Why Are So Many People Fat? Stress, Infection, and Genetics May Play a Role

         It is tempting to blame the current obesity epidemic on laziness (or inactivity), lack of self-control, and eating too much of the wrong foods. But the issue is more complicated than that. In fact, scientists who study obesity have realized for several years that there is more going on. David Berreby, writing at Aon Magazine, explains:

[M]any researchers believe that personal gluttony and laziness cannot be the entire explanation for humanity’s global weight gain. Which means, of course, that they think at least some of the official focus on personal conduct is a waste of time and money. As Richard L Atkinson, Emeritus Professor of Medicine and Nutritional Sciences at the University of Wisconsin and editor of the International Journal of Obesity, put it in 2005: ‘The previous belief of many lay people and health professionals that obesity is simply the result of a lack of willpower and an inability to discipline eating habits is no longer defensible.’ 

Consider, for example, this troublesome fact, reported in 2010 by the biostatistician David B Allison and his co-authors at the University of Alabama in Birmingham: over the past 20 years or more, as the American people were getting fatter, so were America’s marmosets. As were laboratory macaques, chimpanzees, vervet monkeys and mice, as well as domestic dogs, domestic cats, and domestic and feral rats from both rural and urban areas. In fact, the researchers examined records on those eight species and found that average weight for every one had increased. The marmosets gained an average of nine per cent per decade. Lab mice gained about 11 per cent per decade. Chimps, for some reason, are doing especially badly: their average body weight had risen 35 per cent per decade. Allison, who had been hearing about an unexplained rise in the average weight of lab animals, was nonetheless surprised by the consistency across so many species. ‘Virtually in every population of animals we looked at, that met our criteria, there was the same upward trend,’ he told me. 

It isn’t hard to imagine that people who are eating more themselves are giving more to their spoiled pets, or leaving sweeter, fattier garbage for street cats and rodents. But such results don’t explain why the weight gain is also occurring in species that human beings don’t pamper, such as animals in labs, whose diets are strictly controlled. In fact, lab animals’ lives are so precisely watched and measured that the researchers can rule out accidental human influence: records show those creatures gained weight over decades without any significant change in their diet or activities. Obviously, if animals are getting heavier along with us, it can’t just be that they’re eating more Snickers bars and driving to work most days. On the contrary, the trend suggests some widely shared cause, beyond the control of individuals, which is contributing to obesity across many species. 

Such a global hidden factor (or factors) might help to explain why most people gain weight gradually, over decades, in seeming contradiction of Bloomberg’s thermodynamics. This slow increase in fat stores would suggest that they are eating only a tiny bit more each month than they use in fuel. But if that were so, as Jonathan C K Wells, professor of child nutrition at University College London, has pointed out, it would be easy to lose weight. One recent model estimated that eating a mere 30 calories a day more than you use is enough to lead to serious weight gain. Given what each person consumes in a day (1,500 to 2,000 calories in poorer nations; 2,500 to 4,000 in wealthy ones), 30 calories is a trivial amount: by my calculations, that’s just two or three peanut M&Ms. If eliminating that little from the daily diet were enough to prevent weight gain, then people should have no trouble losing a few pounds. Instead, as we know, they find it extremely hard. 

Many other aspects of the worldwide weight gain are also difficult to square with the ‘it’s-just-thermodynamics’ model. In rich nations, obesity is more prevalent in people with less money, education and status. Even in some poor countries, according to a survey published last year in the International Journal of Obesity, increases in weight over time have been concentrated among the least well-off. And the extra weight is unevenly distributed among the sexes, too. In a study published in the Social Science and Medicine journal last year, Wells and his co-authors found that, in a sample that spanned 68 nations, for every two obese men there were three obese women. Moreover, the researchers found that higher levels of female obesity correlated with higher levels of gender inequality in each nation. Why, if body weight is a matter of individual decisions about what to eat, should it be affected by differences in wealth or by relations between the sexes?

Berreby goes on to discuss several other lines of research that provide other (partial) causes or explanations.

          First, he notes that some foods and chemicals actually alter the body's biochemistry so that it tilts in favor of storing fat. "If candy’s chemistry tilts you toward fat, then the fact that you eat it at all may be as important as the amount of it you consume."

          Second, metabolism is altered by more than activity or inactivity. "Sleeplessness and stress, for instance, have been linked to disturbances in the effects of leptin, the hormone that tells the brain that the body has had enough to eat." The use of artificial light (i.e., disrupting normal day/night cycles) has also been shown to have an impact, as has the use of heaters and air conditioners to regulate our environments. Industrial chemicals (such as BPA) may be connected with changes in metabolism. Moreover, research has shown that environmental factors (such as hunger) in one generation can lead to fat retention in a subsequent generation. Yes, a person may be fat now because his parents are grandparents were starved.

         Finally, there is the possibility that obesity may be contagious:

A virus called Ad-36, known for causing eye and respiratory infections in people, also has the curious property of causing weight gain in chickens, rats, mice and monkeys. Of course, it would be unethical to test for this effect on humans, but it is now known that antibodies to the virus are found in a much higher percentage of obese people than in people of normal weight. A research review by Tomohide Yamada and colleagues at the University of Tokyo in Japan, published last year in the journal PLoS One, found that people who had been infected with Ad-36 had significantly higher BMI than those who hadn’t. 

As with viruses, so with bacteria. Experiments by Lee Kaplan and colleagues at Massachusetts General Hospital in Boston earlier this year found that bacteria from mice that have lost weight will, when placed in other mice, apparently cause those mice to lose weight, too. And a study in humans by Ruchi Mathur and colleagues at the Cedars-Sinai Medical Center in Los Angeles, published in the Journal of Clinical Endocrinology and Metabolism earlier this year, found that those who were overweight were more likely than others to have elevated populations of a gut microorganisms called Methanobrevibacter smithii. The researchers speculated that these organisms might in fact be especially good at digesting food, yielding up more nutrients and thus contributing to weight gain.

         The Wellness Mama blog recently posted an article called "How to Relax & Reduce Cortisol" that addresses some of the metabolic effects of stress and lack of sleep:

Prolonged stress also contributes to aging and weight gain, which I am not a fan of myself. Weight gain around the mid section (especially in women) is actually often a symptom of impaired adrenals and the low progesterone that results. In these periods of chronic stress caused by not sleeping enough, not eating quality foods, inadequate exercise, and mental/emotional stress, the body will let certain aspects of health deteriorate because it thinks it is keeping you alive in a period of danger (more danger than a missed deadline at work!).

She goes on to discuss some techniques for reducing stress.