Since we know that calories are not the real problem, we can start to focus on what is really the cause of obesity (the etiology of obesity). You can review the calorie series here for an in-depth discussion of why calories are not relevant. The entire obsession with calories was a 50-year dead end. We can only start to address the problem of weight loss and gain by understanding the real causes. So what is the real cause of obesity? Let’s go back in time and see what people thought about obesity in the past.

William Banting, 1796–1878, is considered to have written the first diet book. He started off at a normal weight in his teens and 20s. However, as he went through his 30s, 40s, and 50s, he started to gain some weight. Not much, but a few pounds per year. Before long, he was age 62 and weighed 202 pounds. Not bad by modern standards, but a real chunky monkey by the standards of that time. So on the advice of his physicians, he tried to eat less. But then, he felt tired and hungry, and he wasn’t really losing any weight. Then, he tried to exercise more. He rowed the Thames and became quite physically fit. However, he was still not able to keep the weight off.

Finally, on the advice of a French surgeon, he started a new diet. He would severely restrict not calories but sugars and starches—what we now call refined carbohydrates. He avoided all bread, milk, beer, sweets, and potatoes. Poor fellow loved his carbs, too. He lost so much weight and felt so well that he decided to publish his findings in “Letter on Corpulence Addressed to the Public.” This pamphlet was really the first modern diet book. Based on personal experience, Mr. Banting felt that it was not calories that caused weight gain but refined carbohydrates.

Many of his ideas that sugars and starches caused obesity persisted through the next 100 years or so. Sir William Osler—the influential Canadian physician who wrote “The Principles and Practice of Medicine”—illustrates that most doctors of the early 1900s considered that refined carbohydrates were the chief cause of obesity. In his famous textbook, he described the treatment of obesity with diets predominantly featuring meat and eggs and low in refined carbohydrates.

In his 1882 monograph “Obesity and Its Treatment,” Dr. Osler felt that fatty foods were crucial to reducing obesity because they increased satiety (feeling of fullness). Contrast this to the modern demonization of dietary fats. This coincides neatly with the obesity epidemic. Maybe the good Dr. Osler was onto something after all. By the 1950s, it was fairly standard advice. If you were to ask your grandparents “back in the day” what caused obesity, they would not talk about calories. Calories as a unit of energy were largely unknown at that time. They would say instead that sweets and starchy foods cause obesity.

Dr. Spock’s “Baby and Child Care”—a bible of child-rearing of the 1950s—describes the gaining or losing of weight as mostly dependent upon the number of desserts and plain, starchy foods consumed. Dr. Passmore, in the British Journal of Nutrition in 1963, wrote, “Every woman knows that carbohydrate is fattening.”  Every. Woman. Knows. This was no secret. Everybody knew it. These ideas had withstood the test of time. Common sense and empiric observation served to confirm the truth of the matter. The ideas were “Antifragile,” as the great Nassim Taleb puts it. And obesity wasn’t such a great problem back then. This is what they thought.

Things started to change in the 1950s. There was a perceived increase in the incidence of heart disease. Whether this is actually true or not is debatable. Gary Taubes argues that this was not true in his groundbreaking book “Why We Get Fat.“ Nevertheless, people started to search for the reason behind this ”great epidemic” of heart disease. Their gaze soon fell upon dietary fat. The “Diet-Heart Hypothesis” started to gain traction in the 1960s. Ancel Keys, a very influential nutrition “expert,” played an instrumental role in popularizing these ideas. With great enthusiasm and shaky science, the demonization of dietary fat (a food that humans had been eating since, well, we became humans) started.

There was a problem, though we didn’t see it at the time. Dietary protein tends to remain fairly constant in human diets. It is actually quite difficult to increase dietary protein to more than 20 percent to 30 percent of calories without resorting to protein bars, shakes, etc. So if one were to restrict dietary carbohydrates, then one must increase dietary fats and vice versa. This is the result: Low Fat = High Carb and Low carb = High Fat. Since dietary fat was now the villain of the hour, the “heart-healthy” recommended diet became a high-carbohydrate one. Since carbohydrates in the Western hemisphere tended to be refined, we ate more and more low-fat bread and pasta. After all, we weren’t giving up hamburgers for cauliflower and kale but for bread and big plates of pasta.

Through the 1950s and 1960s, scientific debate (occasionally very acrimonious) raged back and forth. Some believed that dietary fat was the villain, whereas others, such as John Yudkin, believed that refined carbohydrates were the problem. His book, “Pure, White and Deadly—How Sugar is Killing Us,” is eerily prescient and should certainly win the award for Best Book Title—Ever. The vitriol sometimes reached extreme levels. Jean Mayer of Harvard University once likened the carbohydrate-reduced diet “in a sense, equivalent to mass murder.” Just a little extreme. The American Heart Association felt that these diets were also dangerous fads. Umm…dude. Really? A 200-year-old fad? Ideas that withstood the test of time? Dietary fats that humans have been eating for, like, a bazillion years? That’s what was killing us? Didn’t it occur to these geniuses that if dietary fat were going to kill us, it would have already done so in the preceding, oh, 1 million years?