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11.11.2014

Polyunsaturated fatty acids make you slimmer and more muscular

For a few days now we, the unworldly compilers of this free web blog, have been immersed in studies on the effect of fatty acid composition in the diet on muscle tissue and body fat. Recently we wrote about a human study which has shown that a high intake of omega-6 fatty acids inhibits fat accumulation and boosts muscle increase. Today we read that all plant-based polyunsaturated fatty acids probably have this effect.

High fat
We draw this cautious conclusion from an animal study published by researchers at the University of Fribourg in Switzerland in 2011. In that study the researchers gave rats a high-fat diet, in which almost 60 percent of the calories were derived from fat.

To start with the researchers gave their rats half of the amount of food they would normally eat for a few weeks. The animals therefore lost weight. Then the rats were given the calorie-rich high-fat diet for four weeks, and put on weight.

The type of fat the researchers gave the rats varied. The figure below shows what happened to the animals' fat and lean body mass when fed with lard, rapeseed oil, safflower oil, grapeseed oil, sunflower oil or maize oil.

As you can see, the rats that were given vegetable oil all built up more lean body mass and less fat than the rats that were given lard. The best results were achieved with safflower oil.

If you look at the composition of the fats that were used you can see that it's above all the amount of polyunsaturated fatty acids [PUFA] that determines the effect on body composition: the more polyunsaturated fatty acids, the more muscle and the less fat the rats built up.

N-6 fatty acids
The polyunsaturated fatty acids in the oils mentioned above are mainly of the n-6 type. The researchers were curious to know whether n-3 fatty acids would have a different effect, so they repeated their experiments, this time using linseed oil. Linseed oil contains large amounts of the n-3 fatty acid alpha linolenic acid.

Conclusion
"Taken together, the possibility therefore arises that diets enriched with more modest amounts of PUFA as linoleic acid and/or alpha linolenic acid than shown here to be effective in improving body composition in rats may have relevance for improving body composition [...] in humans", the researchers conclude.

"Whether diets providing such high PUFA intake, exceeding 25% of total energy intake, are safe and effective in modulating body composition and metabolic health in humans are issues that must be considered with caution."

Source:
Br J Nutr. 2011 Jun 28;105(12):1750-63.

More:
Weight gain? The kind of fat in your diet helps determine how much muscle mass you build up 07.11.2014