A higher-carbohydrate, lower-fat diet reduces fasting glucose concentration and improves β-cell function in individuals with impaired fasting glucose

Low-added sugar dietary intervention study to mitigate glucose intolerance and improve body composition in adults with cystic fibrosis: a protocol of a double-blind, randomised study

INTRODUCTION

People with cystic fibrosis (PwCF) are at high risk for developing cystic fibrosis (CF)-related diabetes (CFRD), which worsens morbidity and mortality. Although the pathological events leading to the development of CFRD are complex and not completely understood, dietary factors may play a role. For example, habitual intake of dietary added sugar (i.e., sugar not naturally occurring in foods) has been shown to be increased in PwCF and this excess intake of added sugar could increase the risk of CFRD.

METHODS AND ANALYSIS/DESIGN

The goal of this ongoing double-blind, randomised, parallel-group clinical trial is to recruit approximately 60 clinically stable adults with CF to determine if a low-added sugar intervention improves beta-cell responsiveness and insulin sensitivity (Aim 1), reduces visceral adipose tissue (VAT) and other ectopic fat deposition (Aim 2) and improves plasma redox status (Aim 3) over 8 weeks compared with a typical CF diet. All foods will be provided. Participant selection criteria include confirmed CF diagnosis without CFRD, ≥18 years of age, and baseline estimated daily total added sugar intake >16 tsp. Eligible participants will be randomised to one of two arms: a low-added sugar diet (<5% of kcal from added sugars) or a high-added sugar (≥13% kcal from added sugars) diet. The two diets will be isocaloric and provide 35%-40% kcal from fat. Participants will be seen in the research unit for a screening, baseline/randomisation and 4-week and 8-week follow-up visits. Major study endpoints are changes in beta-cell responsiveness determined by a glucose-potentiated arginine stimulation test (primary endpoint), VAT assessed by magnetic resonance imagin (MRI) and fasted plasma cysteine redox potential. Diet tolerance, body weight and compliance are monitored weekly by phone by an unblinded study dietitian. All analyses will be intention-to-treat. Changes in study endpoints will be assessed with repeated-measures analysis. Models will assess the effects by study arm, time on study, and the interaction between arm and time on study.

ETHICS AND DISSEMINATION

The National Institutes of Health (NIH) funds this study (R01 DK133523). The study protocol was approved by the Emory Institutional Review Board (IRB approval number: 000004517). Any protocol modifications will be reviewed and approved by the IRB prior to implementation and communicated with the study team and participants, as relevant.We will provide reports of the findings to the NIH and Emory IRB in regular progress reports and post the findings on www.

CLINICALTRIALS

gov. We will inform the findings of the study to the scientific community through presentations and peer-reviewed publications. Authorship for any resulting publications will follow the guidelines established by the International Committee of Medical Journal Editors.

TRIAL REGISTRATION NUMBER

This research study is registered at www.

CLINICALTRIALS

gov (NCT05766774).

Calorie Restriction Using High-Fat/Low-Carbohydrate Diet Suppresses Liver Fat Accumulation and Pancreatic Beta-Cell Dedifferentiation in Obese Diabetic Mice

In diabetes, pancreatic β-cells gradually lose their ability to secrete insulin with disease progression. β-cell dysfunction is a contributing factor to diabetes severity. Recently, islet cell heterogeneity, exemplified by β-cell dedifferentiation and identified in diabetic animals, has attracted attention as an underlying molecular mechanism of β-cell dysfunction. Previously, we reported β-cell dedifferentiation suppression by calorie restriction, not by reducing hyperglycemia using hypoglycemic agents (including sodium-glucose cotransporter inhibitors), in an obese diabetic mice model (db/db). Here, to explore further mechanisms of the effects of food intake on β-cell function, db/db mice were fed either a high-carbohydrate/low-fat diet (db-HC) or a low-carbohydrate/high-fat diet (db-HF) using similar calorie restriction regimens. After one month of intervention, body weight reduced, and glucose intolerance improved to a similar extent in the db-HC and db-HF groups. However, β-cell dedifferentiation did not improve in the db-HC group, and β-cell mass compensatory increase occurred in this group. More prominent fat accumulation occurred in the db-HC group livers. The expression levels of genes related to lipid metabolism, mainly regulated by peroxisome proliferator-activated receptor α and γ, differed significantly between groups. In conclusion, the fat/carbohydrate ratio in food during calorie restriction in obese mice affected both liver lipid metabolism and β-cell dedifferentiation.

