Drinking four cups of coffee per day could reduce how much fat you gain after eating unhealthy food, according to a study on rats.

The experiment discovered that caffeine stopped the body from producing as much fat in the blood and meant fat cells stored less inside them than normal.

The rats consumed the equivalent caffeine of four cups of coffee and ate a carbohydrate-heavy diet high in fat and sugar for four weeks.

They gained 16 per cent less weight than rats in a non-caffeine group and built up 22 per cent less body fat.

Scientists said this could be because the effects of caffeine reduce action in a gene which is known to contribute to weight gain.

The researchers, from the University of Illinois, set out to see if a type of herbal tea called mate tea had health benefits, and found caffeine from coffee had the same effect.

‘Considering the findings, mate tea and caffeine can be considered anti-obesity agents,’ said Dr Elvira Gonzalez de Mejia, an author of the study.

‘The results of this research could be scaled to humans to understand the roles of mate tea and caffeine as potential strategies to prevent overweight and obesity, as well as the subsequent metabolic disorders associated with these conditions.

‘The consumption of caffeine from mate or from other sources alleviated the negative impact of a high-fat, high-[sugar] diet on body composition due to the modulation of certain enzymes in both [fat] tissue and the liver.’

Researchers gave the rats mate tea, which is a herbal hot drink popular in Latin America and packed with phytochemicals, flavonoids, and amino acids.

It contains about 65 to 130mg of caffeine per serving, compared to between 30 and 300mg (average 95mg) in a cup of brewed coffee, the researchers said.

The animals were also given synthetic caffeine and caffeine extracted from coffee to compare the effects.

They found that, regardless of its source, caffeine decreased the accumulation of lipids (fat molecules) in fat cells by between 20 and 41 per cent.

At the end of the experiment, the team said the amount of body fat on the rats which consumed caffeine and those which didn’t was ‘significantly’ different.

The study, published in The Journal of Function Foods, said the beverages could be considered ‘anti-obesity agents.’

The team explained this effect was probably caused by the effects caffeine had on two genes in particular – Fasn and Lpl.

Fasn – the fatty acid synthase gene – was about 31-39 per cent less active in the rats which were being fed caffeine, meaning the body was converting less sugar into fat.

And Lpl – the lipoprotein lipase gene – was around 51-69 per cent less active, which also reduced the amount of fat which was created.

The suppression of these genes also meant less cholesterol was produced in the liver, the study added.