An article appearing in the August 2001 issue of Lipids reported that Swedish researchers at Uppsala University have concluded that those taking conjugated linoleic acid (CLA) over the course of a 14- week trial experienced body fat reductions of 3.8 percent. This research is the latest in a series of four published medical studies that all have demonstrated fat loss. The findings suggest that CLA prevents fat from accumulating in the body, thereby reducing body fat mass.
"We continue to be excited as we learn more about the many metabolic properties of CLA," said Dr. Annika Smedman, Unit for Clinical Nutrition Research, Uppsala University, Sweden. "The results of our study indicate that supplementation with CLA may reduce the proportion of body fat in humans."
Conjugated linoleic acid is the common name of a group of fatty acids found in dairy and meat products. However, over the last 50 years, changes in livestock feeding practices have largely removed naturally occurring CLA from our diets. In several recent studies, CLA has received considerable attention due to its apparent metabolic and other health benefits and anti-cancer properties in animals, as well as some similar, initial results in humans. The effects seen in animals include reduced body fat content, improved serum lipid profiles, decreased aortic lipid deposition, and improved glucose control and delayed onset of diabetes.
"This study coming from Uppsala University, in combination with previous studies, continues to demonstrate that CLA reduces fat deposition in the body," said Delbert Dorscheid, MD, PhD, University of British Columbia. "CLA reduces body fat and it increases lean tissue in both animals and humans. This action generates a healthier body with more lean muscle and less fat, particularly belly fat which can be associated with many other medical problems."
In the Uppsala University study, 53 men and women were randomly assigned to either a CLA-treated group, or to a control group that received olive oil capsules. At baseline, there were no statistical differences between the groups. During the initial two weeks of the study, all subjects were given control capsules containing olive oil. During the remaining 12 weeks, in a randomized, double-blind design, the subjects in the CLA group were given capsules containing 4.2 g/d of CLA, while the control groups continued taking the olive oil capsules. All participants were asked not to change their diet or physical activity regimens, and to not supplement their diets with other vitamins, mineral or fatty acids during the trial to prevent confounding the action of CLA with regard to body fat content.
Previous studies published by the American Chemical Society, The Journal of Nutrition, The International Journal of Obesity, and Lipids presented human studies ranging in numbers from 17 to 63 persons. Each study concluded that CLA possesses properties that diminish the percentage of body fat in humans. The CLA used in all of the studies was Tonalin® CLA, manufactured by Natural, Inc.
Supplementation with conjugated linoleic acid (CLA) induces a number of physiological effects in experimental animals, including reduced body fat content, decreased aortic lipid deposition, and improved serum lipid profile. Controlled trials on the effects of CLA in humans have hitherto been scarce. The aim of this study was to evaluate the effects of supplementation with CLA in healthy humans on anthropometric and metabolic variables and on the fatty acid composition of serum lipids and thrombocytes. Fifty-three healthy men and women, aged 23-63 yr, were randomly assigned to supplementation with CLA (4.2 g/d) or the same amount of olive oil during 12 wk in a double-blind fashion. The proportion of body fat decreased (-3.8%, P< 0.001) in the CLA-treated group, with a significant difference from the control group (P = 0.050). Body weight, body mass index, and sagittal abdominal diameter were unchanged. There were no major differences between the groups in serum lipoproteins, nonesterified fatty acids, plasma insulin, blood glucose, or plasminogen activator inhibitor 1 (PAI-1). In the CLA group the proportions of stearic, docosatetraenoic, and docosapentaenoic acids increased in serum lipids and thrombocytes, while proportions of palmitic, oleic, and dihomo-gamma-linolenic acids decreased, causing a decrease of the estimated delta-6 and delta-9 and an increase in the delta-5 desaturase activities. These results suggest that supplementation with CLA may reduce the proportion of body fat in humans and that CLA affects fatty acid metabolism. No effects on body weight, serum lipids, glucose metabolism, or PAI-1 were seen.
Smedman A, Vessby B. Conjugated linoleic acid supplementation in humans--metabolic effects. Lipids. 2001 Aug;36(8):773-81. PMID: 11592727