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What is CLA?

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THE BASICS

CLA is a newly discovered good fat called "conjugated linoleic acid" that may be a potent cancer fighter. In animal studies, very small amounts of CLA have blocked all three stages of cancer: 1) initiation, 2) promotion, and 3) metastasis. Most anti-cancer agents block only one of these stages. What's more, CLA has slowed the growth of an unusually wide variety of tumors, including cancers of the skin, breast, prostate, and colon. (1)

Human CLA research is in its infancy, but a few studies have suggested that CLA may have similar benefits in people. A recent survey determined that women with the most CLA in their diets had a 60 percent reduction in the risk of breast cancer. (2)

Where do you get CLA? Many people take a synthetic version that is widely promoted as a diet aid and muscle builder. New research shows that the type of CLA in the pills may have some potentially serious side effects, including promoting insulin resistance, raising glucose levels, and reducing HDL (good) cholesterol. (3)

Few people realize that CLA is also found in nature, and this natural form does not have any known negative side effects. The most abundant source of natural CLA is the meat and dairy products of grassfed animals. Research conducted since 1999 shows that grazing animals have from 3-5 times more CLA than animals fattened on grain in a feedlot. Simply switching from grainfed to grassfed products can greatly increase your intake of CLA. (4)

Click here to find a local supplier of grass-fed meat and dairy products—all naturally rich in the healthy form of CLA.  

BEYOND THE BASICS

On the molecular level, CLA resembles another type of fat called "linoleic acid" or LA. (Both CLA and LA have 18 carbon atoms and two double bonds holding the chain together. The main difference is in the placement of those bonds.) However, CLA and LA appear to have opposite effects on the human body. For example, LA promotes tumor growth but CLA blocks it.

There are 28 possible types (isomers) of CLA, each one with a slightly different arrangement of chemical bonds. The type most commonly found in meat and dairy products has double bonds between the 9th and 11th carbon atoms and is referred to as "cis 9, trans-11 CLA" or "rumenic acid."


From Eatwild's News and News Archives...

Three Times More CLA in a Grass-fed Hamburger

A lean hamburger from grass-fed cattle has two and a half times more conjugated linoleic acid (CLA) than an equally lean hamburger from cattle raised in a feedlot. CLA (conjugated linoleic acid) is a healthy fat that has been shown to fight obesity, cancer, and diabetes in lab animals. Human studies are now underway.

“A literature Review of the Value-Added Nutrients Found in Grass-Fed Beef Products.” Nutrition Journal, June 2006 (In Press.)


Milk from Grass-Fed Cows Higher in Vitamin E

Cows that get all their nutrients from grazed grass—their natural diet—produce milk with 86 percent more vitamin E (alpha-tocopherol) than cows fed a standard dairy diet, according to a recent study.

The standard dairy diet consists of large amounts of “concentrate,” which is typically a dry mixture of corn and soy. Some organic dairies raise their cows on pasture and supplement them with organic concentrate; others keep their cows indoors and feed them organic concentrate and stored grasses. The more freshly grazed grass in a cow’s diet, the more vitamin E, omega-3 fatty acids, and CLA. Organic Valley is a nation-wide organic dairy that emphasizes grazing.

Leiber, F., M. Kreuzer, et al. (2005). Lipids 40(2): 191-202.


Alpine milk may be the healthiest of all

Milk from one hundred percent grass-fed cows is healthier than milk from grain-fed cows because it contains more of a number of key nutrients, including omega-3 fatty acids, beta-carotene, and conjugated linoleic acid or CLA. New research shows that cows that graze at relatively high altitudes may produce the healthiest milk of all. Compared with lowland grazers, milk from high altitude grazers (3700-6200 ft) has even more omega3s and CLA and significantly less saturated fat.

Why? Plants growing in higher altitudes have more omega-3 fatty acids, fats which solidify at lower temperatures than other fats and therefore act as a form of anti-freeze. The cows eat this enriched pasture and pass the nutrients on to their milk.

