suggested that dynamic feeding patterns may affect hepatic lipid metabolism via regulation of the circadian clock.

Triglyceride Paradox Is Related to Lipoprotein Size, Visceral Adiposity and Stearoyl-CoA Desaturase Activity in Black Versus White Women

RATIONALE

In black women, triglycerides are paradoxically normal in the presence of insulin resistance. This relationship may be explained by race-related differences in central adiposity and SCD (stearoyl-CoA desaturase)-1 enzyme activity index.

OBJECTIVE

In a cross-sectional study, to compare fasting and postprandial triglyceride-rich lipoprotein particle (TRLP) concentrations and size in black compared with white pre- and postmenopausal women and determine the relationship between TRLP subfractions and whole-body insulin sensitivity, hepatic and visceral fat, and SCD-1 levels.

METHODS AND RESULTS

In 122 federally employed women without diabetes mellitus, 73 black (58 African American and 15 African immigrant) and 49 white; age, 44±10 (mean±SD) years; body mass index, 30.0±5.6 kg/m², we measured lipoprotein subfractions using nuclear magnetic resonance. Hepatic fat was measured by proton magnetic resonance spectroscopy, insulin sensitivity index calculated by minimal modeling from a frequently sampled intravenous glucose test, and red blood cell fatty acid profiles were measured by gas chromatography and were used to estimate SCD-1 indices. Hepatic fat, insulin sensitivity index, and SCD-1 were similar in black women and lower than in whites, regardless of menopausal status. Fasting and postprandial large, medium, and small TRLPs, but not very small TRLPs, were lower in black women. Fasting large, medium, and very small TRLPs negatively correlated with insulin sensitivity index and positively correlated with visceral and hepatic fat and SCD-1 activity in both groups. In multivariate models, visceral fat and SCD-1 were associated with total fasting TRLP concentrations (adjR2, 0.39; P=0.001). Black women had smaller postprandial changes in large (P=0.005) and medium TRLPs (P=0.007).

CONCLUSIONS

Lower visceral fat and SCD-1 activity may contribute to the paradoxical association of lower fasting and postprandial TRLP subfractions despite insulin resistance in black compared with white pre- and postmenopausal women. Similar concentrations of very small TRLPs are related to insulin resistance and could be important mediators of cardiometabolic disease risk in women.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01809288.

Body Mass Index Z-Score Modifies the Association between Added Sugar Intake and Arterial Stiffness in Youth with Type 1 Diabetes: The Search Nutrition Ancillary Study

The relationship between added sugar and arterial stiffness in youth with type 1 diabetes (T1D) has not been well-described. We used data from the SEARCH for Diabetes in Youth Study (SEARCH), an ongoing observational cohort study, to determine the association between added sugar and arterial stiffness in individuals diagnosed with T1D <20 years of age (n = 1539; mean diabetes duration of 7.9 ± 1.9 years). Added sugar intake was assessed by a food frequency questionnaire, and arterial stiffness measures included pulse wave velocity (PWV) and augmentation index. Separate multivariate linear regression models were used to evaluate the association between added sugar and arterial stiffness. Separate interaction terms were included to test for effect modification by body mass index (BMI) z-score and physical activity (PA). Overall, there was no association between added sugar and arterial stiffness (P > 0.05); however, the association between added sugar and arterial stiffness differed by BMI z-score (P for interaction = 0.003). For participants with lower BMI z-scores, added sugar intake was positively associated with PWV trunk measurements, whereas there was no association for those who had a higher BMI z-score. PA did not significantly modify the association between added sugar and arterial stiffness. Further research is needed to determine the longitudinal relationship and to confirm that obesity differentially affects this association.

