Doctors have been telling fat people to eat less and exercise more for at least 2,500 years.
Here’s Hippocrates, father of Western medicine: “It is very injurious to health to take in more food than the constitution will bear, when, at the same time one uses no exercise to carry off this excess.”
And here’s the blunt advice of Polybus, student (and son-in-law) of Hippocrates: “Persons of a gross relaxed habit of body, the ﬂabby, and red-haired, ought always to use a drying diet . . . Such as are fat, and desire to be lean, should use exercise fasting; should drink small liquors a little warm; should eat only once a day, and no more than will just satisfy their hunger.”
Public health experts no longer disparage red-haired folks, and as far as I know, they don’t recommend drinking warmed-up liquors. But they’re still spreading the message of the harms of obesity, via television, magazines, school curricula, and even First-Lady policy agendas. These efforts have some merit. People who are obese (defined as having a BMI of 30 or higher) have an increased risk of developing heart disease, diabetes and some cancers compared with people who are not obese. And people who are severely obese have a higher death rate than thin people.
The message that thinner = better just seems intuitive, doesn’t it? I’ve certainly heard it all my life (or at least since 3rd grade, when I was mortified to be one of the chubby kids in gym class to not get the President’s Physical Fitness Award badge) and have never questioned it. But over the past few months, while researching a story published in today’s Naturein today’s Nature, I’ve started to wonder whether we’ve gone too far in our cultural war against fat.
Weight is just one factor of many — sleep, diet, fitness, psychological health, socioeconomic status — that influence whether we are healthy or sick. But politicians don’t talk about a sleep deprivation epidemic; there is no Biggest Loser of Poverty reality TV show.
What’s more, the health risks of being “overweight” (defined as a BMI between 25 and 30) are not at all clear. As I describe in depth in the new story, mortality rates of people in the overweight category are actually 6 percent lower than those in the “normal” category, and some people who are overweight (and even mildly obese) show no signs of illness. Conversely, lots of thin people out there have heart disease and diabetes.
Yes, being obese usually takes a toll on health, no question. But guess how many obesity drugs or diet-and-exercise regimes have been proven to last more than a year or two?
Oh, right, zero.
And yet, the battle cry remains: if you’re obese, just crank up that willpower! Eat less, move more!
“I would like to believe that modern medicine and modern science can be better than just repeating a 2,000-year-old recommendation,” says Jeffrey Friedman, a molecular biologist and trained medical doctor at The Rockefeller University in New York. Friedman has many strong opinions about the so-called obesity “epidemic,” which we talked about at length over coffee recently.
Friedman has been studying the genetic roots of obesity for more than 30 years. In 1994 he made headlines for the discovery of leptin, a hormone that circulates in blood and turns off hunger signals in the brain. Subsequent studies have found genetic mutations in the leptin gene that cause rare cases of obesity. Twin studies have also shown that obesity has strong genetic roots (it’s about as heritable as height, in fact, and yet we don’t think of being too short or too tall as some kind of moral failing).
Despite these unquestionable genetic contributions, most of us think of weight as environmentally driven: a direct consequence of a person’s personal eating habits. It’s this emphasis on behavior that “gives the public a license to stigmatize the obese,” Friedman says.
“A lot of people try to couch it in ways that don’t as directly lead to stigmatization, but they end up always getting there,” Friedman says. “Because you end up saying, at some level, that the obese have made a series of poor choices that have led them to this.”
Friedman sees things quite differently, as he eloquently explained in a 2003 commentary in Science. Each of us, he argues, has a different genetic predisposition to obesity, shaped over thousands of years of evolution by a changing and unpredictable food supply. In modern times, most people don’t have to deal with that nutritional uncertainty; we have access to as much food as we want and we take advantage of it. In this context, some individuals’ genetic make-up causes them to put on weight — perhaps because of a leptin insensitivity, say, or some other biological mechanism.
In other words, morbidly obese people lost the genetic lottery. “The irony is, it’s the people who are the most obese who are stigmatized the most, and in fact, they’re the people who can do the least about it,” Friedman says.
Environment is important, of course: No one, no matter what their genome looks like, can become obese without food. But scientists don’t know most of the details of how the environment interacts with genes to control our eating habits. They don’t know why this system has such extreme variability in the human population. They don’t know why a (very select) few obese people can lose 50 percent of their weight and maintain that loss for decades. And, as I found in my story, researchers definitely don’t know why extra weight leads to sickness in some people but not in others. (It’s not even clear that fat tissue itself is harmful; it could just be an innocuous byproduct of a harmful diet, say, or of not exercising enough.)
This whole subject is steeped in political controversy and a wide array of financial interests, which has made it difficult for me to write about and to think about. But I’ve tried to be provocative in this post. Considering the economic and cultural investment we’ve put into the war on obesity, doesn’t the public deserve more transparent and rigorous discussions about it?
Is this a public health emergency that warrants the $1+ billion a year the U.S. is spending on it? Or are we fighting a war that’s unjustified, unjust, and impossible to win?
Quotes from Hippocrates and Polybus cited in this 2007 commentary by D. Haslam (.pdf here)