Determination of the relationship between plasma leptin levels and physical activity among children in rural Tanzania

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Patients with anorexia nervosa (AN) severely restrict their food intake and nevertheless show increased levels of physical PA. These patients, just like undernourished individuals in general, are characterized by a subnormal percentage of body fat. Hence, only a low concentration of the satiety hormone leptin, which is primarily secreted by adipocytes, can be detected in plasma. In developing countries, especially in rural parts, poverty and a poor nutritional status are quite common. Single studies from these countries (e.g. Kenya, Mozambique or Colombia) have revealed that poor undernourished/underweight children are physically more active than the better nourished. Based on our previous studies of AN patients and the semi-starvation rat model we hypothesize that low leptin levels trigger increased PA which might represent a foraging behavior upon initiation of starvation. Because subnormal leptin levels are uncommon in children of developed countries we resort to children of developing countries to test this hypothesis. The aim of the study is to determine the relationship between plasma leptin levels (from capillary blood) and PA (accelerometry) in 200 9- to 12-year old children from rural Tanzania. Analogous to our findings in AN patients and semi-starved rats, we assume that otherwise healthy albeit undernourished children with a significantly decreased fat mass and hypoleptinemia have a higher PA than better nourished minors. Apart from low plasma leptin concentrations as a driving force for increased PA, environmental factors including the ambient temperature, socio-economic status of parents, parental health, food insecurity, and walking distances to school or to fulfill household chores will be assessed. The study will be helpful (1) to explain inter-individual variance of PA in populations of developing countries, (2) to understand the mechanisms of adaptation to a reduced food supply, and (3) to explain for the first time a biological contribution to the so-called physical activity transition (improved nutritional situation accompanied by reduced PA within the scope of the transition from a developing country to a newly industrializing country). We will cooperate with Dr. Akwilina Mwanri whose research interests are among others physical activity and food security in Tanzania.