I recently saw the popular movie Forks Over Knives. In case you’re unfamiliar with its basic premise, the movie is based on the book The China Study, which was referred to as the “Grand Prix of epidemiology” by The New York Times. Essentially, the authors, T. Colin Campbell and Thomas M. Campbell, extol the alleged health benefits of a strictly “plant-based diet,” particularly one that is also void of processed food. Similarly, the movie champions the idea that a diet void of animal products is optimal to maximize human health. Perhaps not surprisingly given my nature, I found myself to be skeptical of this claim.
Before I proceed, however, I’d like to clear one thing up. I’m interested in eviscerating the health based reasons for avoiding all animal products that were provided in the movie, not in addressing the ethical reasons for avoiding animal products. People who choose to avoid animal products for ethical reasons are unlikely to be moved by empirically based health reasons, and I can certainly respect that choice.
So why exactly am I skeptical of the “plant-based diet is optimal” claim? I think that’s because I got the impression that the authors used science to promote their pet views, instead of using science to promote the truth. My basic problem with their claims is that they are predicated on an empirical approach that ignores important, yet subtle nuances in the functioning of complex systems like the human body and food digestive apparatus. It’s not, however, within the scope of this post to sift through all the faults with the empirical work used to promote these beliefs. Instead, I will focus on one tacit assumption, which I believe is false, i.e., that all animal products are created equal.
There is a number of things about which I do agree with the movie’s perspective. I, like the producers, believe that diet and lifestyle are an important component of the overall general health picture. Also, I can get on board with the message the movie offers about processed foods, i.e., that processed foods are at least partly to blame for many of our collective health woes. Here are my reasons for this belief: in the evolutionary picture, processed foods haven’t been around for all that long, yet they currently make up a large portion of our diets. We also know that diabetes, hypertension, and certain types of cancer have dramatically increased in roughly the same time frame as the widespread consumption of processed foods. Based on the empirical work and the type of logic presented in the film then, I believe that removing processed foods does improve health, at least to some degree.
However, the movie also discusses a correlation between the absence of animal products and improved health measures. What do I make of that? We all know the hackneyed cliche that correlation doesn’t imply causation, although sometimes when two things are correlated, one of them is indeed causing the other. The problem is that it’s often easy to mistakenly get the causation backwards, or to ignore the presence of a third but unaccounted for critical element.
For instance, let’s assume that people report improved health markers when they eat fewer processed foods, which also means they eat less sugar. Let’s also assume that they eat fewer animal products too. In this oversimplified example, is it the removal of animal products that is causing the improvement in health? Based on the information provided in the example, we don’t know, and it is at least as possible that the sugar is the culprit instead of the animal products.
Here’s another interesting question: is techno-manufactured meat from sick animals bad for you? I happen to think so. Does this mean that all types of meat are equally bad for you? Not necessarily. My main issue with the movie’s producers is that they seem to demonize all forms of animal products, while ignoring that there are differences in the quality of meats out there. For example, the meat in a McDonalds hamburger is not of the same quality as that of a 100% grass-fed New York strip steak. If one were to eat McDonalds hamburgers every day, then get sick, it simply wouldn’t logically follow that all meat is thus unhealthy. After all, there are also studies showing that there are health benefits from grass-fed and pasture-raised meat. There is absolutely no mention of controlling for meat quality differences in the film.
For comparison, let’s look at a few interesting examples of various cultural dietary habits. On the one hand, the Masai live almost exclusively from their cattle and eat lots of saturated fat, all the while remaining free of Western diseases. On the other hand, there are groups of people, like the Peruvians and Kitavans, who eat massive amounts of carbohydrates (in the form of tubers) and also remain free of Western diseases. How can this be?
The bottom line is that causation is very difficult to determine in complex systems, like the human body. The medical establishment has, for decades, demonized saturated fat because of an alleged connection to increased heart disease. “What If It’s All Been A Big Fat Lie” though? In the carbohydrate versus fat debate, many people ignore the possibility that other factors, such as significantly reduced sugar consumption, are at play. The producers of Fork Over Knives only perpetuate the problem by ignoring this possibility.
Ultimately, movies like Forks Over Knives are explained by the fact that most of us like to take sides and join tribes. And of course we want other people to join our tribe! If we believe that saturated fat is good for us (or at least not bad for us), there is also a temptation to jump on the bandwagon of demonizing carbohydrates. However, this is problematic from a rational perspective because people the world over remain healthy on all types of diets with varying macronutrient contents. Perhaps what healthy people have in common isn’t what macronutrient they eat or don’t eat, but what specific manufactured crystalline carbohydrates (sugars) they don’t eat. So instead of worrying about what macronutrients to remove entirely from our diets, perhaps we should worry about removing processed foods and sugar from our diets. And we probably should be consuming quality (grass-fed and pasture-raised) meats as well.
Greg Linster is a graduate student studying the applied branch of philosophy called economics at the University of Denver. While he spends much of his time studying Homo economicus, he has a strong interest in behavioral economics as well. As an avid writer and inveterate reader, Greg also writes a blog called Coffee Theory and maintains a site called Aphoristic Cocktails, which is dedicated to the beautiful literary form known as the aphorism. His writing has appeared in several popular blogs and webzines, and also in the magazine Philosophy Now. Greg is particularly interested in examining the world from an evolutionary perspective and in practical philosophy. One of his chief goals in life is to try and be a philosopher while remaining a nice guy.