Energy Requirement Is Higher During Weight-Loss Maintenance in Adults Consuming a Low- Compared with High-Carbohydrate Diet

BACKGROUND

Longer-term feeding studies suggest that a low-carbohydrate diet increases energy expenditure, consistent with the carbohydrate-insulin model of obesity. However, the validity of methodology utilized in these studies, involving doubly labeled water (DLW), has been questioned.

OBJECTIVE

The aim of this study was to determine whether dietary energy requirement for weight-loss maintenance is higher on a low- compared with high-carbohydrate diet.

METHODS

The study reports secondary outcomes from a feeding study in which the primary outcome was total energy expenditure (TEE). After attaining a mean Run-in weight loss of 10.5%, 164 adults (BMI ≥25 kg/m2; 70.1% women) were randomly assigned to Low-Carbohydrate (percentage of total energy from carbohydrate, fat, protein: 20/60/20), Moderate-Carbohydrate (40/40/20), or High-Carbohydrate (60/20/20) Test diets for 20 wk. Calorie content was adjusted to maintain individual body weight within ± 2 kg of the postweight-loss value. In analyses by intention-to-treat (ITT, completers, n = 148) and per protocol (PP, completers also achieving weight-loss maintenance, n = 110), we compared the estimated energy requirement (EER) from 10 to 20 wk of the Test diets using ANCOVA.

RESULTS

Mean EER was higher in the Low- versus High-Carbohydrate group in models of varying covariate structure involving ITT [ranging from 181 (95% CI: 8-353) to 246 (64-427) kcal/d; P ≤0.04] and PP [ranging from 245 (43-446) to 323 (122-525) kcal/d; P ≤0.02]. This difference remained significant in sensitivity analyses accounting for change in adiposity and possible nonadherence.

CONCLUSIONS

Energy requirement was higher on a low- versus high-carbohydrate diet during weight-loss maintenance in adults, commensurate with TEE. These data are consistent with the carbohydrate-insulin model and lend qualified support for the validity of the DLW method with diets varying in macronutrient composition. This trial was registered at clinicaltrials.gov as NCT02068885.

Effects of Sugar-Sweetened, Artificially Sweetened, and Unsweetened Beverages on Cardiometabolic Risk Factors, Body Composition, and Sweet Taste Preference: A Randomized Controlled Trial

Background

A 2018 American Heart Association science advisory indicated that, pending further research, artificially sweetened beverages (ASBs) may be an appropriate initial replacement for sugar‐sweetened beverages (SSBs) during transition to unsweetened beverages (USBs).

Methods and Results

We randomly assigned 203 adults (121 males, 82 females; 91.6% retention), who habitually consumed SSBs, to 3 groups and delivered free SSBs, ASBs, or USBs to their homes for 12 months. Outcomes included serum triglyceride to high‐density lipoprotein cholesterol ratio (primary), body weight, and sweet taste preference (experimental assessment, 0%–18% sucrose solutions). Change in serum triglyceride to high‐density lipoprotein cholesterol ratio was not different between groups. Although overall change in weight also was not different between groups, we found effect modification (P=0.006) by central adiposity. Among participants in the highest tertile of baseline trunk fat but not other tertiles, weight gain was greater (P=0.002) for the SSB (4.4±1.0 kg, estimate±SE) compared with ASB (0.5±0.9 kg) or USB (−0.2±0.9 kg) group. Both sweetness threshold (–1.0±0.2% m/v; P=0.005) and favorite concentration (–2.3±0.4% m/v; P<0.0001) decreased in the USB group; neither changed in the SSB group. In the ASB group, sweetness threshold did not change, and favorite concentration decreased (–1.1±0.5% m/v; P=0.02). Pairwise comparison between the ASB and USB groups indicated a difference in sweetness threshold (P=0.015).

Conclusions

Replacing SSBs with noncaloric beverages for 12 months did not affect serum triglyceride to high‐density lipoprotein cholesterol ratio. Among individuals with central adiposity, replacing SSBs with either ASBs or USBs lowered body weight. However, USBs may have the most favorable effect on sweet taste preference.

Registration

URL: https://www.clinicaltrials.gov; unique identifier: NCT01295671.

