High level of free-living energy expenditure in rural Gambian men: lack of behavioural adaptation between low and normal BMI groups.

Objective: To explore if a behavioural adaptation--such as a reduction in total free-living energy expenditure (EE)--occurs in Gambian individuals with low body mass index (BMI < 18.5 kg/m2).

Design: Cross-sectional comparative study of young Gambian men living in rural area.

Methods: Total daily free-living EE was assessed from the heart rate method (using individual regression line between heart rate and EE determined in a respiration chamber).

Subjects: One group of underweight men (n = 26, BMI = 17.2 +/- 0.2 kg/m2 compared to a control group with normal BMI matched for age and height (n = 28, BMI = 23.3 +/- 0.2 kg/m2).

Results: In absolute value, the free-living EE of the low BMI group was significantly lower than that of the control group (10.3 +/- 0.5 vs 12.7 +/- 0.5 MJ/d, P < 0.001). Expressed per kg body weight or kg fat-free mass, the differences between the two groups disappeared. In both groups, the level of free-living EE averaged approximately two times the basal metabolic rate.

Conclusions: Rural Gambian men with low BMI and normal BMI have similar levels of free-living EE when normalized for body weight or fat-free mass. Their level of activity can be judged as moderate to heavy. Within the range of BMIs studied there was no evidence of behavioural adaptation to save energy.