A collaborative study between Aberdeen University and the Chinese Academy of Sciences looked at what components of food intake caused weight gain.
The research used mice, therefore, conclusions of what would result in humans is limited.
Mice were put on 30 different diets that vary in their fat, carbohydrate (sugar) and protein contents over a period of 3 months. Over 100,000 measurements were made of body weight changes and their body fat was measured using a micro MRI machine.
Professor John Speakman of Aberdeen University 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.
“A clear limitation of this study is that it is based on mice rather than humans. 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 results of the study were published in the journal Cell Metabolism.