Ketogenic diet but not free-sugar restriction alters glucose tolerance, lipid metabolism, peripheral tissue phenotype, and gut microbiome: RCT

Restricted sugar and ketogenic diets can alter energy balance/metabolism, but decreased energy intake may be compensated by reduced expenditure. In healthy adults, randomization to restricting free sugars or overall carbohydrates (ketogenic diet) for 12 weeks reduces fat mass without changing energy expenditure versus control. Free-sugar restriction minimally affects metabolism or gut microbiome but decreases low-density lipoprotein cholesterol (LDL-C). In contrast, a ketogenic diet decreases glucose tolerance, increases skeletal muscle PDK4, and reduces AMPK and GLUT4 levels. By week 4, the ketogenic diet reduces fasting glucose and increases apolipoprotein B, C-reactive protein, and postprandial glycerol concentrations. However, despite sustained ketosis, these effects are no longer apparent by week 12, when gut microbial beta diversity is altered, possibly reflective of longer-term adjustments to the ketogenic diet and/or energy balance. These data demonstrate that restricting free sugars or overall carbohydrates reduces energy intake without altering physical activity, but with divergent effects on glucose tolerance, lipoprotein profiles, and gut microbiome.

Different carbohydrate exposures and weight gain-results from a pooled analysis of three population-based studies

BACKGROUND

The role of carbohydrate quantity and quality in weight gain remains unsolved, and research on carbohydrate subcategories is scarce. We examined total carbohydrates, dietary fiber, total sugar, and sucrose intake in relation to the risk of weight gain in Finnish adults.

METHODS

Our data comprised 8327 adults aged 25-70 years in three population-based prospective cohorts. Diet was assessed by a validated food frequency questionnaire and nutrient intakes were calculated utilizing the Finnish Food Composition Database. Anthropometric measurements were collected according to standard protocols. Two-staged pooling was applied to derive relative risks across cohorts for weight gain of at least 5% by exposure variable intake quintiles in a 7-year follow-up. Linear trends were examined based on a Wald test.

RESULTS

No association was observed between intakes of total carbohydrate, dietary fiber, total sugar or sucrose and the risk of weight gain of at least 5%. Yet, total sugar intake had a borderline protective association with the risk of weight gain in participants with obesity (RR 0.63; 95% CI 0.40-1.00 for highest vs. lowest quintile) and sucrose intake in participants with ≥10% decrease in carbohydrate intake during the follow-up (RR 0.78; 95% CI 0.61-1.00) after adjustments for sex, age, baseline weight, education, smoking, physical activity, and energy intake. Further adjustment for fruit consumption strengthened the associations.

CONCLUSIONS

Our findings do not support an association between carbohydrate intake and weight gain. However, the results suggested that concurrent changes in carbohydrate intake might be an important determinant of weight change and should be further examined in future studies.

Physiological responses to carbohydrate overfeeding

PURPOSE OF REVIEW

To consider emerging research into the physiological effects of excessive dietary carbohydrate intake, with a particular focus on interactions with physical activity.

RECENT FINDINGS

A single episode of massive carbohydrate overload initiates physiological responses to stimulate additional peptide hormone secretion by the gut and the conversion of carbohydrate into lipid by the intestine, liver and adipose tissue. These acute responses maintain glycaemic control both via increased oxidation of carbohydrate (rather than lipid) and via nonoxidative disposal of surplus carbohydrate into endogenous glycogen and lipid storage depots. Sustained carbohydrate overfeeding therefore results in a chronic accumulation of lipid in the liver, skeletal muscle and adipose tissue, which can impair insulin sensitivity and cardiometabolic health in general. Beyond any direct effect of such lipid deposition on body mass/composition, there is not yet clear evidence of physiologically meaningful metabolic or behavioural adaptations to carbohydrate overfeeding in terms of other components of energy balance. However, regular physical exercise can mitigate the negative health effects of carbohydrate overfeeding, independent of any effect on the net carbohydrate surplus.

SUMMARY

Research in this area has advanced understanding regarding the mechanisms of weight gain and associated health outcomes within the modern context of an abundant supply of dietary carbohydrate.

