An economic analysis of decisions on physical activity and energy imbalance: cross-sectional evidence from a panel of middle-aged adults

Ample evidence indicates that regular physical activity has many human health benefits. Maintenance of good physical fitness enables one to meet the physical demands of work and leisure comfortably and be less prone to a number of illnesses. In addition to physical inactivity, a poor diet is another factor in energy imbalance (more calories consumed than expended). According to the Dietary Guidelines for Americans 2005, physical inactivity and poor diets are the two most important factors contributing to the increase in overweight and obesity in the United States. Overweight and obesity are major risk factors for certain chronic diseases such as diabetes, cardiovascular diseases and some forms of cancer. However, over the past forth-five years, the obesity rate of U.S. adults has almost tripled, rising from 13% to 35%.The objective of this study is to examine women's and men's decisions to participate in demanding physical activity and attain a healthy weight. To achieve this, a productive household model of investment in health is first derived. Second, both trivariate probit and seemingly-unrelated-regression models of decisions on physical activity and BMI or obesity are developed. These outcomes are hypothesized to be related to health attitudes, prices of food, drink and health care services and products, the respondent's personal characteristics (such as education, adjusted family income, opportunity cost of time, occupation, marital status, race and ethnicity) and the respondent's BMI or being overweight at age 25. Third, data from the 2004 round of the National Longitudinal Survey of Youth (NLSY79) are used to fit the models.Due to basic physiological differences in men and women, separate analyses are undertaken for men and women. Also, two physical activity equations, one for participating in moderate physical activity and the other one for participating in vigorous physical activity, are fitted. Findings include: an individual who has a higher adjusted family income has a lower current BMI or a lower likelihood of being obese; females with higher education are more likely to be obese or have higher BMI, while males with higher education are less likely to be obese or have lower BMI; older males within our cohort have higher BMI or higher likelihood of being obese; higher prices for fresh fruits and vegetables and non-alcoholic drinks increase BMI and likelihood of obesity for females but not for males; and higher prices for processed fruits and vegetables reduce BMI and likelihood of obesity for females but not for males. In a joint test of the null hypothesis of no food and drink price effects on the possibility to be obese, the hypothesis was rejected for women but not for men. When exercise is measured in minutes and weight as BMI, the hypothesis of no effects of the prices of food and drink on BMI is rejected for women but not for men. When individuals are classified as over-weight or not over-weight at age 25 and exercise is measure in minutes and weight is measured as BMI, the null hypothesis of no impact of food and drink prices on these outcomes is rejected for early non-overweight females, but not for males or early overweight females.