Hauswirth, C. B., M. R. Scheeder, and J. H. Beer. "High Omega-3 Fatty Acid Content in Alpine Cheese: The Basis for an Alpine Paradox." Circulation 109, no. 1 (2004): 103-7.


Natural CLA from grazing animals superior to pills

Tens of thousands of people who want to lose weight or reduce body fat have been taking a synthetic version of conjugated linoleic acid or CLA. A new study shows that the pills may cause more harm than good. After reviewing 13 randomized studies, a group of researchers concluded that the pills do not reduce body weight or body fat to a significant degree. Unfortunately, the promising results seen in animal studies do not seem to apply to humans.

Worse yet, the researchers found that a kind of CLA found in the pills (CLA (t10, c12) may cause serious health complications, including an enlarged liver, lower levels of HDL (good) cholesterol, and insulin resistance.

Meanwhile, the main type of CLA found in meat and dairy products (c9, t11 or "rumenic acid") has been given a clean bill of health. Once again, a natural product has been found to be superior to its synthetic counterpart.

Larsen, T. M., S. Toubro, et al. (2003). "Efficacy and safety of dietary supplements containing conjugated linoleic acid (CLA) for the treatment of obesity-evidence from animal and human studies." J Lipid Res.


Latitude and altitude —
hidden factors that influence omega-3 and CLA levels in milk

The amount of beneficial CLA and omega-3 fatty acids in a cow's milk is influenced by a host of factors in addition to diet, including her breed, individual genetics, age, and even the time of year. Now one more factor has been added to the list: prevailing temperatures. Milk and cheese from alpine grazers or cows raised in colder climates appear to have the omega-3 and CLA edge.

The reason? It has to do with plant antifreeze. Omega-3 fatty acids stay fluid at colder temperatures than other, more saturated fats. A plant that has to withstand the cold needs more of this natural antifreeze to keep its cell membranes fluid. Cows that graze on this cold climate grass ingest more omega-3s, which they then convert to another good fat—CLA. In a recent study, cows that grazed in alpine meadows had more than twice the amount of CLA in their milk as similar cows that grazed down in the valley.

"Composition of milk fat and correlation with fodder plants" Marius Collomb, Jacques-Olivier Bosset, Ueli Bütikofer, Robert Sieber, Hans Eyer,
Email: marius.collomb@fam.admin.ch


Natural CLA from milk products is a better cancer-fighter than CLA pills

Many people are not aware that there are many types of the cancer-fighting fat CLA, depending on minute differences in molecular structure. It now appears that, in test tube studies, the kind of CLA found in butter and animal fat is the most potent cancer-fighter. Human breast cancer cells were incubated in milk fat high in CLA or in an isolated form of CLA without any milk fat. The high CLA milk fat decreased cancer growth by 90 percent but the isolated CLA decreased it by only 60 percent. When the cells were incubated in linoleic acid, the kind of fat that is most abundant in grain and grain-fed animals, cell growth increased by 25 percent.

Milk products from 100 percent grassfed cows are as much as seven times higher in cancer-fighting CLA than ordinary milk and far lower in cancer-promoting linoleic acid.

(Cancer Letters 1997;116:121-130)


Autumn milk has more CLA

Valerie Dantoin from Full Circle Farm in Seymour, Wisconsin, has gone the extra mile to verify that her Northern Meadows cheddar cheese is high in CLA—she's had samples of the milk tested at the University of Wisconsin throughout the grazing season.

As you can see from the graph below, there is a marked difference in the CLA levels of the milk from month to month. The cows were turned out to pasture in May and remained on pasture for the remainder of the study period. The CLA content in April (before the cows started grazing) is similar to the amount found in ordinary supermarket milk. By September, the CLA content was three times higher than at the start of the grazing season. (In addition to the pasture, the cows were supplemented with 15 pounds of high-moisture corn, 5 pounds of corn silage and 4 pounds of added protein from soybean meal and roasted beans. Milk from cows given no additional supplement is even higher in this cancer-fighting fat.


