Healthy Low-carbohydrate Diets Research Articles

Switching diets after 6-months does not result in renewed weight loss: a secondary analysis of a 12-month crossover randomized trial.

Weight change trajectory from diet and lifestyle interventions typically involves rapid weight loss followed by a weight plateau after approximately 6months. Changing from one weight-loss diet to another at the time of the plateau could instigate renewed weight loss. Therefore, our secondary analysis aimed to assess trajectory of weight loss in a 12-month, randomized, cross-over study. Forty-two adults were randomized to eat a healthy low-fat or healthy low-carbohydrate diet for 6months then switched to the opposite diet for an additional 6months. Regardless of diet assignment, participants experienced rapid initial weight loss, which slowed between 3 to 6months. After switching diets at 6months, weight modestly decreased until 9months, but at a rate slower than the initial 3months and slower than the rate from 3 to 6months. This suggests that the weight loss plateau typically seen at 6months is physiological and cannot be overcome by simply switching to a different weight-loss diet.

Abstract P346: Effect of Low-Fat versus Low-Carbohydrate Diet on Visceral Fat

Introduction: A healthy low fat (HLF) and healthy low carbohydrate (HLC) diet are common strategies for weight loss that vary in their effects on adiposity and metabolism. Visceral adipose tissue (VAT) is the major contributor to metabolism deregulation, beyond subcutaneous adipose tissue (SAT). Despite strong biological evidence that a HLC diet preferentially decreases VAT relative to SAT, the difficulty in measuring adipose sub-types has impeded its use in diet trials. To address this research gap, we measured VAT and SAT in a secondary analysis of the Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) weight loss trial to compare the effects of HLF and HLC diets and potential effect modification by sex and insulin resistance status. Hypothesis: We hypothesized that a HLC diet is associated with greater VAT loss compared with a HLF diet. Secondly, we hypothesized that men and those with greater baseline insulin secretion assigned to HLC diet would experience greater VAT loss. Methods: DIETFITS was a single-site, parallel-group, weight loss diet trial, randomizing 609 adults with overweight and obesity to a HLC or HLF diet for 12 months. Data collection occurred at baseline, 6 months, and 12 months. Insulin resistance status was proxy measured using insulin concentration 30 minutes after a glucose challenge (INS 30). In this secondary analysis, we measured VAT and SAT in the abdominal region by reanalyzing the dual-energy x-ray absorptiometry (DXA) scans. We fit a linear mixed model to evaluate the change in VAT after 6 and 12 months on HLF and HLC, with fixed effects: time, diet, and their interaction; and a random effect for repeated observations. We built separate models for each of the secondary hypotheses, with additional fixed effects INS 30 and sex, respectively. Results: We included 449 participants with baseline DXA (60% women; mean age 40 years). From baseline to 6-months, participants assigned to a HLC diet experienced a significant 10.6 cm 2 (95% CI: 5.1, 16.1) greater decrease in mean VAT compared to those assigned to a HLF diet. The 12-month difference in diets attenuated to 5.5 cm 2 (95% CI: -0.1, 11.1). Contrary to our hypothesis, INS 30 did not modify the diet-related changes in VAT. Among men, both diets resulted in a 12-month decrease in VAT. The HLC diet was associated with a 12.1 cm 2 (95% CI: 1.6, 22.7) greater loss of VAT compared to HLF. Among women, HLF but not HLC was associated with decreased VAT, and there was no difference in VAT loss between diets 1.8 cm 2 (95% CI: -4.1, 7.6). Models controlling for SAT indicated that VAT decreased independently of SAT. Conclusion: These findings contribute to the understanding of the nuanced impacts of HLF and HLC diets on adipose sub-types and underscore the relevance of considering sex in designing effective dietary interventions targeting VAT reduction and metabolic health.

