The study was done using mice, but researchers at the Ohio State University are excited about what they have found so far: About half of the vaccenic acid consumed in milk fat is metabolized into conjugated linoleic acid (CLA). The process is called desaturation, explains Donald Palmquist, lead researcher on the study. And it sheds new light on the benefits of milk.

Vaccenic acid is found mainly in the milk and meat fats of cows and other ruminants. It occurs in these fats at concentrations up to five times greater than the concentration of CLA.

Palmquist and colleagues found that about 50 percent of the vaccenic acid stored in the tissues of test mice was desaturated to CLA, marking the first time the process has been quantified.

The finding demonstrates the importance of vaccenic-acid desaturation to the body's total supply of CLA, Palmquist said. There may be up to twice as much CLA available to the body than was previously estimated, he added.

"We don't know what all of the biological effects are, and there has been a rush in the food-fat industry to use CLA to lose weight, but it has not been shown effective in losing weight," he said. "The specific isomer highest in normal milk fat has been shown to be the isomer that has anticancer effects.

The digestive system of ruminants is key. Bacteria in the system break down food and forage, including plant cellulose, which humans can't digest. Unsaturated fatty acids in the food and forage are converted mostly into saturated fatty acids. The process is called biohydrogenation, and it forms, among other things, CLA and vaccenic acid.

"Over the past 10 to 15 years, there has been a lot of interest in CLA and milk fat because [CLA] has been found in experimental animals and cell cultures to have strong anticancerous effects," Palmquist said. "Industries jumped in right away to try to create the product themselves. The problem is that you get a mixture of isomers, and different isomers have different biological effects. People should get their CLA from milk fat and not from synthetic pills."

CLA is the only fatty acid known to have anticarcinogenic properties. Still unknown is whether it works in the same way in humans.

The study, which appeared in the Journal of Nutrition, was recently recognized as a Fast-breaking Paper by ISI Essential Science Indicators, a research analysis and tracking service. According to ISI's Web site, Fast-breaking Papers are highly cited by other scientists and rank in the top one percent of research in their field — in this case, agricultural science — in the year of publication.

The study was supported by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, which is the research arm of Ohio State's College of Food, Agricultural, and Environmental Sciences.

OSU press release