Seasonal variation in CLA levels

To learn more about Full Circle Farm and to purchase their cheese, visit Valerie's website at http://www.fullcirclefarm.net/


CLA in North American hunter/gatherer diets

CLA, the cancer-fighting fat, has been found in North American game animals, suggesting that CLA has been a part of the human diet since the first spear was thrown. Deer, elk, and moose have about the same amount of CLA as cattle. Surprisingly, mountain lions and black bears have more (7 and 9 mg/g of fat, respectively) even though they are not herbivores.

Now, when is someone going to test and publish the CLA levels of free-range bison?


A welcome source of high CLA butter

To our knowledge, there are no American farms or cooperatives that are currently marketing butter from 100% grassfed cows. Although cheese from all grassfed cows is available from many suppliers on the Eat Wild Pastured Products directory, grassfed butter cannot be found. Restrictive government regulations and lack of consumer awareness keep small-scale butter operations from being profitable.

Until a US supplier gets up and running, it is possible to purchase excellent butter imported from Ireland by the Kerrygold company. The butter is made from cows that are raised on pasture or grass silage, making it five times higher in CLA and also higher in vitamin E and beta carotene than commercial butter, whether organic or non-organic. It costs about twice as much as ordinary butter and about the same as organic butter. It is yellower than butter from cows raised in confinement, melts at a lower temperature, and has a terrific taste. Look for Kerrygold butter in up-scale supermarkets and specialty stores. To see if there's a store in your neck of the woods, search Kerrygold for "where to buy." You can also order their butter and cheese on-line from http://www.foodireland.com (Once at the site, go to the "Irish Deli" section.) You may be able to convince your local supermarket to stock it, eliminating the high cost of shipping.

Learn more about Kerrygold...


Lab animals fed CLA-rich butterfat have stronger bones

Animal studies suggest that CLA enhances bone formation. Chicks and rats fed CLA-rich butterfat had greater bone growth than animals fed other fats. Researchers attribute the stronger bones to CLA's ability to block excess production of an inflammatory substance called PGE2. Grassfed dairy meat and dairy products have from 2-5 times more CLA than ordinary products.

Watkins, B. A. and M. F. Seifert (2000). "Conjugated linoleic acid and bone biology." J Am Coll Nutr 19(4): 478S-486S.


Wild game has CLA, too

CLA, a type of healthy fat found in the meat and milk of ruminants, is found in wild game as well, according to researchers Larry Cordain and Bruce Watkins. They discovered that CLA levels are especially high in the bone marrow. This finding is significant because there is evidence to suggest that our hunter/gatherer ancestors sought out bone marrow to add calories and fat to their lean diet. Thus, although CLA is new to modern science, it may have played a key role in human nutrition for eons.

Cordain et al, "A Detailed Fatty Acid Analysis of Selected Tissues in Elk, Mule Deer, and Antelope." Food Composition 670.1-670.6


Two new studies suggest that grassfed meat and dairy products may reduce the risk of breast cancer

CLA (conjugated linoleic acid) is a cancer-fighting fat that is most abundant in grassfed products. Two new European studies link a diet high in CLA with a lower risk of breast cancer. In Finland, researchers measured CLA levels in the serum of women with and without breast cancer. Those women with the most CLA had a significantly lower risk of the disease. Meanwhile, French researchers measured CLA levels in the breast tissues of 360 women. Once again, the women with the most CLA had the lowest risk of cancer. In fact, the women with the most CLA had a staggering 74% lower risk of breast cancer than the women with the least CLA.

The most natural and effective way to increase your intake of CLA is to eat the meat and dairy products of grassfed animals.

A. Aro et al, Kuopio University, Finland; Bougnoux, P, Lavillonniere F, Riboli E. "Inverse relation between CLA in adipose breast tissue and risk of breast cancer. A case-control study in France." Inform 10;5:S43, 1999


Milk from grassfed cows has hidden benefits

Until recently, all of the experiments demonstrating the cancer-fighting properties of CLA (conjugated linoleic acid) have used synthetic CLA. To see whether the CLA that occurs naturally in cow's milk has similar cancer-fighting properties, researchers recently compared the two. They fed one group of rats butter that was high in CLA and fed another group of rats an equivalent amount of synthetic CLA. As one would expect, the natural CLA proved to be just as effective in blocking tumor growth as the man-made variety. (In both cases, cancer yield was reduced by about 50 percent.) However, the high CLA butter had an added benefit: the rats eating the butter accumulated even more CLA in their tissues than the rats fed an equivalent amount of synthetic CLA. The reason? Researchers believe that the rats were converting another "good" fat found in the butter, trans-vaccenic acid or TVA, into CLA, giving them a second helping of this cancer-fighting fat. (Click here for more information about TVA.)

