Calories or Physical Activity: What’s to Blame for Weight Gain?

We are well aware that Americans’ waistlines have made sizable increases over the past several decades. However, debate over the root of this weighty issue continues. Some say we’re eating more. Others say we’re less active. Many believe both are true. Can a recent report end the debate?

The study, published in The American Journal of Medicine (2014; 127 [8], 717–27e.12), comprised data collected by the National Health and Nutrition Examination Survey from 1988 to 2010. The researchers specifically looked at leisure-time physical activity rates, calorie intake, body mass intake and waist circumference. BMI increased by 0.37% per year among both men and women. Waist circumference grew more rapidly in women—at an annual rate of 0.37% versus 0.27% among men.

While this data is hardly mind-blowing, it may surprise you to learn that the researchers found no significant increase in calorie intake among the subjects. They did find massive changes in leisure-time physical activity. According to the study, 51.7% of women in 2010 reported no leisure-time physical activity, compared with 19.1% in 1988. Men were generally more active, but still, their physical inactivity levels nearly quadrupled—from 11.4% to 43.5%.

“Our analyses highlight important dimensions of the public health problem of obesity, including trends in younger women and in abdominal obesity, and lend support to the emphasis placed on physical activity by the Institute of Medicine,” the authors explained.

The authors noted that the study was limited in that the data was self-reported. They suggested that respondents may have underreported calorie intake and overestimated physical activity levels. However, the investigators underscored the stark increase in physical inactivity.