Effect of liver fatty acid binding protein (L-FABP) gene ablation on lipid metabolism in high glucose diet (HGD) pair-fed mice

Liver fatty acid binding protein (L-FABP) is the major fatty acid binding/"chaperone" protein in hepatic cytosol. Although fatty acids can be derived from the breakdown of dietary fat and glucose, relatively little is known regarding the impact of L-FABP on phenotype in the context of high dietary glucose. Potential impact was examined in wild-type (WT) and Lfabp gene ablated (LKO) female mice fed either a control or pair-fed high glucose diet (HGD). WT mice fed HGD alone exhibited decreased whole body weight gain and weight gain/kcal food consumed-both as reduced lean tissue mass (LTM) and fat tissue mass (FTM). Conversely, LKO alone increased weight gain, lean tissue mass, and fat tissue mass while decreasing serum β-hydroxybutyrate (indicative of hepatic fatty acid oxidation)-regardless of diet. Both LKO alone and HGD alone significantly altered the serum lipoprotein profile and increased triacylglycerol (TG), but in HGD mice the LKO did not further exacerbate serum TG content. HGD had little effect on hepatic lipid composition in WT mice, but prevented the LKO-induced selective increase in hepatic phospholipid, free-cholesterol and cholesteryl-ester. Taken together, these findings suggest that high glucose diet diminished the effects of LKO on the whole body and lipid phenotype of these mice.

Effect of Nutrient and Micronutrient Intake on Chylomicron Production and Postprandial Lipemia

Postprandial lipemia, which is one of the main characteristics of the atherogenic dyslipidemia with fasting plasma hypertriglyceridemia, low high-density lipoprotein cholesterol and an increase of small and dense low-density lipoproteins is now considered a causal risk factor for atherosclerotic cardiovascular disease and all-cause mortality. Postprandial lipemia, which is mainly related to the increase in chylomicron production, is frequently elevated in individuals at high cardiovascular risk such as obese or overweight patients, type 2 diabetic patients and subjects with a metabolic syndrome who share an insulin resistant state. It is now well known that chylomicron production and thus postprandial lipemia is highly regulated by many factors such as endogenous factors: circulating factors such as hormones or free fatty acids, genetic variants, circadian rhythms, or exogenous factors: food components, dietary supplements and prescription drugs. In this review, we focused on the effect of nutrients, micronutrients and phytochemicals but also on food structure on chylomicron production and postprandial lipemia.

PEDF promotes nuclear degradation of ATGL through COP1

Adipose triglyceride lipase (ATGL) plays a compelling role in hepatic lipid turnover and in the pathophysiology of non-alcoholic fatty liver disease. Hepatic ATGL is post-transcriptionally regulated by E3 ubiquitin ligase constitutive photomorphogenic1 (COP1) through polyubiquitylation and proteasomal degradation. However the physiological cue for COP1-mediated hepatocellular degradation of ATGL remained unknown. Here we checked for the role of pigment epithelium-derived factor (PEDF), a moonlighting hepatokine and the so-called ligand of ATGL for its stability in hepatocytes. We show that PEDF diminishes ATGL protein stability by promoting its proteasomal degradation in COP1-dependent manner. Despite being a secretory glycoprotein, PEDF is also sequestered in the nuclear compartment so as COP1. Interestingly, PEDF enhances nuclear import of predominantly cytosolic ATGL protein for its subsequent proteasomal degradation in the nucleus. PEDF also controls cell autonomous hepatocyte lipid accumulation and mobilization through COP1-ATGL axis, thereby unraveling a novel pathway for hepatic lipid metabolism.

Dietary fat: From foe to friend?

For decades, dietary advice was based on the premise that high intakes of fat cause obesity, diabetes, heart disease, and possibly cancer. Recently, evidence for the adverse metabolic effects of processed carbohydrate has led to a resurgence in interest in lower-carbohydrate and ketogenic diets with high fat content. However, some argue that the relative quantity of dietary fat and carbohydrate has little relevance to health and that focus should instead be placed on which particular fat or carbohydrate sources are consumed. This review, by nutrition scientists with widely varying perspectives, summarizes existing evidence to identify areas of broad consensus amid ongoing controversy regarding macronutrients and chronic disease.