Short Mediterranean diet screener detects risk of prediabetes in Taiwan, a cross-sectional study

We aimed to determine whether the 14-item Mediterranean diet adherence screener (MEDAS) is suitable in Taiwan and associate the MEDAS score with the risk of prediabetes. In this cross-sectional study 346 patients were recruited between 2014 and 2019 at Taipei Tzu Chi Hospital. The MEDAS score was obtained with a 14-item MEDAS used in the PREDIMED trial. The blood glucose level is measured by fasting glucose and HbA1c. The results of the screener were analyzed for internal consistency and compared with the blood glucose level using multivariate regression models. The MEDAS score was significantly (p = 0.001) and inversely associated with both measures of blood glucose level. Adjusted data (95% CI) showed that each additional point in the MEDAS score decreases the risk of prediabetes with abnormal fasting glucose (> 100 mg/dL) level by 60% and the risk of prediabetes with abnormal HbA1c (> 5.7%) by 22.4%. Consuming at least 3 servings of legumes each week was significantly (p = 0.007) related to a lower risk of prediabetes under logistic regression. A higher score on the 14-item MEDAS screener was significantly associated with a lower risk of prediabetes.

Chlorogenic acid and β-glucan from highland barley grain ameliorate β-cell dysfunction via inhibiting apoptosis and improving cell proliferation

Recent studies have reported that highland barley as a whole grain diet has anti-hyperglycemic effects, however little information is available about the active compounds that ameliorate pancreatic β-cell dysfunction and the related mechanisms. In this study, chlorogenic acid (CA) and β-glucan (BG) were identified as the active compounds that ameliorated β-cell dysfunction. CA ameliorated β-cell dysfunction by inhibiting cell apoptosis and improving glucose-stimulated insulin secretion via targeting G protein-coupled receptor 40 (GPR40) and regulating the phospholipase C β (PLCβ) pathway. BG ameliorated β-cell dysfunction by improving cell proliferation via targeting mammalian target of rapamycin (mTOR) and regulating the protein kinase B (Akt)/glycogen synthase kinase-3β (GSK-3β) pathway. Furthermore, CA and BG improved β-cell sensitivity and pancreatic insulin secretion, and inhibited β-cell apoptosis in impaired glucose tolerance (IGT) mice. Notably, CA restored homeostasis model assessment (HOMA)-β values and Ca²⁺-ATP and K⁺-ATP levels back to normal levels, and BG at 300 mg per kg BW restored β-cell insulin contents back to normal levels in IGT mice. Additionally, the combination of CA and BG had an additive effect on ameliorating β-cell dysfunction. These results help develop whole highland barley grain as a functional food for preventing type 2 diabetes by ameliorating pancreatic β-cell damage.

Potentiation of incretin hormones and modulation of metabolic enzymes as possible mechanisms behind the insulin sensitizing effects of cabbage-metformin treatment

In our study, we treated high fructose diet-induced insulin resistance in rats with any of metformin, cabbage (80%w/w) or combined metformin and cabbage (MetCabb), and observed the activities of glycolysis and gluconeogenesis regulatory enzymes, incretin hormones and other hormones affecting glucose homeostasis. Comparisons were made with normoglycemic noninsulin resistance rats (control) and insulin-resistant untreated rats (INres). Baseline analysis showing elevated fasting blood sugar (>250 mg/dl), insulin (>25 µIU/ml) and HOMA-IR (>10) satisfied the criteria for recruitment into the insulin-resistant groups. Treatment lasted for 12 weeks. HOMA-IR values significantly (P < 0.05) decreased from 24.7 to 5.5 and 10.6 respectively with MetCabb treatment. MetCabb normalized HOMA-IR values and mean β-cell responsiveness of the INres. Cabbage and metCabb normalized the leptin levels relative to control. The mean fasting blood sugar, insulin, and c-peptide levels with MetCabb treatment reverted to control levels. We found a strong positive linear correlation between the glucagon levels (r = 0.9145) and increasing HOMA-IR values while both incretin hormones; GLP-1 and GIP negatively regressed (r = -0.8084 and -0.8488). MetCab treatment produced comparable values of GLP-1 and GIP to the control. A strong positive correlation was found between the HOMA-IR values and the PEPCK (r = 0.9065), F-1,6-BPase (r = 0.7951), and G-6-Pase (r = 0.7893). The hexokinase (r = -0.807), PFK (r = -0.9151), and PK (r = -0.7448) levels regressed as HOMA-IR values increased. The glycolytic and gluconeogenic enzymes except PEPCK reverted to control levels with MetCabb treatment. Combination of metformin and cabbage was more effective than individual treatments.

Effects of total fat intake on body fatness in adults

BACKGROUND

The ideal proportion of energy from fat in our food and its relation to body weight is not clear. In order to prevent overweight and obesity in the general population, we need to understand the relationship between the proportion of energy from fat and resulting weight and body fatness in the general population.

OBJECTIVES

To assess the effects of proportion of energy intake from fat on measures of body fatness (including body weight, waist circumference, percentage body fat and body mass index) in people not aiming to lose weight, using all appropriate randomised controlled trials (RCTs) of at least six months duration.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, Clinicaltrials.gov and the WHO International Clinical Trials Registry Platform (ICTRP) to October 2019. We did not limit the search by language.

SELECTION CRITERIA

Trials fulfilled the following criteria: 1) randomised intervention trial, 2) included adults aged at least 18 years, 3) randomised to a lower fat versus higher fat diet, without the intention to reduce weight in any participants, 4) not multifactorial and 5) assessed a measure of weight or body fatness after at least six months. We duplicated inclusion decisions and resolved disagreement by discussion or referral to a third party.

