Time magazine memorably captured this thinking again in 1961 when it kicked off the apalling mistake of what became the low-fat diet movement with an influential cover story on the University of Minnesota nutritionist Ancel Keys. Just as Newburgh was central to disseminating the notion that the only meaningful difference between the fat and the lean is in their ability to control their appetite, Keys managed to convince medical authorities worldwide that we get heart disease because we eat too much fat or at least too much saturated fat. Time’s story on Keys and the evils of fat—both dietary and body fat—quoted the textbook Harrison’s Principles of Internal Medicine referring to “the most common form of malnutrition” as “caloric excess or obesity,” as though the two were one and the same. The Time article then observed that obesity in Puritan New England was seen as sinful, implying that perhaps it should still be, and quoted Keys saying, “Maybe if the idea got around again that obesity is immoral, the fat man would start to think.” The ridiculous implication, of course, was that if we did think about it (or if that self-indulgent, menopausal housewife did, rather than nibbling bonbons while she played bridge with her lady friends), we’d stop eating too much or at least stop eating immoderately; we’d control our portion sizes and our cravings and be lean. Our problem would be solved. Whether they know it or not, every doctor, every dietitian and physical trainer and friendly neighbor and sibling, every figure of authority who has ever counseled that we eat less and exercise more to lose weight, that we count our calories and so try to consume fewer than we expend, is wedded to this idea that the lean and the eventually-to-become-obese are physiologically identical; only their behavior sets them apart. This belief system has dominated our thinking on obesity since the 1950s, and we have to leave it behind. There are so many things wrong with this idea, things that were already known to be wrong in 1961 and even 1931, that it’s hard to enumerate all of them. One of the most obvious problems with this thinking is that the logic is circular. Some very good obesity researchers pointed this out repeatedly in the mid-twentieth century, but these physicians-and-nutritionists-turned-moralists didn’t seem to care. If we get fatter, more massive, we are clearly taking in more energy than we expend, and yes, the excess is stored as fat (although technically as fat and some muscle or lean tissue to support it and move it around as necessary). So we must be overeating during this fattening process. But that tells us nothing about the cause. Here’s the circular logic: Why do we get fat? Because we’re overeating. How do we know we’re overeating? Because we’re getting fatter. And why are we getting fatter? Because we’re overeating. Logicians know this kind of round-and-round logic as tautology. It’s saying the same thing in two different ways but offering no explanation for either. If we’re getting fatter, it means our body mass is increasing, our energy stores are increasing, and so we are indeed taking in more energy—calories—than we expend. Okay, we’re overeating. But by the same token, if we’re getting taller we’re taking in more calories than we expend. But nobody would say we get taller because we overeat. If we’re getting richer, we’re making more money than we’re spending. But nobody would say we get rich because we overearn. That’s clearly absurd, even if overearning is what’s happening as we get rich, which it is—by definition. So why is this kind of circular explanation considered acceptable for obesity? It only appears to be an explanation. There is no causal information.

Gary Taubes. The Case for Keto: Rethinking Weight Control and the Science and Practice of Low-Carb/High-Fat Eating (Kindle Locations 664-668). Knopf. Kindle Edition.