Abdominal fat accumulation prevented by unsaturated fat

The study involved 39 young adult men and women of normal weight, who ate 750 extra calories per day for seven weeks. The goal was for them to gain three per cent of their starting weight. The project received considerable attention when it started in 2011, partly because the extra calories were ingested in the form of muffins with high fat content, baked in the lab by Fredrik Rosqvist, a doctoral candidate and first author of the study.

One half of the subjects were random to eat surplus calories from polyunsaturated fat (sunflower oil), while the other half got their surplus calories from saturated fat (palm oil). Both diets contained the same amount of sugar, carbohydrates, fat, and protein; the only difference between muffins was the type of fat.

The increase in body fat and the distribution of fat in the body was measured using a magnetic resonance imaging (MRI scans) before and after the weight gain, as was the muscle mass in the body. Gene activity was measured in the abdominal visceral fat before and after the weight gain with the help of a gene chip that studies several thousand genes at a time.

Despite comparable weight gains between the two diet groups, the surplus consumption of saturated fat caused a markedly greater increase in the amount of fat in the liver and abdomen (especially the fat surrounding the internal organs, visceral fat) in comparison with the surplus consumption of polyunsaturated fat. Moreover the total amount of body fat was greater in the saturated fat group, while, on the other hand, the increase in muscle mass was three times less for those who ate saturated fat compared with those who ate polyunsaturated fat. Thus, gaining weight on excess calories from polyunsaturated fat caused more gain in muscle mass, and less body fat than overeating a similar amount of saturated fat. Since most of us are in positive energy balance, and consequently gain weight slowly but gradually over time, the present results are highly relevant for most Western populations.

“Liver fat and visceral fat seems to contribute to a number of disturbances in metabolism. These findings can therefore be important for individuals with metabolic diseases such as diabetes. If the results regarding increased muscle mass following consumption of polyunsaturated fat can be confirmed in our coming studies, it will potentially be interesting for many elderly people, for whom maintaining muscle mass is of great importance in preventing morbidity,” says Ulf Risérus, associate professor at