DATA COLLECTION AND ANALYSIS

We extracted data on the population, intervention, control and outcome measures in duplicate. We extracted measures of body fatness (body weight, BMI, percentage body fat and waist circumference) independently in duplicate at all available time points. We performed random-effects meta-analyses, meta-regression, subgrouping, sensitivity, funnel plot analyses and GRADE assessment.

MAIN RESULTS

We included 37 RCTs (57,079 participants). There is consistent high-quality evidence from RCTs that reducing total fat intake results in small reductions in body fatness; this was seen in almost all included studies and was highly resistant to sensitivity analyses (GRADE high-consistency evidence, not downgraded). The effect of eating less fat (compared with higher fat intake) is a mean body weight reduction of 1.4 kg (95% confidence interval (CI) -1.7 to -1.1 kg, in 53,875 participants from 26 RCTs, I² = 75%). The heterogeneity was explained in subgrouping and meta-regression. These suggested that greater weight loss results from greater fat reductions in people with lower fat intake at baseline, and people with higher body mass index (BMI) at baseline. The size of the effect on weight does not alter over time and is mirrored by reductions in BMI (MD -0.5 kg/m², 95% CI -0.6 to -0.3, 46,539 participants in 14 trials, I² = 21%), waist circumference (MD -0.5 cm, 95% CI -0.7 to -0.2, 16,620 participants in 3 trials; I² = 21%), and percentage body fat (MD -0.3% body fat, 95% CI -0.6 to 0.00, P = 0.05, in 2350 participants in 2 trials; I² = 0%). There was no suggestion of harms associated with low fat diets that might mitigate any benefits on body fatness. The reduction in body weight was reflected in small reductions in LDL (-0.13 mmol/L, 95% CI -0.21 to -0.05), and total cholesterol (-0.23 mmol/L, 95% CI -0.32 to -0.14), with little or no effect on HDL cholesterol (-0.02 mmol/L, 95% CI -0.03 to 0.00), triglycerides (0.01 mmol/L, 95% CI -0.05 to 0.07), systolic (-0.75 mmHg, 95% CI -1.42 to -0.07) or diastolic blood pressure(-0.52 mmHg, 95% CI -0.95 to -0.09), all GRADE high-consistency evidence or quality of life (0.04, 95% CI 0.01 to 0.07, on a scale of 0 to 10, GRADE low-consistency evidence).

AUTHORS' CONCLUSIONS

Trials where participants were randomised to a lower fat intake versus a higher fat intake, but with no intention to reduce weight, showed a consistent, stable but small effect of low fat intake on body fatness: slightly lower weight, BMI, waist circumference and percentage body fat compared with higher fat arms. Greater fat reduction, lower baseline fat intake and higher baseline BMI were all associated with greater reductions in weight. There was no evidence of harm to serum lipids, blood pressure or quality of life, but rather of small benefits or no effect.

Effect of diet composition on insulin sensitivity in humans

Diet composition has a marked impact on the risk of developing type 2 diabetes and cardiovascular disease. Prospective studies show that dietary patterns with elevated amount of animal products and low quantity of vegetable food items raise the risk of these diseases. In healthy subjects, animal protein intake intensifies insulin resistance whereas plant-based foods enhance insulin sensitivity. Similar effects have been documented in patients with diabetes. Accordingly, pre-pregnancy intake of meat (processed and unprocessed) has been strongly associated with a higher risk of gestational diabetes whereas greater pre-pregnancy vegetable protein consumption is associated with a lower risk of gestational diabetes. Population groups that modify their traditional dietary habit increasing the amount of animal products while reducing plant-based foods experience a remarkable rise in the frequency of type 2 diabetes. The association of animal protein intake with insulin resistance is independent of body mass index. In obese individuals that consume high animal protein diets, insulin sensitivity does not improve following weight loss. Diets aimed to lose weight that encourage restriction of carbohydrates and elevated consumption of animal protein intensify insulin resistance increasing the risk of developing type 2 diabetes and cardiovascular disease. The effect of dietary components on insulin sensitivity may contribute to explain the striking impact of eating habits on the risk of type 2 diabetes and cardiovascular disease. Insulin resistance predisposes to type 2 diabetes in healthy subjects and deteriorates metabolic control in patients with diabetes. In nondiabetic and diabetic individuals, insulin resistance is a major cardiovascular risk factor.

