What’s the cause of the obesity epidemic? Why have close to 70% of the people in the U.S. become overweight or obese? Why is the state with the lowest rate of obesity currently fatter than any state was in 1980?
Many experts have tried to explain it. Possibly the most popular current theory asserts that we eat too much and don’t exercise enough. The theory is popular because it’s simple: too many calories from food results in fat storage when we don’t use them up through exercise. This is the calories in, calories out theory (CICO).
As H.L. Mencken, said, for every complex problem, there is an answer that’s clear, simple, and wrong. CICO fits this description.
Why is CICO wrong? For one thing, empirically, it doesn’t work. Diets that count on reducing input and increasing output of calories have a terrible record in long-term weight loss. As we recently saw, most of the contestants on the TV show The Biggest Loser regained all of their weight, and in some cases even more.
CICO also doesn’t take into account the body’s dynamics. The typical physiological response to a reduction in calories is a lowering of basal metabolism, that is, energy expenditure. Totally makes sense: the body senses a food shortage, so it compensates to conserve energy and, ultimately, life.
Enter Jason Fung, M.D., with his book, The Obesity Code.
Dr. Fung’s rich, informative book does a thorough job in demolishing CICO and other commonly held ideas in the field of obesity research. He meticulously describes how we’ve gotten so much wrong, what the real answers are, and how to implement genuine solutions for weight loss and the obesity epidemic.
Dr. Fung ascribes the beginning and continuation of the obesity epidemic to the promulgation of the U.S. Dietary Guidelines in 1977. The idea behind them was to lower cholesterol levels to combat heart disease by decreasing the amount of dietary fat. Carbohydrates were thought benign, so their consumption was encouraged. But not only did the experts get cholesterol wrong as a cause of heart disease, they didn’t understand the consequences of increased carbohydrates, and especially sugar, in the diet.
But Fung points out that it’s been known for literally a couple of hundred years at least that carbohydrates are fattening, and that even until a few decades ago, it was common knowledge, even among doctors, that cutting carbohydrates was the most effective way to lose weight.
Fung shows that obesity is highly heritable, with up to 70% of variation in obesity explained by genes. Yet, as he also points out, and as I’ve argued with many people who ought to know better, the obesity epidemic arose within a single generation, so genes can’t account for it. No, it’s something in our environment.
The thrifty gene hypothesis, the notion that humans have a tendency to gain fat as a protection against famine, doesn’t wash either. Being fat also has disadvantages, for example in the speed from which you can escape a predator – in the case of humans, that other predator is most likely another human. If he can outrun you or overpower you, you’re finished. Animals don’t gain fat in the wild except when nature tells them, most obviously in preparation for hibernation.
The truth is that fat accumulation, like all other tissues and processes in the body, is highly regulated.
CICO theory runs into problems because the body responds to inputs and outputs. And the responses don’t necessarily go in the predicted direction. Not only does basal metabolism drop in response to fewer calories, but all calories are not the same. Hormonal and physiological responses differ greatly depending on whether the calorie in question is fat, protein, or carbohydrate.
If fat is regulated by hormones, which it is, could the differing hormonal responses to types of food contribute to obesity? Yes, they could. The most important hormonal response, Fung points out, is the insulin response. (More on that below.)
Why can’t we just exercise more, and and with the same number of calories taken in, lose excess fat that way?
This idea has at least three problems that render it ineffective. One, exercise makes us hungry. The body sensibly responds to an increase in energy expenditure by increasing out appetite so that we make up for calories burned.
Second, we respond to increased exercise by decreasing energy expenditure elsewhere, in non-exercise activities.
Third, most people greatly overestimate how many calories are used up in exercise. Basal metabolism and non-exercise physical activity make up a far greater fraction of most people’s energy expenditure.
Fung discusses the paradox of eating too much. Overfeeding experiments in humans have shown that many people have great difficulty gaining weight, and that when they do, they lose it right away upon cessation of overfeeding.
Similarly, in starvation experiments, people lose weight, but focus their entire mental and physical being on food. They think about it, dream about it, and their metabolic rates drop dramatically. Upon cessation of the starvation experiment, they rapidly gain all the weight back, and often even more. You can see this in The Biggest Loser contestants.
