Diet and adult acne.
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Diet and adult acne.

Junk food doesn't just make you fat. Turns out it can give you zits, too. For a long time doctors chalked up the whole diet-acne connection to urban legend. But now more and more research is pinning processed foods, sweets, and even dairy products as primary causes of acne – even in adults.

A review just published in the 'Journal of the Academy of Nutrition and Dietetics' examined reams of research on diet and acne spanning back to the early 20th century. Although a few popular studies from the sixties dispelled the junk food pimple link – making chocolate lovers cheer – newer trials put certain foods back in the hot seat.

According to lead researcher Jennifer Burris, a dietitian at New York University, the major acne culprits are candy, chips, soda, and other highly processed foods that rank high on the glycemic index. These items require little effort for your body to digest, so they cause your blood sugar to spike super quickly. Burris says this sets off a domino effect, as your system cranks out extra insulin to get the glucose in check, as well as a particular hormone that tells your skin to produce oil. The excess oil plugs up your pores and gives pimple-causing bacteria lots to feed on. And there you have it: zits.

Burris says dairy's link to acne is a bit murkier. Milk and cheese contain carbohydrates that boost blood sugar, but not enough to cause a big problem for the skin. Rather, she believes that all the hormones and growth factors in dairy, which are similar to those in the human body, cause excess oil production and eventually acne.

As these connections become clearer, more dermatologists are telling their blemish-plagued patients to stop blaming genetics and start watching what they eat. "I think the high-glycemic American diet explains a lot of the adult acne we see," says Dr. Valori Treloar, an integrative dermatologist and coauthor of 'The Clear Skin Diet' (Cumberland House, 2007). Along with cutting down on dairy and low-nutrient processed junk, Treloar suggests eating lots of antioxidant-rich and high-fiber whole foods that are low on the glycemic index. "In general, eating for clear skin is the same as eating for good health," she says. "Your skin needs building blocks to regenerate and repair just as the rest of your body does."

Treloar points out that everyone responds differently to different foods, but she offers her general prescription for clear skin: "For breakfast, lunch, and dinner, half of your plate should be covered with nonstarchy vegetables," she says. "A palm-sized serving of eggs, fish, or lean meat should fill up one-quarter of the plate, and get about a cup (more if you're very active) of a carb-rich food such as squash, sweet potatoes, or whole grains. Eat fruit two or more times daily, and snack on seeds and nuts."

Don't expect instant results. Burris says it usually takes 12 weeks for the acne cycle to clear out. But tweaking your diet now might just score you clear skin by summer – and most likely a trimmer waistline to boot.