CLA: The Modern Food Chain’s Weak Link

Lynnette Harris
UAES Information Office
Conjugated linoleic acid is a mouthful of a name for a compound that used to be easy to swallow. That was before before the advent of the modern low-fat diet. Now science is indicating that one side-effect of people cutting out fat is cutting out CLA, a component of fat that has been shown to slow the process of some types of cancer and heart disease, and appears to actually help reduce body fat and increase lean muscle mass. “We have a tendency to get a little information and think that all fat is bad,” says Dr. Tilak Dhiman, a USU dairy nutritionist who is examining ways to increase the CLA content of milk, cheese and meat. “We must distinguish between types of fats. We tend to think all fat is bad for us, but nutrition is very complex and we don’t know everything about it.”

CLA is a fatty acid that occurs naturally in many foods and is especially high in milk and meat from ruminant animals such as cows, sheep and goats. CLA is produced by bacteria in the rumen. While the relationship between diet and cancer is extremely complex, CLA has been found to inhibit the growth of chemically-induced skin and stomach cancers in mice, as well as cancer in the mammary glands of rats. Studies in other animals have produced similar results. Synthetic CLA also changed the body composition of laboratory animals; they developed more muscle and had less body fat.

Regular cow’s milk available at the grocery store contains an average of 4.5 milligrams of CLA per gram of fat. This is only one-quarter the lowest effective intake found in research with laboratory animals. The lower the fat content of the milk, the less CLA. Dr. Dhiman and others have found that CLA content of milk is as much as five times higher when cows graze green, growing pastures than when they eat diets consisting of 50 percent conserved forage, such as alfalfa and corn silage and 50 percent grain. Researchers have also found that feeding higher amounts of conserved forage in the diet increases CLA content of milk. However, the CLA level is not as high as in milk from cows grazing pasture. Dr. Dhiman says it is possible that something in green grass enhances the growth of the particular bacteria in the rumen that are responsible for producing CLA. Or it may be that grazing cows have different microbes in the rumen than cows fed inside the barn. “We cut our consumption of CLA when we changed the ways we feed our animals,” Dr. Dhiman says, noting that 30 or 40 years ago animals mostly grazed on pasture. Now their feed is controlled, which might be having a negative impact on human health, he adds. “Today we are producing milk more efficiently,” Dr. Dhiman says. “However, we need to couple this efficiency with milk quality. CLA could be considered a value-added product of grass-fed cows depending on how much people come to value it.”

In ongoing research in cooperation with USU Animal, Dairy and Veterinary Science Associate Professor Kenneth C. Olson, Dr. Dhiman is working toward understanding exactly what the mechanism is that produces CLA in the rumen and how to enhance its production. At this point, Dr. Dhiman has determined that CLA levels can be boosted by supplementing the cow’s diet. Roasted cracked soybeans added to a diet of alfalfa and corn silage resulted in increases of CLA content of milk. When soybean oil and linseed oil were added to dry feed in amounts comprising 2-4 percent of the cow’s diet, CLA levels in their milk came close to those of cows eating green pasture. But adding oil at higher levels than 4 percent can affect the digestibility of the feed. One of Dhiman’s studies found that cows fed full fat extruded soybeans and cottonseed produced milk with almost double the usual amounts of CLA. Many farmers already supplement the cow’s diet with cottonseed and soybeans, but the fat or oil must be easily available to the digestive system. Dr. Dhiman has found that cracking and roasting the seeds help release the important chemicals.

CLA appears to be very stable, Dr. Dhiman says, meaning it is not affected by cooking and processing. Dr. Dhiman and Dr. Don J. McMahon, professor of Nutrition and Food Science and director of the Western Dairy Research Center at USU, recently prepared cheese using milk from cows fed extruded soybeans and cottonseed. The increased CLA content in the milk was retained in the cheese.

In addition to cutting our CLA intake by taking cows off pasture and feeding them conserved forage, many Americans have also made CLA intake a casualty of their war on fat. Milk is a good source of CLA, but the beneficial fatty acid comes along with the fat grams. Information from the International Dairy Foods Association indicates that American milk consumption has dropped to about 24 gallons per person annually in 1996 from 31 gallons annually per person in 1970. A portion of the decline may be due to concern about fat in foods because sales of nonfat and reduced-fat milk have doubled since 1970 while consumption of whole milk has dropped to less than half its 1970 level.

In the billion-dollar business that accompanies the American quest for leaner bodies, some manufacturers of health supplements are selling capsules containing CLA synthesized from sunflower oil. A component of fat, CLA, may actually slow some types of cancer and heart disease and help reduce body fat and increase lean muscle. Consequently CLA tablets are showing up in health food stores. Dr. Dhiman, who says a new brand of CLA capsules seems to appear nearly every month, is about to begin a study in which he will feed this form of CLA to laboratory mice and monitor changes in the muscle and fat composition of their bodies. Similar studies in other laboratories have found rats, mice and chickens fed a CLA-rich diet reduced body fat and increased lean body mass. Studies in other areas are tracking long-term changes in human subjects, he says. Until the results are in, dietary moderation is still the best advice for humans, he says, cautioning that people might want to think about the milligrams of CLA they are passing up in their efforts to cut out all the dairy and meat fats from their menus.

Editor’s note: More information on current USU research into CLA can be found on the Internet at http://advs.usu.edu/advs/Dhiman/milkfat.html.