At this transition time of the year, ‘tis the season for top ten lists. Lists appear, for example, of the top ten films, theater, and books of the past year. Late night comedian David Letterman has made popular his "Top Ten" list each evening, but there is nothing funny about why we as a nation are increasingly overweight and obese.There are dire predictions, in fact, from some researchers, that if we don’t get a handle on the problem, eventually all Americans will be obese or at least overweight in another 35 years. In the U.S. alone, according to the most recent statistics about 2/3 are overweight and of this number, 1/3 are obese. Excess fat has been linked to cardiac disease, hypertension, type II diabetes and other endocrine disorders (e.g. the metabolic syndrome), as well as sleep apnea, sexual dysfunction, complications of pregnancy, osteoarthritis, and many types of cancer such as those of the colon and breast. There is even the suggestion that obesity may be linked to Alzheimer’s Disease. But why are we getting fatter? No one really knows for sure, but there are many promising leads, including a "top ten" list of reasons.
David B. Allison, Ph.D., from the Department of Biostatistics at the University of Alabama in Birmingham, oversaw a project that involved some of the most prestigious names in the field of obesity, including Louis J. Aronne, M.D. of Weill Cornell Medical College, to explore “ten putative contributors to the obesity epidemic.” Their concern was that this epidemic had become a "global issue" and showed "no signs of abating." Their report was published several years ago in Critical Reviews in Food Science and Nutrition in a comprehensive article that included extensive evidence from both human and animal studies (and almost 500 references). More recently, their findings have been presented in a considerably abridged version by Dr. Aronne and his colleague Suzanne B. Wright, from the Comprehensive Weight Control Program at Weill Cornell, and published in 2012 in the journal Abdominal Imaging.
Here is a list of ten explanations, though not necessarily in any order of importance, to account for the burgeoning worldwide obesity epidemic:
1. the current food environment: increased availability of relatively inexpensive,highly caloric food (particularly laden with fat, sugar, and salt) served in enormous portions
2. decreases in physical activity: increased time spent in sedentary activities such as watching television or using computers; advanced technology enables less caloric expenditure (e.g. escalators, TV remote controls, electric garage door openers, etc.)
3. decreases in sleeping time; trend over the years of decreased amount of sleep in the general population(from around 9 hours before WWI to less than 7 hours more recently), with many people chronically “sleep deprived”; “sleep debt” exerts “profound effects on metabolic hormones” that may lead to changes in circadian rhythms, increased food intake, weight gain, and even diseases such as type II diabetes and cardiac disease
4. drug-induced weight gain: many more people taking medications that lead to weight gain (e.g. medications for depression, anxiety, psychosis, hypertension, diabetes, contraception). Even antihistamines can lead to weight gain; lithium for mania can lead to a 35 lb weight gain in some.
5. decline in cigarette smoking: smoking can lead to weight control and giving up smoking can be associated with often considerable weight gain
6. exposure to “endocrine disruptors:” industrial chemicals ubiquitous in our environment have been associated with increased weight gain (e.g. phthalates, pesticides, flame-retardants, bisphenol A); these disrupt hormonal functioning and adipose tissue regulation
7. infections: several viruses have been associated with increased weight gain, both in animals and humans; adenovirus 36 is most commonly implicated; even changes in bacteria in the gut can lead to weight gain
8. intra-uterine effects: so called "epigenetic effects;" maternal weight (either overnutrition or undernutrition for the fetus) may lead to obesity later in life
9. increased maternal age: women postponing childbearing because of improved contraception and more women in the workforce; obesity rates in children reportedly higher with older mothers
10. temperature control and decreased variability in ambient temperatures with air conditioning and central heating: may lead to decreased metabolic rate and weight gain
This is not an exhaustive list. Even the huge genetic contribution of "assortative mating" (e.g. fat people tend to marry fat people) may be a factor. For those particularly interested in the details behind the "top ten" list, please consult Dr. Allison's original article.