Dietary Interventions for the Prevention of Type 2 Diabetes in High-Risk Groups: Current State of Evidence and Future Research Needs

A series of large-scale randomised controlled trials have demonstrated the effectiveness of lifestyle change in preventing type 2 diabetes in people with impaired glucose tolerance. Participants in these trials consumed a low-fat diet, lost a moderate amount of weight and/or increased their physical activity. Weight loss appears to be the primary driver of type 2 diabetes risk reduction, with individual dietary components playing a minor role. The effect of weight loss via other dietary approaches, such as low-carbohydrate diets, a Mediterranean dietary pattern, intermittent fasting or very-low-energy diets, on the incidence of type 2 diabetes has not been tested. These diets-as described here-could be equally, if not more effective in preventing type 2 diabetes than the tested low-fat diet, and if so, would increase choice for patients. There is also a need to understand the effect of foods and diets on beta-cell function, as the available evidence suggests moderate weight loss, as achieved in the diabetes prevention trials, improves insulin sensitivity but not beta-cell function. Finally, prediabetes is an umbrella term for different prediabetic states, each with distinct underlying pathophysiology. The limited data available question whether moderate weight loss is effective at preventing type 2 diabetes in each of the prediabetes subtypes.

Association of dietary sodium:potassium ratio with the metabolic syndrome in Chinese adults

Several epidemiological studies have investigated that Na or K intakes might be associated with the metabolic syndrome (MetS). However, little evidence has evaluated the association between Na:K ratio and the MetS. In this study, we assessed the association between the dietary Na:K ratio and the MetS. The cross-sectional study was conducted among adults aged 18 years and older in Nanjing, using a multi-stage random sampling method, which resulted in a sample size of 1993 participants. Dietary Na and K intakes were assessed by 3 consecutive days of dietary recollection combined with condiments weighing method. Health-related data were obtained by standardised questionnaires, as well as physical examinations and laboratory assessments. The prevalence rate of the MetS was 36·5 % (728/1993). After adjusting for various lifestyle and dietary factors of the MetS, participants in the highest quartile of dietary Na:K ratio were at a higher risk of developing MetS (OR=1·602; 95 % CI 1·090, 2·353) compared with those in the lowest quartile. Each 1-sd increase in dietary Na:K ratio was associated with a higher risk of prevalent MetS (OR=1·166; 95 % CI: 1·018, 1·336). Among the components of the MetS, dietary Na:K ratio was positively associated with high blood pressure (quartile 3 v. quartile 1: OR=1·656; 95 % CI 1·228, 2·256) and hypertriacylglycerolaemia (quartile 4 v. quartile1: OR=1·305; 95 % CI 1·029, 1·655) in multivariate analysis. These results revealed that higher dietary Na:K ratio significantly increased the risk of the MetS in Chinese adults. Further studies are needed to verify this association.

A Plant-Based Dietary Intervention Improves Beta-Cell Function and Insulin Resistance in Overweight Adults: A 16-Week Randomized Clinical Trial

The aim of this study was to test the effect of a plant-based dietary intervention on beta-cell function in overweight adults with no history of diabetes. Participants (n = 75) were randomized to follow a low-fat plant-based diet (n = 38) or to make no diet changes (n = 37) for 16 weeks. At baseline and 16 weeks, beta-cell function was quantified with a mathematical model. Using a standard meal test, insulin secretory rate was calculated by C-peptide deconvolution. The Homeostasis Model Assessment (HOMA-IR) index was used to assess insulin resistance while fasting. A marked increase in meal-stimulated insulin secretion was observed in the intervention group compared with controls (interaction between group and time, Gxt, p < 0.001). HOMA-IR index fell significantly (p < 0.001) in the intervention group (treatment effect −1.0 (95% CI, −1.2 to −0.8); Gxt, p = 0.004). Changes in HOMA-IR correlated positively with changes in body mass index (BMI) and visceral fat volume (r = 0.34; p = 0.009 and r = 0.42; p = 0.001, respectively). The latter remained significant after adjustment for changes in BMI (r = 0.41; p = 0.002). Changes in glucose-induced insulin secretion correlated negatively with BMI changes (r = −0.25; p = 0.04), but not with changes in visceral fat. Beta-cell function and insulin sensitivity were significantly improved through a low-fat plant-based diet in overweight adults.

The influence of intensive lifestyle intervention on patients with isolated impaired fasting glucose: a meta-analysis

AIM

To evaluate the effect of intensive lifestyle intervention on patients with isolated impaired fasting glucose.

BACKGROUND

The application of lifestyle intervention to clinical nursing can help improve outcomes of patients with impaired fasting glucose.

DESIGN

We performed a meta-analysis of randomized controlled trials using methods outlined in the Cochrane Handbook.

METHODS

We performed keyword searches of the literature databases up to September 2014 and performed manual searches of selected article reference lists. Data were extracted by the lead reviewer, cross-checked by the second reviewer, entered into RevMan5·3, and pooled and analysed using the fixed effect inverse-variance model or random effects model to determine the mean difference and calculate the weighted mean difference. The heterogeneity statistic (I² ), overall effect (Z) and P-value were calculated.

RESULTS

A total of five studies were included in our analysis. Following the heterogeneity test statistic, overall effect Z score with P-value was calculated. The targets of fasting plasma glucose, weight, body mass index, triglycerides, high-density lipoprotein cholesterol and total cholesterol all showed significant differences between the intervention and control groups.