Low-Carbohydrate Diet Macronutrient Quality and Weight Change

The associations of low-carbohydrate diets (LCDs) with long-term weight management remains unclear, and the source and quality of macronutrients within LCDs are less explored. To prospectively examine associations between changes in LCD indices and weight change among US adults. This prospective cohort study included initially healthy participants at baseline from the Nurses' Health Study (NHS; 1986-2010), Nurses' Health Study II (NHSII; 1991-2015), and Health Professionals Follow-up Study (HPFS; 1986-2018). Data analysis was performed between November 2022 and April 2023. Five LCD indices were examined: (1) a total LCD (TLCD) emphasizing overall lower carbohydrate intake; (2) an animal-based LCD (ALCD) that emphasized animal-sourced protein and fat; (3) a vegetable-based LCD (VLCD) that emphasized plant-sourced protein and fat; (4) a healthy LCD (HLCD) emphasizing less refined carbohydrates, more plant protein, and healthy fat; and (5) an unhealthy LCD (ULCD) emphasizing less healthful carbohydrates, more animal protein, and unhealthy fat. The outcome of interest was 4-year changes in self-reported body weight. A total of 123 332 participants (mean [SD] age, 45.0 [9.7] years; 103 320 [83.8%] female) were included in this study. The median carbohydrate intake (as a percentage of energy) of the highest quintiles of TLCD score at baseline ranged from 38.3% in HPFS to 40.9% in NHSII. Mean weight gain over 4-year intervals among participants varied from 0.8 kg in the HPFS to 1.8 kg in the NHSII. After adjusting for demographics and baseline and concomitant changes of selected lifestyle factors, each 1-SD increase in TLCD score was associated with 0.06 (95% CI, 0.04-0.08) kg more weight gain over the 4-year periods. Similarly, participants gained 0.13 (95% CI, 0.11 to 0.14) kg per each 1-SD increase in ALCD score and 0.39 (95% CI, 0.37 to 0.40) kg per each 1-SD change in ULCD score. In contrast, each 1-SD increase in VLCD score was associated with 0.03 (95% CI, 0.01 to 0.04) kg less weight gain, and each 1-SD increase in HLCD score was associated with 0.36 (95% CI, 0.35 to 0.38) kg less weight gain. The associations were more pronounced among obese individuals (per 1-SD increase in HLCD score: BMI ≥30, 0.88 [95% CI, 0.80, 0.97] kg less weight gain; BMI <25, 0.23 [95% CI, 0.20, 0.26] kg less weight gain; P for interaction < .001). These findings suggest that the quality of LCDs may play a critical role in modulating long-term weight change. Only LCDs that emphasized high-quality protein, fat, and carbohydrates from whole grains and other plant-based foods were associated with less weight gain.

A Healthy, Low-Carbohydrate Diet During Pregnancy Is Associated With a Reduced Risk of Gestational Diabetes Mellitus.

Evidence on the associations of low-carbohydrate diet (LCD) during pregnancy with gestational diabetes mellitus (GDM) has been limited and inconsistent. We aimed to prospectively evaluate the risk of GDM associated with the LCD considering the quality of macronutrients. All participants were from a prospective cohort in Wuhan, China. The overall, healthy LCD (emphasizing low-quality carbohydrates, plant protein, and unsaturated fat), and unhealthy LCD (emphasizing high-quality carbohydrates, animal protein, and saturated fat) scores were calculated according to the percentage of energy intake from carbohydrates, protein, and fat. GDM was screened by a 75-g oral glucose tolerance test between 24 and 28 weeks. Poisson regression models were used to calculate relative risks (RRs) and 95% CIs. Of 2337 pregnant women, 257 (11.0%) were diagnosed with GDM. Overall LCD score was not associated with risk of GDM, but the healthy and unhealthy LCD scores were associated with the risk of GDM. The multivariable-adjusted RRs (95% CI) were 0.68 (0.49-0.94) and 1.52 (1.11-2.08) for healthy and unhealthy LCD scores comparing the highest with the lowest quartile. Substituting high-quality carbohydrates for low-quality carbohydrates and animal protein, and substituting unsaturated fat for saturated fat, were associated with a 13% to 29% lower risk of GDM. A healthy LCD during pregnancy characterized by high-quality carbohydrates, plant protein, and unsaturated fat was associated with a lower risk of GDM, whereas an unhealthy LCD consisting of low-quality carbohydrates, animal protein, and saturated fat was associated with a higher risk of GDM.

Weight, insulin resistance, blood lipids, and diet quality changes associated with ketogenic and ultra low-fat dietary patterns: a secondary analysis of the DIETFITS randomized clinical trial.

The DIETFITS trial reported no significant difference in 12-month weight loss between a healthy low-fat and healthy low-carbohydrate diet. Participants were instructed to restrict fat or carbohydrates to levels consistent with a ketogenic or ultra low-fat diet for 2 months and to subsequently increase intakes until they achieved a comfortable maintenance level. To compare 3- and 12-month changes in body weight and cardiometabolic risk factors between a subsample of participants who reported 3-month fat or carbohydrates intakes consistent with either a ketogenic-like diet (KLD) or ultra low-fat diet (ULF). 3-month and 12-month weight and risk factor outcomes were compared between KLD (n = 18) and ULF (n = 21) sub-groups of DIETFITS participants (selected from n = 609, healthy overweight/obese, aged 18-50 years). Less than 10% of DIETFITS participants met KLD or ULF criteria at 3-months. Both groups achieved similar weight loss and insulin resistance improvements at 3-months and maintained them at 12- months. Significant differences at 3-months included a transient ~12% increase in LDL cholesterol (LDL-C) for KLD with a concomitant greater reduction in log(TG/HDL), a measure of LDL-C's atherogenic potential. The latter was maintained at 12-months, despite substantial diet recidivism for both groups, whereas LDL-C levels were similar for ULF at baseline and 12-months. KLD participants achieved and maintained the greatest reductions in added sugars and refined grains at 3- months and 12-months, whereas ULF participants reported a 50% increase in refined grains intake from baseline to 12-months. Among the ~10% of study participants that achieved the most extreme restriction of dietary fat vs. carbohydrate after 3 months, weight loss and improvement in insulin sensitivity were substantial and similar between groups. At 12 months, after considerable dietary recidivism, the few significant differences in diet quality and blood lipid parameters tended to favor KLD over ULF.

