Weight gain, according to pretty much everyone who has studied the subject, is the result of an energy imbalance: consuming more calories than your body burns. Some experts, of course, have proposed that our current obesity epidemic is based on factors more complex than this simple equation, such as an increase in sugar consumption or even changes in our epigenome. But while these proposed explanations may explain certain habits, cravings, and even metabolic changes, none of them directly contradict the understanding that weight, in the end, depends on energy balance.
So a study released late last month, showing that average calorie consumption in the United States has fallen while the rate of obesity has climbed, was a surprise to many — including the study’s own authors. Published online by the American Journal of Clinical Nutrition, the study used data on food consumption from nine national surveys conducted between 1971 and 2010, covering over 60,000 adults between the ages of 20 and 74. According to the data from these surveys, average daily calorie intake rose from 1,955 in the period of 1971–1975 to 2,269 in the period of 2003–2004. By 2009–2010, however, the rate had dropped to 2,195 calories per day, representing a statistically significant drop that should, in theory, have some effect on obesity rates.
But obesity rates, of course, haven’t fallen. According to an article on the study at DiabetesInControl.com, since 1999, the obesity rate for women has remained steady at about 35%. During that same period, however, the obesity rate for men has increased from 27% to 35%. With such a pronounced increase in obesity, one would expect to see a corresponding increase in calories consumed, since there is considerable doubt that a reduction in physical activity could be solely responsible for it.
So what could be the reason for these seemingly incompatible trends? One possible answer is that the conventional wisdom is wrong about the relationship between calories and weight — that at least in some cases, the body’s metabolism could get slower when fewer calories are consumed, leading to weight gain. Another possibility is that Americans, or at least American men, have in fact become far less physically active since 1999; finding data to support this assertion, however, might be difficult. And, of course there is the possibility that the survey data are wrong. As an article at Fox News notes, increased awareness of the dangers of excessive calorie consumption, and possibly of sugary beverages in particular, may have led respondents to underreport their calorie intake in the most recent set of years.
What do you think is the most likely explanation for the reported drop in calorie consumption, in the face of rising obesity rates? Have you ever gained weight despite eating less, or despite an unchanged diet? If so, what do you think was the most likely explanation for the weight gain? Have you witnessed a general drop in physical activity in your community, or is there another factor aside from diet that you think might be contributing to weight gain? Leave a comment below!