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Background: Western diets, obesity, and sedentary lifestyles are associated with increased cancer risk. The mechanisms responsible for this increased risk, however, are not clear.

Objective: We hypothesized that long-term low protein, low calorie intake and endurance exercise are associated with low concentrations of plasma growth factors and hormones that are linked to an increased risk of cancer.

Design: Plasma growth factors and hormones were evaluated in 21 sedentary subjects, who had been eating a low-protein, low-calorie diet for 4.4 ± 2.8 y (x̄ ± SD age: 53.0 ± 11 y); 21 endurance runners matched by body mass index (BMI; in kg/m²); and 21 age- and sex-matched sedentary subjects eating Western diets.

Results: BMI was lower in the low-protein, low-calorie diet (21.3 ± 3.1) and runner (21.6 ± 1.6) groups than in the Western diet (26.5 ± 2.7; P < 0.005) group. Plasma concentrations of insulin, free sex …