Evidence for the carbohydrate–insulin model in a reanalysis of the Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) trial

BackgroundThe Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) trial demonstrated that meaningful weight loss can be achieved with either a “healthy low-carbohydrate diet” (LCD) or “healthy low-fat diet” (LFD). However, because both diets substantially decreased glycemic load (GL), the dietary factors mediating weight loss remain unclear. ObjectivesWe aimed to explore the contribution of macronutrients and GL to weight loss in DIETFITS and examine a hypothesized relationship between GL and insulin secretion. DesignThis study is a secondary data analysis of the DIETFITS trial, in which participants with overweight or obesity (aged 18–50 y) were randomized to a 12-mo LCD (N = 304) or LFD (N = 305). ResultsMeasures related to carbohydrate intake (total amount, glycemic index, added sugar, and fiber) showed strong associations with weight loss at 3-, 6-, and 12-mo time points in the full cohort, whereas those related to total fat intake showed weak to no associations. A biomarker of carbohydrate (triglyceride/HDL cholesterol ratio) predicted weight loss at all time points (3-mo: β [kg/biomarker z-score change] = 1.1, P = 3.5 × 10−9; 6-mo: β = 1.7, P = 1.1 × 10−9; and 12-mo: β = 2.6, P = 1.5 × 10−15), whereas that of fat (low-density lipoprotein cholesterol + HDL cholesterol) did not (all time points: P = NS). In a mediation model, GL explained most of the observed effect of total calorie intake on weight change. Dividing the cohort into quintiles of baseline insulin secretion and GL reduction revealed evidence of effect modification for weight loss, with P = 0.0009 at 3 mo, P = 0.01 at 6 mo, and P = 0.07 at 12 mo. ConclusionsAs predicted by the carbohydrate–insulin model of obesity, weight loss in both diet groups of DIETFITS seems to have been driven by the reduction of GL more so than dietary fat or calories, an effect that may be most pronounced among those with high insulin secretion. These findings should be interpreted cautiously in view of the exploratory nature of this study. Trial RegistrationClinicalTrials.gov (NCT01826591).

Healthy and unhealthy low-carbohydrate diets and plasma markers of cardiometabolic risk.

Previous studies have reported inconsistent associations between low-carbohydrate diets (LCD) and plasma lipid profile. Also, there is little evidence on the role of the quality and food sources of macronutrients in LCD in cardiometabolic health. We investigated the cross-sectional associations between LCD and plasma cardiometabolic risk markers in a nationwide representative sample of the US population. Diet was measured through two 24-h recalls. Overall, healthy (emphasising unsaturated fat, plant protein and less low-quality carbohydrates) and unhealthy (emphasising saturated fat, animal protein and less high-quality carbohydrate) LCD scores were developed according to the percentage of energy as total and subtypes of carbohydrate, protein and fat. Linear regression was used to estimate the percentage difference of plasma marker concentrations by LCD scores. A total of 34785 participants aged 18-85 years were included. After adjusting for covariates including BMI, healthy LCD was associated with lower levels of insulin, homoeostatic model assessment for insulin resistance (HOMA-IR), C-reactive protein (CRP) and TAG, and higher levels of HDL-cholesterol, with the percentage differences (comparing extreme quartile of LCD score) of -5·91, -6·16, -9·13, -9·71 and 7·60 (all Ptrend < 0·001), respectively. Conversely, unhealthy LCD was associated with higher levels of insulin, HOMA-IR, CRP and LDL-cholesterol (all Ptrend < 0·001). Our results suggest that healthy LCD may have positive, whereas unhealthy LCD may have negative impacts on CRP and metabolic and lipid profiles. These findings underscore the need to carefully consider the quality and subtypes of macronutrients in future LCD studies.

Low-Carbohydrate Diets Score and Mortality Among Adults with Incident Type 2 Diabetes