Obesity and impaired metabolic health in patients with COVID-19

Preliminary data suggest that people with obesity are at increased risk of severe COVID-19. However, as data on metabolic parameters (such as BMI and levels of glucose and insulin) in patients with COVID-19 are scarce, increased reporting is needed to improve our understanding of COVID-19 and the care of affected patients.

The Ketogenic Diet: Evidence for Optimism but High-Quality Research Needed

For >50 y, dietary guidelines in the United States have focused on reducing intakes of saturated and total fat. However, rates of obesity and diabetes rose markedly throughout this period, with potentially catastrophic implications for public health and the economy. Recently, ketogenic diets have received substantial attention from the general public and nutrition research community. These very-low-carbohydrate diets, with fat comprising >70% of calories, have been dismissed as fads. However, they have a long history in clinical medicine and human evolution. Ketogenic diets appear to be more effective than low-fat diets for treatment of obesity and diabetes. In addition to the reductions in blood glucose and insulin achievable through carbohydrate restriction, chronic ketosis might confer unique metabolic benefits of relevance to cancer, neurodegenerative conditions, and other diseases associated with insulin resistance. Based on available evidence, a well-formulated ketogenic diet does not appear to have major safety concerns for the general public and can be considered a first-line approach for obesity and diabetes. High-quality clinical trials of ketogenic diets will be needed to assess important questions about their long-term effects and full potential in clinical medicine.

Effects of Dietary Carbohydrate Content on Circulating Metabolic Fuel Availability in the Postprandial State

Context

According to the carbohydrate-insulin model of obesity, an elevated insulin-to-glucagon ratio in response to a high-carbohydrate diet directs metabolic fuels toward storage, resulting in lower circulating energy.

Objective

To determine differences in total circulating energy post-meal related to dietary carbohydrate.

Design

Ancillary study within the Framingham State Food Study.

Setting

University community.

Participants

29 adults (aged 20 to 65 years) with overweight or obesity (body mass index ≥25 kg/m²)

Intervention

After achieving 10% to 14% weight loss on a run-in diet, participants were randomized to weight-loss-maintenance test diets varying in carbohydrate content (high-carbohydrate, 60% of total energy, n = 11; moderate-carbohydrate, 40%, n = 8; low-carbohydrate, 20%, n = 10) and controlled for protein (20%). During 24-hour metabolic ward admissions between 10 and 15 weeks on the test diets, metabolic fuels and hormones were measured.

Main Outcome Measure

Energy availability (EA) based on energy content of blood glucose, beta-hydroxybutyrate, and free fatty acids, in the late postprandial period (180 to 300 minutes). Insulin at 30 minutes into the test meal (Meal Insulin-30) was measured as an effect modifier.

Results

Insulin-to-glucagon ratio was 7-fold higher in participants on the high- vs low-carbohydrate diet (2.5 and 0.36, respectively). Late postprandial EA was 0.58 kcal/L lower on the high- vs low-carbohydrate diet (P < 0.0001), primarily related to suppression of free fatty acids. Early postprandial EA (30 to 180 minutes) declined fastest in the high-carbohydrate group, and Meal Insulin-30 modified this diet effect.

Conclusions

During weight-loss maintenance on a high-carbohydrate diet, late postprandial EA is reduced, consistent with the carbohydrate-insulin model.

Testing the carbohydrate-insulin model of obesity in a 5-month feeding study: the perils of post-hoc participant exclusions

A large feeding study reported that total energy expenditure (TEE) was greater on a low- versus high-carbohydrate diet, supporting the carbohydrate-insulin model of obesity. Recently, the validity of this finding was challenged in a post-hoc analysis excluding participants with putative non-adherence to the study diets. Here, we show why that analysis, based on a post-randomization variable linked to the outcome, introduced severe confounding bias. With control for confounding, the diet effect on TEE remained strong in a reanalysis. Together with sensitivity analyses demonstrating robustness to plausible levels of non-adherence, these data provide experimental support for a potentially novel metabolic effect of macronutrients that might inform the design of more effective obesity treatment.

Discrepancies in the Registries of Diet vs Drug Trials

This cross-sectional study examines discrepancies between registered protocols and subsequent publications for drug and diet trials whose findings were published in prominent clinical journals in the last decade.