Interactions of Carbohydrate Intake and Physical Activity with Regulatory Genes Affecting Glycaemia: A Food4Me Study Analysis

INTRODUCTION

Carbohydrate intake and physical activity are related to glucose homeostasis, both being influenced by individual genetic makeup. However, the interactions between these 2 factors, as affected by genetics, on glycaemia have been scarcely reported.

OBJECTIVE

We focused on analysing the interplay between carbohydrate intake and physical activity levels on blood glucose, taking into account a genetic risk score (GRS), based on SNPs related to glucose/energy metabolism.

METHODS

A total of 1,271 individuals from the Food4Me cohort, who completed the nutritional intervention, were evaluated at baseline. We collected dietary information by using an online-validated food frequency questionnaire, a questionnaire on physical activity, blood biochemistry by analysis of dried blood spots, and by analysis of selected SNPs. Fifteen out of 31 SNPs, with recognized participation in carbohydrate/energy metabolism, were included in the component analyses. The GRS included risk alleles involved in the control of glycaemia or energy-yielding processes.

RESULTS

Data concerning anthropometric, clinical, metabolic, dietary intake, physical activity, and genetics related to blood glucose levels showed expected trends in European individuals of comparable sex and age, being categorized by lifestyle, BMI, and energy/carbohydrate intakes, in this Food4Me population. Blood glucose was inversely associated with physical activity level (β = -0.041, p = 0.013) and positively correlated with the GRS values (β = 0.015, p = 0.047). Interestingly, an interaction affecting glycaemia, concerning physical activity level with carbohydrate intake, was found (β = -0.060, p = 0.033), which also significantly depended on the genetic background (GRS).

CONCLUSIONS

The relationships of carbohydrate intake and physical activity are important in understanding glucose homeostasis, where a role for the genetic background should be ascribed.

Quantification of On-Farm Pomegranate Fruit Postharvest Losses and Waste, and Implications on Sustainability Indicators: South African Case Study

While there is a growing body of scientific knowledge on improved techniques and procedures for the production and handling of quality pomegranate fruit to meet market demand, little is known about the magnitude of losses that occur at the farm and post-farmgate. This study revealed the amount of pomegranate fruit lost on the farm and the causes of loss and estimated the impacts of losses. The direct measurement method, which involved sorting and counting of individual fruit, was used since physical identification of the causes of fruit losses on individual fruit was necessary for data collection. Furthermore, qualitative data were collected by physical observation during harvesting and interaction with farm workers. At the case study farm in Wellington, Western Cape Province of South Africa, a range of 15.3–20.1% of the harvested crop was considered lost, as the quality fell below marketable standards for retail sales. This amounted to an average of 117.76 tonnes of pomegranate fruit harvested per harvest season in the case study farm, which is removed from the value chain and sold mainly at a low value for juicing and other purposes and translates to an estimated R10.5 million ($618,715.34) economic loss to the farmer. Environmental factors are the main causes of on-farm fruit losses. In the three pomegranate cultivars studied, sunburn and crack were identified as the leading cause of fruit loss, accounting for about 43.9% of all on-farm fruit losses. The lost fiber, carbohydrate, protein, iron and ascorbic acid contents associated with lost fruit were estimated to meet the daily recommended nutrition intake of 2, 9, 4, 2 and 24 people, respectively. Strategies to control and reduce pomegranate fruit losses and waste at the farm level should focus on environmental factors and mechanical damage since they account for the highest sources of fruit losses. This will ensure improved revenue to farmers, sustainable use of natural resources, reduction of the environmental impacts of the fruit industry, and more availability of quality fruit for nutritional security.

