subject: The Real Cause Of Obesity -- It's Not What You Think [print this page] As we enter the holiday season, a time rife with images of marvelous foodstuffs, from spiraled hams to sweet potatoes to gingerbread houses, we are all constantly reminded of how devastating these treats are to our waistlines, engendering guilt and remorse over what used to be a treasured tradition. Well, I'm here to tell you, from a strictly scientific perspective, to eat, drink and be merry once again, for without a doubt, the greatest medical myth of all time is that excess body fat is a direct result of excessive food intake and/or insufficient exercise. Ask anybody--literally. Ask 100 people, including scientists and health care practitioners, and 99 will tell you this. Ask 100,000, and 99,999 will give the same answer. The other one doesn't speak English. Yet despite this widespread belief, there is no good research behind this mythology, and plenty of scientific evidence to the contrary.
You will often hear that obesity must be the result of caloric imbalance, because the First Law of Thermodynamics cannot be controverted, and indeed, this is the case. What people are failing to understand is that caloric balance is not a voluntarily controllable variable--at least not long-term, and not through the standard remedies of diet and exercise. Although we can adjust the amount of food we put into our mouths and how much physical activity we perform every day, our bodies determine what percentage of the available energy to use in the production of heat and physical energy and how much to store as fat. This is the real reason that overweight people often feel tired, sickly, and run-down; their bodies apportion input calories more in the direction of fat storage than energy production, and reducing calorie intake or increasing physical exercise only makes the situation worse.
Let's consider some numbers. Typically, research on dietary and exercise approaches to weight loss will last three months, as that is assumed to be a sufficient period of time for analyzing changes in body composition. Funny thing about three months, though--it happens to be just about the amount of time the average person's body needs to completely adjust to an artificially imposed caloric imbalance (i.e., a low-calorie diet).
In Michael Weintraub's "Long-term weight control study I" (Clin Pharmacol Ther. 1992 May;51(5):586-94), a group of overweight people were treated with a medically-supervised, low-calorie diet, moderate exercise, and "behavior modification" program for about six months. From weeks 1-8, they steadily lost weight; from weeks 9-16, they continued to lose, but much more slowly; and after 16 weeks, their weight remained stable. Before I hear the tired argument about how their lower body weights required fewer calories, realize that the average weight loss at this point was only about 15 lbs, or 7% of their starting weight. Their calories had been cut drastically, so this was not a matter of the intake now being "just right" for their new size, but rather, of their metabolisms slowing to a sub-normal level to avoid further reductions in the body fat mass.
So is life just not fair? Well, actually, it is fair, because fortunately, the opposing relationship also exists between caloric balance and weight. That is, intentionally increasing caloric intake above current maintenance levels results first in rapid weight gain, then slower weight gain, and finally, weight maintenance at the new higher levels of both weight and calories. In fact, studies have shown that it is just as hard for an otherwise weight-stable person to gain beyond a certain level (~10% of current weight) and to keep it on, as the reverse. In "Gluttony 1. An Experimental Study of Overeating Low- or High-Protein Diets" (D.S. Miller and Pamela Mumford, Am. J. Clin. Nutr. 20: 1212, 1967), the reverse of the trend from the Weintraub study is observed. Although this study only lasted four weeks, the pattern of weight gain from overindulgence is initially rapid, but by the end of the study, is clearly approaching a level maximum.
And in what was probably the seminal study on the issue, E.A. Sims, an obesity researcher in Vermont, enlisted a group of naturally lean prison inmates to willingly overeat their way into obesity in order to study the effects of the disease as separate from the genetic factors that cause it. But much to his dismay, he found that, despite their best efforts--which included eating 6-7,000 calories a day and refraining from all work and exercise--the prisoners struggled to add and then retain the requisite 25% to their weights, even though they were eating twice their previous maintenance intake. One particularly lean fellow could never gain more than twelve pounds (9% of his initial weight) after months of stuffing his face and lounging around in his striped pajamas. In an alternate universe where "Weight Watchers" is a support group for overly thin people trying to bulk up, this poor guy would have been labelled lazy, undisciplined, and probably stupid, as well, for not doing what was needed to meet his weight goal.
So, must we simply learn to live with what we were born with (or became endowed with as we aged)? Thankfully, no. There are biochemical differences between those who stay easily lean and those who easily gain, and if we can understand those differences, we can do something about them, and eventually attain both the look and the feeling of health and well-being that we all deserve.
