S E Hurst graduated from the University of Tennessee with a PhD in Comparative and Experimental Medicine in 2012.
Doing Your Body Good with CLA
There may be a better way to combat the problems of obesity and its medical complications while not resorting to invasive surgery. Along with diet and exercise, a group of positional and geometric isomers of linoleic acid may be the answer millions of people seek. Conjugated linoleic acid (CLA) has been shown through some research to reduce body fat mass, increase lean tissue mass, and more importantly, aid in the treatment and prevention of such diseases as arteriosclerosis, breast and skin cancer, diabetes, heart disease, and immunity problems1.
Food Sources of CLA
Conjugated linoleic acid refers to the group of isomers from octadecadienoic acid or linoleic acid. The structures of both active isomers and linoleic acid are shown below. CLA was first isolated in 1983 by a research team led by Dr. Michael W. Pariza at the University of Wisconsin-Madison2. CLA was originally extracted from ground beef and has since been found almost exclusively in ruminant animal products. According to one study, lamb, beef, and veal contain more CLA than any other meat2. Further studies have shown cooking the meat increases the level of CLA sometimes five fold. Researcher Dr. David Kritchevsky, at the Wistar Institute in Pennsylvania, states that since CLA is found mainly in animal fat, it “is proof God has a sense of humor”1. Dairy products from ruminants (cows, sheep, goats, etc.) have been shown to be the major source of CLA for humans. This is important because humans themselves cannot produce CLA3. The microorganism Butyrivibrio fibrisolvens4, that lives in the rumen of cows, sheep, etc., creates CLA from the breakdown of linoleic acid to stearic acid5. Because ruminants feed on grasses and grains, which typically contain a high proportion of long chain polyunsaturated fatty acids, microbial activity causes biohydrogenation of the unsaturated fatty acids6. This reaction causes considerable rearrangement of bonds, which is crucial to the formation of the CLA fatty acid.
Prior to 1951, it was believed by the scientific community that naturally occurring fatty acids were classified by their straight chains and even number of carbons6. Due to CLA and odd-numbered, branched chain fatty acids, it is now known that this is not the case. Odd-numbered chains as well as branched chains have been discovered in the blood serum of many ruminants, making these fatty acids readily available for absorption into the milk6.
CLA levels vary depending on a few factors. Studied mainly in cows, the major determinants were breed, diet, age, and lactation state7. In a study using Holstein and Brown Swiss breeds of cattle, Brown Swiss had naturally more CLA and TVA (trans-vaccenic acid) when compared to levels of CLA and TVA in the Holsteins8. TVA is thought to be a precursor to CLA as stearoyl-coenzyme A desaturase coverts TVA to the cis 9, trans 11 form of CLA. Differences in the rumen biohydrogenase and desaturase activity in mammary tissue also contribute to the varying levels of CLA9. Probably the most important factor that alters CLA levels is diet. Over the last 50 years, changes in stock diet have greatly reduced the natural levels of CLA in the human diet10. The problem lies in the feed given to the livestock. Several studies have shown livestock allowed to graze on pasture grasses have considerably more CLA concentrations than those fed on grain and silage. One study measuring the dependence of CLA levels on the season was conducted to add validity to this claim. In the study, researchers discovered that during the summer months, CLA concentration was greater than when compared to the CLA concentration in the winter months2. These results are reasonable due to the availability of fresh grasses and hay during the warmer seasons. For the group given grain and silage, there was no such seasonal deviation of CLA levels. Based on this and other similar studies, scientists have made attempts to boost natural CLA levels by adding supplements to the livestock diet. One research team added dietary marine algae (Schizochytrium sp.) to the rations11. After testing was completed, a fatty acid profile was collected for each group. The control group had no statistical change while the fatty acid profile of the experimental group was dramatically altered. The amount of total saturated fats had decreased, and the levels of unsaturated fats and CLA had increased. Fish oil and soybeans were added to the livestock diet in a study conducted by Whitlock et al.8 Soybeans were used because they are rich in linoleic acid. The use of fish oil was to stimulate the conversion of TVA to CLA. The combination of both supplements increased the CLA composition to 23.56 grams per 100 grams of fatty acid as well as increasing the total concentration of other long chain fatty acids. Normal milk fat CLA composition can range from 4 to 7 mg CLA/g of fatty acid12.
