For 80 per cent of teenagers, it is the scourge of their lives and, for a third, a problem that can persist into adulthood. There are signs, too, that acne is on the increase among 20- and 30-year-olds who never had it when they were younger. Almost all of those who suffer have probably been assured that it is a myth that junk food causes spots. But the results of a study published recently in the American Journal of Clinical Nutrition fly in the face of nearly four decades of conventional thinking.
Nutritionists at the Royal Melbourne Institute of Technology in Australia followed two groups of young males (aged 15-25) with acne. Fifty per cent were allowed to follow their regular diet, which included plenty of processed foods with a high glycaemic index (GI), while the rest were given a meal plan of low GI foods. After 12 weeks, the low GI group had 51 per cent fewer pimples than when they embarked on the programme. "The acne of the boys who were on the higher-protein, lower-glycaemic index diet improved dramatically by over 50 per cent," says Professor Neil Mann, who led the study. "That is more than you would see in a topical acne solution."
High GI diets are known to raise levels of insulin and insulin-like growth factor (called IGF-1), leading to the production of more of the male hormone testosterone. That triggers the overproduction of sebum, the greasy substance that blocks pores and causes spots. "A diet rich in processed foods pushes glucose and insulin levels higher, exacerbating this problem," says Mann. The trial was small, and more thorough investigations are necessary, but it is the first to look specifically at the effects of carbohydrate type and the latest to provide evidence that diet is influential in causing acne. Five years ago, Dr Loren Cordain, an exercise and health scientist at Colorado State University who has since written a book called The Dietary Cure for Acne, showed how high GI foods, such as white bread, trigger "a hormonal cascade" that leaves people more prone to pimples.
A radical shift in thinking about what causes acne occurred in 1969 when findings published in the Journal of the American Medical Association seemed to prove that chocolate consumption had no effect on acne incidence. It was followed by research showing that peanuts, milk and cola also had little influence, and the case for food triggering acne appeared to fall apart. But Cordain says the results of the earlier study were misinterpreted. "In the 1969 study, one group was fed chocolate and another placebo, and it turns out the placebo had the same GI load as chocolate," he says. "Virtually all the ingredients were the same except for cocoa."
Dr Robyn Smith, a colleague of Mann's, says further evidence that eating a high GI diet is bad for the skin comes from surveys she and her team have done on Inuits, who become prone to acne only when they start eating western-style food. "Along with acne, the Inuits also developed higher rates of obesity, diabetes, dental cavities and heart disease," she says. "It is interesting that these other maladies are commonly associated with diets, yet acne isn't."
It is not only the high GI aspect of diet that is being linked to acne. Other experts have long thought that dairy consumption plays a part. As far back as the 1970s, William Danby, an assistant professor in dermatology at Dartmouth Medical School in the US, suspected that some of his patients' acne was linked to dairy food. Between 1973 and 1980, Danby kept a detailed log of his patients' diets and it became clear that those who ate the most dairy produce also had the most severe acne. Although his early hunch was based on anecdotal evidence, Danby has since worked with Professor Walter Willett, a nutritionist at Harvard Medical School, to publish several clinical studies confirming that milk, in particular, might play a role in acne.
Neither Danby nor Willetts is sure why dairy seems to cause spots. But the most likely explanation is hormonal. It is thought that milk from pregnant cows contains hormones that are converted to testosterone. "Milk contains hormones that 'turn on' oil glands," Danby says. "The cows that give the milk are pregnant and milking most of their lives. These hormones are not injected into the cows - they are natural hormones that cows make during every 'menstrual' cycle, but during pregnancy these hormones are produced continuously at high levels and so are found in all cows' milk."
Official recommendations from organisations such as the American Academy of Dermatology and the British Association of Dermatologists do not recognise any link between dairy and acne. But Dr Jeffrey Dover, a spokesman for the AAD and an associate clinical professor at Yale School of Medicine, admits he has had some success with patients he has advised to avoid dairy. "I've seen at least a handful of patients with improvement of acne that was very stubborn up to the point they changed their diet to limit dairy," Dover says. Danby, whose website www.acnemilk.com proposes a no milk or dairy diet, says "it's all about finding your personal threshold so that you can eat what you enjoy without your skin paying the price". While it is too early for dermatologists to change their advice completely, they are no longer refuting the diet connection. "So far, there is some limited evidence that certain foods cause acne," says Nina Goad, a spokeswoman for the British Association of Dermatologists. "The latest link concerning glycaemic load is plausible, but it does require more research before any firm conclusions can be made and a change of diet won't be the answer for everyone."
Low GI foods to eat Whole grains, 70 per cent dark chocolate, lentils, brown rice, porridge, -apples, dried apricots High GI foods to avoid Processed and refined foods, burgers, chips, crisps, fizzy drinks, sweets, white bread, pasta Zinc/copper According to the Institute of Optimum Nutrition in the UK, 60 to 90mg a day of this mineral improves some people's acne. If taking extra zinc, your body will also need 1 to 2mg each day of copper to avoid deficiency. Vitamin A Large quantities of -vitamin A have been shown to treat severe acne. However, in many cases the studies were conducted using a synthetic prescription version such as Accutane - which can cause mood changes and depression. Too much vitamin A can be toxic and should be taken under medical supervision. Vitamin B6 Studies suggest that 50mg per day of vitamin B6 may alleviate premenstrual flare-ups of acne. But the findings are inconclusive.