(Ip, C., S. Banni, et al. (1999). "Conjugated Linoleic Acid-Enriched Butter Fat Alters Mammary Gland Morphogenesis and Reduces Cancer Risk in Rats." J Nutr 129(12): 2135-2142.)


Feedlot cattle fattened on stale gummy bears

Some commercial feedlots feed stale candy to cattle in an effort to reduce costs. According to a recent review, milk chocolate and candy "are often economical sources of nutrients, particularly fat. They may be high in sugar and/or fat content. Milk chocolate and candy may contain 48% and 22% fat, respectively. They are sometimes fed in their wrappers. Candies, such as cull gummy bears, lemon drops, or gum drops are high in sugar content." The article recommends that "upper feeding limits for candy or candy blends and chocolate are 5 and 2 lb. per cow per day, respectively."

As long as beef producers are not accountable for the ultimate nutritional value of the meat, they will continue to formulate feedlot diets on a least cost basis and American consumers will continue to eat meat that is artificially high in fat and low in vitamin E, beta carotene, omega-3 fatty acids, and CLA.

("By-Product Feedstuffs in Dairy Cattle Diets in the Upper Midwest." Randy D. Shaver, Ph.D.
Associate Professor, Extension Nutritionist, Department of Dairy Science, College of Agricultural and Life Sciences, University of Wisconsin)


Feed them grass, not grease!

In yet another short-sighted experiment, researchers at Washington State University are feeding recycled restaurant grease to feedlot cattle in an attempt to raise the CLA levels of their meat. Although grease will indeed enhance CLA levels, it cannot compete with grass when the total nutritional value of the meat is taken into consideration. Meat from cattle raised on grass and legumes is not only five times higher in CLA than meat from feedlot cattle, it is also higher in vitamin E, beta carotene, and omega-3 fatty acids. Also, restaurant grease is high in a type of fat called "linoleic acid" or LA that is known to stimulate tumor growth. Although grease-fed cattle will have more of the cancer-fighting CLA, they will also have higher levels of the cancer-promoting LA, perhaps canceling out the anticipated benefits.

Comments: As long as researchers focus on artificial ways to raise CLA levels in animals, we will continue to have beef that is nutritionally inferior in other areas. We will also be plagued with all the problems linked with the feedlot industry including nutrient leaching, odor, diseased animals, and the indiscriminate use of growth promoting hormones and antibiotics.


New findings on CLA clarify the benefits of meat and dairy products

Conjugated linoleic acid or CLA has demonstrated a multitude of benefits in animal studies, including fat reduction, increase in lean muscle mass, reduced risk of diabetes, reversal of arteriosclerosis, and a marked reduction in tumor growth.

Many people do not realize, however, that there are 16 different types of CLA, each with a slightly different molecular shape. New research reveals that each type of CLA has a different set of benefits. The type of CLA most abundant in meat and dairy products (referred to by chemists as "cis-9, trans-11, CLA") appears to be the champion cancer fighter. Compared with another common type of CLA (trans 10, cis 12, CLA) it was a third more effective in blocking the growth of human cancer cells. (78% versus 58% reduction)

But the type of CLA found in meat and dairy products does not appear to reduce fat or increase lean muscle mass in humans. (That property is linked with trans 10, cis 12, CLA)

It will be some time before researchers match each type of CLA with its particular benefits.

