Conjugated linoleic acid's role in diabetes management

Nutrition Research Newsletter, Nov, 2004

The current diabetes epidemic is placing quite a burden on global health and the global economy. It is necessary to identify effective dietary strategies to decrease the effect of type 2 diabetes. The clustering of metabolic abnormalities associated with type 2 diabetes is known as the metabolic syndrome. Low-grade inflammation is also a feature of type 2 diabetes and has been implicated in the development of atherosclerosis. Cardiovascular disease (CVD) is the number 1 cause of morbidity and mortality among individuals with type 2 diabetes. While little can be done regarding the genetic component of the disease, modifiable lifestyle changes can make a significant difference. Conjugated linoleic acid (CLA) has received attention as a potential therapeutic nutrient with respect to insulin resistance and hyperlipidemia. There have been few human intervention studies regarding CLA.

The objective of a recent study was to determine the effect of CLA supplementation (providing equal proportions of cis9, trans11 and trans10, cis12 CLA) in patients with stable, diet-controlled type 2 diabetes. Multiple aspects of the metabolic syndrome, including insulin and glucose metabolism, lipoprotein metabolism, and markers of coagulation and inflammation were measured to ascertain the effect of CLA in persons with diet-controlled type 2 diabetes.

Thirty-two subjects with type 2 diabetes, controlled by diet therapy alone, participated in the study. All subjects had stable body weight and were following healthy eating guidelines as recommended by the American Diabetes Association. The randomized, double-blinded, placebo-controlled study was conducted on a free-living, outpatient basis. Subjects received 3.0 grams CLA per day or placebo for 8 weeks. All participants were asked to maintain their usual dietary and lifestyle habits, and 4-day food records were obtained on two occasions. Blood samples were taken before and after intervention (weeks 0 and 8). Blood was analyzed for cholesterol, triacylglycerol, LDL, interleukin 6 (IL-6), insulin, and C-peptide concentrations. Anthropometric measurements were taken.

CLA supplementation significantly increased fasting glucose concentrations (6.3%; P<0.05) and reduced insulin sensitivity as measured by homeostasis model assessment, oral glucose insulin sensitivity, and the insulin sensitivity index (composite) (P = 0.05). Total HDL-cholesterol concentrations increased by 8% (P<0.05), which was due to a significant increase in HD[L.sub.2]-cholesterol concentrations (P<0.05). The ratio of LDL to HDL cholesterol was significantly reduced (P<0.01). CLA supplementation reduced fibrinogen concentrations (P<0.01) but had no impact on the inflammatory markers of CVD (C-reactive protein and IL-6).

In this study, CLA had an adverse effect on insulin and glucose metabolism. However, it had a positive impact on HDL and fibrinogen. Further research is needed to determine CLA's role in diabetes management.

F. Moloney, T. Yeow, A. Mullen, et al. Conjugated linoleic acid supplementation, insulin sensitivity, and lipoprotein metabolism in patents with type 2 diabetes mellitus. Am J Clin Nutr; 80:887-895 (October, 2004). [Correspondence: HM Roche, Trinity Centre for Health Sciences, St James's Hospital, James's Street, Dublin 8, Ireland. E-mail: hmroche@tcd.ie].