Weight-Loss Supplement Shows Good and Bad Traits

A supplement some people turn to in hopes of losing a few pounds may have some previously unknown, unsavory side effects, suggest two new studies.

Researchers studied how mice and rats responded to the supplement conjugated linoleic acid (CLA), an essential amino acid found in trace amounts primarily in beef, lamb and milk. Synthetic forms of CLA are marketed as supplements that help reduce body fat, and some manufacturers also tout CLA for reducing the risk of diabetes and certain types of cancer.

The mice and rats responded in very different ways to CLA, said Martha Belury, the lead author of both studies and an associate professor of human nutrition at Ohio State University.

Mice fed a CLA-supplemented diet lost weight very fast, but also accumulated excessive amounts of fat in their livers – a common side effect of rapid weight loss. Excessive fat accumulation in the liver is linked to insulin resistance, a hallmark of Type 2 diabetes.

Yet CLA didn’t help rats lose weight they had gained prior to taking the supplement. But it effectively decreased the amount of fat that had accumulated in the animals’ livers due to the weight gain. In turn, the rats were less resistant to insulin.

“Many people take CLA as a supplement in hopes of trimming body fat, and it seems to work,” Belury said. “But we’re not sure what else it does to the body. Studying CLA’s effects in two different animal models may help us to better understand any additional effects in humans.

“It seems that these mice and rats represent a continuum of possible side effects induced by CLA,” she continued. “The question is, are humans more like mice or rats? We’re probably somewhere in between.”

The current mouse study appears in a recent issue of the Journal of Lipid Research, while the rat study will appear in an upcoming issue of the Journal of Nutritional Biochemistry.

In a study from 2003, Belury found that CLA supplements lowered body mass and blood sugar levels of diabetics. The study participants took CLA supplements for two months.

Researchers fed two groups of mice different diets. The first group ate a diet containing CLA for four weeks, followed by four weeks of a diet without CLA.

The second group of animals ate a CLA-free diet for two weeks followed by two weeks of a diet that included CLA. During the latter two weeks, some of the mice received daily injections of the anti-diabetes drug rosiglitazone. Rosiglitazone makes the body more sensitive to insulin. Mice serving as controls for both groups did not consume CLA.

The researchers monitored insulin sensitivity in all mice throughout the study. They also monitored levels of adiponectin, a hormone secreted by fat tissue and thought to play a role in insulin resistance.

“Adiponectin helps regulate insulin levels,” Belury said. “Lowered levels are associated with obesity and type 2 diabetes.”