CLA Offers a Variety of Benefits

Conjugated Linoleic Acid Fights Cancer, Heart Disease, and More
CLA, found in milk, could be a hitherto unrecognized nutrient

ometimes a small change can make a big difference. One wrong note in an otherwise beautifully played tune, for example, can make you grimace in pain. A pinch of saffron, on the other hand, might make an otherwise ordinary dish sublime and have you beaming. And what if the decimal point in your paycheck or your electricity bill were accidentally moved - would that ever make a difference! (Whether you grimaced or beamed would depend, of course, on which way it was moved.)

In the infinitely varied world of molecular structures, seemingly insignificant changes can have effects so far-reaching that they sometimes spell the difference between health and sickness, or even between life and death. Take linoleic acid, for example. It's one of the essential fatty acids, meaning that our bodies require it but can't synthesize it, so we must get it from food sources. We can't be healthy without a certain amount of linoleic acid in our diet, because we need it for the formation of cell membranes and as a precursor to other compounds, such as prostaglandins.

Like all chemical compounds, linoleic acid has a specific molecular structure that accounts for all its physical and chemical properties. These, in turn, determine its biological activity, i.e., its effects on the physiology of a living organism. Although linoleic acid is essential for our health, it has a dark side too: at high levels it becomes carcinogenic (cancer-causing) - at least in laboratory animals. But when a certain tiny change is made in the molecular structure of linoleic acid, something remarkable happens: it becomes anticarcinogenic!

The tiny change in question results in a form of linoleic acid called conjugated linoleic acid (CLA), which is actually a mixture of closely related molecules all having exactly the same chemical formula as linoleic acid but with different molecular structures owing to different arrangements of the atoms in the molecules. These sibling compounds are called isomers of one another, and collectively they constitute CLA.

CLA is a remarkable substance that some scientists believe may be a hitherto largely overlooked nutrient for humans. In our bodies, some of the CLA we ingest winds up being incorporated into molecules called phospholipids, which are the principal structural components of cell membranes. Although CLA may not be essential in the same sense that linoleic acid is, it is nonetheless important because of its varied health benefits. Let's look at the principal ones.

Research on CLA has shown it to be a potent anticancer agent, and scientists are excited by the fact that this effect occurs at much lower levels than is true of most other naturally occurring anticarcinogens. CLA is the only fatty acid that has been shown unequivocally to inhibit cancer in animals. In mice, e.g., it has been found to inhibit the development of cancer of the skin, stomach, liver, lungs, and mammary glands.1

CLA is a potent anticancer agent,
and scientists are excited that this
effect occurs at much lower levels
than is true of most other naturally
occurring anticarcinogens.

There have been very few human clinical trials on the effects of CLA, but experiments on human cancer cells in vitro ("in glass," i.e., in the laboratory) have confirmed CLA's anticancer properties, especially against malignant melanoma and colorectal, prostate, breast, and lung cancers.2 It was formerly believed that CLA's anticancer and other therapeutic properties were due largely to an antioxidant effect. More recent research, however, has failed to demonstrate any such effect.1 There are many theories and speculations about how CLA works, but no clear answers.

Another benefit of CLA is its ability to inhibit atherosclerosis by reducing the levels of lipids - mainly cholesterol and triglycerides (fats) - that circulate in the blood and that are highly susceptible to damaging oxidation by free radicals. This lipid-lowering effect has been observed in mice, rats, rabbits, chickens, hamsters, and other animals.1 Supplementation with CLA in these animals has also produced significant regression in atheromatous lesions, i.e., lesions on arterial walls that foster the buildup of harmful, artery-clogging plaque. Both of these effects - reducing blood lipid levels and suppressing atheromatous lesions - are instrumental in reducing the risk of heart attack and stroke.

In prediabetic animals, CLA has been found to help normalize impaired glucose tolerance, a condition in which blood glucose levels are abnormally high after a meal, and to reduce excessive insulin levels, which can occur in response to the elevated glucose levels.1 In other words, CLA helps the animal to utilize glucose more efficiently when this vital mechanism has been impaired. In humans, such impairment is a common feature of aging, even in those without diabetes, and it is a harbinger of the disease.

Many studies have shown that CLA can modify the body composition of a variety of laboratory animals. Specifically, it reduces body fat and increases lean body mass. In one such study, for example, mice that were fed a CLA-supplemented diet exhibited dramatic reductions in body fat (57% in the males and 60% in the females) and significant increases in lean body mass (5% in the males and 14% in the females), compared with controls.3 No differences were found in body weight. In other words, the loss in fat was compensated, to a significant degree, by a gain in muscle.

After two decades of CLA research on animals, human clinical trials are finally being conducted. A group of Swedish researchers has recently published the results of the first randomized, double-blind, placebo-controlled trial to assess the effects of CLA on obesity in humans.4 In a 4-week trial, 24 men aged 39-64 were given either CLA (4.2 g/day) or placebo to assess the effects of CLA on abdominal fat and other cardiovascular risk factors. None of the men had a history of heart problems or type 2 (adult-onset) diabetes, but all were abdominally obese and showed signs of the metabolic syndrome (see the sidebar).