CONCLUSION

Lifestyle intervention can improve glycaemic control in patients with isolated impaired fasting glucose. It also reduces blood-lipid levels and promotes weight loss. Larger patient cohorts and adequate follow-up should be included in future trials.

Relatively Low β-Cell Responsiveness Contributes to the Association of BMI with Circulating Glucose Concentrations Measured under Free-Living Conditions among Pregnant African American Women

BACKGROUND

Body mass index (BMI, in kg/m(2)) is positively associated with plasma glucose in late pregnancy and with risk of adverse obstetric outcomes. Much of the existing research uses single-clinic measures of plasma glucose, which may not accurately reflect circulating glucose under free-living conditions. Furthermore, little is known about circulating glucose concentrations of African American women, who tend to have poorer diet quality and a greater risk of obstetric complications.

OBJECTIVE

The objective of the study was to test the hypothesis that the positive association of BMI in early pregnancy with third-trimester circulating glucose concentrations measured under free-living conditions among African American women would be at least partially attributable to lower β-cell insulin secretion relative to insulin sensitivity [i.e., lower disposition index (DI)].

METHODS

Using a prospective, observational design, 40 pregnant African American women (mean ± SD age: 23.1 ± 4.0 y; mean ± SD BMI: 28.4 ± 7.5) wore continuous glucose monitors and accelerometers for 3 d at 32-35 wk of gestation and concurrently maintained a food diary to report their self-selected meals. The DI was derived from a 75-g oral glucose tolerance test. Linear regression modeling was used to calculate the association of BMI with the 24-h glucose (GLUC24h) and 2-h (GLUC2hPP) postprandial glucose areas under the curve and with the percentage of time the glucose concentrations were >120 mg/dL.

RESULTS

The positive associations between BMI and GLUC24h (standardized β = 0.36, P = 0.03) and the percentage of time glucose concentrations were >120 mg/dL (standardized β = 0.40, P = 0.02) were independent of total carbohydrate intake and physical activity and were attenuated when DI was added to the model. The positive association of BMI with GLUC2hPP was attenuated when DI was added to the model, and DI itself was independently associated with GLUC2hPP after self-selected breakfast and dinner (standardized β = -0.33 and -0.42, respectively; P = 0.01).

CONCLUSIONS

The association of BMI with high circulating glucose in free-living pregnant African American women is at least partially attributable to lower β-cell responsiveness.

Metabolic responses to a traditional Mexican diet compared with a commonly consumed US diet in women of Mexican descent: a randomized crossover feeding trial

BACKGROUND

Mexican immigrants are disproportionally affected by diet-related risk of metabolic dysfunction. Whether adhering to a traditional Mexican diet or adopting a US diet contributes to metabolic changes associated with future risk of type 2 diabetes and other chronic diseases has not been investigated.

OBJECTIVE

The purpose of this study was to test in a randomized crossover feeding trial the metabolic responses to a Mexican diet compared with a commonly consumed US diet.

DESIGN

First- and second-generation healthy women of Mexican descent (n = 53) were randomly assigned in a crossover design to consume a Mexican or US diet for 24 d each, separated by a 28-d washout period. Diets were eucaloric and similar in macronutrient composition. The metabolic responses to diets were assessed by measuring fasting serum concentrations of glucose, insulin, insulin-like growth factor 1 (IGF-1), insulin-like growth factor binding protein 3 (IGFBP-3), adiponectin, C-reactive protein (CRP), and interleukin 6 (IL-6), as well as the homeostasis model assessment of insulin resistance (HOMA-IR) at the beginning and end of each period. Linear mixed models tested the intervention effect on the biomarkers, while adjusting for diet sequence, feeding period, baseline and washout biomarker concentrations, age, acculturation, and BMI.

RESULTS

Compared with the US diet, the Mexican diet reduced insulin by 14% [geometric means (95% CIs): 9.3 (8.3, 10.3) compared with 8.0 (7.2, 8.9) μU/mL; P = 0.02], HOMA-IR by 15% [2.0 (1.8, 2.3) compared with 1.7 (1.6, 2.0); P = 0.02], and IGFBP-3 by 6% (mean ± SEM: 2420 ± 29 compared with 2299 ± 29 ng/mL; P < 0.01) and tended to reduce circulating concentrations of IGF-1 by 4% (149 ± 2.6 compared with 144 ± 2.5 ng/mL; P = 0.06). There was no significant intervention effect on serum concentrations of glucose, adiponectin, CRP, or IL-6 in the US compared with the Mexican diet.

CONCLUSION

Compared with the commonly consumed US diet, the traditional Mexican diet modestly improved insulin sensitivity under conditions of weight stability in healthy women of Mexican descent, while having no impact on biomarkers of inflammation. This trial was registered at clinicaltrials.gov as NCT01369173.

Effects of total fat intake on body weight

BACKGROUND

In order to prevent overweight and obesity in the general population we need to understand the relationship between the proportion of energy from fat and resulting weight and body fatness in the general population.

