Acne and diet
It turns out, Grandma was right… Chocolate gives you pimples.
In the 1930-60's it was widely believed that too much chocolate was responsible for acne. Two relatively weak studies in the late 1960's/early 70's however showed no link, and from then through to around 2012, it was all considered a myth.
However, there are now numerous, robust scientific studies that show that the consumption of high glycemic index food is associated with acne. The glycemic index (GI) refers to the effect different carbohydrate-containing foods have on blood sugar levels, and hence the body's insulin levels. A high GI food leads to a rapid rise in insulin secretion. The insulin, and associated insulin-like growth factor (IGF-1) both lead to changes in the skin and oil glands that cause acne. In addition, they result in increased androgens (male hormones known to stimulate acne).
Milk also stimulates insulin, and therefore has the same effects on acne. In addition, cows milk contains IGF-1 (identical to human IGF-1), and a number of dihydrotestosterone precursors (androgens). The evidence for the role of milk in acne is based on less robust data, but there are numerous observational studies that support it. The studies suggest skim-milk to be particularly acne-stimulating, likely because of a higher whey protein concentration.
Finally, whey protein containing supplements (e.g. body-building) are highly likely to cause acne based on their ability to stimulate insulin. Whey protein is the soluble milk product left over after the coagulation process in cheese-making.
So, chocolate can give you pimples after all…
Further information regarding the GI index, including an extensive searchable database of foods is available at glycemicindex.com