Stanford’s Christopher Gardner Tackles the Low-Carb vs. Low-Fat Question


For decades, we’ve been pursuing a low-fat diet as a public health message. Then all of a
sudden there seemed to be a flip-flop. People said the low-fat thing was wrong. It was the opposite, it was supposed to be low-carb. It seems like there’s been this very active debate and
opponents on either side. The acronym for our study is the DIET FIT study. We don’t really think there’s one diet for everyone. One of the issues that would help people, if we could find out which diet is best for whom. In this particular study, we wanted them to both be very high-quality low-carb and very high-quality low-fat. We wanted them to be huge differences. We actually weren’t sure how far we should push people. We came up with this idea that we would push both groups in the first eight weeks of the 12-month study to try to get to 20 grams of fat or 20 grams of carb. If you don’t know much about diet, those are huge changes from what they had at baseline. Another point we hit home all the time was quality. Want you to go to
the farmers’ markets, want you to cook more for yourself, want you to sit down with your family. Don’t want you to snack in front of the TV, don’t want you to eat in the car. We told both groups, low-fat and low-carb, as little or no added sugar if possible, as little or no refined grain if possible, and as many vegetables as you can. With that as the backbone, they went in their low- fat or low-carb direction. This required quite a few people. We ended up with 609 enrolling in the study with more than 300 assigned to each diet. All of them were this wide range of genetic predisposition potentially, and insulin/glucose regulation variability potentially. The premise was that if we teased that apart and then looked by diet group, could we explain the individual variability that we consistently see in these studies? That’s what we were after. In order to test the hypotheses we had going into this study, we had to meet a lot of the assumptions that we thought we would get. One of them was that people would lose a lot of weight in a weight-loss study. They did. They lost collectively 6,500 pounds. The other thing that had to happen was that we needed people to have a wide variability of weight change on both diets. Some of the participants lost 40, 50, 60 pounds, some gained 10 to 20, and everything in between. At the end of the day, neither of our original hypotheses proved to be true. There’s a low- fat genotype. There was a low- carb genotype. High percentages of people fell into both categories, not predictive at all of who was more or less successful on either diet. No matter what their insulin glucose dynamics were, in our hands, there was no ability to predict if one diet was better than another. Close the doors on our original two hypotheses, but the future is full of opportunity for building on this study. People are going to want to know what to recommend. Not going to recommend low-fat over low-carb, or vice versa, because that’s not what we found. Depending on how you choose to define low-fat or low-carb in terms of food choices and food
patterns, you can make a plausible mechanistic link between either camp, low-fat or low-carb, and better health. The more I’ve looked into this, the more conferences I go to, I continually see three factors come up again and again. Get rid of added sugar, get rid of refined grain, and eat as many vegetables as you can. Those are all enormous challenges in the American diet and many diets globally. Yet, we’re battling about points on the fringe of this whole debate without getting to the core. I think if we really focused on added sugar and refined grain decrease or elimination, and we worked with some of our favorite chefs to make vegetables even more unapologetically delicious, a lot of the debates would go away…

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