BACKGROUND: No previous study has sought to examine the influence of dietary composition on acne vulgaris. OBJECTIVE: We sought to compare the effect of an experimental low glycemic-load diet with a conventional high glycemic-load diet on clinical and endocrine aspects of acne vulgaris. METHODS: A total of 43 male patients with acne completed a 12-week, parallel, dietary intervention study with investigator-masked dermatology assessments. Primary outcomes measures were changes in lesion counts, sex hormone binding globulin, free androgen index, insulin-like growth factor-I, and insulin-like growth factor binding proteins. RESULTS: At 12 weeks, total lesion counts had decreased more in the experimental group (-21.9 [95% confidence interval, -26.8 to -19.0]) compared with the control group (-13.8 [-19.1 to -8.5], P = .01). The experimental diet also reduced weight (P = .001), reduced the free androgen index (P = .04), and increased insulin-like growth factor binding protein-1 (P = .001) when compared with a high glycemic-load diet. LIMITATIONS: We could not preclude the role of weight loss in the overall treatment effect. CONCLUSION: This suggests nutrition-related lifestyle factors play a role in acne pathogenesis. However, these preliminary findings should be confirmed by similar studies.