New Study on Insulin, Genes, and Diet

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New Study on Insulin, Genes, and Diet

Post by sharperhawk on Wed Feb 21, 2018 12:25 pm

A new study sponsored by NuSI, Gary Taubes' research foundation, has been published in JAMA. The lead author is Christopher Gardner, whom you may know from his "A to Z" diet study. The new study compared low-fat and low-carb diet interventions and also took genetic markers and insulin response to see whether those would predict how much weight people lost.

A post on has an excellent write-up for a general audience: Low-fat vs low-carb? Major study concludes: it doesn’t matter for weight loss. It has some nice graphs and an interview with Gardner.

The study is titled "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." Below is the abstract.
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.

The diet comparison has been done several times before. The insulin response tests an interesting hypothesis: maybe insulin-resistant people do better on low carb. These data say no difference. I am not familiar with the genetic markers used; the null results may just mean that some different set of genes will prove useful in matching person to diet.

Another point of interest is that both diet interventions emphasized whole foods and neither involved counting calories. Previous studies typically compare Atkins (low-carb, ad libitum, processed foods) with Ornish (low-fat, calorie counting, whole foods), so this new one did a better job of looking only at macro differences.

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Re: New Study on Insulin, Genes, and Diet

Post by Ellito on Thu Mar 01, 2018 2:37 pm

They actually compared the diets fairly. Usually the low-carb diet is less than 20 grams of carbs and the "low" fat diet is still 30% fat. In this study, "low" actually meant 30%, for both groups.

I like it.


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