Protein quality and quantity influence the effect of dietary fat on weight gain and tissue partitioning via host-microbiota changes

We investigated how protein quantity (10%-30%) and quality (casein and whey) interact with dietary fat (20%-55%) to affect metabolic health in adult mice. Although dietary fat was the main driver of body weight gain and individual tissue weight, high (30%) casein intake accentuated and high whey intake reduced the negative metabolic aspects of high fat. Jejunum and liver transcriptomics revealed increased intestinal permeability, low-grade inflammation, altered lipid metabolism, and liver dysfunction in casein-fed but not whey-fed animals. These differential effects were accompanied by altered gut size and microbial functions related to amino acid degradation and lipid metabolism. Fecal microbiota transfer confirmed that the casein microbiota increases and the whey microbiota impedes weight gain. These data show that the effects of dietary fat on weight gain and tissue partitioning are further influenced by the quantity and quality of the associated protein, primarily via effects on the microbiota.

Carbohydrates to Prevent and Treat Obesity in a Murine Model of Diet-Induced Obesity

INTRODUCTION

The biggest risk factor for obesity and its associated comorbidities is a Western diet. This Western diet induces adipose tissue (AT) inflammation, which causes an AT dysfunction. Since AT is a vital endocrine organ, its dysfunction damages other organs, thus inducing a state of chronic inflammation and causing various comorbidities. Even though it is evident a Western diet, high in fat and carbohydrates, induces obesity and its complications, it is not known yet which macronutrient plays the most important role. Therefore, the aim of this study was to investigate the effect of macronutrient composition on obesity and to reverse the Western diet-induced metabolic risk via caloric restriction (CR) or a change of diet composition.

MATERIALS AND METHODS

Male, C57BL/6JRj mice were fed with a diet high in fat, sucrose, fructose, sucrose and fructose, starch, a Western diet, or a control diet for 15 weeks. To assess reversibility of the metabolic risk, mice were first made obese via 15 weeks of WD and then put on either a CR or switched to a sucrose-rich diet.

RESULTS

A sucrose-rich and high-starch diet induced less obesity and a better metabolic profile than a Western diet, evidenced by less hepatic steatosis, lower plasma cholesterol, and less insulin resistance. Furthermore, these diets induced less intra-abdominal AT inflammation than a Western diet, since mRNA levels of pro-inflammatory markers were lower and there was less macrophage infiltration. Expression of tight junction markers in colon tissue was higher in the sucrose-rich and high-starch group than the Western group, indicating a better intestinal integrity upon sucrose-rich and high-starch feeding. Additionally, CR induced weight loss and decreased both metabolic abnormalities and AT inflammation, regardless of macronutrient composition. However, effects were more pronounced upon CR with sucrose-rich or high-starch diet. Even without CR, switching obese mice to a sucrose-rich diet induced weight loss and decreased AT inflammation and metabolic aberrations.

DISCUSSION

A diet high in sucrose or starch induces less obesity and obesity-associated complications. Moreover, switching obese mice to a sucrose-rich diet elicits weight loss and decreases obesity-induced metabolic complications, highlighting the potential of carbohydrates to treat obesity.

A Systematic Review and Meta-Analysis Comparing Heterogeneity in Body Mass Responses Between Low-Carbohydrate and Low-Fat Diets

OBJECTIVE

An important notion in personalized medicine is that there is clinically relevant treatment response heterogeneity. Low-carbohydrate (CHO) and low-fat diets are widely adopted to reduce body mass. To compare individual differences in responses between two dietary interventions, a formal statistical comparison of response variances between study arms in a randomized controlled trial (RCT) is crucial.

METHODS

The change in variances in RCTs for the body mass responses to low-CHO dietary interventions versus change variances for the low-fat groups (typically considered as the comparator intervention) were compared. A literature search identified relevant RCTs (n = 25; 3,340 participants). The means and SDs of body mass change in low-CHO and low-fat study arms were extracted to calculate the variances of individual responses. These were meta-analyzed in a random-effects model and converted to the SD for individual responses.

RESULTS

The pooled SD for individual responses for body mass was 1.4 kg (95% CI: -1.1 to 2.3) with a wide 95% prediction interval of -6.3 to 10.4 kg.

CONCLUSIONS

Evidence is insufficient to suggest the response heterogeneity to low-CHO diets differs from that observed with low-fat diets.

