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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: The DIETFITS Randomized Clinical Trial

Author/s: 
Gardner, Christopher G., Trepanowski, John F., Del Gobbo, Liana C., Hauser, Michelle E., Rigdon, Joseph, Ionnidis, John P. A., Desai, Manisha, King, Abby C.

Importance

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.

Objective

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.

Design, Setting, and Participants

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.

Interventions

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.

Main Outcomes and Measures

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.

Results

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.

Conclusions and Relevance

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.

Keywords 
diet weight loss

Short- and Long-Term Outcomes after Bariatric Surgery in the Medicare Population

Author/s: 
Orestis, A. Panagiotou, Markozannes, Georgios, Kowalski, Rishi, Di, Mengyang, Bond, Dale S., Ryder, Beth A., Adam, Gaelen P., Trikalinos, Thomas A.

Introduction. We conducted a technology assessment to summarize and appraise the current evidence regarding the effectiveness and safety of bariatric surgery in the Medicare-eligible population.

Data Sources. We searched six bibliographic databases and the reference lists of published clinical practice guidelines, relevant narrative and systematic reviews, and scientific information packages from manufacturers and other stakeholders on the outcomes and prediction models of different bariatric procedures studied in the Medicare-eligible population.

Results. Of 126 eligible studies, 83 described outcomes after bariatric therapy and 43 described predictors of body weight loss or absolute body weight after bariatric therapy. We did not identify any randomized clinical trials in the Medicare-eligible population. Studies examined surgical modalities. There were no studies on endoscopically-performed bariatric procedures. Only 15 studies had a design and/or analytical approach that allowed inferences for causal treatment effects on weight loss outcomes, adverse events/complications, or other non-weightloss outcomes. Bariatric surgery in the Medicare-eligible population leads to improvements in weight loss and non-weight-loss outcomes, particularly mortality, metabolic, cardiovascular, respiratory, and musculoskeletal outcomes, and polypharmacy but the strength of evidence is low to moderate. There is moderate evidence that Roux-en-Y gastric bypass performs better compared to sleeve gastrectomy or adjustable gastric banding for metabolic, cardiovascular, and renal function outcomes and for postoperative complications. Finally, no models to predict weight loss have undergone internal or external validation.

Conclusions. Relatively few nonrandomized studies examine the comparative effectiveness and safety of bariatric therapies in the Medicare population. Large gaps remain in regard to comparisons of individual bariatric surgical procedures to each other, and very limited evidence exists in regard to patient-centered outcomes such as quality of life after surgery.

Keywords 
medicare gastric bypass weight loss bariatric surgery
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