ObjectivesIt is unclear whether adherence to low carbohydrate diet (LCD) patterns is beneficial towards type 2 diabetes (T2D) patients. The present study aims to prospectively examine the association between post-diagnostic LCD patterns and mortality among T2D patients.MethodsWe included participants from the Nurses’ Health Study and Health Professionals Follow-Up Study who were diagnosed with T2D during the follow-up. An overall total low carbohydrate diet score (TLCDS) was calculated based on the percentage of energy as total carbohydrates. In addition, plant (PLCDS) and animal-based LCD scores (ALCDS) emphasizing plant or animal protein and fat consumption, respectively, healthy LCD (HLCDS) and unhealthy LCD (ULCDS) emphasizing high or low quality of carbohydrates and fats, respectively, were further derived. All LCDS were cumulative averaged since the T2D diagnosis. Cause of death was identified from death certifications or review of medical records. A multivariable-adjusted Cox models were used to assess the association between LCDS and mortality.ResultsAmong 10,101 participants with incident T2D contributing 139,417 person-years during follow-up, we documented 4,452 deaths of which 1,326 and 875 cases were attributed to cardiovascular disease (CVD) and cancer, respectively. The pooled multivariable-adjusted hazard ratios (HRs, 95% CIs) of total mortality per 10 points increment of post-diagnostic LCDS were 0.87 (0.82,0.92) for TLCDS, 0.75 (0.70,0.80) for PLCDS, and 0.78 (0.73,0.84) for HLCDS. Both PLCDS and HLCDS were also associated with significantly lower CVD and cancer mortality. Each 10 points increase of TLCDS, PLCDS, and HLCDS from pre-diagnostic to post-diagnostic period were associated with 13% (7%, 18%), 16% (20%, 31%), and 15% (20%, 31%) lower total mortality. Increasing pre-to-post-diagnostic PLCDS and HLCDS were also associated with significantly lower CVD mortality and cancer mortality. No significant associations were observed for either cumulative averaged or change of ALCDS and ULCDS.ConclusionsAmong diabetes patients, greater adherence to LCD patterns that emphasize high quality sources of macronutrients was significantly associated with lower total, cardiovascular, and cancer mortality.Funding SourcesNational Institute of Health.

550-P: A Randomized Trial of Low-Carbohydrate Diet on Hemoglobin A1c among Individuals with Elevated Hemoglobin A1c

Background: Low-carbohydrate diets decrease hemoglobin A1c among patients with type 2 diabetes mellitus. However, evidence on effects of low-carbohydrate diets on hemoglobin A1c among individuals with prediabetes is limited. Methods: We conducted a randomized parallel-group trial of 150 adults aged 40-70 years with untreated hemoglobin A1c from 6.0-6.9%. Participants were assigned to a healthy low-carbohydrate diet (target &amp;lt;40 grams net carbohydrates months 1-3; &amp;lt;60 grams months 3-6) or usual diet. The low-carbohydrate arm received regular dietary counseling. Data on hemoglobin A1c and other metabolic risk factors were collected at 0, 3, and 6 months. Results: Mean age was 59 years; 72% were female and 59% were Black. 95% completed the study. Participants in the low-carbohydrate arm had significantly greater 6-month decrease in hemoglobin A1c (net difference, -0.23% [95% CI, -0.32 to -0.14%]) , fasting plasma glucose (net difference, -10.3 mg/dL [95% CI, -15.7 to -4.9 mg/dL]) , and body weight (net difference, -5.9 kg [95% CI, -7.2 to -4.7 kg]) compared with usual diet arm. At 6 months, 53% in the low-carbohydrate arm and 32% in the usual diet arm had hemoglobin A1c &amp;lt;6.0% (p=0.01) . Conclusion: A healthy low-carbohydrate diet led to improvements in glycemic and other cardiometabolic outcomes in adults with elevated hemoglobin A1c and could be recommended for prevention of type 2 diabetes mellitus. Disclosure K.S.Dorans: None. M.J.O'brien: None. G.I.Uwaifo: None. J.He: None. L.A.Bazzano: None. L.Qi: None. H.He: None. J.Chen: None. L.J.Appel: n/a. F.Hu: None. J.Samet: None. K.T.Mills: None. Funding National Institute of General Medical Sciences (1P20GM109036-01A1) . The California Walnut Commission (Folsom, CA) supported the study by providing walnuts. Shakes and bars were donated by The Simply Good Foods Company (Denver, CO) . Sugar replacement samples were provided by Swerve LLC (New Orleans, LA) .

Abstract P126: Identifying Successful Predictors Of Body Fat Reduction In The Dietfits Trial

Background: Reducing excess body fat is important for overall health, but individual success at reducing body fat varies considerably. Because dietary modification plays a key role in reducing body fat and maintaining a healthy body weight, there has been speculation if one particular dietary pattern is superior to another for losing weight. Previously we reported no significant differences in the effectiveness of either a low-carbohydrate diet or a low-fat diet for weight loss in the DIETFITs Trial. However, there is less literature that has specifically focused on body fat reduction. Therefore the purpose of this study was to assess if 12-month dietary changes were associated with body fat reduction. Methods: Participants were men and women with overweight or obesity that participated in the DIETFITS trial, a randomized clinical trial comparing the effectiveness of a healthy low-fat diet to a healthy low-carbohydrate diet for weight loss. The primary outcome was body fat percent loss, which was measured with dual-energy x-ray absorptiometry (DEXA) scans. Demographic information was collected from online surveys at baseline, dietary data were assessed from participants 24-hour recalls, and physical activity was assessed with the Stanford Seven-Day Physical Activity Recall questionnaire. Linear regression models were conducted to assess the association between changes in energy intake, dietary fat, and carbohydrates with body fat reduction, while controlling for demographic variables and physical activity. Results: Data were available for 272 participants with DEXA scans and dietary data. In the main model both baseline physical activity (coef = -0.26, p = 0.016) and changes in physical activity (coef = -0.36, p &lt; 0.01) were significantly associated with body fat reduction. When stratified by dietary assignment, changes in physical activity remained significant for each group (low-carb group: coef = -0.30, p = 0.002 and low-fat group coef = -0.35, p = 0.006), while changes in dietary fat, as a percentage of energy intake, was associated with body fat reduction in the low-fat group only (coef = 0.15, p = 0.006). Race was also significantly associated with body fat reduction in all models, indicating non-White participants gained more body fat at the end of the intervention compared to Whites. Conclusions: The reduction in body fat appears to be mostly driven from participants increasing their physical activity levels. Identifying other predictors of body fat reduction warrant further study.

