Activity reduction as an adaptive response to seasonal hunger

This paper investigates whether physical activity and productive work effort are reduced in response to nutritional stress during hunger seasons by examining patterns of association between nutritional status and both physical activity and behavior patterns among Lese horticulturists of northeast Zaire. Three predictions are derived and tested: (1) reduction of physical activity will not occur until after significant depletion of body energy stores, (2) reduction of physical activity will be correlated with weight loss and with loss of lean body mass, and (3) less essential activities will be curtailed prior to more essential activities. Anthropometric dimensions and behavioral observations were taken during the 3½ month 1991 Lese hunger season. Among men with a BMI <18.5 kg/m2 and among men with summed skinfolds (SSF) below the median, physical activity level was negatively correlated with percentage loss of body weight and percentage loss of upper arm muscle area (UAMA), while there were no significant correlations in men above these thresholds, supporting predictions 1 and 2. Among women, there was no significant association between nutritional stress and physical activity level. However, patterns of association between nutritional stress and activity budgets suggested that activities that were not essential for short-term survival were curtailed in response to nutritional stress. Among men with SSF below the median, farmwork was negatively correlated with percentage loss of UAMA and positively correlated with minimum SSF, supporting a cycle model of seasonal hunger.