Just Read: DIETFITS study design – Healthy Low Carbohydrate and Healthy Low Fat Diet Comparison for Weight Loss in non-diabetic humans

h/t to @DrWillYancy for connecting me to this work (I am still working to catch up…) & paper which describes the DIETFITS study but not the results, which are not published yet. The study continues the concept that “one size does not fit all” when it comes to nutrition.

To try and get at this, the 609 subjects who participated over 12 months were told (and educated, over 22 classes total)

  • Go as “low as you can go” on either carbohydrates (in the Low Carbohydrate arm) or fat (in the Low Fat arm)
  • Add back carbohydrates and fat to and assess “their satisfaction with their daily intake (e.g., satiety, palatability, and enjoyment) and their weight loss progress.”
  • Eat real/high quality food (both arms) – healthy fats and oils and/or healthy grains, beans – so, not just low carb or low fat, healthy low carb or healthy low fat
    • I can see how this is an improvement if previous studies have not judged the quality of fats or carbohydrates, which can have significant metabolic impacts
  • Get recommended amount of exercise, and if already at the recommended amount, push the amount higher
    • Given that there isn’t evidence of exercise as an intervention for weight loss, I am curious how this will come out in the analysis

Not a study of which diet is better

Very important point:

the study was not designed to identify which of the two study diets was the one best for weight loss, but rather, which diet was best for which individuals for weight loss.- (i.e., the “whiches conundrum”)

Not a study of management of diabetes

  • Also very important that this is a study of healthy, non-diabetic people, who are aged 18-50, not on any lipid-lowering drugs (long list of exclusions)

A few preliminary results

Some preliminary results have been announced that show similar levels of weight loss, spontaneous calorie reduction for both arms, and no interaction with measured insulin sensitivity or genotype pattern.

There’s a note about the original intent to stratify by genotype:

…original plan to stratify randomization to the two diet groups by multi-locus genotype pattern was altered. Prior to ini- tiating the study we determined that the evidence supporting the proposed genotype patterns remained unclear, and we wanted to explore other possible genotype interactions and asso- ciations. We still plan to test the original multi-locus genotype patterns, but we will also evaluate other SNPs secondarily in an exploratory manner, as described in the original aims of the grant application.

The final results of the study will be interesting to see, along with the dialogue that accompanies it 🙂 .

Comment on some of the conclusions published already

Conclusions being made in the press it doesn’t really matter what diet a person chooses, are in my opinion, premature, not relevant at all to people who would be excluded from the study, and really not the intent of the study anyway.


  • Dialogue between Gary Taubes (@GaryTaubes) and Christopher Gardner, PhD (lead investigator) from 2012 that presages this study: YouTube:

1 Comment

Agree with @tedeytan that we should not interpret the current state of diet research as proving that it does not matter which diet one chooses. On the contrary, the diet that many choose is precisely the wrong diet for their health. What the research really shows is that several nutritional approaches can be effective at improving health, and we should consider each of those several approaches to find the one that works best for an individual. Look forward to the official results of the DIETFITS study and hope it can help us move closer to identifying more quickly the best diet for each.

Ted Eytan, MD