Genetic Evidence That Carbohydrate-Stimulated Insulin Secretion Leads to Obesity

BACKGROUND

A fundamental precept of the carbohydrate-insulin model of obesity is that insulin secretion drives weight gain. However, fasting hyperinsulinemia can also be driven by obesity-induced insulin resistance. We used genetic variation to isolate and estimate the potentially causal effect of insulin secretion on body weight.

METHODS

Genetic instruments of variation of insulin secretion [assessed as insulin concentration 30 min after oral glucose (insulin-30)] were used to estimate the causal relationship between increased insulin secretion and body mass index (BMI), using bidirectional Mendelian randomization analysis of genome-wide association studies. Data sources included summary results from the largest published metaanalyses of predominantly European ancestry for insulin secretion (n = 26037) and BMI (n = 322154), as well as individual-level data from the UK Biobank (n = 138541). Data from the Cardiology and Metabolic Patient Cohort study at Massachusetts General Hospital (n = 1675) were used to validate genetic associations with insulin secretion and to test the observational association of insulin secretion and BMI.

RESULTS

Higher genetically determined insulin-30 was strongly associated with higher BMI (β = 0.098, P = 2.2 × 10^-21), consistent with a causal role in obesity. Similar positive associations were noted in sensitivity analyses using other genetic variants as instrumental variables. By contrast, higher genetically determined BMI was not associated with insulin-30.

CONCLUSIONS

Mendelian randomization analyses provide evidence for a causal relationship of glucose-stimulated insulin secretion on body weight, consistent with the carbohydrate-insulin model of obesity.

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.

Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial

OBJECTIVE

To determine the effects of diets varying in carbohydrate to fat ratio on total energy expenditure.

DESIGN

Randomized trial.

SETTING

Multicenter collaboration at US two sites, August 2014 to May 2017.

PARTICIPANTS

164 adults aged 18-65 years with a body mass index of 25 or more.

INTERVENTIONS

After 12% (within 2%) weight loss on a run-in diet, participants were randomly assigned to one of three test diets according to carbohydrate content (high, 60%, n=54; moderate, 40%, n=53; or low, 20%, n=57) for 20 weeks. Test diets were controlled for protein and were energy adjusted to maintain weight loss within 2 kg. To test for effect modification predicted by the carbohydrate-insulin model, the sample was divided into thirds of pre-weight loss insulin secretion (insulin concentration 30 minutes after oral glucose).

MAIN OUTCOME MEASURES

The primary outcome was total energy expenditure, measured with doubly labeled water, by intention-to-treat analysis. Per protocol analysis included participants who maintained target weight loss, potentially providing a more precise effect estimate. Secondary outcomes were resting energy expenditure, measures of physical activity, and levels of the metabolic hormones leptin and ghrelin.

RESULTS

Total energy expenditure differed by diet in the intention-to-treat analysis (n=162, P=0.002), with a linear trend of 52 kcal/d (95% confidence interval 23 to 82) for every 10% decrease in the contribution of carbohydrate to total energy intake (1 kcal=4.18 kJ=0.00418 MJ). Change in total energy expenditure was 91 kcal/d (95% confidence interval -29 to 210) greater in participants assigned to the moderate carbohydrate diet and 209 kcal/d (91 to 326) greater in those assigned to the low carbohydrate diet compared with the high carbohydrate diet. In the per protocol analysis (n=120, P<0.001), the respective differences were 131 kcal/d (-6 to 267) and 278 kcal/d (144 to 411). Among participants in the highest third of pre-weight loss insulin secretion, the difference between the low and high carbohydrate diet was 308 kcal/d in the intention-to-treat analysis and 478 kcal/d in the per protocol analysis (P<0.004). Ghrelin was significantly lower in participants assigned to the low carbohydrate diet compared with those assigned to the high carbohydrate diet (both analyses). Leptin was also significantly lower in participants assigned to the low carbohydrate diet (per protocol).

CONCLUSIONS

Consistent with the carbohydrate-insulin model, lowering dietary carbohydrate increased energy expenditure during weight loss maintenance. This metabolic effect may improve the success of obesity treatment, especially among those with high insulin secretion.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02068885.

