Only fat in diet contributes to weight gain, study finds

A new study has concluded that fat consumption is the only cause of weight gain, with carbohydrates and protein having no effect.

Scientists from the University of Aberdeen and the Chinese Academy of Sciences examined a set of diets in mice, which have similar physiology and metabolism to humans.

The study included 30 diets that varied in their fat, carbohydrate and protein contents.

The mice were fed the diets for three months, said to be the equivalent to nine years in humans.

In total, more than 100,000 measurements were made of body weight changes and their body fat was measured using a micro MRI machine.

Professor John Speakman, who led the study, said: “The result of this enormous study was unequivocal - the only thing that made the mice get fat was eating more fat in their diets.

“Carbohydrates including up to 30% of calories coming from sugar had no effect. Combining sugar with fat had no more impact than fat alone.

“There was no evidence that low protein (down to 5%) stimulated greater intake, suggesting there is no protein target. These effects of dietary fat seemed to be because uniquely fat in the diet stimulated the reward centres in the brain, stimulating greater intake.''

Prof Speakman said it is difficult to conduct such studies on humans where what they eat is controlled for long enough periods to work out the most important factors.

“A clear limitation of this study is that it is based on mice rather than humans,'' he said.

“However, mice have lots of similarities to humans in their physiology and metabolism, and we are never going to do studies where the diets of humans are controlled in the same way for such long periods.

“So the evidence it provides is a good clue to what the effects of different diets are likely to be in humans.''

The study has been published in the journal Cell Metabolism