Low-carbohydrate dietary pattern on glycemic outcomes trial (ADEPT) among individuals with elevated hemoglobin A1c: study protocol for a randomized controlled trial

BackgroundType 2 diabetes mellitus (T2DM) is a major cause of morbidity and mortality globally. Strong evidence supports the importance of diet and other lifestyle factors in preventing T2DM. Among individuals with T2DM, low-carbohydrate diets lead to decreases in hemoglobin A1c (HbA1c). However, research on the effects of low-carbohydrate diets on glycemic outcomes among individuals not currently on glucose-lowering medications who have elevated HbA1c is limited.MethodsThe objective of this randomized controlled trial is to study the effect of a healthy low-carbohydrate diet achieved through behavioral intervention and key food supplementation compared with usual diet on HbA1c and other metabolic risk factors among individuals with HbA1c from 6.0 to 6.9% who are not on glucose-lowering medications. In this parallel trial, 150 participants will be randomized to the intervention or control group for 6 months. The healthy low-carbohydrate diet target is < 40 g of net carbohydrates during the first 3 months and < 40 to 60 net grams for months 3 to 6. This diet is characterized by abundant unsaturated fat and protein, high-fiber foods such as non-starchy vegetables and nuts, and minimal refined carbohydrates. The primary outcome is the difference in HbA1c change from baseline to 6 months in the intervention compared with usual diet group. Secondary outcomes include differences between groups in 6-month changes in fasting glucose, systolic blood pressure, total-to-high-density lipoprotein (HDL) cholesterol ratio, and body weight. Exploratory outcomes include differences in 6-month changes in fasting insulin, homeostasis model assessment of insulin resistance, diastolic blood pressure, waist circumference, and 10-year cardiovascular disease risk. An intention-to-treat analysis will be used.DiscussionWe expect that the results from this study will lead to new approaches for developing and implementing dietary approaches (other than the most commonly used reduced fat diet) that will substantially reduce risk of cardiometabolic disease among adults with or at high risk of T2DM. The study intervention involves behavioral counseling and promotes consumption of dietary components thought to reduce risk of cardiometabolic disease and has expected applicability in clinical practice.Trial registrationClinicalTrials.gov NCT03675360. Registered on September 18, 2018 (prior to enrolment of the first participant).

Long-term dietary intervention reveals resilience of the gut microbiota despite changes in diet and weight

With the rising rates of obesity and associated metabolic disorders, there is a growing need for effective long-term weight-loss strategies, coupled with an understanding of how they interface with human physiology. Interest is growing in the potential role of gut microbes as they pertain to responses to different weight-loss diets; however, the ways that diet, the gut microbiota, and long-term weight loss influence one another is not well understood. Our primary objective was to determine if baseline microbiota composition or diversity was associated with weight-loss success. A secondary objective was to track the longitudinal associations of changes to lower-carbohydrate or lower-fat diets and concomitant weight loss with the composition and diversity of the gut microbiota. We used 16S ribosomal RNA gene amplicon sequencing to profile microbiota composition over a 12-mo period in 49 participants as part of a larger randomized dietary intervention study of participants consuming either a healthy low-carbohydrate or a healthy low-fat diet. While baseline microbiota composition was not predictive of weight loss, each diet resulted in substantial changes in the microbiota 3-mo after the start of the intervention; some of these changes were diet specific (14 taxonomic changes specific to the healthy low-carbohydrate diet, 12 taxonomic changes specific to the healthy low-fat diet) and others tracked with weight loss (7 taxonomic changes in both diets). After these initial shifts, the microbiota returned near its original baseline state for the remainder of the intervention, despite participants maintaining their diet and weight loss for the entire study. These results suggest a resilience to perturbation of the microbiota's starting profile. When considering the established contribution of obesity-associated microbiotas to weight gain in animal models, microbiota resilience may need to be overcome for long-term alterations to human physiology. This trial was registered at clinicaltrials.gov as NCT01826591.

Baseline Psychosocial and Demographic Factors Associated with Study Attrition and 12-Month Weight Gain in the DIETFITS Trial.