(Information gleaned from abstracts presented at the 91st American Oil Chemists Society April 25-28, 2000 annual meeting. Special supplement to Inform, vol 11, no 5, 2000)


French cheese has more CLA than ordinary American cheese

French cheeses are among the most carefully crafted and coveted in the world. Now there's another reason to seek them out: they're especially high in cancer-fighting CLA . A 1998 survey found that CLA levels in French cheese range from 5.3 to 15.8 mg/g of fat. American cheese from conventional dairies has half this amount, with levels ranging from 2.9 to 7.1. The reason? Typically, American dairies raise their cows in confinement and feed them a grain-based diet. French dairies are more likely to raise their cows on pasture, resulting in naturally high levels of CLA

Fortunately, cheese from American pasture-based dairies has the same CLA advantage as French cheese. Search the Eat Wild Pastured Products Directory for cheese suppliers and treat yourself to an extra helping of CLA.

(JAOCS 75, 343­352 (1998))


TVA — yet another good fat in grassfed products?

Evidence is mounting that dairy products from grassfed cows supply yet another "good" fat to our diet---trans-vaccenic acid or TVA. Technically, TVA is classified as a "trans-fatty acid," a type of fat nutritionists tell us to avoid. But TVA appears to behave differently from the man-made fat that comes from the hydrogenization of vegetable oil. Unlike the trans-fatty acids found in fast foods and margarine, TVA is not linked with an increased risk of cardiovascular disease and may help inhibit tumor growth and obesity.

Interestingly, TVA may perform these feats by being converted into CLA in our own bodies. In fact, dairy scientist David Schingoethe from South Dakota State University suggests that eating diary foods high in TVA may be a more effective way to increase CLA levels than ingesting CLA itself.

Schingoethe and colleagues are experimenting with increasing TVA in dairy cows by feeding them fish meal and soybeans. But raising cows on fresh pasture and withholding all grain may prove just as effective. In fact, grassfed cows produce milk that is naturally high in both CLA and TVA, a potentially lifesaving combination. Stay tuned!

(To learn more, read "Making Milk Better," by Jamie Lammers.)


The Irish are making the most of their "unfair" advantage

Milk from grassfed Irish cows is 2–3 times higher in conjugated linoleic acid (CLA) than milk from grainfed American cows. Experiments are underway in Ireland to increase this CLA advantage. Recent experiments show that feeding oilseeds to grassfed dairy cows boosts their CLA production even more. Rapeseeds (the seeds that make canola oil) increase the CLA content of the milk an extra 60%. (To read more, refer to "Milk and Dairy Products for Better Human Health," by D. McDonagh, et al.)

The Irish get added health benefits from their grassfed beef as well, according to a soon-to-be-published study. Compared with animals fed supplemental grain, meat from cattle raised on pasture alone was lower in saturated fat, but higher in the "good fats," including monounsaturated fats, omega-3 fats, and CLA. Commented the researchers, "These data indicate that many Irish beef producers, due to their grass-based production systems, have a natural advantage in producing beef that is more beneficial to human health than beef produced from concentrate-based systems."
(For study details, refer to R&H Hall Technical Bulletin Issue No. 4 ~1999)

(French, P., Stanton, C., Lawless, F., O'Riordan, E.G., Monahan, F., Caffrey, P.J. and Moloney, A.P. 1999a. Fatty acid composition, including conjugated linoleic acid, of intra-muscular fat from steers offered grazed grass, grass silage or concentrate-based diets. Journal of Animal Science. Submitted)


Some types of cheese have more CLA than others

The way that cheese is made influences its CLA (conjugated linoleic acid) content. In general, the longer cheese is aged, the lower the CLA. Thus, hard cheeses such as Parmesan and Romano tend to have less CLA than softer cheeses such as cream cheese, cottage cheese, feta, farmer's cheese, ricotta, and Brie. In addition, cheese that is aged through "bacterial surface ripening" (Brick and Muenster) has more CLA than cheese that does not go through this process. Finally, a serving of high-fat cheese will have more CLA than a similar serving of low-fat cheese. (The CLA is measured in terms of grams of CLA per gram of total fat; the more total grams of fat in a serving of cheese, the more CLA it will have Reduced fat swiss is an anomaly, for unknown reasons..)