OBJECTIVES

To assess the effects of proportion of energy intake from fat on measures of weight and body fatness (including obesity, waist circumference and body mass index) in people not aiming to lose weight, using all appropriate randomised controlled trials (RCTs) and cohort studies in adults, children and young people

SEARCH METHODS

We searched CENTRAL to March 2014 and MEDLINE, EMBASE and CINAHL to November 2014. We did not limit the search by language. We also checked the references of relevant reviews.

SELECTION CRITERIA

Trials fulfilled the following criteria: 1) randomised intervention trial, 2) included children (aged ≥ 24 months), young people or adults, 3) randomised to a lower fat versus usual or moderate fat diet, without the intention to reduce weight in any participants, 4) not multifactorial and 5) assessed a measure of weight or body fatness after at least six months. We also included cohort studies in children, young people and adults that assessed the proportion of energy from fat at baseline and assessed the relationship with body weight or fatness after at least one year. We duplicated inclusion decisions and resolved disagreement by discussion or referral to a third party.

DATA COLLECTION AND ANALYSIS

We extracted data on the population, intervention, control and outcome measures in duplicate. We extracted measures of weight and body fatness independently in duplicate at all available time points. We performed random-effects meta-analyses, meta-regression, subgrouping, sensitivity and funnel plot analyses.

MAIN RESULTS

We included 32 RCTs (approximately 54,000 participants) and 30 sets of analyses of 25 cohorts. There is consistent evidence from RCTs in adults of a small weight-reducing effect of eating a smaller proportion of energy from fat; this was seen in almost all included studies and was highly resistant to sensitivity analyses. The effect of eating less fat (compared with usual diet) is a mean weight reduction of 1.5 kg (95% confidence interval (CI) -2.0 to -1.1 kg), but greater weight loss results from greater fat reductions. The size of the effect on weight does not alter over time and is mirrored by reductions in body mass index (BMI) (-0.5 kg/m(2), 95% CI -0.7 to -0.3) and waist circumference (-0.3 cm, 95% CI -0.6 to -0.02). Included cohort studies in children and adults most often do not suggest any relationship between total fat intake and later measures of weight, body fatness or change in body fatness. However, there was a suggestion that lower fat intake was associated with smaller increases in weight in middle-aged but not elderly adults, and in change in BMI in the highest validity child cohort.

AUTHORS' CONCLUSIONS

Trials where participants were randomised to a lower fat intake versus usual or moderate fat intake, but with no intention to reduce weight, showed a consistent, stable but small effect of low fat intake on body fatness: slightly lower weight, BMI and waist circumference compared with controls. Greater fat reduction and lower baseline fat intake were both associated with greater reductions in weight. This effect of reducing total fat was not consistently reflected in cohort studies assessing the relationship between total fat intake and later measures of body fatness or change in body fatness in studies of children, young people or adults.

Dietary models of insulin resistance

Insulin resistance is a significant factor in the development of type 2 diabetes mellitus, however the connection between the Western diet and the development of insulin resistance has not been fully explained. Dietary macronutrient composition has been examined in a number of articles, and diets enriched in saturated fatty acids, and possibly in fructose, appear to be most consistently associated with the development of insulin resistance. However, mechanistic insights into the metabolic effects of such diets are lacking, and merit further study.

A lower-carbohydrate, higher-fat diet reduces abdominal and intermuscular fat and increases insulin sensitivity in adults at risk of type 2 diabetes

BACKGROUND

Obesity, particularly visceral and ectopic adiposity, increases the risk of type 2 diabetes.

OBJECTIVE

The aim of this study was to determine if restriction of dietary carbohydrate is beneficial for body composition and metabolic health.

METHODS

Two studies were conducted. In the first, 69 overweight/obese men and women, 53% of whom were European American (EA) and 47% of whom were African American (AA), were provided with 1 of 2 diets (lower-fat diet: 55%, 18%, and 27% of energy from carbohydrate, protein, and fat, respectively; lower-carbohydrate diet: 43%, 18%, and 39%, respectively) for 8 wk at a eucaloric level and 8 wk at a hypocaloric level. In the second study, 30 women with polycystic ovary syndrome (PCOS) were provided with 2 diets (lower-fat diet: 55%, 18%, and 27% of energy from carbohydrate, protein, and fat, respectively; lower-carbohydrate diet: 41%, 19%, and 40%, respectively) at a eucaloric level for 8 wk in a random-order crossover design.

