For the past 30 years, doctors, facialists and high school health-ed teachers alike have assured us up and down that, contrary to what our grandmothers may have believed, junk food does not cause acne. Snickers bars, soda and ice cream, they told us, might be unhealthy—but at least they didn’t affect our complexions. According to the American Academy of Dermatology, the belief that chocolate caused zits was an old wives’ tale, somewhere along the lines of “shaving your legs makes the hair grow back faster.”
As it turns out, those old wives may have been right all along. This past July, a study published in the American Journal of Clinical Nutrition showed a measurable link between high-glycemic diets and acne. The study followed two groups of acne-plagued males ages 15 to 25 who were told they were participating in a study on carbohydrates and protein. The first group continued to eat their usual diet, which included plenty of sugar and processed grains—foods that have a high glycemic index. The other was given whole grains, lean meat and fish, fruits and vegetables—foods with a low glycemic index. After 12 weeks, a team of dermatologists determined that the subjects in the latter group had 51 percent fewer pimples than when they started.
“It all comes down to insulin,” says Neil Mann, a professor of human nutrition at RMIT University in Melbourne, Australia, and the study’s lead researcher. Foods with a high glycemic index cause blood sugar to rise, forcing the body to bring it down with a surge of insulin. And insulin can lead to acne, both by accelerating cell growth in the pores and stimulating oil-producing hormones called androgens. This radical shift in thinking about acne challenges a stance that dates back to 1969. That was the year that three researchers published a study in the influential Journal of the American Medical Association that seemed to show that chocolate does not cause acne. Two years later, another well-known study argued that peanuts, milk and cola were also blameless. Whereas previously, medical textbooks had recommended whole-grain bread and avoidance of ice cream in the treatment of pimples, a new generation of doctors were taught that there was no connection between diet and acne.