And so, the insulin would have made you fat, hungry, and not eager to exercise.
As an analogy, teenaged boys don't grow tall because you're feeding them so much and they're sleeping late in the morning. Hormones tell their bodies to grow, and growing makes them hungry. So too, if your insulin levels are too high, your body wants to grow fat, and that makes you hungry.
According to the metabolic theory, eating processed carbohydrates, which cause big spikes in blood glucose levels, is what is driving the high insulin levels. Interestingly, this theory is not new, but it was rejected in the early 1970s, when people had started blaming everything on fat.
Of course not everyone who eats a lot of processed carbohydrate foods gets fat. Some people are less apt to become insulin resistant than others, and they can tolerate more carbs. Even some people with diabetes seem to do well with more carbohydrates than others.
And in fact, this is one flaw that I see in Taubes's book. He doesn't address the "YMMV" or "your mileage may vary" aspect of dietary recommendations. This was also a major flaw in the USDA's notorious Food Pyramid. A few studies showed that lowering fat intake helped some people who were at high risk for heart disease, and they then recommended this diet to the entire nation.
Intense hunger is often the factor that causes formerly fat people to regain all the weight they lost. Anyone will lose weight under concentration camp conditions. But no one but a saint or a masochist could endure this type of deprivation long term if not forced to do so. However, hunger is not the only reason that people eat. There are many other factors involved.
I tend to eat when I'm bored as well as when I'm hungry. I lose weight on vacations, when I'm doing interesting things. Many people eat when offered tasty food even if they're not hungry. Others can't stand to waste. Taubes also ignores the roles of other hormones like leptin and ghrelin.
I can understand why Taubes ignores some of the fine points. His book is already so large and so dense and full of so much information that I'm sure a lot of people won't get through it. When one is trying to topple an accepted paradigm -- namely, that the only way to be healthy is to eat less fat -- I think it's important to focus on a few main points, and even to simplify them. This is what the USDA did when they said, "Eat less fat" instead of, "Eat less of certain types of fats, although some other ones are OK and others are actually beneficial."
There is evidence for the metabolic theory. Taubes presents a lot. As one small example, women put on fat on their chest and their hips at puberty and men don't because that's what their hormones tell them to do, not because the women are eating too much. If the food were causing the rounding of women's figures, boys, who eat a lot more, would be even rounder.
