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Exercise Addiction in Men Is Associated With Lower Fat-Adjusted Leptin Levels

Objective:To test a hypothesized association between resting leptin levels (adjusted for body fat percentage) and symptoms of primary exercise addiction. Design:Cross-sectional design. Setting:Habitual amateur exercisers participating in running, fitness, weight training, and biking. Participants:Twenty men with exercise addiction as defined by the Exercise Addiction Inventory (EAI scores 24-30) and 20 men in an exercise control group (EAI scores 6-16) matched on body mass index. Main Outcome Measures:Plasma leptin and sex hormones were measured in blood samples collected under fasting and resting conditions. Body composition was assessed by dual-energy x-ray absorptiometry. Eating disorder symptoms were identified by the Eating Disorder Inventory 2. Results:The exercise addiction group had significantly (P < 0.001) lower leptin levels (1.1 &mgr;g/L, SD = 1.3) than controls (4.3 &mgr;g/L, SD = 2.9). Even when adjusted for body fat percentage, the addiction group had significantly (P < 0.001) lower leptin levels (0.1 &mgr;g/L, SD = 0.1) than the controls (0.2 &mgr;g/L, SD = 0.1). Body fat–adjusted leptin correlated with free bioavailable testosterone, but it was only significant in nonaddictive exercisers. None of the exercisers seemed to suffer from an eating disorder. Conclusions:This is the first study showing that excessive training in exercise addiction is associated with low levels of body fat–adjusted leptin levels. Clinical relevance:Hypoleptinemia could be involved in the pathogenesis of exercise addiction. However, further studies are needed to explore the potential causal relationship.