Diet plays a real role in acne and psoriasis, but not through the simple fixes many people expect, according to dietitian Dr Emily Leeming.
Leeming said cutting out chocolate or dairy alone is unlikely to clear up spots. Instead, research points to the overall glycaemic load of a person's diet, a measure of how fast food raises blood sugar and how much of it is eaten, as more important for acne than any single food.
A 2007 study published in the American Journal of Clinical Nutrition found that young men who switched to a lower glycaemic load diet saw a significant drop in the number of inflamed acne spots over three months, compared with men who kept their usual diet. The men swapped refined carbohydrates and sugary foods, such as sweetened cereals, biscuits and pastries, for wholegrain bread and pasta, fruit, and protein-rich foods including lean meat, poultry and fish.
A smaller trial in 2012, published in the journal Acta Dermato-Venereologica, found similar results. People with acne who followed a lower glycaemic load diet for ten weeks saw their inflamed spots fall by about 30 per cent, while those on their normal diet saw no meaningful change.
Why sugar may trigger breakouts
Leeming explained that foods which release energy quickly, such as sugary dishes, push up insulin levels fast. This may in turn raise levels of IGF-1, a hormone that acts on the skin's oil-producing cells and tells them to make more oil. IGF-1 also causes the cells lining the pore to multiply faster, and the extra dead cells can block the pore. A pore that is both oilier and blocked allows bacteria on the skin to multiply, leading to an inflamed spot.
There is not enough evidence to add diet to treatment guidelines, Leeming said, but people with painful acne could try building meals around slower-release carbohydrates such as oats, wholegrains and pulses, while keeping sweet, fast-releasing foods such as pastries, biscuits, white bread and chips to a minimum.
The link between milk and acne
An analysis of the dietary habits of nearly 80,000 children, teenagers and young adults, published in the journal Nutrients in 2018, found a possible small link between milk and acne, though Leeming described the link as vague. A few glasses of milk a week appeared to have little impact, but drinking two or more glasses a day was linked to more acne.
Skimmed and low-fat milk showed a stronger link than full-fat milk, which Leeming said is likely because skimmed milk contains just as much protein and sugar as full-fat milk but lacks the fat that would normally slow its digestion, meaning it pushes up insulin and IGF-1 levels more. She cautioned that the finding does not prove milk causes acne, as it could be down to other factors.
Leeming said people who drink a lot of milk and have stubborn spots could try cutting back for six to eight weeks to see if it helps, while getting calcium from other sources such as fortified plant milks. She said people with psoriasis, where an over-reactive immune system makes skin cells reproduce too fast and causes patches of raised, scaly skin, could benefit from a similar approach.
Walnuts and cholesterol
As a separate tip, Leeming noted that eating a daily handful or two of walnuts can help keep damaging LDL cholesterol, which is linked to heart disease, in check, according to a review of studies. This is down to the healthy fats and fibre in walnuts, which help reduce the amount of cholesterol taken into the bloodstream.
Mediterranean diet and psoriasis
A small study published last year in JAMA Dermatology found that people with mild-to-moderate psoriasis who followed a Mediterranean-style diet, rich in olive oil, vegetables and oily fish, alongside prescription creams, saw greater improvement in their skin than those on a general low-fat diet. Nearly half of the Mediterranean diet group saw their psoriasis improve by three-quarters, compared with none in the comparison group.
Leeming said the Mediterranean diet is known to be anti-inflammatory, and psoriasis is linked to inflammation. Following it means eating along similar lines to a lower glycaemic load diet, with more vegetables, fruit, beans, wholegrains and fish.
Do collagen supplements work?
Leeming said collagen supplements, often taken for wrinkles, do appear to help when every trial is pooled together. But once studies funded by collagen companies and lower-quality studies are set aside, that benefit disappears, according to a review published last year in the American Journal of Medicine.
Collagen-containing foods such as bone broth or chicken skin are also unlikely to help, she said, because the body breaks collagen down into amino acids before building its own collagen, which is then used throughout the body rather than just for the skin.
Leeming said microbes in the gut ferment dietary fibre into compounds that appear to lower inflammation around the body, and plausibly the skin too. Keeping vegetables and fruit central to the diet, alongside wholegrains, beans, nuts and seeds, could benefit the complexion over the long term, though not overnight.
Leeming advised anyone convinced a specific food is fuelling a skin complaint to speak to a doctor or dermatologist before cutting anything out. She noted that a spot may appear to form overnight, but has usually been forming beneath the skin's surface for weeks, meaning a meal or snack from the previous day is not the cause.
