Dairy foods and meat contain conjugated linoleic acid (CLA). It is also available as a dietary supplement. CLA contains a mixture of different chemical forms -- or isomers -- of linoleic acid, a type of fat your body needs to function properly. Preliminary findings, based largely on animal studies, suggest that CLA may have both beneficial and harmful effects with respect to diabetes, as well as other diseases. Because of the inconsistent data, anyone with diabetes should consult their doctor before using this supplement.
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Sources of CLA
CLA is found naturally in milk fat and the meat of ruminants -- animals that chew their cud, like cows and sheep. The amount of CLA in these foods depends on what the animal has eaten. For example, according to an October 1999 article in the "Journal of Dairy Science," the CLA content of milk from grass-fed cows is five times higher than that from grain-fed cows. CLA is also sold as a dietary supplement. The supplements are not derived from ruminants, but are instead made by chemically altering vegetable oils. Because of this, the two sources have slightly different chemical structures.
The Evidence -- Animal Research
The effect of CLA on diabetes is mixed. For example, studies of rats with diabetes published in the July 2003 issue of the "American Journal of Physiology -- Endocrinology and Metabolism" and the May 2001 issue of "Diabetes" have demonstrated that CLA makes cells more responsive to insulin -- the hormone that lowers blood glucose -- and improves how the body handles glucose. However, studies of mice published in the September 2000 issue of "Diabetes" and the September 2002 issue of the "Journal of Lipid Research" suggest that CLA supplementation impairs the action of insulin, and also increases fat accumulation in the liver, both of which may increase the risk of diabetes.
The Evidence -- Human Research
CLA studies in humans also report conflicting results. For example, one group of researchers found that CLA supplementation was associated with lower blood glucose levels in people with diabetes, as reported in the January 2003 issue of the "Journal of Nutrition." Others have reported that CLA had no effect on insulin sensitivity, and may actually worsen insulin action and increase blood glucose levels, as published in the October 2004 issue of the "American Journal of Clinical Nutrition" and the September 2002 issue of "Diabetes Care."
The Fine Print
In addition to the fact that some studies were completed on rodents, and the human studies were small in sample size, there are other barriers to interpreting and applying these research results. For example, the CLA supplements used in the research protocols varied with respect to dosage and exact chemical structure. There were also study differences in terms of the length of time the supplement was administered and the health of the participants. Some had an established diagnosis of diabetes, whereas others had signs of pre-diabetes. These factors further complicate analysis, and larger scale human studies are needed to obtain accurate answers on CLA supplementation in diabetes.
Warnings and Precautions
Because of the mixed study results, CLA should be used only if approved by your primary diabetes doctor, after a discussion about potential medication interactions or other side effects. For example, in addition to the potential worsening of blood glucose control, CLA supplements may also cause mild to moderate nausea, diarrhea, bloating and flatulence. Given the lack of evidence regarding the safety of CLA supplements, they are not recommended for women who are pregnant or breastfeeding.
The U.S. Food and Drug Administration regulates dietary supplements as foods rather than medications, which means manufacturers do not have to prove that their products are safe or effective before selling them.