Exercise addiction in men is associated with lower fat-adjusted leptin levels

To test a hypothesized association between resting leptin levels (adjusted for body fat percentage) and symptoms of primary exercise addiction.

Cross-sectional design.

Habitual amateur exercisers participating in running, fitness, weight training, and biking.

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.

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.

The exercise addiction group had significantly (P < 0.001) lower leptin levels (1.1 μg/L, SD = 1.3) than controls (4.3 μg/L, SD = 2.9). Even when adjusted for body fat percentage, the addiction group had significantly (P < 0.001) lower leptin levels (0.1 μg/L, SD = 0.1) than the controls (0.2 μg/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.

This is the first study showing that excessive training in exercise addiction is associated with low levels of body fat-adjusted leptin levels.

Hypoleptinemia could be involved in the pathogenesis of exercise addiction. However, further studies are needed to explore the potential causal relationship.