Conjugated linoleic acid, a fatty acid found in dairy products and other animal fats, has many beneficial biological effects. So many, in fact, that CLA may be a previously unrecognized nutrient, say researchers at the University of Wisconsin-Madison. Unfortunately, our consumption of CLA may be decreasing.
Researchers in the College of Agricultural and Life Sciences have been studying the compound since the 1970s. In 1987 Michael Pariza, director of UW-Madison”s Food Research Institute, discovered CLA”s anti-carcinogenic properties. Pariza also found CLA significantly reduces atherosclerosis (heart disease) in rabbits. In 1990, poultry nutritionist Mark Cook and Pariza found that CLA fed to livestock reduces weight loss from immune stimulation induced by vaccines and illness.
In 1994 Pariza and Cook reported CLA, fed to pregnant rats, did not affect litter size nor cause adverse effects in the offspring. But rats fed CLA grew faster after birth than rats not fed CLA.
“These findings make sense,” said Pariza. “CLA is in the blood of cows and newborn calves, which suggests it may have beneficial effects to mammalian development and is not likely to be harmful.”
Pariza and Cook also found that CLA improved feed efficiency in laboratory rats. Their more recent findings indicate that CLA reduces the percentage of body fat in mice, rats and chicks, while increasing muscle tissue and bone density. Preliminary results in hogs also indicate CLA reduces back-fat deposition.
It is not known if CLA has the same effects in both animals and people, although CLA is found in human blood and breast milk.
According to the researchers, CLA may act by signaling the immune system and regulating metabolism by inhibiting cellular enzymes that take up fat. “All cellular membranes are made out of fat, and fatty acids (the building blocks of fat) are involved in cellular signaling,” said Cook. “Fat is a very important constituent of life.”
With the decrease in the consumption of dairy products, and the current health emphasis on reducing our intake of animal fats, our consumption of CLA may also be decreasing, said Cook. This does not mean we should increase our total fat intake. But, researchers are investigating which fatty acids in fats are harmful and which are beneficial.
For example, linoleic acid, also a polyunsaturated fatty acid, differs from CLA only in the placement of two double bonds in the fatty acid chain. The placement of the two double bonds changes the molecules” biological functions. According to Pariza, linoleic acid is beneficial in limited amounts and is essential to growth. However, excess linoleic acid can enhance malignant tumor growth.
The amount of the compound that is needed for biological effects is also different. Linoleic acid is optimal at 1 percent of the diet in most mammals. The researchers found CLA has optimal biological effects at one-half of a percent of the diet in rats, but they have seen beneficial effects as low as one-twentieth of a percent. So far they haven”t found any negative effects from excess CLA.
CLA, unlike linoleic acid, is not known to be an essential nutrient. However, the researchers believe it is an important nutrient due to its anti-carcinogenic properties and wide range of beneficial effects.
“If you can show a compound cures a deficiency, it will gain acceptance quickly. For example, Vitamin C cures scurvy.” said Pariza. “CLA is more like fish oil as a nutrient. Sufficient data had to be accumulated before fish oils were accepted as beneficial,” he said.
The UW-Madison results have been duplicated in other labs, including those at the University of Massachusetts, Washington State University, and the U.S. Food and Drug Administration.
“Prior to 1987, when we discovered CLA is an anti-carcinogen, there were very few studies,” said Pariza. “Today there are more than 100 intensive studies with CLA.” Pariza and Cook plan to conduct human clinical trials to study the effects of CLA on obesity.