Body mass index is increasing faster among taller

Background: During the past 40 y, there has been a trend toward more eating away from home, increased food availability, the opportunity to order extra-large portion sizes, and general weight gain. Objective: Because shorter people need fewer calories than taller people to maintain their weight, our goal was to determine whether the body mass index (BMI)-height relation has changed over time. Design: Data are from 3581 nonpregnant women and 3091 men examined in the 1959-1962 National Health Examination Survey and 4651 nonpregnant women and 4691 men examined in the 2001 2004 National Health and Nutrition Examination Survey. We tested whether the relation between BMI and height has changed for men and women, after adjustment for other demographic changes. Results: In the past, on average, shorter American men and women had significantly higher BMIs than taller people. However taller people have been increasing their BMI during the past 40 y at a faster rate than shorter people. Conclusions: This study documents that the obesity epidemic has changed the height-BMI relation. The data cannot identify causal pathways, and there are numerous explanations. A plausible hypothesis is that changes in the food environment may have eliminated constraints on weight gain for taller people that existed in a more calorie-constrained environment.