The purpose of this study was to examine correlates of failure-trial attrition and weight gain-in a randomized clinical weight-loss trial. The Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) trial included 609 adults (18-50 years; BMI 28-40). Participants were randomized to a 12-month healthy low-fat or healthy low-carbohydrate diet for weight loss. At baseline, participants completed psychosocial, demographic, and anthropometric measures. Stepwise logistic regressions identified baseline factors associated with (1) study attrition and (2) among trial completers, weight gain at 12 months. Having higher baseline food addiction and self-efficacywas linked to treatment failure. Being younger, not having a college education, having higher outcome expectations and quality of life, and having lower social functioning and self-control increased the odds of trial attrition. Identifying as other than non-Hispanic white; not being married or cohabitating; having higher cognitive restraint and self-control; and having lower amotivation, family encouragement, and physical limitations increased the odds of gaining weight by treatment's end. Participants' baseline psychosocial and demographic factors may support or impede successful weight loss. Trialists should attend to these factors when designing treatments in order to promote participants' likelihood of completing the trial and achieving their weight-loss goals.

Changes in blood lipid concentrations associated with changes in intake of dietary saturated fat in the context of a healthy low-carbohydrate weight-loss diet: a secondary analysis of the Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) trial

For low-carbohydrate diets, a public health approach has focused on the replacement of carbohydrates with unsaturated fats. However, little research exists on the impacts of saturated fat intake on the lipid profile in the context of whole-food-based low-carbohydrate weight-loss diets. The primary aim of this secondary analysis of the DIETFITS weight loss trial was to evaluate the associations between changes in percentage of dietary saturated fatty acid intake (%SFA) and changes in low-density lipoproteins, high-density lipoproteins, and triglyceride concentrations for those following a healthy low-carbohydrate (HLC) diet. The secondary aim was to examine these associations specifically for HLC dieters who had the highest 12-month increases in %SFA. In the DIETFITS trial, 609 generally healthy adults, aged 18-50 years, with body mass indices of 28-40 kg/m2 were randomly assigned to a healthy low-fat (HLF) or HLC diet for 12 months. In this analysis, linear regression, both without and with adjustment for potential confounders, was used to measure the association between 12-month change in %SFA and blood lipids in 208 HLC participants with complete diet and blood lipid data. Participants consumed an average of 12-18% of calories from SFA. An increase of %SFA, without significant changes in absolute saturated fat intake, over 12 months was associated with a statistically significant decrease in triglycerides in the context of a weight-loss study in which participants simultaneously decreased carbohydrate intake. The association between increase in %SFA and decrease in triglycerides was no longer significant when adjusting for 12-month change in carbohydrate intake, suggesting carbohydrate intake may be a mediator of this relationship. Those on a low-carbohydrate weight-loss diet who increase their percentage intake of dietary saturated fat may improve their overall lipid profile provided they focus on a high-quality diet and lower their intakes of both calories and refined carbohydrates. This trial was registered at clinicaltrials.gov as NCT01826591.

Abstract P214: Dietary Adherence and Dietary Quality Are Associated With Weight Loss Success Among Those Following Low-fat and Low-carbohydrate Diets

Introduction: Dietary modification is the cornerstone of most successful weight loss strategies. Low-fat and low-carbohydrate diets are among the most studied approaches, but neither has been shown to be consistently superior for weight loss in the general population. Previous studies suggest that eating a high-quality diet or adhering to a given dietary strategy may influence weight loss, however these two factors have not been examined concurrently for those following macronutrient-limiting diets. Objective: To determine whether improvement in dietary quality, change in dietary macronutrient composition or the combination of these factors leads to differential weight loss for those instructed to follow a healthy low-fat (HLF) or healthy low-carbohydrate (HLC) diet. Methods: Generally healthy, non-diabetic adults, aged 18-50 years, BMI 28-40 kg/m 2 , were randomized to HLF or HLC diets for 12 months (n=609) as part of the DIETFITS weight loss study. Participants that provided complete 24-hour dietary recall data at baseline and 12 months were included in this secondary analysis (n=448; n=224 HLF, n=224 HLC). Within each diet assignment arm, our analysis divided participants into four subgroups according to 12-month change in diet quality score (HEI-2010, above the median was defined as high quality (HQ); below the median was defined as low quality (LQ)) and 12-month change in macronutrient intake (below the median was defined as high adherence (HA) and above the median was defined as low adherence (LA) for fat (g) or digestible carbohydrate (g) for HLF and HLC, respectively). Multiple linear regression adjusted for age, sex, baseline weight and baseline fat (or digestible carbohydrate) intake was used to compare the primary outcome, baseline to 12-month change in mean BMI (kg/m 2 ), for those in the HQ/HA, HQ/LA, LQ/HA subgroups versus the LQ/LA subgroup within HLF and HLC. Results: For HLF, changes (95% CI) in mean BMI were -1.11 kg/m 2 (-2.10, -0.11) for HQ/HA, -0.26 (-1.26, 0.75) for HQ/LA, and -0.66 (-1.74, 0.41) for LQ/HA compared with the LQ/LA subgroup. For HLC, changes (95% CI) in mean BMI were -1.15 kg/m 2 (-2.04, -0.26) for HQ/HA, -0.30 (-1.22, 0.61) for HQ/LA, and -0.80 (-1.74, 0.14) for LQ/HA compared with the LQ/LA subgroup. Conclusions: Within both the HLF and HLC diet arms, the 12-month decrease in BMI was significantly greater for those in the High Quality/High Adherence subgroups relative to the Low Quality/Low Adherence subgroups. Neither High Quality nor High Adherence alone were significantly different than the Low Quality/Low Adherence subgroups. While further investigation is needed, the results of this secondary analysis support the importance of the combination of dietary adherence and high-quality diets for weight loss.

Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion

Dietary modification remains key to successful weight loss. Yet, no one dietary strategy is consistently superior to others for the general population. Previous research suggests genotype or insulin-glucose dynamics may modify the effects of diets. To determine the effect of a healthy low-fat (HLF) diet vs a healthy low-carbohydrate (HLC) diet on weight change and if genotype pattern or insulin secretion are related to the dietary effects on weight loss. The Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) randomized clinical trial included 609 adults aged 18 to 50 years without diabetes with a body mass index between 28 and 40. The trial enrollment was from January 29, 2013, through April 14, 2015; the date of final follow-up was May 16, 2016. Participants were randomized to the 12-month HLF or HLC diet. The study also tested whether 3 single-nucleotide polymorphism multilocus genotype responsiveness patterns or insulin secretion (INS-30; blood concentration of insulin 30 minutes after a glucose challenge) were associated with weight loss. Health educators delivered the behavior modification intervention to HLF (n = 305) and HLC (n = 304) participants via 22 diet-specific small group sessions administered over 12 months. The sessions focused on ways to achieve the lowest fat or carbohydrate intake that could be maintained long-term and emphasized diet quality. Primary outcome was 12-month weight change and determination of whether there were significant interactions among diet type and genotype pattern, diet and insulin secretion, and diet and weight loss. Among 609 participants randomized (mean age, 40 [SD, 7] years; 57% women; mean body mass index, 33 [SD, 3]; 244 [40%] had a low-fat genotype; 180 [30%] had a low-carbohydrate genotype; mean baseline INS-30, 93 μIU/mL), 481 (79%) completed the trial. In the HLF vs HLC diets, respectively, the mean 12-month macronutrient distributions were 48% vs 30% for carbohydrates, 29% vs 45% for fat, and 21% vs 23% for protein. Weight change at 12 months was -5.3 kg for the HLF diet vs -6.0 kg for the HLC diet (mean between-group difference, 0.7 kg [95% CI, -0.2 to 1.6 kg]). There was no significant diet-genotype pattern interaction (P = .20) or diet-insulin secretion (INS-30) interaction (P = .47) with 12-month weight loss. There were 18 adverse events or serious adverse events that were evenly distributed across the 2 diet groups. In this 12-month weight loss diet study, there was no significant difference in weight change between a healthy low-fat diet vs a healthy low-carbohydrate diet, and neither genotype pattern nor baseline insulin secretion was associated with the dietary effects on weight loss. In the context of these 2 common weight loss diet approaches, neither of the 2 hypothesized predisposing factors was helpful in identifying which diet was better for whom. clinicaltrials.gov Identifier: NCT01826591.

Food Revolution.

Recent research has found important links between poor dietary choices, a toxic food environment, and high national and global burdens of chronic diseases. These findings serve as an impetus for a Food Revolution. The Gardner Nutrition Studies Research Group, along with a diverse range of collaborators, has been focusing on solution-oriented research to help find answers to the problems that plague the current food system. Research topics include (1) a recently completed weight loss diet study contrasting Healthy Low-Fat to Healthy Low-Carbohydrate diets among 609 overweight and obese adults; (2) a quasi-experimental study conducted among Stanford undergraduates that examined social and environmental, rather than health-focused, motivations for dietary change; (3) links between dietary fiber, the human microbiome, and immune function; and (4) ongoing collaborations with university chefs to create unapologetically delicious food for campus dining halls that is also healthy and environmentally sustainable. Most of these approaches emphasize plant-based diets. The decreased consumption of animal products has created some concern over the ability of one to obtain adequate protein intake. Evidence is presented that adequate protein is easily obtainable from vegetarian, vegan, and other diets that contain significantly less meat and fewer animal foods than the standard American diet.

