Body Mass Index Versus Body Fat Percentage in Prospective National Football League Athletes: Overestimation of Obesity Rate in Athletes at the National Football League Scouting Combine

Obesity has been previously noted as a major issue in the National Football League (NFL), where it has been shown that 97% of all players demonstrate a body mass index (BMI) of >=25.0 with a reported obesity rate of 56% (BMI >= 30.0). However, BMI does not take into account body composition by mass, and may overestimate prevalence of obesity. The purposes of this study were (a) to determine the validity of BMI as a measure of body fat percentage and obesity in athletes at the NFL Combine, (b) to define the obesity rate based on body fat percentage compared with BMI, and (c) to determine the relationship between draft status and body composition. It was hypothesized that the rate of obesity, as measured by air displacement plethysmography (ADP), would be less than the rate of obesity as measured using BMI. Athletes who competed at the 2010 through 2016 NFL Combines were included in this study. Air displacement plethysmograph testing at the Combine was performed through BOD POD Body Composition Tracking System with collection of the following metrics: body fat percentage (%), and compared with BMI based on weight and height. In addition, the metrics were evaluated for differences over the 7-year study period to determine temporal changes and to determine draft status based on position relative to BOD POD calculations. A total of 1,958 NFL Combine participants completed ADP body composition testing. Based on BMI (>=30.0), the obesity rate was 53.4% versus an 8.9% obesity rate when using ADP. Drafted players demonstrated a significantly lower body fat percentage than undrafted players (p <= 0.05), with the exception of quarterbacks and running backs. All 8 positions of play, with the exception of defensive linemen, demonstrated a decrease in body fat percentage between 2010 and 2017. However, total body mass by position of play remained relatively constant with no significant change noted in any position. In conclusion, the obesity rate in prospective athletes at the NFL Combine was overestimated when calculated based on the BMI. Body fat percentage was more valid for determining an NFL player candidate's true body composition. Drafted players demonstrated a significantly lower body fat percentage in 6 of 8 positions compared with undrafted players. This is important to recognize for a strength and conditioning professional to use the correct metric when evaluating NFL players who could have been erroneously categorized in the obese population by their BMI. Furthermore, a higher percentage of fat translates to lower chances of becoming drafted.