So it appears that the body has a weight or body fat set point. If body weight is below the set point, physiological mechanisms kick in to cause weight gain. These mechanisms include lower metabolism and greater appetite.
If body weight is above the set point, metabolic rate increases and hunger decreases, causing weight loss.
So the obesity epidemic can be explained by the idea that most people’s body fat set points increased.
How did that happen?
Fung explains that the hormone insulin is the main player in setting the body’s fat set point. He says, “I can make you fat” by giving you insulin. He shows that either insulin itself given exogenously, or conditions or medications that increase insulin production internally, cause weight gain. Likewise, lowering insulin produces weight loss.
We’ve heard about the carbohydrate hypothesis of obesity. Carbohydrates raise insulin levels the most of any macronutrient, and thus cause weight gain. There’s much to be said for this.
And yet, as Fung points out, certain populations, for example in Asia, have eaten large amounts of refined carbohydrates and were not fat. In Japan and China, white rice made up a large fraction of food, yet until recently have not had an obesity problem. Similarly, the famous Kitavans eat about 70% of calories as carbohydrate — mostly sweet potatoes — and obesity is unknown there.
The key to obesity is not insulin, as the carbohydrate theory has it, but insulin resistance, the failure to respond adequately to insulin. As a result, the body’s levels of insulin increase, stay high, and never go down.
We normally avoid insulin resistance, as we avoid resistance to every other hormone, because these hormones are emitted in pulses, and the body never develops resistance to them. The hormones increase, have an effect, then decrease before resistance develops. growth hormone, for example, is largely released during sleep, then it decreases.
Normally, in response to a mixed meal, insulin rises, then when it’s done its job, falls. The body does not develop resistance.
When insulin rises and doesn’t fall, resistance develops in a vicious circle: more insulin, more resistance, then more insulin secreted to try to overcome resistance, etc.
Low insulin levels are required for fat loss. When insulin levels stay high, the release of fats from adipose tissue is greatly inhibited.
So how does insulin resistance come into being in the first place?
One of the main culprits in insulin resistance is constant eating. In this part of the book, I was happy to see that Dr. Fung echoes what I wrote in my book Stop the Clock: When you eat is as important as what you eat.
Think back to the 1960s, before the obesity epidemic began. (Easy for me, I was a kid then.) Did people eat health foods, tons of fruits and vegetables, watch the fat intake, avoid sugar? Hell, no. They (we) ate lots of crappy food. Oreos, soft drinks, pizza, and my favorite, Hostess Cupcakes. Though we didn’t eat these all the time. Most meals were eaten at the table, and little was eaten elsewhere, in contrast to now. And was 70% of the population overweight or obese? No.
Back in the 60s, we didn’t eat all the time. The twelve or so hours between dinner and breakfast provided a natural period of abstention from food, of fasting, that helped prevent insulin resistance.
It follows that “grazing”, the highly promoted practice of eating often, has been one of the most destructive of allegedly beneficial health practices devised in modern times. Snacking is great for promoting insulin resistance too.
Dr. Fung ends his book by showing what is needed for truly sustainable weight loss. Among his steps are a reduction in sugar and refined carbohydrates, moderate protein intake, and increased consumption of natural fats and of fiber.
But perhaps more importantly, and something that sets this book apart from others in its genre, is Fung’s advocacy of intermittent fasting. The practice of fasting can help reset the body weight set point by decreasing insulin resistance.
The practice of fasting has generally been denigrated in the mainstream. I hear people refer to it as “starvation”. Among the experts, you often hear that “breakfast is the most important meal of the day” – an assertion that Dr. Fung shows to be utterly false.
Why is fasting so denigrated, or at the very least, unappreciated?
Here again, I’m happy to see that Dr. Fung reaches the same conclusion that I have here and in many other health interventions: no one makes any money by telling you to eat less often.
The Obesity Code is an instant classic in this field, and is fully worthy of being placed in the same category as Gary Taubes’ Good Calories, Bad Calories and Nina Teicholz’s The Big Fat Surprise. While I’ve touched on some of Dr. Fung’s main points in this review, there’s far more in the book, and I highly recommend it to anyone interested in the topic of obesity, whether from a theoretical or practical point of view. I learned a great deal from it, and it’s fascinating and well-written, a genuine page turner.