Jeffrey Bland, PhD summarizes and interprets a 2018 Stanford randomized trial by Christopher Gardner et al. (published in JAMA) comparing effective low-fat versus low-carbohydrate diets over 12 months in ~600 overweight adults. Participants were counseled to eat whole foods (avoiding added sugars and white flour) with similar calorie guidance; both diet groups lost similar weight and body-composition improvements, and selected genotype SNPs and insulin secretion did not predict differential weight loss. Bland emphasizes that macronutrient source/quality (minimally processed carbohydrates and whole-food fats) matters more than simple percent calories from fat or carbohydrate.
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I'd like to talk briefly about Dr. Christopher Gardner and the extraordinary work that he and his colleagues are doing at Stanford University in the nutrition area. Some of you might remember that Dr. Gardner was a superb presenter at a past Institute for Functional Medicine International symposium in San Francisco when he talked a little bit about diet quality and its effect on physiology and outcome in individuals and the concept of obesity. Well, such now we can roll forward to 2018 and look at this really amazing PA that was just published by Dr. Gardner and his colleagues entitled Effective Low Fat versus Low Carbohydrate Diets on a 12 Month Weight Loss in Overweight Adults in Association with Genotype Patterns and Insulin Secretion. I think this is a really wonderfully designed study and tells us a lot about the nature of each of these individual components, insulin sensitivity, genotypic sensitivity to weight loss or to obesity, and whether there's a difference in outcome whether the diet is low in fat, fat or low in carbohydrate. This, by the way, was published this paper with an editorial comment in the February 26 issue, 2018 of the Journal of the American Medical Association. About 600 people were involved in this trial went on for a year. And it's very important to note that these people were counseled about the use of whole foods and maintaining their regular activity patterns. They were not put on restrictive kind of unusual diets, but rather just told to eat right based upon certain principles that would either be higher in complex carbohydrate or higher in friendly fats, in whole fat like nuts and seeds and so forth. And over the course of several weeks of run in, they were able to get compliance with these individuals to move their diets more and more towards either a higher fat, lower carbohydrate, or a higher carbohydrate, lower fat. Now, I think it's important to point out that in both of these cases the consult was to stay away from added sugars, hidden sugars, and stay away from white flour. So when we talk about carbohydrate and fat here, we're really talking about in the context of a natural diet, not a highly processed diet. And what was found very interestingly and maybe not totally surprisingly, is that there was no difference in weight loss between the group that was on the higher fat, lower carbohydrate, versus the group was on the higher carbohydrate, lower fat. Again, remembering, they were both using natural foods and there was no requirement for calorie restriction, but their calorie intake was counseled to be about the same in both groups. They both lost about the same amount of weight over the course of the 12 months. So the success was that there was favorable weight loss, improvement of body composition, and that neither diet, high fat, higher fat or higher carbohydrate was preferable. They also found that there was no genomic sensitivity of the three common SNPs that are often associated with weight loss. And previous papers have been published. FTO and ppr, gamma and fatty acid transport genes. These three genes in different patterns and combinations were not found with different SNPs to actually predict weight loss or predict weight gain. So they did not appear to hold water in this trial. Secondly, they also didn't find that insulin sensitivity had a big role to play in affecting weight loss in cohort and sub cohort analysis. So my takeaway from this is, first of all that we can say that a good diet, be it either higher in fat or higher than carbohydrate, probably is not a big variable in outcome. But what is most important to me is that this would really contrast to a diet that was highly processed, that was high in hidden sugars, high in added synthetic, not synthetic, but let's call it chemicalized fats, higher in white flour, lower in fiber. That would be a different kind of diet study, and that would be a different way of calling it a high carbohydrate. That would be a high processed carbohydrate diet. And I think for me, this is a very, very important point because there are literally thousands of diet trials that have been published in the literature over the years past, and they talk about the variation of carbohydrate, fat and protein without calling out specifically, what are the forms of carbohydrate, what are the forms of fat, what are the forms of protein? And now we're starting to recognize, and Dr. Gardner's work, I think, exemplifies that. The source and the type of the nature of each of those compartments, those macronutrients, fat, protein and carbohydrate, are as important as their personalities in terms of calorie percent. So if you have minimally processed, high complex carbohydrate, that's very different than a high carbohydrate, white flour, white sugar type of diet in terms of the impact it has on metabolism. So I think we have to be very cautious about how we use these terms fat, carbohydrate and protein in dietary advice and make sure that we're talking about the same thing as it relates to its physiological effect. Sugar and white flour have a different physiochemical effect on insulin sensitivity and metabolic performance and hormones than does a similar carbohydrate that is unprocessed, fiber rich, nutrient rich, and in different physical form based upon the minimum processing. So wonderful study of Dr. Gardner, but lots of news to use out of this and take away value in how we really translate this into dietary advice and into compliance and into eating a diet that's healthy, that's fun, tasty, and also leads to proper weight management and metabolism.
