More Recent Evidence of Dietary Influence on Acne
Importantly, the available research does not demonstrate that diet causes acne but rather that it may influence or aggravate existing acne. Data collection for acne studies also can be confounded by the interplay of many factors, such as increased access to health care, socioeconomic status, and shifting cultural perceptions of skin care and beauty.4 An important facet of any therapeutic recommendation is that it should be supported by confirmable mechanistic pathways.
GI and GL
Over the last few decades, a number of observational and intervention studies have focused on the possible influence of the GI/GL of foods on acne incidence and/or severity. A high GI diet is characterized by a relatively high intake of carbohydrate-containing foods that are quickly digested and absorbed, increasing blood glucose and insulin concentrations. Glycemic load takes the portion size of dietary carbohydrates into consideration and therefore is a measure of both the quality and quantity of carbohydrate-containing foods.9 TheGI/GL values of more than 2480 food items are available in the literature.10
Evidence from several studies supports the role of high GI/GL diets in exacerbating acne and suggests that transitioning to low GI/GL diets may lead to decreased lesion counts after 12 weeks.11-13 In one randomized controlled trial, male participants aged 15 to 25 years with mild to moderate facial acne were instructed either to eat a high protein/low GI diet or a conventional high GL control diet.13 After 12 weeks, total lesion counts had decreased more in the low GI diet group than the control. As partial confirmation of a mechanistic pathway for a high GI diet and acne, the low GI group demonstrated lower free androgen index and insulin levels than the control group.13 In a Korean study, a 10-week low GL regimen led to a reduction in acne lesion count, a decrease in sebaceous gland size, decreased inflammation, and reduced expression of sterol regulatory element-binding protein 1 and IL-8.14
More recent studies have further solidified the role of high GI/GL diets in acne severity.9,15,16 High GI/GL diets are believed to stimulate acne pathways by stimulating insulinlike growth factor 1 (IGF-1), which induces proliferation of both keratinocytes and sebocytes and simulates androgen production.17 An excellent diagram showing the connection between high GI diets (and dairy) and IGF-1, insulin and its receptors, androgen and its receptors, mammalian target of rapamycin, and the pilosebaceous unit was published in the literature in 2016.4 Interestingly, metformin has been shown to be an effective adjunctive therapy in the treatment of moderate to severe acne vulgaris.18,19
Milk and Dairy Consumption
Milk consumption also has been examined for its potential role in the pathogenesis of acne, including its ability to increase insulin and IGF-1 levels and bind to the human IGF-1 receptor as well as the fact that it contains bovine IGF-1 and dihydrotestosterone precursors.20 Although not studied quite as extensively or rigorously as GI/GL, consumption of milk and dairy products does appear to have the potential to exacerbate acne lesions. Beginning with a series of retrospective and prospective epidemiologic studies published from 2005 to 2008,21-23 a link between clinical acne and milk or dairy consumption in adolescent subjects was reported. A recent meta-analysis found a positive relationship between dairy, total milk, whole milk, low-fat milk, and skim milk consumption and acne occurrence but no significant association between yogurt/cheese consumption and acne development.24