If you've been grazing on 'healthy' snacks but the weight still won't budge, scientists may have an explanation. And it might not be what you want to hear.

According to a study published by the International Journal of Research in Marketing, eating "light" snacks and drinks can give you 13 per cent more calories than the full fat versions.

Experts put it down to people finding it easier to justify overindulging when the food is labelled as healthier.

Study leader Joost Penings, from Maastricht University in the Netherlands, told The Huffington Post that the snacks themselves may be healthier, but how people react to labels and branding is a different story.

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"'Light' products may help, but behavioral responses to the light claim may wash out the positive effect," he said. "Understanding the psychological effect of the claim that a product is 'light' needs further investigation."

Others put it down to a "halo effect", where eating 'diet' food can make people feel as though they have the green light to indulge in other junk foods.

A study from September last year found those who drink diet soft drinks were more likely to treat themselves to fat-laden fast foods.

The study, published in the Journal of the Academy of Nutrition and Dietetics, found those who drank the standard, sugary soft drink versions consumed less calories overall per day than people who drank diet drinks.

-nzherald.co.nz