The table below shows CLA levels in cheese purchased at a grocery store in 1992. In all likelihood, the milk came from confinement dairy operations. If the milk had come from grassfed animals, the CLA content would have been five times higher.

TYPE OF CHEESE CLA (mg/gram of fat)
Brick 7.1
Reduced Fat Swiss 6.7
Natural Muenster 6.6
Colby 6.1
Blue 5.7
Ricotta 5.6
Velveeta 5.2
Medium Cheddar 4.1
Sharp Cheddar 3.6
Parmesan 3.0
Romano 2.9

(Chin et al, "Dietary Sources of Conjugated Dienic Isomers of Linoleic Acid, a Newly Recognized Class of Anticarcinogens." J. of Food Composition and Analysis 5:185-197 1992)


Red clover increases CLA levels in the milk of grassfed dairy cows

The type of grasses and legumes growing in a pasture can influence the amount of CLA in cow's milk. When dairy cows grazed pasture that contained 20 percent red clover, they produced 50 percent more cancer-fighting, fat-busting CLA than cows that grazed on grasses alone. (Search for the study titled, "Paddocks containing red clover compared to all grass paddocks support high CLA levels in milk.")


Sheep are the CLA winners

Dr. Gerhard Jahreis from the Institut Ernaehrung und Umwelt in Germany has studied the CLA content of human milk and milk from a variety of animals. He reports that horses have the lowest CLA content and sheep the highest. Human milk is in the middle. (Mare's milk < sow's milk < human milk < goat's milk < cow's milk < ewe's milk.)

There are fewer than 100 sheep dairy farms in the United States (we imported 66 million pounds of sheep's milk cheese in 1994, valued at $118 million.) With this new finding about CLA, perhaps more US farmers will consider milking sheep.

(Jahreis, G. et al, The potential anticarcinogenic conjugated linoleic acid in milk of different species: cow, goat, ewe, sow, mare, woman." Nutr Res 1999. 19:1541-9.)


Soft cheese has more CLA than aged cheese

All cheese made from the milk of grassfed cows is rich in conjugated linoleic acid (CLA). However, the cheese making process itself can increase or decrease this amount. In a comprehensive survey, the highest amounts of CLA were found in soft cheeses aged approximately three months. Longer aging periods reduced this highly desirable fat.

(Chin, S. F. et al (1992)). "Dietary Sources of Conjugated Dienoic Isomers of Linoleic Acid, a Newly Recognized Class of Anticarcinogens." J of Food Composition 5: 185-97.)


Turkeys make CLA, too

CLA (conjugated linoleic acid) is highest in products from grazing animals on a diet of fresh pasture, and it is very low in non-ruminants such as chickens and pigs. But turkeys appear to be an exception, having about 2.5 mg of CLA per gram of fat. (For comparison, chickens have 0.9 and pigs 0.6 mg. per gram of fat.) To date, no one has tested the CLA content of turkeys raised on pasture rather than in confinement, an experiment that begs to be done. It is possible that turkeys with a significant amount of greens in their diet will have even more CLA.

(Chin, S. F. et al. (1992)). "Dietary Sources of Conjugated Dienoic Isomers of Linoleic Acid, a Newly Recognized Class of Anticarcinogens)


Cows that graze on "ecologically managed" pasture may have more CLA

Raising dairy cows on fresh pasture instead of a standard dairy diet increases the CLA content of their milk five-fold. Now there is some evidence that grazing on organic pasture may boost the CLA even further. In a study conducted in Germany, cows on organic pasture had almost twice as much CLA as those grazing on a nearby, non-organic farm. More research is needed.

(Jahreis, G. et al. (1997). "Conjugated linoleic acid in milk fat: high variation depending on production system." Nutrition Research 17(9): 1479-1484.)

Learn more about the health benefits of products from pasture-raised animals.

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References

1. Ip, C., J. A. Scimeca, et al. (1994). "Conjugated linoleic acid. A powerful anticarcinogen from animal fat sources." Cancer 74(3 Suppl): 1050-4.

