After sailing through high school with barely a blemish in sight, twin sisters Nina and Randa Nelson couldn't understand why their skin went downhill as they entered their 20s.

The vegan advocates, who live in Los Angeles and have more than 600,000 followers on their YouTube channel, said their whole lives were turned upside down — and their acting ambitions put on hold — when their skin flared up with severe, cystic acne.

"We became hermits," Nina told news.com.au.

"We became depressed. Our friends would ask us to come out, and we wouldn't go.

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"I had an acting audition once, and my skin looked so horrible my audition was almost cut short," Randa added.

"I felt so bad about myself, going on dates was the last thing on your mind. I just didn't want to talk to anyone.

'For us, the food we were eating was showing up on our face,' the girls said. Photo / Instagram
'For us, the food we were eating was showing up on our face,' the girls said. Photo / Instagram

The Nelson twins, who live in Chatsworth, California, described their acne as both physically and emotionally painful.

After going on antibiotics for a year, the now 24-year-olds say their acne would often come back far worse after finishing a round of medication. It was a vicious cycle they had no control over, so they approached a dermatologist with a months-long waiting list for an appointment.

"They didn't know what to do," Nina said.

"He prescribed us Roaccutane and handed us a book on how it would work.

"We did consider going on it, but we had friends who had pretty bad side-effects," Randa added.

"We thought it sounded terrible, and we had a hunch that we shouldn't go on it."

So instead of following advice, they took things into their own hands and overhauled their diet, following a plan rich in vegetables and low in fat.

"We were already on a vegan diet," Randa said. "And while we were only having a small bit of oil and fat, the small amount was still doing so much damage.

"We are still getting fatty acids for our bodies," Nina added. "So it's not a no fat diet, it's a low-fat diet.

"I've now noticed that if I'm going to have peanut butter, I'll eat it, and while the breakout isn't anywhere near what I used to get, I do get something. So we prefer not to eat it now."

Their new low-fat, plant-based eating plan, which is detailed in the sisters' new book, The Clear Skin Diet, began to clear up their skin within days, according to the Nelsons.

The twins, whose experience is their own and not based on medical research, said their skin has remained clear for four years since making the diet change and within six months every blemish was completely gone.

They didn't change their skincare regimen outside their daily cleansing gel and an oil-free moisturiser.

They said changing their diet completely cleared their skin. Photo / Instagram
They said changing their diet completely cleared their skin. Photo / Instagram

"For us, the food we were eating was showing up on their face," Nina said.

"The things we don't eat include all animal products, dairy, fish or chicken, and we don't have any oils, nuts, peanut butter or avocado.

"We now eat a lot of potatoes, beans, rice, pasta, bread, oats, fruit and smoothies. You don't even realise how simple and easy, it's typically eating in a way that doesn't have fat or oils included."

Research conducted in Australia by Clearskincare Clinics has found that an astonishing 35 per cent of adult women and 50 per cent of adult men suffer from acne — and we're not just talking a pimple or two. We're talking full blown, cystic acne — the kind you thought only existed in your teens, and were dismayed to find out continues on — or starts — in your 20s and 30s.

The Journal of the American Academy of Dermatology found that one third of people with facial acne also have some amount of body acne and, much to the dismay of adult acne sufferers, a study on post-adolescent acne featured in the International Journal of Cosmetic Science stated that "there appears to be an increase in post-adolescent acne, and the disease is lasting longer and is requiring treatment well into the mid-forties".

Speaking to news.com.au, dermatologist Dr Natasha Cook said that while diet has an impact on the skin, she wouldn't advise stripping an eating plan of all fats.

"You should aim for a diet based on protein, good healthy fats and above-ground green vegetables which are low in carbs and low in sugar," she said.

"The only fruit you should eat are those that have anti-oxidants and anti-inflammatories such as blueberries. Otherwise fruit is just feeding you excess sugar which drives your insulin levels and hormone levels out of control.

Twin sisters Nina and Randa Nelson both developed severe acne at the end of their teenage years. Photo / Instagram
Twin sisters Nina and Randa Nelson both developed severe acne at the end of their teenage years. Photo / Instagram

"We find that the good fats actually help insulin stabilise and have powerful anti-inflammatory role. We only recommend olive oil, butter avocado. Cut out margarine, canola oil, vegetable oil, seed-based oils as these are pro-inflammatory fats.

"You must remember that some fat is needed as the brain is full of fat and needs it to function."

The Nelson twins, whose experience is their own and not based on medical research, said their skin has remained clear for four years since making the diet change.

The twins say the diet and book is largely inspired by US physician Dr John McDougall, who is a high-profile advocate of a plant-based diet.

"When we were babies our mum had a rare auto-immune disease and went vegan [on Dr. McDougall's plan] and two months later she went into remission," Nina told ABC America.

"Our dad was like, 'Why don't you look up to see if Dr McDougall has something on acne?' and he did."

According to McDougall, dairy products, meat and poultry are known to increase insulin-like growth hormone-1, elevated levels of which are "associated with more acne".