"We then looked at other studies that examined incidents of acne in similar populations -- South Americans and New Guineans now living in westernized settings," he tells WebMD. "We found that when they become more westernized and start eating like Americans, they do develop acne," he notes. "So it's not genetics."
His advice: Eat foods with a low glycemic index -- a prediction of how much a particular food will raise your insulin levels. Low glycemic foods include lean meat and fish, vegetables, and fruit. A new study is under way in Australia to test the effect that high- and low-glycemic foods have on acne-laden teens.
"This study shows the American people that there is a link between diet and acne and that it is treatable by altering diet," Cordain tells WebMD.
But not all are convinced. "Hypothetically, a high-load glycemic diet could lead to (acne), but I'm not convinced that going on a low-glycemic diet would improve acne," says Diane Berson, MD, of Cornell Medical College and a spokeswoman for the American Academy of Dermatology. "There are many factors that play a role in acne -- genetics, stress. It could be these people studied were genetically less susceptible or that their lifestyle is less stressful than western civilizations. It's hard to definitively conclude that diet is the factor."
Meanwhile, the academy has no plans to rewrite this long-standing policy: "Acne is not caused by food. While some people feel that their acne is aggravated by certain foods, particularly chocolate, colas, peanuts, shellfish and some fatty foods, there is no scientific evidence that suggests food causes or influences acne. Avoid any foods which seem to worsen your acne and, for your overall health, eat a balanced diet -- but diet shouldn't really matter if the acne is being appropriately treated."
That policy -- along with the thinking of Berson and most health experts -- stems largely from studies in the 1960s and 1970s that found no scientific cause for the popular notion (at least by patients) that breakouts occurred after certain foods were consumed.
"One of the ways in which everyone kind of blew off the food connection was because of a paper published in 1969 in TheJournal of the American Medical Association examining whether chocolate caused acne," says Cordain. "One group was fed chocolate and another fed a placebo. And lo and behold, the incidences were the same. But the placebo had the same glycemic load as the chocolate - virtually all the ingredients were the same except for cocoa. Bingo!"