Body composition and resting metabolic rate of Japanese college Sumo wrestlers and non-athlete students: are Sumo wrestlers obese?

Abstract

The body mass index [BMI = body weight/height² (kg/m²)] is widely used as an indicator of obesity. However, BMI is not the best way to assess obesity, because obesity is an excess of body fat, not body weight. The difference between obesity assessments based on BMI and those based on the percentage of body fat (%Fat) causes problems in evaluating extraordinarily large people, such as Sumo wrestlers, who have both a large fat mass and a large muscle mass. We assessed obesity in male college Sumo wrestlers (n = 15) and non-athlete students (n = 20) using BMI and %Fat as reference indices. Anthropometric parameters and resting metabolic rate (in the sitting position) were measured. The mean body weight, BMI, and %Fat for Sumo wrestlers were 125.1 kg, 40.0, and 25.6%, respectively, which were extraordinarily high, as compared to non-athlete students (P < 0.01). All of the Sumo wrestlers were categorized as obese using the BMI criteria proposed by the World Health Organization: eight were ‘severely obese’ (35 ≤ BMI < 40) and seven were ‘very severely obese’ (BMI ≥ 40). However, only 40% of the wrestlers (n = 6) were categorized as obese when %Fat was used as the reference (%Fat > 25%). Furthermore, the body composition chart clearly showed that some Sumo wrestlers were no more adipose than the non-athlete students. Due to their remarkable muscle development, Sumo wrestlers have an excessive fat-free mass. Thus we conclude that it is necessary to consider both BMI and %Fat to assess obesity in excessively muscular people, such as Sumo wrestlers. Furthermore, we propose new criteria and methods for documenting obesity in Sumo wrestlers based on energy metabolism that considers physical activity and dietary intake.