He held a well-paying job and was a good performer at work, but John (not his real name) bore a deep secret.

Often after dinner with friends, he would sneak off for a second meal, gobbling up portions enough to fill the stomachs of three people.

He would eat till he felt nauseous, and once, even found himself vomiting while having a bout of diarrhoea at the same time.

He suspected he might have some kind of unhealthy addiction to food. But tell someone that you are a food addict and you might simply be brushed off.

Counsellor Eleanor Ong of addiction clinic The Cabin Singapore said, because of that, genuine food addicts might not be getting the help they need.

"In Singapore, when you tell people you are a food addict they won't take you seriously. They will say 'ya, me too' because the country is such a foodie place. But it is very different from just loving food," said Ms Ong, who is John's counsellor.

"They are eating till they are sick, till they don't want to eat anymore but they can't stop themselves."

The scientific community remains on the fence as to whether food addiction is an affliction, due to the lack of scientific evidence.

But The Cabin Singapore has classified 10 of its clients as food addicts since it opened in 2013. Four were treated this year.

Nonetheless, food addiction is still considered a rare problem at the clinic, where two-thirds of the 400 people treated were hooked on either alcohol or sex. The rest were treated mostly for gambling and gaming addictions.

Those who were treated for food addiction were, like John, mostly high-functioning people.

They were able to hide their addiction from others well, maintain good relationships with others and perform at work.

Ms Ong added that not all of them are obese. A few worked in the health or sports sectors and managed to keep their weight down by exercising.

For John, a hint of a nascent food intake problem was his fluctuating weight. At his worst, he weighed more than 130kg.

"Nothing seemed to stick - all sort of diets, juice fasts and medication such as appetite suppressants from the doctor. I even tried having a gastric balloon in my stomach," he said, referring to temporary inflated silicon balloons that leave less room for food.

"It really bothered me but I kept thinking I just needed to be more disciplined," John, who is in his 30s, told The Straits Times.

He has been "sober" for more than eight months now, but still recalls vividly that dark period of his life - an ordeal that lasted more than 10 years.

He said: "After I eat with friends, when everyone else has gone home, I will eat by myself. I will eat the equivalent of three meals in one sitting. One fried spring chicken, popiah... And after that, still have chocolate.

"I will spend $10 to $15 on tidbits at 7-Eleven and finish them immediately."

On a particularly bad occasion, he stuffed himself with so much food that he had the runs. But while sitting on the toilet bowl, he felt like he needed to puke as well.

He got up to vomit but ended up soiling his pants from diarrhoea.

"I told myself, this is really problematic. I felt like a heroin addict," he said.

It was a liberating moment for him last year, when he came across a food addiction study by Yale University in the United States, which carried a self-assessment scale.

He went through the test and the score rated him as a likely candidate for food addiction.

Published in 2011, the Yale study studied 48 women ranging from lean to obese and found that those with higher food addiction scores showed greater activity in parts of the brain responsible for cravings and the motivation to eat, but less activity in the regions responsible for inhibiting urges such as the desire to drink a milkshake.

It concluded that, similar to drug addicts, food addicts may struggle with elevated cravings and stronger motivation to eat in response to food cues.

They may also feel more out-of-control when eating highly palatable foods.

Food addiction is still a controversial topic as few studies have attempted to determine the "addictive" properties of foods using rigorous scientific criteria.

Scientists are also baffled as to what the addictive substance in food is - fat, sugar, salt or just anything that tastes good?

But the literature on food addiction has been growing gradually.

Another study published in 2011 by Brookhaven National Laboratory, a research institution in the US, found that the mere sight or smell of a binge eater's favourite food triggers a spike in dopamine.

This does not happen for ordinary obese subjects. Dopamine is a brain chemical linked to reward and motivation.

Another study by Boston Children's Hospital published in 2013 found that consuming highly processed, rapidly digested carbohydrates such as white bread and potatoes can cause excess hunger and stimulate brain regions involved in reward and cravings.

This has helped people like John.

"Instead of me being problematic, it turned out that I had a problem," he said.

He went through a three-month programme comprising group sessions three times a week and weekly one-on-one counselling.

He was also referred to a nutritionist and taught how to avoid relapses, for instance, by not going for meals alone.

So far, he has managed to shed 24kg with a better diet and more exercise, and now weighs 109kg.

"It has been a painful but liberating process," he said.