Introduction

Way back in the 1950s, any popular food eaten by a teenager was made to be the cause of acne. This was despite a lack of actual research evidence available at the time to actually prove diet and acne were linked. The situation has changed relatively little since then. Several studies have shown that 30% to 40% of teenagers, medical students, doctors and nurses, still believe that diet causes acne.

Such beliefs are due to overwhelming interest generated by the media about a link between diet and health. This obsessive concern for health has spurred more research on nutrition bringing the subject into mainstream medicine. But, due to overriding commercial concerns, much of the research literature is pseudo-scientific and has only generated more myths. Today, irrefutable evidence based on good quality research is still lacking, making any conclusive statement on the link between diet and acne impossible. At most, a survey of currently held opinions can be given. People’s perceptions are, however, important since treatments are often based on such perceptions.

Acne and diet link

The link between diet and acne is believed to be shown by the lower incidence of acne among non-western societies as compared to western societies. Also cited as evidence is the fact that when non-western societies migrate to a western life style the incidence of acne goes up. A good example is the Inuit Indians of Canada, among whom acne was absent when they lived in their traditional way. On adopting a western life style, acne incidence among the Inuits reached the levels seen in Western Caucasian societies. Similar observations have been noted in studies on other populations of different ethnicities.

Hyperinsulinemia effect on acne

Chronic hyperinsulinemia may be a key link between acne and diet, high testosterone levels and low levels of molecules called sex hormone binding globulins (SHBG). SHBG is antagonistic to testosterone, binding to free molecules of testosterone and rendering it inactive. So having more SHBG effectively reduces androgen hormone activity.

At one level, the androgen testosterone may be maintaining insulin levels. At another level they may be promoting insulin resistance. Considerable evidence now shows that in women with polycystic ovarian syndrome, hyperinsulinemia increases androgen production and decreases production of SHBG in the liver. Thus, a vicious circle is created where this increased androgen leads to decreased SHBG, further promotes insulin resistance leading to increased hyperinsulinemia.

Many believe that hyperinsulinemia, caused by high fat and carbohydrate diets in western societies may be causing acne by stimulating androgen production and affecting the sebaceous glands and follicular keratinization.

Dietary influence on sebum composition and secretion rate

The interpretation of studies on the effect of dietary carbohydrates and fats on sebum composition and secretion is confusing, but some general themse seem to be emerging. Some animal studies showed an increase in sebaceous output on feeding them a high fat or carbohydrate diet. Studies on humans showed changes in sebum composition and 40% reduction in sebum secretion, on total and prolonged calorie deprivation.

A long held opinion that sebaceous glands produced their own fluids and did not draw anything from the bloodstream was proved wrong by Pappas et al. They convincingly showed that sebaceous glands can and do use fatty acids from the bloodstream for the production of sebum. However, these studies do not conclusively prove that diet affects sebum composition and secretion.

In general these results suggest that dietary fat and carbohydrate might have an effect on sebaceous gland activity. However other evidence suggests that diet and acne are not linked (see below).

Interventional studies

Studies on groups under different dietary regimes did not show any correlation between acne and diet. A study on 2720 soldiers showed no link between acne and obesity in adolescents although the study did find a link among older subjects. In another study, no difference in sugar consumption was found in 16 subjects with acne and matched controls wiothut acne. An important and large study conducted on monozygotic and dizygotic twins found no significant differences, in weight, height, birth weight, body mass index and reproductive factors, between acne and non-acne affected twins.

Chocolate - a cause?

In 1969, a controlled study was done to find out the truth or otherwise of chocolateand its effect on worsening the acne condition. For one month 65 subjects with moderate acne daily ate one bar containing ten times the chocolate contained in a normal bar or ate a similar one that contained no chocolate. After measuring the acne in the study volunteers, the authors concluded that chocolate did not significantly affect the acne condition.

However, critics found serious methodological flaws in the study. Most importantly, only changes in the number of lesions were considered for significance. The qualitative clinical changes like conversion of comedones into pustular flares were totally ignored. This meant that conversion of 10 comedones into 10 pustules was not a significant change for the study. Usually, patients with food related acne first complain of pustular flares and not comedones. The critics have a case, but larger scale, better designed studies have not been conducted.

In conclusion it must be said that, based on the present state of evidence, the jury is still out on the link between acne and diet.