Low-Protein Diets with Fixed Carbohydrate Content Promote Hyperphagia and Sympathetically Mediated Increase in Energy Expenditure

SCOPE

Dietary protein restriction elicits hyperphagia and increases energy expenditure; however, less is known of whether these responses are a consequence of increasing carbohydrate content. The effects of protein-diluted diets with fixed carbohydrate content on energy balance, hormones, and key markers of protein sensing and thermogenesis in tissues are determined.

METHODS AND RESULTS

Obesity-prone rats (n = 13-16 per group) are randomized to diets containing fixed carbohydrate (52% calories) and varying protein concentrations: 15% (control), 10% (mild protein restriction), 5% (moderate protein restriction) or 1% (severe protein restriction) protein calories, or protein-matched to 5% protein, for 21 days. Propranolol and ondansetron are administered to interrogate the roles of sympathetic and serotonergic systems, respectively, in diet-induced changes in energy expenditure. It is found that mild-to-moderate protein restriction promotes transient hyperphagia, whereas severe protein restriction induces hypophagia, with alterations in meal patterns. Protein restriction enhances energy expenditure that is partly attenuated by propranolol, but not ondansetron. Moderate to severe protein restriction decreases gains in body weight, lean and fat mass, decreased postprandial glucose and leptin, but increased fibroblast growth factor-21 concentrations. Protein-matching retains lean mass suggesting that intake of dietary protein, but not calories, is important for preserving lean mass. Notably, protein restriction increases the protein and/or transcript abundance of key amino acid sensing molecules in liver and intestine (PERK, eIF2α, ATF2, CHOP, 4EBP1, FGF21), and upregulated thermogenic markers (β2AR, Klotho, HADH, UCP-1) in brown adipose tissue.

CONCLUSION

Low-protein diets promote hyperphagia and sympathetically mediated increase in energy expenditure, prevent gains in tissue reserves, and concurrently upregulate hepatic and intestinal amino acid sensing intermediaries and thermogenic markers in brown adipose tissue.

Associations between Macronutrient Intakes and Obesity/Metabolic Risk Phenotypes: Findings of the Korean National Health and Nutrition Examination Survey

Obesity is a risk factor for many health issues, as are metabolic abnormalities. However, few studies have addressed the associations between obesity/metabolic risk phenotypes and dietary macronutrient intakes (carbohydrate, protein, and fat). Therefore, this study examined the associations between macronutrient intakes and obesity/metabolic risk phenotypes in a Korean population. We used data from the Korean National Health and Nutrition Examination Survey, a cross-sectional survey of Korean civilians, conducted in 2014 and 2016, and data on a total of 7374 participants were analyzed. Macronutrient intakes were defined as the proportions of energy derived from carbohydrate, protein, and fat. Those exhibiting obesity/metabolic risk phenotypes (or not) were divided into four groups: normal weight without metabolic abnormalities; obese without metabolic abnormalities; normal weight with metabolic abnormalities; and obese with metabolic abnormalities. After adjusting for age, smoking status, alcohol consumption, extent of physical activity, household income, and daily fiber intake, no association was found between the proportions of carbohydrate, protein, or fat intakes and obesity/metabolic risk phenotypes except for a positive association between metabolically healthy but obese status and low protein intake in females. Further studies are required to evaluate the effects of macronutrient intakes on obesity/metabolic risk phenotypes and associated health outcomes.

Vegetarian Diets Are Associated with Selected Cardiometabolic Risk Factors among Middle-Older Aged South Asians in the United States

Background

Following a vegetarian diet is considered to be beneficial for overall health and is associated with a lower risk of chronic disease.

Objective

This study examined whether South Asians in the United States who consume a vegetarian diet have a lower prevalence of cardiometabolic risk factors.

Methods

Data from the Mediators of Atherosclerosis in South Asians Living in America study, which included 892 South Asians (47% women), with an age range of 40-83 y and a mean ± SD age of 55 ± 9.4 y, were used. Participants were classified as vegetarian if they reported no consumption of meat, poultry, or fish in the previous year on a validated and culturally appropriate food-frequency questionnaire. Adjusted linear and logistic regression models were used to examine associations of a vegetarian diet with cardiometabolic risk factors.

