Ask anybody what they think about obesity. Chances are they'll tell you that carrying around extra weight is dangerous for a variety of reasons. Fat people are thought to be at greater risk for conditions like heart disease and diabetes, and to die earlier as a result. But the association between overweight, obesity, and poor health may not be as strong as we take for granted, and the underlying cause of all three may be very different as well.
In recent years, a growing body of research has begun to challenge the idea that extra body fat is by itself unhealthy. Particularly compelling are studies investigating fat metabolism, which suggest that weight gain is a response to overeating that helps us stay healthy. According to one study published in Bioenergetics, increased body fat is associated with a number of health benefits including "... protection against starvation in times of food scarcity, protection against osteoporosis, fractures, frailty, and premature mortality in the elderly, as well as reduced mortality rates in the face of certain severe illnesses or injuries." Other studies have found that people can greatly improve their health by making dietary changes and exercising regularly, regardless of their weight. Paradoxically, observational research has also suggested that weight loss can increase risk for premature death.
So if the evidence that weight gain is dangerous isn't all that strong, why do most of us think otherwise? The likely reason is that discussions about the obesity epidemic today start with overeating as the cause. Fat people, the theory goes, get that way because they eat too many calories. Since gaining weight and raising disease risk are the result of personal choices, fat people are willingly living unhealthy lifestyles. But scientists have known for many years that the relationship isn't that simple.
Though what and how much we eat undeniably affect fat storage and body weight, it's also clear that our genes play a major role in determining body composition. As it relates to this discussion, there is clear evidence that people respond to the number of calories they consume very differently. Some people are naturally programmed not to store the excess calories they consume as body fat, while others very easily gain weight when they eat the same amount of food. The research highlighted in this BBC documentary provides a good overview of how the process works.
Researchers recruited 10 naturally thin people in order to study how they would respond to a doubling of their normal caloric intake for four weeks. All of them reported at the beginning of the experiment that they had never dieted or otherwise gone out of their way to maintain their weight. Or as one participant put it, "I've always eaten whatever I want to eat, and my weight has always been quite stable. My friends hate me."
At the end of the month, some of the study participants had gained the amount of weight they were expected to based on the calories in, calories out equation; others gained less and some gained no weight at all. What's key, however, is that all who gained weight over the four week study period very easily lost it by returning to their normal eating habits, no calorie counting or excessive exercise required. Clearly, then, the rise in obesity can't be attributed only to a lack of personal responsibility. If people respond differently to the same foods in the same amounts, it's neither good science nor public policy to claim otherwise.
In light of this information, what can we do to maintain good health lose weight within the confines of genetics? This is where the disagreement arises. The majority of researchers, including those responsible for the studies discussed above, say that those of us prone to fat storage gain weight because our toxic food environment. We are relatively wealthy, inactive and surrounded by all sorts of delicious but unhealthy food. The predictable result is increasing rates of obesity and related conditions like heart disease.
As believable as that explanation seems, it's hindered by a lot of contradictory evidence. There are and always have been populations around the world who are both poor and very physically active who have obesity rates very similar to those of the United States and other Western societies. Under this paradigm, there are certain foods — mainly carbohydrates — that stimulate an insulin response and cause weight gain. Avoiding these foods is probably a good idea for those of us who easily store body fat.
But whatever view you take of the relationship between obesity, genetics, and our environment, it's abundantly clear that weight gain is far more complex an issue than we often assume. By itself, extra body fat isn't necessarily unhealthy and getting rid of it isn't just a matter of self control. These are important points to keep in mind as we learn more about weight regulation and try to keep ourselves healthy as a matter of policy.