When I was young and running 90-100 miles a week, I could eat all the things without gaining weight. Time is doubly cruel in that it slowed my metabolism and reduced my ability to endure high mileage. Inundated with the usual abundance of high calorie foods, I found I was building an unsightly pudge band around my middle. My first reaction was to try to get back to my old mileage, but I found that I now top out at 70 miles a week and anything more starts breaking me down. Since I could not exercise more, I was faced with the terrible option of eating less. Being something of an expert on critical thinking, I dismissed all the fad diets and turned to science to glean the best way to beat the bulge. Being a philosopher, I naturally misapplied the philosophy of science to this problem with some interesting results.
Before getting into the discussion, I am morally obligated to point out that I am not a medical professional. As such, what follows should be regarded with due criticism and you should consult a properly credentialed expert before embarking on changes to your exercise or nutrition practices. Or you might die. Probably not; but maybe.
As any philosopher will tell you, while the math used in science is deductive (the premises are supposed to guarantee the conclusion with certainty) scientific reasoning is inductive (the premises provide some degree of support for the conclusion that is less than complete). Because of this, science suffers from the problem of induction. In practical terms, this means that no matter how carefully the reasoning is conducted and no matter how good the evidence is, the conclusion drawn from the evidence can still be false. The basis for this problem is the fact that inductive reasoning involves a “leap” from the evidence/premises (what has been observed) to the conclusion (what has not been observed). Put bluntly, inductive reasoning can always lead to a false conclusion.
Scientists and philosophers have long endeavored to make science a deductive matter. For example, Descartes believed that he could find truths that he could know with certainty and then use valid deductive reasoning to generate a true conclusion with absolute certainty. Unfortunately, this science of certainty is the science of the future and always will be. So, we are stuck with induction.
The problem of induction obviously applies to the sciences that study nutrition, exercise and weight loss and, as such, the conclusions made in these sciences can always be wrong. This helps explain why the recommendations about these matters change relentlessly.
While there are philosophers of science who would disagree, science is mostly a matter of trying to figure things out by doing the best that can be done at the time. This is limited by the resources (such as technology) available at the time and by human epistemic capabilities. As such, whatever science is presenting at the moment is almost certainly at least partially wrong; but the wrongs get reduced over time. Or increase sometimes. This is true of all the sciences—consider, for example, the changes in physics since Thales began it. This also helps explain why the recommendations about diet and exercise change constantly.
While science is sometimes presented as a field of pure reason outside of social influences, science is obviously a social activity conducted by humans. Because of this, science is influence by the usual social factors and human flaws. For example, scientists need money to fund their research and can thus be vulnerable to corporations looking to “prove” various claims that are in their interest. As another example, scientific matters can become issues of political controversy, such as evolution and climate change. This politicization tends to derange science. As a final example, scientists can be motivated by pride and ambition to fudge or fake results. Because of these factors, the sciences dealing with nutrition and exercise are significantly corrupted and this makes it difficult to make a rational judgment about which claims are true. One excellent example is how the sugar industry paid scientists at Harvard to downplay the health risks presented by sugar and play up those presented by fat. Another illustration is the fact that the food pyramid endorsed by the US government has been shaped by the food industries rather than being based entirely on good science.
Given these problems it might be tempting to abandon mainstream science and go with whatever fad or food ideology one finds appealing. That would be a bad idea. While science suffers from these problems, mainstream science is vastly better than the nonscientific alternatives—they tend to have all of the problems of science without having its strengths. So, what should one do? The rational approach is to accept the majority opinion of the qualified and credible experts. One should also keep in mind the above problems and approach the science with due skepticism.
So, what are some of the things the best science of today say about weight loss? First, humans evolved as hunter-gatherers and getting enough calories was a challenge. As such, humans tend to be very good at storing energy in the form of fat which is one reason the calorie rich environment of modern society contributes to obesity. Crudely put, it is in our nature to overeat—because that once meant the difference between life and death.
Second, while exercise does burn calories, it burns far less than many imagine. For most people, the majority of calorie burning is a result of the body staying alive. As an example, I burn about 4,000 calories on my major workout days (estimated based on my Fitbit and activity calculations). But, about 2,500 of those calories are burned just staying alive. On those days I work out about four hours and I am fairly active the rest of the day. As such, while exercising more will help a person lose weight, the calorie impact of exercise is surprisingly low—unless you are willing to commit considerable time to exercise. That said, you should exercise—in addition to burning calories it has a wide range of health benefits.
Third, hunger is a function of the brain and the brain responds differently to different foods. Foods high in protein and fiber create a feeling of fullness that tends to turn off the hunger signal. Foods with a high glycemic index (like cake) tend to stimulate the brain to cause people to consume more calories. As such, manipulating your brain is an effective way to increase the chance of losing weight. Interestingly, as Aristotle argued, habituation to foods can train the brain to prefer foods that are healthier—that is, you can train yourself to prefer things like nuts, broccoli and oatmeal over cookies, cake, and soda. This takes time and effort, but can obviously be done.
Fourth, weight loss has diminishing returns: as one loses weight, one’s metabolism slows and less energy is needed. As such, losing weight makes it harder to lose weight, which is something to keep in mind. Naturally, all of these claims could be disproven in the next round of scientific investigation—but they seem quite reasonable now.