Results

Thirty-eight percent of the cohort participants were classified as vegetarian. Vegetarians reported more frequent weekly eating occasions of whole grains (median frequency/wk: 10 compared with 9, P = 0.012) and beans and legumes (median frequency/wk: 8.5 compared with 5.1, P < 0.001), and less frequent weekly eating occasions of sweets and desserts (median frequency/wk: 1.9 compared with 2.3, P < 0.001). Consuming a vegetarian diet was associated with lower body mass index (P = 0.023), fasting glucose (P = 0.015), insulin resistance (P = 0.003), total cholesterol (P = 0.027), and LDL cholesterol (P = 0.004) and lower odds of fatty liver (OR: 0.43; 95% CI: 0.23, 0.78, P = 0.006). The odds of having any coronary artery calcium were lower for vegetarian men (OR: 0.53; 95% CI: 0.32, 0.87, P = 0.013); however, no significant associations were observed among women.

Conclusions

Among US South Asians, a vegetarian diet was associated with fewer cardiometabolic risk factors overall and with less subclinical atherosclerosis among men.

Association between carbohydrate intake and body composition: The Korean National Health and Nutrition Examination Survey

OBJECTIVE

Several studies have investigated the effects of dietary carbohydrate intake on body composition. However, the results are controversial and few studies have been conducted on an Asian population. The aim of this study was to investigate whether dietary carbohydrate intake is associated with body composition in Korean adults.

METHODS

The present study used data from the Korean National Health and Nutrition Examination Survey, a cross-sectional survey of Korean civilians, conducted from 2008 to 2011. The study analyzed 9594 participants. Carbohydrate intake was defined as the proportion of energy consumed from carbohydrate. Waist circumference, body mass index, and lean and fat mass using a whole-body dual-energy x-ray absorptiometry scanner were measured as body composition parameters.

RESULTS

After adjusting for age, household income, smoking, alcohol consumption, physical activity, history of diabetes, hypertension, dyslipidemia, and intake of energy and fiber per day, the proportion of carbohydrate intake was positively correlated with total limb lean mass in men (β = 0.141, P = 0.046), and in women, the proportion of carbohydrate intake was positively associated with appendicular skeletal muscle mass index (β = 0804, P = 0.003) but negatively associated with trunk fat percentage (β = -0.075, P = 0.026). Total limb lean mass and appendicular skeletal muscle mass index in women showed an increasing trend as the proportion of carbohydrate intake increased.

CONCLUSIONS

No positive association was found between the proportion of carbohydrate intake and any measure of obesity or body fat mass in either men or women. Further studies are needed to evaluate the effects of quantity and quality of carbohydrate intake on body composition.

Carbohydrate intake and the risk of prostate cancer

BACKGROUND

Prostate cancer (PCa) is one of the leading cause cancer among men worldwide. Many epidemiologic studies have reported an association between carbohydrate intake and PCa. However, the evidence from epidemiologic studies is inconsistent. We conducted a comprehensive meta-analysis to explore the associations between carbohydrate intake and PCa risk and to investigate potential dose-response relationships.

METHODS

We searched PubMed and EMBASE for studies published from 1980 to 2018. 21 studies were included with 98,739 participants and 11,573 cases. Multivariate-adjusted odds ratios (ORs) were pooled using random-effect models. Potential dose-response relationships were evaluated for PCa risk.

RESULTS

We did not detect an association about higher carbohydrate intake and PCa risk (OR:1.11, 95% confidence interval [CI]: 0.98-1. 26, I² = 62.7%), nor association was detected about higher carbohydrate intake with advanced PCa risk (OR:0.95, 95% CI: 0.78-1.16, I² = 14.1%) or non-advanced Pca risk (OR:1.01, 95% CI: 0.79-1.29, I² = 64.4%). There was not a significant dose-response association observed for carbohydrate intake with PCa risk and advanced PCa risk.

CONCLUSIONS

Our meta-analysis shows no association between carbohydrate intake and prostate cancer risk. Nor is association detected about carbohydrate intake with advanced or non-advanced Pca risk. More studies are needed for a further dose-response meta-analysis.