Abstract MP052: Neither Insulin Secretion nor Genotype Pattern Modify 12-Month Weight Loss Effects of Healthy Low-Fat vs. Healthy Low-Carbohydrate Diets Among Adults with Obesity

Background: Dietary modification remains an essential component of successful weight loss strategies. No one dietary strategy has been determined to be superior to others for the general population. Studies that contrast reducing dietary fat vs. carbohydrate report consistently high within-group variability in dietary adherence and weight loss. Previous research by our group and others suggest that insulin-glucose dynamics or genotype patterns may modify diet effects. Objective: To determine if within-group weight loss variability on a Healthy Low-Fat (HLF) vs. a Healthy Low Carbohydrate (HLC) diet can be attributed to underlying factors such as insulin-glucose dynamics (i.e., insulin resistance and secretion) or genotype pattern. We hypothesized the above factors would be effect modifiers of HLF and HLC diets on 12-month weight loss. Methods: Generally healthy, non-diabetic adults, 18-50 years, BMI 28-40 kg/m 2 , were randomized to HLF or HLC with no specific prescribed energy restriction for 12 months (n=609). Health educators delivered the intervention in 22 1-hr group classes. Data were collected at 0, 3, 6, &amp; 12 months. Dietary intake was assessed by three 24-hour recalls/time point. Clinical data includes: 75-g glucose oral glucose tolerance tests (insulin concentration at 30 minutes [Ins-30], a measure of insulin secretion), genotyping (3-SNP multilocus genotype: Low-Fat Genotype vs. Low-Carb Genotype, UK Biobank Axiom® array), body composition (DXA), resting energy expenditure (indirect calorimetry), epigenetics, proteomics, subcutaneous adipose tissue, microbiota, and standard CVD risk indicators. Results: At 12 months participants collectively lost 6,559 lbs. Retention was 79%, with equal dropout between arms. Range of weight change in both diet arms was ~80 lbs (-60 to +20 lbs). Macronutrient distribution at 12 months was 48% vs. 30% carbohydrate, 29% vs. 45% fat, and 21% vs. 23% protein for HLF and HLC, respectively. Both groups reported achieving and maintaining an average ~500 kcal deficit relative to baseline. Weight loss was similar for HLF vs. HLC: -12.1 ± 1.1 lbs vs. -13.8 ± 1.0 lbs, mean ± SEM. Neither Ins-30 (p for interaction = 0.84) nor genotype pattern (p for interaction = 0.20) modified the effect of diet on 12-month weight loss. Conclusions: Despite substantial weight loss, high within-group variability, and strong dietary differentiation between groups, neither baseline Ins-30 nor genotype pattern modified the effect of diet on 12-month weight loss. Focus on a healthy diet in both diet arms is novel in the context of many previous Low-Fat vs. Low-Carb studies and may have diminished expected effect modification. The extensive data set collected will be used to explore this and other potential explanatory factors.

Abstract P226: Improved Insulin Sensitivity with a Healthy Low Fat or a Healthy Low Carbohydrate Weight Loss Diet: A Twelve Month Randomized Trial

Background: The abilities of healthy low fat (HLF) and healthy low carbohydrate (HLC) weight loss diets to improve insulin sensitivity over the long term are not well understood. Objective: To examine whether HLF and HLC weight loss diets improve insulin sensitivity over 12 months, and to determine if either diet is superior for these improvements. Methods: Healthy adults without diabetes, aged 18-50 years, BMI between 28 and 40 kg/m 2 , were randomized to HLF or HLC for 12 months (n = 609). Health educators delivered the interventions in 22 1-hr group classes. Dietary intake was assessed by three 24-hour recalls per time point. Glucose and insulin were measured at times 0, 30, 60, and 120 min during a 75-g oral glucose tolerance test. Indices of hepatic insulin sensitivity (homeostasis model assessment of insulin resistance; HOMA) and whole-body insulin sensitivity (Matsuda index and the plasma concentration ratio of triglyceride to HDL-cholesterol; TG/HDL-C) were measured. Data were collected at baseline and 12 months. Statistical analyses were performed on study completers. Results: Complete data were available for n = 193 for HLF, and n = 197 for HLC. BMI and all indices of insulin sensitivity were similar between groups at baseline (p &gt; 0.25 for all). Macronutrient distributions at 12 months were 48% vs. 30% carbohydrate, 29% vs. 45% fat, and 21% vs. 23% protein for HLF and HLC, respectively. Changes in BMI (mean ± SEM) were similar between groups (HLF: 33.38 ± 0.28 to 31.48 ± 0.29; HLC: 33.01 ± 0.25 to 30.69 ± 0.28; p = 0.11). Improvements within each group were observed for HOMA (HLF: 3.81 ± 0.17 to 3.16 ± 0.12; HLC: 3.60 ± 0.13 to 3.00 ± 0.12), Matsuda index (HLF: 3.13 ± 0.14 to 3.92 ± 0.18; HLC: 3.10 ± 0.12 to 3.86 ± 0.14), and TG/HDL-C (HLF: 3.16 ± 0.17 to 2.74 ± 0.14; HLC: 2.91 ± 0.15 to 2.09 ± 0.14) (p &lt; 0.001 for all). The improvement in TG/HDL-C was greater for HLC (p = 0.013), while the improvements in HOMA and Matsuda index did not differ significantly between groups (p &gt; 0.75 for both). Conclusions: All indices of insulin sensitivity were improved with both diets after 12 months. Neither diet was superior for improving HOMA. The HLC diet was more effective for improving TG/HDL-C, but not the Matsuda index.