Before Harry Smith, now 12, received professional help for his avoidant/restrictive food intake disorder (Arfid), he would eat only baby food. “What we went through,” sighs his mother, Angela Smith, 45, from Sheffield. “We had no understanding of what we were dealing with. Nobody mentioned Arfid to us at all. It took 10 years to realise there was something wrong with Harry, that he wasn’t just picky ... We thought it was just: ‘Harry who wouldn’t eat.’”

Angela is a full-time carer to Harry, who is on the autism spectrum. For years, her life revolved around obtaining the foods Harry was willing to eat – HiPP baby food and Heinz toddler meals. Because supermarkets never had enough stock, she would place bulk orders online, purchasing 50 or 100 jars at a time. Harry would take the jars of food to school with him, where staff would heat them up. The other children bullied him. The family sought help from the NHS, but nothing worked. “We had all sorts of suggestions over the years, including starving him, or filling his baby food jars up with adult food to see if he’d eat that,” Angela says. “It put a huge strain on my marriage. We eventually separated.”

Individuals with Arfid – once known as selective eating disorder – will eat only a very limited range of foods and may have significant phobias around trying new foods. Arfid made headlines recently when it was reported that a Bristol teenager lost his sight permanently after suffering damage to his optic nerves caused by malnutrition from eating only chips, crisps, sausages, processed ham and white bread. The anonymous 19-year-old, who can’t tolerate the texture of fruit and vegetables, was given vitamin supplements aged 14, but didn’t take them often enough or improve his diet.

Because Arfid was recognised only recently – it was added to the Diagnostic and Statistical Manual of Mental Disorders, the pre-eminent resource in the US for diagnosing psychiatric conditions, in 2013 – there isn’t adequate data on its prevalence, although it is thought to be more common in people with autism. One study of 1,444 Swiss schoolchildren found that Arfid was prevalent in 3.2% of eight- to 13-year-olds. Prof Keith Williams, a paediatrician who specialises in childhood eating disorders at the Milton S Hershey Medical Center, part of Pennsylvania State University’s medical school, believes Arfid is on the rise. “We’re seeing it a lot more often. I’ve been seeing kids for 30 years with nutritional deficiencies, but not as many as we’ve been seeing in the past few years.”

It doesn’t affect children alone, explains the psychologist Felix Economakis, who specialises in the disorder and treated Harry. “The older generation say: ‘I thought it was just me, that I was set in my ways. I didn’t realise I had a phobia towards food.’” Economakis has treated patients with Arfid in their 50s and 60s.

“It’s not uncommon for us to see children who have never tasted a vegetable,” says Williams. Typically, they get most of their calories from snack foods or “the dreaded chicken nugget”. He tells me about one four-year-old boy whose daily diet consists of water, one apple, cheese puffs and Pringles.

When individuals eat such a limited diet, they can become dangerously nutritionally deficient. “When you hear the word scurvy, you think about pirates in the 18th century,” Williams says. “You don’t think about kids today. But it’s becoming more common.” He has diagnosed six children with scurvy this year, including the four-year-old boy. Children can also become anaemic or develop pellagra, a potentially fatal disease caused by niacin (vitamin B3) deficiency that was largely eradicated in the 30s thanks to food-fortification programmes. “We saw a kid with pellagra this year,” says Williams. “No one sees that.” It is not always as simple as prescribing these children vitamin supplements. In many cases, children will refuse to take them.

The causes of Arfid are not known, but the prevalence of junk food in modern diets may be a factor. “Junk food is highly preferred, because it’s full of salt, sugar and fat,” Williams says. Once children start eating junk food, it is hard to wean them off it. “The children resist, object or throw a tantrum, and the parents avoid that behaviour by giving them the diet they want ... It’s hard to get out of habits when they have been established.”

However, Williams is reluctant to play the blame game. “I don’t know how helpful it is to blame the parents,” he says. The biggest misconception about children with Arfid is that they would eat properly if they were forced to by their parents – that they are just fussy. “You see a lot of comments like: ‘When I was little, you ate what was in front of you,’ ‘They’re all princesses,’” says Angela. She finds it frustrating. “That’s why that poor kid’s gone blind. It’s not that they don’t want to eat, it’s that they can’t eat.”

Individuals with Arfid may struggle to be treated on the NHS. While the NHS doesn’t publish specific guidelines for Arfid, there are doctors at Great Ormond Street hospital in London who specialise in treating children with the condition. Across the UK in general, the picture may be more challenging. “The NHS is still pretty ignorant about it, to be honest with you,” says Economakis. “The specialist eating disorder clinics are only trained in anorexia and bulimia.” Cognitive behavioural therapy may be prescribed, but it is ineffective for many with Arfid. An NHS England spokesperson says: “We are on track to ensure 95% of children and young people are treated for their eating disorder in a week if it is urgent by 2021, and we are also funding seven pilots across the country to train staff so they can improve the care they provide for patients with Arfid.”

Economakis treats patients using an integrated approach including cognitive therapy, neurolinguistic programming and solution-focused therapy. “It’s about re-educating the mind about food, not lecturing and saying: ‘Vegetables are good for you.’ That’s not going to work.”

After treatment with Economakis in 2014, Harry now eats a range of foods. Angela will always be grateful. “We can sit down now and have a Christmas dinner,” she says. “Five years ago, if you’d said that to me, I’d never have believed you.”