Obesity is scientifically identified as a key factor in the development of various pathologies, and we also know, that regular practice of physical activity mitigates the risk of suffering from these. A new study examining trends in obesity, physical activity and caloric intake in adults from 1988 to 2010 in the US has analysed data from the well-known National Health and Nutrition Examination Survey (NHANES). The researchers concluded that the reduction in physical activity was associated with the increase in the prevalence of obesity between 1988 and 2010, but that calorie intake did not change significantly and was not associated with the prevalence of obesity during this period.

These results were published in The American Journal of Medicine, and show that during the 22-year period of the study average body mass index (BMI) increased by 0.37% per year for both men and women. Waistline measurements also increased an average 0.37% per year for women and 0.27% for men. During this time the prevalence of obesity also rose, with young women (from 18-30 years old) experiencing the most marked increases.

The percentage of adults reporting no engagement in any physical activity in their spare time has increased notably in the last two decades, going from 19.1% to 51.7% in the case of women, and from 11.4% to 43.5% for men. Grouping these adults further by their level of physical activity (those who practice no physical activity, those who practice intermediate physical activity and those who practice "ideal" physical activity, in line with the health standards), showed there was also an observable reduction in the number of people who reported they were engaged in an intermediate or "ideal" level of physical activity.

Standards similar to the US Government recommendations were used to group people according to their physical activity level. These involve doing thirty minutes or more of moderate activity at least five days a week, or seventy-five minutes or more of vigorous activity per week, or one hundred fifty minutes per week of a combination of moderate and vigorous activity.

According to the data reported in this study, the average daily caloric intake did not vary significantly in men or women between 1988 and 2010 (although it increased significantly among women who reported not engaging in physical activity in their free time and dropped significantly among men who reported they maintained physical activity levels considered as ideal).

Although the researchers did not examine the type of food and drink consumed during the study period, they observed that the total amount of calories per day, and the amounts of fats, carbohydrates and proteins consumed, did not change significantly in this period, but obesity rates among the population have increased. The study report notes that "[our results] do not suggest that caloric intake is not an important determinant of obesity at the level of an individual. A previous analysis of NHANES 1971-1975 through 1999-2002 reported an increase in food energy density roughly parallel to US obesity prevalence rates." It further states, "Our study has limitations…caloric intake may be under-reported and physical activity overestimated."

However, the study clearly concluded that "Our results do not support the popular notion that the increase in obesity in the United States can be attributed primarily to a sustained increase over time in the average daily caloric intake of Americans."

Ladabaum U, Mannalithara A, Myer PA, Singh G. Obesity, Abdominal Obesity, Physical Activity, and Caloric Intake in U.S. Adults: 1988-2010. The American Journal of Medicine, 2014;127:717-727.