If a clinical trial shows a diet has benefits relative to what people normally eat, it can be hard to know which of the many dimensions in which that diet is different is doing the trick. (See “Hints for Healthy Eating from the Nurse's Health Study” for examples of how carefully one must parse the typical kind of evidence.) The GEICO Study analyzed by Ulka Agarwal, Suruchi Mishra, Jia Xu, Susan Levin, Joseph Gonzales, and Neal D. Barnard in “A Multicenter Randomized Controlled Trial of a Nutrition Intervention Program in a Multiethnic Adult Population in the Corporate Setting Reduces Depression and Anxiety and Improves Quality of Life: The GEICO Study” is a case in point. Many, many diets are better than what Americans normally eat. I have advocated on this blog a low-insulin-index diet. (See “Forget Calorie Counting; It's the Insulin Index, Stupid” and “Obesity Is Always and Everywhere an Insulin Phenomenon.”) In the case of the GEICO study, I want to argue that its low-glycemic-index vegan diet would have had a moderately low insulin index—much lower than the typical American diet. The reason is that it isn’t just carbs that stimulate insulin: certain proteins stimulate insulin as well. So one place where the glycemic index differs most markedly from the insulin index is that meat and skim milk are higher on the insulin index than one would predict from where they are on the glycemic index. So for those who don’t know about the insulin index, going vegan protects them from some of the errors they would make by looking at the glycemic index.
It is worth trying to parse the results of the GEICO Study, because they found some evidence of reduced depression and anxiety and improved productivity from instructing people in this diet. A major part of the instruction was teaching people about the glycemic index. Could lower insulin levels lead to a better mood and increased productivity? I think the answer is yes. Insulin spikes can lower blood sugar levels below normal. Low blood sugar levels can make people feel lousy and low in energy. (They didn’t measure anger. Low blood sugar levels probably increase the incidence of anger. I wrote about this in “How Sugar Makes People Hangry” and “Michael Lowe and Heidi Mitchell: Is Getting ‘Hangry’ Actually a Thing?”)
On particular, testable—but as yet untested—claim I want to make is that the “lowfat” dimension of the diet was not important to any of the good effects. It is more likely that the vegan aspect of the diet was helpful than the lowfat aspect. But that should be tested too. Adding some omega 3 eggs, goat cheese or whole A2 milk to the diet might not hurt any of the results they mention. (On these particular choices, see “What Steven Gundry's Book 'The Plant Paradox' Adds to the Principles of a Low-Insulin-Index Diet” and “Exorcising the Devil in the Milk.”)
Where I worry about animal products, it is about the effect that animal protein might have in helping to promote cancer. Cancer cells are typically damaged metabolically, but some of the easiest chemicals to metabolize—which even cancer cells can manage to get sustenance from—are sugar and some of the amino acids that are abundant in animal protein. See:
The dangers from animal protein—both in raising insulin, and possibly promoting cancer—are a big confounding factor in people’s reading of the evidence on how healthy animal fat is. People usually don’t eat a lot of animal fat without also eating a lot of animal protein. The one big exception is butter, which people tend to eat with bread, which is very high on the insulin index. So as far as much of the evidence goes, animal fat might be OK if one avoids all the things that are usually eaten with animal fat. It would be very interesting to go through all the evidence against animal fat with this in mind.
For someone like me, focused on insulin, it would be great to have much more measurement of the effects of different interventions on insulin. Then all effects should be parceled into the part of the effect that would be expected from the change in insulin levels (after correcting for measurement error in measuring the insulin levels) and the effects that go beyond what one could expect from the change in insulin levels. The most expensive part of trials is getting people to eat differently. Adding measurement of insulin levels is a modest expense by comparison. And if it is measured, it should be a big part of the statistical analysis.
The bottom line is that the GEICO Study seems consistent with the hypothesis that a lower average insulin level from low-insulin-index eating has benefits. Of course, it is also consistent with many other hypotheses! To distinguish between different hypotheses, we need a lot more dietary clinical trials. Given the trillions of dollars worth of harm from the typical American diet (a number I discuss in “The Heavy Non-Health Consequences of Heaviness”), our nation is being penny-wise and pound foolish by not spending more money on dietary clinical trials to figure out what is healthy and what isn’t. Email correspondence with the head of one major study (see “Why a Low-Insulin-Index Diet Isn't Exactly a 'Lowcarb' Diet”) suggested that a reasonably high-quality dietary clinical trial (by current standards), might cost about $8 million. Thus, even without any government assistance, any billionaire could likely do trillions and trillions of dollars worth of good for the world by funding over time the equivalent of 100 dietary clinical trials of that size to test hypotheses about diet and health like those I discuss on this blog (and still have $200 million left over to live on). Some of this is happening, but much, much more needs to be done.
Don’t miss my other posts on diet and health:
I. The Basics
II. Sugar as a Slow Poison
III. Anti-Cancer Eating
IV. Eating Tips
V. Calories In/Calories Out
VIII. Debates about Particular Foods and about Exercise
Julia Belluz and Javier Zarracina: Why You'll Be Disappointed If You Are Exercising to Lose Weight, Explained with 60+ Studies (my retitling of the article this links to)
IX. Gary Taubes
X. Twitter Discussions
XI. On My Interest in Diet and Health
See the last section of "Five Books That Have Changed My Life" and the podcast "Miles Kimball Explains to Tracy Alloway and Joe Weisenthal Why Losing Weight Is Like Defeating Inflation." If you want to know how I got interested in diet and health and fighting obesity and a little more about my own experience with weight gain and weight loss, see “Diana Kimball: Listening Creates Possibilities” and my post "A Barycentric Autobiography.