As the amount of fat or milk fat increases, so should the concentration of CLA. Based on this assumption, the fat in milk, cheese, ice cream, and ruminant meats contains valuable CLA.
Success in these studies would prove very beneficial for consumers. The current intake of CLA through animal products is said to be less than one-third of the recommended level2, which is 500 milligrams13. The levels presently consumed are around 150 milligrams per day for women and 200 milligrams per day for men in the United States14. One reason for the decline of CLA in the diet could be the negative attention given to animal products13. By educating the public and increasing the CLA content in these animal products, the benefits of CLA could perhaps become more pronounced throughout the population. However, negative thoughts will always be associated with CLA because it is found in the fat from ruminants. An example of this can be seen through the research of Dr. Michael Pariza and his colleagues. They discovered that one of the richest sources of CLA was in fact the high fat product, Cheez Whiz ® 2. Thus as the amount of fat or milk fat increases, so should the concentration of CLA. Based on this assumption, the fat in milk, cheese, ice cream, and ruminent meats contains valuable CLA. To help Americans struggling with weight gain, manufacturers produce fat-free or reduced fat varieties of the above products in order for consumers to feel better about eating them. As a result, these products contain little or none of the CLA isomers. Although it is not recommended to eat large quantities of any food, let alone high fat foods, to receive CLA, researchers would argue, “milk really does a body good.”
1. Raloff, J. (2001). The good trans fat; Will one family of animal fats become a medicine? Science News.
2. Reiner, S. (1996). CLA: Does fat have a silver lining? American Council on Science and Health, 8. http://www.asch.org
3. McGraw, L. (2000). Amazing graze. Agricultural Research.
4. Ma, D.W.L, Wierzbicki, A.A., Field, C. J.,& Clandian, M.T. (1999). Conjugated linoleic acid in Canadian dairy and beef products. Journal of Agriculture and Food Chemistry, 47, 1956-1960.
5. Park, Y., Albright, K.J., Cai, Z.Y., & Pariza, M.W.(2001). Comparison of methylation procedures for conjugated linoleic acid and artifact formation by commercial (trimethylsilyl) diazomethane. Journal of Agriculture and Food Chemistry, 49, 1158-1164.
6. Kurtz, F.E. (1974). The lipids of milk: Composition and properties. In B.H. Webb, A.H. Johnson, & J.A. Alford (Eds.), Fundamentals of dairy chemistry (pp. 125-219). Westport, CT: The Avi.
7. Muir, D.D. (1992). Milk chemistry and nutritive value. In R. Early (Ed.), The technology of dairyproducts (pp. 24-38). New York: VCH.
8. Whitlock, L.A, Schingoethe, D.J., Hippen, A.R., Katcheur, K.F., Baer, R.J., Ramaswamy, N., et al. (2002). Fish oil and extruded soybeans fed in combination increase conjugated linoleic acids in milk of dairy cows more than when fed separately. Journal of Dairy Science, 85, 234-243.
9. Peterson, D.G., Kelsey, J.A, & Bauman, D.E. (2002). Analysis of variation in cis-9, trans-11 conjugated linoleic acid (CLA) in milk fat of dairy cows. Journal of Dairy Science, 85, 2164-2172.
10. Journal of international medical research features study on body fat impact of conjugated linoleic acid (CLA): Fifth study in eighteen months confirms body fat activity of CLA in humans. (2002).
11. Franklin, S.T., Martin, K.R., Baer, R.J., Schingoethe, D.J., & Hippen, A.R. (1999). Dietary marine algae (Schizochytrium sp.) increases concentrations of conjugated linoleic, docosahexaenoic and transvaccenic acid in milk of dairy cows. American Society for Nutritional Sciences, 2048- 2054.
12. Heemsta,J. (n.d.) Cancer and fat fighting compound isolated in red meat and milk.
13. Human clinical EFA trial yields 20% reduction in body fat. (1998).
14. Belury, M. A. (2002). Dietary conjugated linoleic acid in health: Physiological effects and mechanisms of action. Annual Review of Nutrition, 22, 505-531.
This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.
© 2018 Sarah Hurst