RESULTS

As previously reported, among overweight/obese adults, after the eucaloric phase, participants who consumed the lower-carbohydrate vs. the lower-fat diet lost more intra-abdominal adipose tissue (IAAT) (11 ± 3% vs. 1 ± 3%; P < 0.05). After weight loss, participants who consumed the lower-carbohydrate diet had 4.4% less total fat mass. Original to this report, across the entire 16-wk study, AAs lost more fat mass with a lower-carbohydrate diet (6.2 vs. 2.9 kg; P < 0.01), whereas EAs showed no difference between diets. As previously reported, among women with PCOS, the lower-carbohydrate arm showed decreased fasting insulin (-2.8 μIU/mL; P < 0.001) and fasting glucose (-4.7 mg/dL; P < 0.01) and increased insulin sensitivity (1.06 arbitrary units; P < 0.05) and "dynamic" β-cell response (96.1 · 10(9); P < 0.001). In the lower-carbohydrate arm, women lost both IAAT (-4.8 cm(2); P < 0.01) and intermuscular fat (-1.2 cm(2); P < 0.01). In the lower-fat arm, women lost lean mass (-0.6 kg; P < 0.05). Original to this report, after the lower-carbohydrate arm, the change in IAAT was positively associated with the change in tumor necrosis factor α (P < 0.05).

CONCLUSION

A modest reduction in dietary carbohydrate has beneficial effects on body composition, fat distribution, and glucose metabolism. This trial was registered at clinicaltrials.gov as NCT00726908 and NCT01028989.

A small amount of dietary carbohydrate can promote the HFD-induced insulin resistance to a maximal level

Both dietary fat and carbohydrates (Carbs) may play important roles in the development of insulin resistance. The main goal of this study was to further define the roles for fat and dietary carbs in insulin resistance. C57BL/6 mice were fed normal chow diet (CD) or HFD containing 0.1–25.5% carbs for 5 weeks, followed by evaluations of calorie consumption, body weight and fat gains, insulin sensitivity, intratissue insulin signaling, ectopic fat, and oxidative stress in liver and skeletal muscle. The role of hepatic gluconeogenesis in the HFD-induced insulin resistance was determined in mice. The role of fat in insulin resistance was also examined in cultured cells. HFD with little carbs (0.1%) induced severe insulin resistance. Addition of 5% carbs to HFD dramatically elevated insulin resistance and 10% carbs in HFD was sufficient to induce a maximal level of insulin resistance. HFD with little carbs induced ectopic fat accumulation and oxidative stress in liver and skeletal muscle and addition of carbs to HFD dramatically enhanced ectopic fat and oxidative stress. HFD increased hepatic expression of key gluconeogenic genes and the increase was most dramatic by HFD with little carbs, and inhibition of hepatic gluconeogenesis prevented the HFD-induced insulin resistance. In cultured cells, development of insulin resistance induced by a pathological level of insulin was prevented in the absence of fat. Together, fat is essential for development of insulin resistance and dietary carb is not necessary for HFD-induced insulin resistance due to the presence of hepatic gluconeogenesis but a very small amount of it can promote HFD-induced insulin resistance to a maximal level.

Risk of postprandial insulin resistance: the liver/vagus rapport

Ingestion of a meal is the greatest challenge faced by glucose homeostasis. The surge of nutrients has to be disposed quickly, as high concentrations in the bloodstream may have pathophysiological effects, and also properly, as misplaced reserves may induce problems in affected tissues. Thus, loss of the ability to adequately dispose of ingested nutrients can be expected to lead to glucose intolerance, and favor the development of pathologies. Achieving interplay of several organs is of upmost importance to maintain effectively postprandial glucose clearance, with the liver being responsible of orchestrating global glycemic control. This dogmatic role of the liver in postprandial insulin sensitivity is tightly associated with the vagus nerve. Herein, we uncover the behaviour of metabolic pathways determined by hepatic parasympathetic function status, in physiology and in pathophysiology. Likewise, the inquiry expands to address the impact of a modern lifestyle, especially one's feeding habits, on the hepatic parasympathetic nerve control of glucose metabolism.

Favourable metabolic effects of a eucaloric lower-carbohydrate diet in women with PCOS

OBJECTIVE

Diet-induced reduction in circulating insulin may be an attractive nonpharmacological treatment for women with polycystic ovary syndrome (PCOS) among whom elevated insulin may exacerbate symptoms by stimulating testosterone synthesis. This study was designed to determine whether a modest reduction in dietary carbohydrate (CHO) content affects β-cell responsiveness, serum testosterone concentration and insulin sensitivity in women with PCOS.

DESIGN

In a crossover design, two diets ('Standard,' STD, 55:18:27% energy from carbohydrate/protein/fat; lower-carbohydrate, 41:19:40) were provided for 8 weeks in random order with a 4-week washout between.

PATIENTS

Thirty women with PCOS.

MEASUREMENTS

β-cell responsiveness assessed as the C-peptide response to glucose during a liquid meal test; insulin sensitivity from insulin and glucose values throughout the test; insulin resistance (HOMA-IR); and total testosterone by immunoassay.

RESULTS

Paired t-test indicated that the lower-CHO diet induced significant decreases in basal β-cell response (PhiB), fasting insulin, fasting glucose, HOMA-IR, total testosterone and all cholesterol measures, and significant increases in insulin sensitivity and dynamic ('first-phase') β-cell response. The STD diet induced a decrease in HDL-C and an increase in the total cholesterol-to-HDL-C ratio. Across all data combined, the change in testosterone was positively associated with the changes in fasting insulin, PhiB and insulin AUC (P < 0·05).

