In a previous blog I discussed the historical perspective that Gary Taubes gives in his new book Good Calories, Bad Calories: Challenging the Conventional Wisdom on Diet, Weight Control, and Disease. Now I'd like to discuss the fascinating way of looking at weight gain, hunger, and exercise that Taubes, a science journalist, came to believe makes the most sense.
One can view the problem of why people gain weight in two different ways. The traditional theory is that people lack self-control and simply eat too much and don't exercise enough. This makes them fat. You can think of this as the overeating theory.
The other theory is that some underlying hormonal imbalance makes people gain weight even when they don't eat very much. The process of storing fat -- and also storing sugar in the liver in the form of glycogen -- depletes the bloodstream of energy-producing substances, namely, fatty acids and glucose. This, in turn, triggers hunger and makes people (or animals) eat more and move less in order to conserve energy. I'll call this the metabolic theory.
In other words: you're not fat because you eat too much and don't exercise enough. You eat too much and don't exercise enough because you're fat.
Here's how the metabolic theory is supposed to work. Normally, after meals, insulin levels rise, and insulin tells the body to store the extra food as glycogen in the liver and as fat in the fat cells. It also tells the body not to break down any of that fat or glycogen to produce energy. You already have enough energy-producing substances from the food you just ate.
Between meals, insulin levels fall, so the process is reversed. Some glycogen is converted to glucose, and fats are released into the bloodstream (as fatty acids). The fatty acids as well as the glucose can be burned for energy.
In a healthy person, this process works very well. Your blood glucose levels stay pretty level, and you don't get hungry between meals.
But something in our modern lifestyle makes this system go crazy. According to the metabolic theory, this "something" is insulin. Insulin levels become too high because you eat too many processed carbohydrate foods. The high insulin levels then stimulate insulin resistance.
If all the cells in your body were equally sensitive to the insulin resistance, you might be OK. But the fat cells seem to become less insulin resistant than other cells. Imagine that your insulin levels doubled. If the insulin resistance in the muscle cells also doubled, the muscle cells would take up the usual amount of glucose from the blood. But if the insulin resistance in the fat cells remained the same, your fat cells would store twice as much fat. [The mathematics of all these effects is obviously more complex than this; I've simplified for the sake of argument.]
And because in order to store fat in the fat cells you'd remove both fatty acids and glucose from the blood, your blood would become deficient in energy-producing substances. As a result your body would tell you to eat -- and you'd get hungry. As an extra safety valve, your body would also tell you not to exercise, because it wouldn't want you to waste your "scarce" energy. You'd actually have a ton of energy stored in your fat cells, but because insulin levels were too high, that fat couldn't get out to be used.
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.
Taubes read papers by or interviewed a lot of researchers before he came to his opinion that processed carbohydrates were the culprits. His evidence is in his book.
I recently and serendipitously came across another opinion that supports the metabolic hypothesis. David Ludwig, chair of pediatric endocrinology at Children's Hospital in Boston, wrote in a recent issue of Focus, the Harvard Medical School's news bulletin, "Studies have linked a high-glycemic diet to diabetes, obesity, and certain cancers in the general population. Rapid changes in blood sugar set into action a sequence of hormonal events that promote deposition of fat, increase hunger, place additional stress on the pancreas, and may cause insulin resistance in key tissues -- ultimately resulting in a range of clinical problems linked to the glycemic load."
It's interesting that he specifies "rapid changes," implying that even a short spike could be deleterious.
He said a recent study of Italians found twice the prevalence of fatty liver disease in people whose three-day diet records showed the highest glycemic index. But "subgroup analysis showed this effect to be present only in individuals who were insulin resistant."
In other words, here is evidence of YMMV. Some lucky people may be able to tolerate high glycemic loads and others cannot. Most people don't know if they or their children are already insulin resistant. Anyone who gains weight easily probably is. And if you've been diagnosed with type 2 diabetes you almost certainly are (although you may turn out to have another type of diabetes). Hence, you should think carefully about the metabolic theory and what it means to you.
As always find out what works for you. We're all different. How do different dietary approaches affect your own hunger? Your weight? Your energy levels? Your blood glucose levels? How do the various diabetes medications affect those same factors?
What if you have to take insulin to control your blood glucose levels? Is the extra insulin making you gain weight? Could you reduce the amount of insulin you're injecting by eating less carbohydrate? By taking another drug or by exercising more to reduce your insulin resistance?
Keep informed by reading the information on sites such as this one. Stay up to date with the latest findings. Don't accept anyone's theory as the last word. Theories are constantly evolving. You need to take charge and discover what works for you. You are the most important person in your battle with diabetes.