According to a meta-study by Dutch nutritionists, CLAs are just as bad for your heart and blood vessels as the dreaded synthetic trans fatty acids that the food industry has been using for years in cookies, margarines and junk foods.

"Intakes from supplements can easily reach 3 grams of CLA a day", the researchers write in their conclusion. "This should increase the LDL to HDL cholesterol ratio by 0.050, which would correspond with a 3 to 12 percent increase in the risk of cardiovascular disease."

That’s still not much. A rule of thumb in nutritional research is that something only becomes interesting if it doubles or halves risk. On the other hand though: CLAs are expensive and their effect is modest. If CLAs also increase your risk of cardiovascular disease it may be a reason for you to go in search of an alternative supplement.

After analyzing the few studies published to date in reduced samples of healthy humans or patients with overweight, obesity, metabolic syndrome, or diabetes, we deduce that there is not enough evidence to show that conjugated linoleic acid has an effect on weight and body composition in humans. However, some of these studies have observed that the administration of various CLA isomers has adverse effects on lipid profile (it decreases HDL cholesterol concentration and increases Lp(a) circulating levels), glucose metabolism (glycemia, insulinemia or insulin sensitivity), lipid oxidation, inflammation, or endothelial function.