An Academia-Industry Partnership for Planning and Executing a Community-Based Feeding Study

A research team from Boston Children's Hospital and Harvard Medical School conducted a community-based feeding study in collaboration with Framingham State University (FSU) and Sodexo, the food service contractor at FSU. The study was a randomized controlled trial, implemented on the FSU campus. For the final year of the study, a satellite feeding site was established at Assabet Valley Regional Technical High School. The purpose of the study was to assess the biological effects of different macronutrient diets. An academia-industry partnership was developed to overcome common challenges associated with hospital-based feeding studies. Benefits included the following: a study site outside of Boston (reducing inconvenience for participants), access to a large commercial kitchen and study-specific kiosk (promoting efficiency), collaboration with Sodexo chefs (ensuring palatability of meals), and opportunity to procure food from contracted vendors. The research (academia) and food service (industry) teams worked together to design, plan, and execute intervention protocols using an integrated approach. During execution, the research team was primarily responsible for overseeing treatment fidelity, whereas the food service team provided culinary expertise, with a strong focus on hospitality and food quality. The study was conducted in 3 cohorts between August 2014 and May 2017. Participants received all of their food for ∼30 wk, totaling >160,000 meals. For all 3 cohorts combined, 234 participants provided informed consent, 229 started a standard run-in weight-loss diet, 164 lost a mean ± SD 12% ± 2% of baseline body weight and were randomly assigned to different macronutrient diets for weight-loss maintenance, and 148 completed the study. During the final and largest cohort, as many as 114 participants received daily meals concurrently. The daily cost per participant for preparation and service of weighed meals and snacks was ∼$65. This academia-industry partnership provides a model for controlled feeding protocols in nutrition research, potentially with enhanced cost-effectiveness, practicality, and generalizability. This trial was registered at http://www.clinicaltrials.gov as NCT02068885.

Source of bias in sugar-sweetened beverage research: a systematic review

OBJECTIVE

Financial conflicts of interest involving the food industry have been reported to bias nutrition studies. However, some have hypothesized that independently funded studies may be biased if the authors have strong a priori beliefs about the healthfulness of a food product ('white hat bias'). The extent to which each source of bias may affect the scientific literature has not been examined. We aimed to explore this question with research involving sugar-sweetened beverages (SSB) as a test case, focusing on a period during which scientific consensus about the adverse health effects of SSB emerged from uncertainty.

DESIGN

PubMed search of worldwide literature was used to identify articles related to SSB and health risks published between 2001 and 2013. Financial relationships and article conclusions were classified by independent groups of co-investigators. Associations were explored by Fischer's exact tests and regression analyses, controlling for covariates.

RESULTS

A total of 133 articles published in English met inclusion criteria. The proportion of industry-related scientific studies decreased significantly with time, from approximately 30 % at the beginning of the study period to <5 % towards the end (P=0·003). A 'strong' or 'qualified' scientific conclusion was reached in 82 % of independent v. 7 % of industry-related SSB studies (P<0·001). Industry-related studies were overwhelmingly more likely to reach 'weak/null' conclusions compared with independent studies regarding the adverse effects of SSB consumption on health (OR=57·30, 95 % CI 7·12, 461·56).

CONCLUSION

Industry-related research during a critical period appears biased to underestimate the adverse health effects of SSB, potentially delaying corrective public health action.

The Carbohydrate-Insulin Model of Obesity: Beyond "Calories In, Calories Out"

Despite intensive research, the causes of the obesity epidemic remain incompletely understood and conventional calorie-restricted diets continue to lack long-term efficacy. According to the carbohydrate-insulin model (CIM) of obesity, recent increases in the consumption of processed, high-glycemic-load carbohydrates produce hormonal changes that promote calorie deposition in adipose tissue, exacerbate hunger, and lower energy expenditure. Basic and genetic research provides mechanistic evidence in support of the CIM. In animals, dietary composition has been clearly demonstrated to affect metabolism and body composition, independently of calorie intake, consistent with CIM predictions. Meta-analyses of behavioral trials report greater weight loss with reduced-glycemic load vs low-fat diets, though these studies characteristically suffer from poor long-term compliance. Feeding studies have lacked the rigor and duration to test the CIM, but the longest such studies tend to show metabolic advantages for low-glycemic load vs low-fat diets. Beyond the type and amount of carbohydrate consumed, the CIM provides a conceptual framework for understanding how many dietary and nondietary exposures might alter hormones, metabolism, and adipocyte biology in ways that could predispose to obesity. Pending definitive studies, the principles of a low-glycemic load diet offer a practical alternative to the conventional focus on dietary fat and calorie restriction.