We, people, love comfort, that's why dieting and exercising to keep a fit body seem too much.

Pharmaceutical companies have developed supplements aimed to help people lose a few pounds, but are they safe for human health?

A team at Ohio State University investigated how the organism of mice and rats reacts to the supplement conjugated linoleic acid (CLA), an essential amino acid found in tiny levels primarily in beef, lamb and milk. Synthetic CLA is sold as supplement to reduce body fat, and it is even claimed to reduce the risk of diabetes and certain types of cancer. Mice that ingested CLA lost weight very quickly, but also stored excessive levels of fat in their livers, a common side effect of rapid weight loss, connected to insulin resistance, which characterizes Type 2 diabetes.

In rats, CLA dropped the fat levels accumulated in the animals' livers during a fattening diet, and the insulin resistance was weaker. "Many people take CLA as a supplement in hopes of trimming body fat, and it seems to work. But we're not sure what else it does to the body."

"It seems that these mice and rats represent a continuum of possible side effects induced by CLA," said Martha Belury, lead author of the studies and associate professor of human nutrition at Ohio State University.

In a 2 months study from 2003, the same team discovered that CLA supplements decreased body mass and blood sugar levels of diabetics. Mice were assigned to two groups, the first one being fed with a diet containing CLA for four weeks, the other was being a placebo group. Other mice were fed only for two weeks with a diet including CLA, some of them receiving daily rosiglitazone, a drug that increases sensitivity to insulin.

The researchers checked insulin sensitivity and adinopectin - a hormone generated by fat tissue and playing a main role in insulin resistance - in mice throughout the study. "Lowered adinopectin levels are associated with obesity and type 2 diabetes." said Belury.

CLA supplementation reduced greatly the body fat in the first group; however, meanwhile excessive levels of fat stored in the livers, connected to a higher insulin resistance. Removing CLA from the diet made animals regain weight, but their liver lost fat and the insulin resistance.

But the rosiglitazone injected group while on a CLA-rich diet neither emaciated nor became insulin resistant. "The drug kept adiponectin levels steady during the weeks the mice consumed CLA," Belury said. "While this is an interesting finding, it doesn't mean that someone taking CLA should also take an anti-diabetic drug," she continued. "It's too soon to tell if that would be the case in humans."

The same team experimented on rats genetically engineered to gain weight quickly. After four weeks of fat rich diet, half of the rats followed for four weeks a low-fat diet supplemented with CLA, and the rest a low-fat diet without CLA. The supplement didn't provoke a weight loss in rats, but it impeded fat from storing in the animals' livers, compared to the rats which did not eat CLA.

It should also be mentioned that 75 % of people with obesity and diabetes present a condition named non-alcoholic fatty liver disease in which fat stores in the liver and turns a person insulin -esistant. Clinical trials are underway for assessing how the human body reacts to CLA.