The researchers measured numerous aspects of the patients' blood chemistry and body measurements that are associated with obesity. After four weeks of treatment, there was a very small reduction in abdominal fat in the CLA group, but none in the control group. Surprisingly, there were no other differences recorded between the two groups.

Experiments on human cancer cells
have confirmed CLA’s anticancer
properties, especially against
malignant melanoma and
colorectal, prostate, breast, and
lung cancers.

The finding of fat loss agrees at least qualitatively with data from numerous animal studies (in which much more pronounced and comprehensive effects have typically been seen), and it jibes as well with the results of another controlled human trial, conducted on healthy, nonobese men and women, in which the CLA group experienced reduced body fat.5 On the other hand, it conflicts with yet another controlled human trial, conducted on healthy, nonobese women, in which the CLA group experienced no fat loss.6

What is the Metabolic Syndrome?

The metabolic syndrome is a group of individual but interacting risk factors that arise from a general derangement of the body's metabolic functions and that, acting together, greatly increase the risk for cardiovascular disease and diabetes - and potentially for stroke, kidney failure, and cancer as well. It is a major threat to public health in the United States and throughout the world.

The metabolic syndrome includes abdominal obesity, high cholesterol and triglyceride (fat) levels, high blood pressure, and high blood glucose levels. Abdominal obesity - a pronounced bulge in the midriff - is specified in this list because it is particularly strongly linked to the risk for the degenerative diseases mentioned.1,2

  • Björntorp P. Visceral obesity: a civilization syndrome. Obes Res 1993; 1:206-22.
  • Després JP. The insulin resistance-dyslipidemic syndrome of visceral obesity: effect on patients risk (review). Obes Res 1998;6(Suppl 1):8-17.

There is reason to be optimistic about the ability of CLA to induce more substantial fat loss in humans, despite the meager evidence to date. Although it is well known that the results of animal experiments cannot necessarily be extrapolated to humans, the sheer variety of animal evidence acquired thus far - in mice, rats, rabbits, hamsters, chickens, and others - does suggest that the effect will probably be confirmed in humans as well.

Most natural anticarcinogens are found in plants. CLA, however, is found almost exclusively in animal products, although it also occurs in small amounts in certain vegetable oils. It is prevalent in the meat and milk of ruminants (cud-chewing animals, such as cows, sheep, and goats). Scientists believe that certain microorganisms that live in the rumen (the first stomach) of such animals convert dietary linoleic acid to CLA, which winds up in their flesh and milk. CLA is found to a lesser extent in other animals, such as pigs and poultry, and also in eggs. Seafood contains very little CLA.

Oddly, cooking the meat can increase the CLA content substantially, which is good news - for everyone except those of you who like to eat raw meat (and you know who you are). CLA was first isolated two decades ago, from hamburger, by Dr. Michael Pariza of the University of Wisconsin.

With our decreasing consumption
of dairy products in general and
the current emphasis on reducing
overall fat intake, our intake of CLA
is probably declining as well -
and our diet probably never did
provide enough of it for optimal
health benefits to begin with.

The primary dietary source of CLA for humans is dairy products, such as milk, cheese, and yogurt (there is also evidence that CLA occurs in human milk and blood). The highest concentrations of CLA in cows' milk occur when the cows are allowed to graze in pastures or when they have been fed supplements, such as corn oil or soybean oil, that are high in unsaturated fatty acids.

There is a catch, however: the CLA is concentrated in the milk fat, so low-fat dairy products - and products made from them, such as cottage cheese and even some ice creams - contain little CLA. And with our decreasing consumption of dairy products in general and the current emphasis on reducing overall fat intake, our intake of CLA is probably declining as well - and our diet probably never did provide enough of it for optimal health benefits to begin with. But trying to compensate by pigging out on foods containing milk fat is a bad idea, because the tradeoff isn't worth it. A better idea is to supplement with CLA, minus the fat.

We all need some fatty acids in our diet, and the trick is to get the right ones, in the right proportions, while avoiding the wrong ones. Without question, one of the right ones is conjugated linoleic acid: CLA.

There are no known significant adverse effects of CLA - which is not surprising for something found in mother's milk. And as Dr. Pariza has said, "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."

So join the vanguard of those who are discovering the many benefits of one of Mother Nature's lesser-known gifts: conjugated linoleic acid.


  1. PDR for Nutritional Supplements. Medical Economics Company, Inc., Montvale, NJ, 2001.
  2. MacDonald HB. Conjugated linoleic acid and disease prevention: a review of current knowledge. J Am Coll Nutr 2000;19(2):111S-118S.
  3. Park Y, Albright KJ, Liu W, Storkson JM, Cook ME, Pariza MW. Effect of conjugated linoleic acid on body composition in mice. Lipids 1997;32:853-8.
  4. Risérus U, Berglund L, Vessby B. Conjugated linoleic acid (CLA) reduced abdominal adipose tissue in obese middle-aged men with signs of the metabolic syndrome: a randomized controlled trial. Int J Obes 2001;25: 1129-35.
  5. Smedman A, Vessby B. Conjugated linoleic acid reduces the body fat content in humans (abstract). Chem Phys Lipids 1999;101:A152.
  6. Zambell et al. Conjugated linoleic acid supplementation in humans: effects on body composition and energy expenditure. Lipids 2000;35(7):777-82.

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