If you gain weight, the kind of fat in your diet partly determines the amount of fat and the amount of muscle in your newfound kilograms. The unsaturated fatty acids in sunflower oil stimulate the growth of muscle; the saturated fatty acids in palm oil – found in many processed foods – lead to an increase the amount of fat. Researchers at the University of Uppsala in Sweden report on this in Diabetes.
If you fatten lab animals, the type of fat you use makes a difference. If you use vegetable oil, which contains lots of unsaturated fatty acids, the animals build up relatively more muscle than if you use products that contain large amounts of saturated fatty acids. The Swedish researchers were curious to know whether these results would also apply to humans, so they performed an experiment with 39 healthy subjects aged between 20 and 38.
The researchers gave their subjects 3 muffins every day for 7 weeks on top of their ordinary food. The muffins provided a total of 750 kcal – of which half were derived from fat.
Half of the subjects were given muffins prepared with sunflower oil, a source of the polyunsaturated fatty acid linoleic acid. The other half were given muffins made with palm oil, a source of the saturated fatty acid palmitic acid.
The subjects did no sports and took no supplements either.
At the end of the 7 weeks, the subjects in both groups had gained just over 1.5 kg in weight. But those who had been given the unsaturated fatty acid [PUFA] had gained three times more muscle mass than the subjects in the other group [SFA].
The type of fatty acid also had an effect on where the fat layers were deposited. The subjects who had eaten the palm-oil muffins accumulated relatively more fat in the abdominal area than those who had eaten sunflower-oil muffins. Abdominal or visceral fat is less healthy than subcutaneous fat, and increases the chance of a number of diseases including type-2 diabetes and some forms of cancer.
“Despite comparable weight gain after 49 days, this double-blind trial showed that overeating energy from polyunsaturated fatty acids prevented deposition of l visceral and total fat compared with saturated fatty acids”, the researchers write.
“Further, the inhibitory effect of polyunsaturated fatty acids on ectopic fat was accompanied by an augmented increase in lean tissue and less total body fat deposition compared with saturated fatty acids. Thus, the type of fat in the diet seems to be a novel and important determinant of liver fat accumulation, fat distribution, and body composition during moderate weight gain.”
Overfeeding polyunsaturated and saturated fat causes distinct effects on liver and visceral fat accumulation in humans.
Excess ectopic fat storage is linked to type 2 diabetes. The importance of dietary fat composition for ectopic fat storage in humans is unknown. We investigated liver fat accumulation and body composition during overfeeding saturated fatty acids (SFAs) or polyunsaturated fatty acids (PUFAs). LIPOGAIN was a double-blind, parallel-group, randomized trial. Thirty-nine young and normal-weight individuals were overfed muffins high in SFAs (palm oil) or n-6 PUFAs (sunflower oil) for 7 weeks. Liver fat, visceral adipose tissue (VAT), abdominal subcutaneous adipose tissue (SAT), total adipose tissue, pancreatic fat, and lean tissue were assessed by magnetic resonance imaging. Transcriptomics were performed in SAT. Both groups gained similar weight. SFAs, however, markedly increased liver fat compared with PUFAs and caused a twofold larger increase in VAT than PUFAs. Conversely, PUFAs caused a nearly threefold larger increase in lean tissue than SFAs. Increase in liver fat directly correlated with changes in plasma SFAs and inversely with PUFAs. Genes involved in regulating energy dissipation, insulin resistance, body composition, and fat-cell differentiation in SAT were differentially regulated between diets, and associated with increased PUFAs in SAT. In conclusion, overeating SFAs promotes hepatic and visceral fat storage, whereas excess energy from PUFAs may instead promote lean tissue in healthy humans.
PMID: 24550191 [PubMed – indexed for MEDLINE]