Conjugated linoleic acid (CLA) is a mixture of positional and geometric isomers of linoleic acid, which is found preferentially in dairy products and meat. Preliminary studies indicate that CLA is a powerful anticarcinogen in the rat mammary tumor model with an effective range of 0.1-1% in the diet. This protective effect of CLA is noted even when exposure is limited to the time of weaning to carcinogen administration. The timing of this treatment corresponds to maturation of the mammary gland to the adult stage, suggesting that CLA may have a direct effect in reducing the cancer risk of the target organ. Of the vast number of naturally occurring substances that have been demonstrated to have anticarcinogenic activity in experimental models, all but a handful of them are of plant origin. Conjugated linoleic acid is unique because it is present in food from animal sources, and its anticancer efficacy is expressed at concentrations close to human consumption levels.

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2. Aro, A., S. Mannisto, I. Salminen, M. L. Ovaskainen, V. Kataja, and M. Uusitupa. "Inverse Association between Dietary and Serum Conjugated Linoleic Acid and Risk of Breast Cancer in Postmenopausal Women." s 38, no. 2 (2000): 151-7.)

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3. Riserus, U., P. Arner, et al. (2002). "Treatment with dietary trans10cis12 conjugated linoleic acid causes isomer-specific insulin resistance in obese men with the metabolic syndrome." Diabetes Care 25(9): 1516-21.

OBJECTIVE: Conjugated linoleic acid (CLA) is a group of dietary fatty acids with antiobesity and antidiabetic effects in some animals. The trans10cis12 (t10c12) CLA isomer seems to cause these effects, including improved insulin sensitivity. Whether such isomer-specific effects occur in humans is unknown. The aim of this study was to investigate whether t10c12 CLA or a commercial CLA mixture could improve insulin sensitivity, lipid metabolism, or body composition in obese men with signs of the metabolic syndrome. RESEARCH DESIGN AND METHODS: In a randomized, double-blind controlled trial, abdominally obese men (n = 60) were treated with 3.4 g/day CLA (isomer mixture), purified t10c12 CLA, or placebo. Euglycemic-hyperinsulinemic clamp, serum hormones, lipids, and anthropometry were assessed before and after 12 weeks of treatment. RESULTS: Baseline metabolic status was similar between groups. Unexpectedly, t10c12 CLA increased insulin resistance (19%; P < 0.01) and glycemia (4%; P < 0.001) and reduced HDL cholesterol (-4%; P < 0.01) compared with placebo, whereas body fat, sagittal abdominal diameter, and weight decreased versus baseline, but the difference was not significantly different from placebo. The CLA mixture did not change glucose metabolism, body composition, or weight compared with placebo but lowered HDL cholesterol (-2%; P < 0.05). CONCLUSIONS: These results reveal important isomer-specific metabolic actions of CLA in abdominally obese humans. A CLA-induced insulin resistance has previously been described only in lipodystrophic mice. Considering the use of CLA-supplements among obese individuals, it is important to clarify the clinical consequences of these results, but they also provide physiological insights into the role of specific dietary fatty acids as modulators of insulin resistance in humans.

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4. Dhiman, T. R., G. R. Anand, et al. (1999). "Conjugated linoleic acid content of milk from cows fed different diets." J Dairy Sci 82(10): 2146-56.

Conjugated linoleic acid in milk was determined from cows fed different diets. In Experiment 1, cows were fed either normal or high oil corn and corn silage. Conjugated linoleic acid was 3.8 and 3.9 mg/g of milk fatty acids in normal and high oil treatments, respectively. In Experiment 2, cows consumed one-third, two-thirds, or their entire feed from a permanent pasture. Alfalfa hay and concentrates supplied the balance of feed for the one-third and two-third pasture treatments. Conjugated linoleic acid was 8.9, 14.3, and 22.1 mg/g of milk fatty acids in the one-third, two-third, and all pasture treatments, respectively.

Cows grazing pasture and receiving no supplemental feed had 500% more conjugated linoleic acid in milk fat than cows fed typical dairy diets.

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