CONCLUSIONS

In women with PCOS, modest reduction in dietary CHO in the context of a weight-maintaining diet has numerous beneficial effects on the metabolic profile that may lead to a decrease in circulating testosterone.

Effects of diet macronutrient composition on body composition and fat distribution during weight maintenance and weight loss

OBJECTIVE

Qualitative aspects of diet may affect body composition and propensity for weight gain or loss. We tested the hypothesis that consumption of a relatively low glycemic load (GL) diet would reduce total and visceral adipose tissue under both eucaloric and hypocaloric conditions.

DESIGN AND METHODS

Participants were 69 healthy overweight men and women. Body composition was assessed by DXA and fat distribution by CT scan at baseline, after 8 weeks of a eucaloric diet intervention, and after 8 weeks of a hypocaloric (1000 kcal/day deficit) diet intervention. Participants were provided all food for both phases, and randomized to either a low GL diet (<45 points per 1000 kcal; n = 40) or high GL diet (>75 points per 1000 kcal, n = 29).

RESULTS

After the eucaloric phase, participants who consumed the low GL diet had 11% less intra-abdominal fat (IAAT) than those who consumed the high GL diet (P < 0.05, adjusted for total fat mass and baseline IAAT). Participants lost an average of 5.8 kg during the hypocaloric phase, with no differences in the amount of weight loss with diet assignment (P = 0.39). Following weight loss, participants who consumed the low GL diet had 4.4% less total fat mass than those who consumed the high GL diet (P < 0.05, adjusted for lean mass and baseline fat mass).

CONCLUSIONS

Consumption of a relatively low GL diet may affect energy partitioning, both inducing reduction in IAAT independent of weight change, and enhancing loss of fat relative to lean mass during weight loss.

Effects of habitual diet on ethnic differences in serum total ghrelin

Ghrelin, an orexigenic hormone, may be involved in the etiology of obesity. African Americans (AA) experience higher obesity rates than European Americans (EA), but it is unclear whether ghrelin differs with ethnicity. This study was designed to compare ghrelin concentrations between overweight AA and EA adults in a post absorptive state, in response to a standard meal, and after 8-week habituation to diets of differing macronutrient profiles. Sixty-one overweight men and women (31 EA and 30 AA) were assigned to either a higher-carbohydrate/lower-fat diet (55% CHO, 18% PRO, 27% FAT) or a lower-carbohydrate/higher-fat diet (43% CHO, 18% PRO, 39% FAT) for 8 weeks. At baseline and week 8, participants ingested a standard liquid mixed meal. Blood was sampled before the meal and serially after ingestion to measure total ghrelin and insulin. Hunger was assessed with a visual analog scale. Composite scores for ghrelin, insulin, and hunger were calculated as area under the curve (AUC), and ghrelin suppression was calculated as the change from fasting concentration. Fasting ghrelin and ghrelin AUC were higher among EA at baseline and week 8 (p < 0.001), and these differences were not affected by diet habituation. Despite greater postprandial ghrelin suppression, EA displayed greater hunger immediately following the test meal (p < 0.05). Overweight EA displayed higher circulating ghrelin and greater ghrelin suppression compared to AA. Further study is warranted to explore the physiological basis for these ethnic differences and to determine whether they may relate to higher obesity rates among AA.

Intestinal fatty acid infusion modulates food preference as well as calorie intake via the vagal nerve and midbrain-hypothalamic neural pathways in rats

The intestine plays important roles in the regulation of feeding behavior by sensing macronutrients. Intestinal fatty acids strongly suppress food intake, but little is known about whether intestinal fatty acids affect food preference. We investigated the effects of jejunal fatty acids infusion on food preference by conducting two-diet choice experiments in rats fed a high-fat diet (HFD) and a high-carbohydrate diet (HCD). Jejunal linoleic acid (18:2) infusion reduced HFD intake dose-dependently, while HCD intake increased with the middle dose of the infusion we examined (100 μL/h) and reduced to the control level with the higher doses (150 and 200 μL/h). α-Linolenic acid (18:3), but not caprylic acid (8:0), altered the food preference and total calorie intake in the same manner as linoleic acid. Linoleic acid infusion dose-dependently increased plasma glucagon-like peptide-1, peptide YY and cholecystokinin levels, but not ghrelin levels. Subdiaphragmatic vagotomy or midbrain transection prevented the change in food preference and total calorie intake by linoleic acid infusion. Jejunal linoleic acid infusion increased norepinephrine turnover in the paraventricular hypothalamic nucleus, while intracerebroventricular injection of idazoxan, an α2-adrenergic receptor (AR) antagonist, suppressed the increased HCD intake, but did not affect the decreased HFD intake. These findings indicated that intestinal long-chain fatty acids modulated food preference as well as total calorie intake via the vagal nerve and midbrain-hypothalamic neural pathways. The effects of the α2-AR antagonist in the brain suggested that the brain distinctly controlled HCD and HFD intake in response to jejunal linoleic acid infusion.