A game that trains the brain to avoid unhealthy food, such as cakes, biscuits and chocolate, can lead to "pain-free" weight loss and cut energy intake by more than 200 calories a day, scientists say.

Psychologists at the University of Exeter in Britain showed that fewer than 10 minutes a day of "brain training" using a game that takes away the "mental reward" of sugary and fatty foods reduces calorie intake.

Professor Natalia Lawrence's Food Trainer app is free and is being launched this month on Android devices.

It is based on neuroscience research that suggests people are more inclined to choose fatty and sugary foods because they activate the brain's reward system, stimulating the release of dopamine and endorphins, which can produce feelings of pleasure and make the person want more.

The game works by flashing pictures of healthy and unhealthy food, and the user has to react by only pressing on the healthy foods to score points. The simple act of ignoring unhealthy foods and stimulating the reward response to healthy foods is enough to retrain the brain to crave healthier options, say scientists.

A study of 83 adults showed that people who played the game online just four times in one week lost weight and consumed an average of 220 calories fewer per day - roughly equivalent to a chocolate-iced donut.

"It's very exciting to see that our free and simple training can change eating habits and have a positive impact on some people's lives," says Lawrence.

"In an age where unhealthy food is so abundant and easily available, and obesity is a growing health crisis, we need to design innovative ways to support people to live more healthily.

"We are optimistic that the way this app is devised will actually encourage people to opt for healthy food, such as fruit and vegetables, rather than junk food."

Studio manager Fiona Furness was one of the first to trial the game and has lost 28 pounds so far.

Furness, who is in her 50s, says the "pounds just melted away".

"The results have been remarkable," she says.

"These days, if I am feeling peckish, I'll go for a banana or a pack of almonds. That's the food I'm craving.

"The weight loss wasn't really my goal, though - I feel younger and more energetic. Perhaps I'm particularly susceptible to this kind of brain training, but it has been transformative for me."

Users of the app - who should ideally use it for a few minutes a day without distractions - can tailor it to reduce compulsions to eat the unhealthy foods they have the most problems with, as well as alcohol, but not to reduce consumption of healthy foods, including vegetables.

Daily Telegraph