Does cutting out dairy clear up spots? Does eating collagen-rich foods lead to a more youthful complexion?

These are two of the most common questions I’m asked about food and skin – and the answers are not straightforward. What you eat can have an impact – but not with the diet tweaks you might expect.

Let’s start with acne. Many people think it comes down to cutting out one culprit such as chocolate, but what little evidence there is points not to a single food, but more to your diet as a whole.

Key to this is what is known as the glycaemic load of your diet, a measure of not just how fast a food raises your blood sugar but also how much of it you eat. In one small study in 2007, young men who switched to a lower glycaemic load diet experienced a significant drop in the number of inflamed acne spots over three months, compared with those who continued with their usual diet, researchers reported in the American Journal of Clinical Nutrition.

In practice, this meant the men swapping refined carbohydrates and sugary foods – such as sweetened cereals, biscuits and pastries – for lower-load options such as wholegrain bread and pasta and fruit, alongside protein-rich foods, including lean meat, poultry and fish.

A second, smaller trial in 2012 had similar findings – when people with acne stuck to a lower glycaemic load diet for ten weeks, the number of inflamed spots they had fell by about 30 per cent, while those who stuck to their normal diet experienced no meaningful change in inflamed spots, according to the journal Acta Dermato-Venereologica.

Why might this dietary change help?

The thinking is that foods that swiftly release their energy, such as sugary dishes, quickly push up insulin levels.

It's been proven that those who switched to a lower glycaemic load diet saw a significant drop in their inflamed acne spots over a few months, writes Dr Emily Leeming

This may in turn raise levels of IGF-1, a hormone that acts on the oil-producing cells in the skin, telling them to make more oil.

IGF-1 also encourages the cells lining the pore to multiply faster, and those extra dead cells can block it.

A pore that is both oilier and blocked is where the bacteria that live on skin multiply, and that’s what leads to an inflamed spot.

There is not enough evidence to add diet to treatment guidelines but if you have painful acne then building meals on slower-release carbohydrates such as oats, wholegrains and pulses, and keeping sweet, fast-releasing stuff – such as pastries, biscuits, white bread and chips – to a minimum is worth a try.

When it comes to dairy, analysis of the dietary habits of nearly 80,000 children, teens and young adults published in the journal Nutrients in 2018, found that milk has a possible small link to acne. But the link is vague.

While a few glasses a week appeared to have little impact, having two or more glasses a day was linked to more acne.

Oddly, skimmed and low-fat milk showed a stronger link than full-fat milk. It’s likely that this is to do with the milk proteins and sugars in milk pushing up insulin and IGF-1.

Skimmed milk has just as much protein and sugar as full-fat milk, minus the fat that would normally slow down its digestion.

We can’t say milk causes acne, as this finding could have been due to other factors.

Some studies found that milk has a possible small link to acne, so cutting back on your intake for six to eight weeks could help to reduce stubborn spots

However, if you drink a lot of milk and have stubborn spots, try cutting back for six to eight weeks to see if it helps – but make sure to get your calcium from other sources, such as fortified plant milks. Meanwhile, those with psoriasis – where an over-reactive immune system makes skin cells reproduce too fast, leading to patches of raised scaly skin – could benefit from trying a similar approach.

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 using prescription creams experienced a greater improvement in their skin than those on a general low-fat diet.

Nearly half the Mediterranean diet group saw their psoriasis improve by three-quarters using this approach, compared with none in the comparison group.

Following the Mediterranean diet (which is known to be anti-inflammatory – and psoriasis is linked to inflammation) means eating broadly along the same lines as you would following a lower glycaemic load diet, including more vegetables, fruit, beans, wholegrains and fish.

If it is wrinkles you’re worried about, you might be tempted by collagen supplements – because collagen is the protein that keeps skin’s structure and strength intact.

If you pool every trial together, the supplements do appear to help – but once you set aside studies funded by collagen companies and the lower-quality ones, that benefit quietly disappears, according to a review that was published last year in the American Journal of Medicine.

Collagen-containing foods, such as bone broth or chicken skin, are also not going to help as your body breaks collagen down into amino acids first, then builds its own collagen which is then used throughout the body, not just for skin.

When it comes to anti- ageing benefits, the good news is that microbes in the gut ferment the fibre you eat into compounds that appear to lower inflammation around the body – and plausibly the skin, too.

This won’t give you younger skin overnight, however keeping vegetables and fruit front and centre of your diet, alongside wholegrains, beans, nuts and seeds, could end up paying dividends for your complexion in the long run.

If you’re convinced that a specific food is fuelling your skin complaint, speak to your doctor or dermatologist before cutting anything out.

And remember, a spot may appear overnight, but it didn’t start overnight.

It has been forming beneath the surface of your skin for weeks, so yesterday’s meal or snack isn’t the culprit.