Trans fats: We've been told that they're worse for our hearts than saturated animal fats. Now, as consumers increasingly turn to food that's trans-fat-free and manufacturers pull them from more and more processed foods, comes a twist. Some trans fats, ones that exist naturally, may be good for you.
In a 4-month study at the University of Alberta presented in March at a scientific meeting, obese rats fed a diet enriched with vaccenic acid -- a naturally occurring trans fat found in milk and yogurt -- had significant reductions in total cholesterol, LDL (or "bad") cholesterol and triglycerides.
The researchers reported that a key benefit of vaccenic acid is its ability to reduce the production of chylomicrons -- small particles of fat, protein and cholesterol formed in the gut that transport fats to various tissues of the body.
Like humans, obese rats produce too many chylomicrons, which raises lipids in the bloodstream. After 16 weeks of consuming vaccenic acid-enriched chow, however, the levels of chylomicrons dropped by more than half.
It's not clear what this finding means for humans. First, the study was done in rats -- the researchers say they're planning some human clinical trials with vaccenic acid supplementation. Second, because the study diets were supplemented with vaccenic acid, the amounts the rats ate relative to their body weight was more than we would naturally eat in our usual diet.
The study is in line with other reports that natural trans fats have different effects on the body than the industrially created ones.
Most of the trans fats we eat -- by far -- come from partially hydrogenated vegetable oils, produced from liquid oils by industrial processing to create a firmer fat. Others occur naturally in milk products, formed in the rumen (or first stomach) of ruminant animals such as cows, goats, sheep and yaks when they're fed a grass-rich diet.
Several studies of large populations have looked at the link between trans fatty acid intake and risk of developing atherosclerosis, and all have shown that the risk goes up only with the intake of "industrial" trans fatty acids, not the natural ones. Several clinical trials -- in which people were fed special diets for weeks or months -- have shown that manufactured trans fats raise LDL cholesterol levels to the same degree as saturated fats, and also lead to lower levels of the good, or HDL, cholesterol. It's been estimated that it takes only about 12 grams of manmade trans fats to see this effect.
