Carbohydrates

The long-held belief that there is no link between diets high in refined sugars and processed foods, and acne, has recently been challenged.[15] The previous belief was based on earlier studies (some using chocolate and Coca Cola) that were methodologically flawed.[15][22][23] The recent low glycemic-load hypothesis postulates that rapidly digested carbohydrate foods (such as soft drinks, sweets, white bread) produce an overload in blood glucose (hyperglycemia) that stimulates the secretion of insulin, which in turn triggers the release of IGF-1.[15] IGF-1 has direct effects on the pilosebaceous unit (and insulin at high concentrations can also bind to the IGF-1 receptor)[24] and has been shown to stimulate hyperkeratosis and epidermal hyperplasia.[25] These events facilitate acne formation. Sugar consumption might also influence the activity of androgens via a decrease in sex hormone-binding globulin concentration.[26][27]

In support of this hypothesis, a randomized controlled trial of a low glycemic-load diet improved acne and reduced weight, androgen activity and levels of insulin-like growth factor binding protein-1.[28] High IGF-1 levels and mild insulin resistance (which causes higher levels of insulin) had previously been observed in patients with acne.[29][30][31] High levels of insulin and acne are also both features of polycystic ovarian syndrome.[15]

According to this hypothesis, the absence of acne in some non-Westernized societies could be explained by the low glycemic index of these cultures' diets.[32] It is possible that genetic reasons account for there being no acne in these populations, although similar populations (such as South American Indians or Pacific Islanders) do develop acne.[33][34] Note also that the populations studied consumed no milk or other dairy products.[35]

Further research is necessary to establish whether a reduced consumption of high-glycemic foods, or treatment that results in increased insulin sensitivity (like metformin) can significantly alleviate acne, though consumption of high-glycemic foods should in any case be kept to a minimum, for general health reasons.[36] Avoidance of "junk food" with its high fat and sugar content is also recommended.[37]