Why We’re Fat: A New Look at the Causes of Our Obesity Epidemic

Healthnotes Newswire (August 17, 2006)—Americans are fat because we’re couch potatoes and we’re being sold too many unhealthful foods—that’s how the most popular story goes. But the real explanation for the increase of obesity in the United States is not so cut and dried, according to new research.

“Undue attention has been devoted to reduced physical activity and food marketing practices,” said Dr. David B. Allison, a professor of Public Health at the University of Alabama at Birmingham and spokesperson for the new study. “There are other potential explanations that are equally compelling.”

In an article published in the International Journal of Obesity, Dr. Allison and colleagues outline ten other plausible, but under-recognized, factors that contribute to the increasing rates of overweight and obesity seen in the US over the past few decades:

Sleep debt. The average amount of sleep has steadily decreased among adults and children over the past several decades. Sleep deprivation increases hunger and appetite and may produce endocrine (hormonal) effects that stimulate weight gain.

Environmental toxins. The presence of hormone-disrupting environmental chemicals in the food chain has increased. These chemicals, such as polychlorinated biphenyls (PCBs), accumulate in human fat tissue and disrupt normal endocrine activity in the body. These hormone disruptors can fatten us in many ways, including interfering with the activity of estrogens, androgens, and other hormones that regulate fat metabolism in the body.

Temperature regulation. More and more, urban dwellers spend time in temperature-regulated environments. Temperature regulation, such as air conditioning and heating, effectively decreases the amount of energy our bodies must use to cool or warm us. This means less burning of fat stores. Also, we tend to eat less in more extreme temperatures. When the air conditioning breaks down, studies show, restaurant sales drop dramatically.

Decreased smoking. Rates of cigarette smoking among adults have declined significantly in the past several decades. While no health professional recommends smoking as a weight-loss strategy, research nonetheless consistently shows that smokers tend to weigh less than nonsmokers, and that weight gain follows smoking cessation.

Pharmaceutical causes. Many of the prescription drugs Americans take induce weight gain. These include antipsychotics (olanzapine, clozapine), antidepressants (selective serotonin reuptake inhibitors), antidiabetics (insulin, sulfonylureas, and thiazolidinediones), antihypertensives (beta-blockers), as well as antihistamines, anti-HIV drugs, protease inhibitors, mood stabilizers, anticonvulsants, steroid hormones, and contraceptives.

Societal changes in age and ethnicity. Some age and ethnic groups have a higher prevalence of obesity than others. The total proportion of people between ages 35 and 54 has increased significantly from 1970 to the present. Similarly, the Hispanic population in the US has grown from under 3% in 1970 to about 13% in 2000. Compared with young European Americans, both of these groups, as well as African Americans, have a markedly higher prevalence of obesity.

Women bearing children later in life. Since 1970, the average age at which women around the world give birth to their first child has risen; in the US, the increase has been 2.6 years. For biochemical reasons that are only partially understood, children born to older mothers are more likely to be overweight or obese than are children of younger mothers.

Genetic causes. In a kind of genetic “feedback loop,” environmental changes that affected previous generations may be perpetuated in offspring. For example, a mother with diabetes while pregnant and breast-feeding, a condition usually accompanied by obesity or overweight, is more likely to have a child with the same condition.

Natural selection. The proportion of body fat is partially inherited and correlates with “reproductive fitness” (in other words, the ability to pass on one’s DNA). Thus, if people with more body fat reproduce more successfully, more often, traits favoring obesity will be selected and passed on to offspring.

Choice of partners. There is clear evidence that humans tend to mate with people of similar body type. Since obesity has a genetic component, this tendency contributes to increased obesity rates over generations.

“Although the effect of any one factor may be small,” Dr. Allison concluded, “the combined effects may be consequential. Moreover, the additional explanations we consider do not exhaust the possibilities.”

After considering all of this, the authors make a point of saying that the “Big Two” explanations for American obesity (inactivity and food marketing) should not be discounted—but that public health programs need to take a broader view.

(Int J Obes 2006 Jun 27 [e-pub ahead of print])

Jeremy Appleton, ND, CNS, is a licensed naturopathic physician, certified nutrition specialist, and published author. Dr. Appleton was the Nutrition Department Chair at the National College of Naturopathic Medicine, has served on the faculty at Bastyr University of Natural Health Sciences, and is a former Healthnotes Senior Science Editor and a founding contributor to Healthnotes Newswire. He has worked extensively in scientific and regulatory affairs in the supplement industry and is now a consultant through his company Praxis Natural Products Consulting and Wellness Services.

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