That's it: the secret of the Chinese figure is to be found in the soy.

A team from University of Illinois focused on how precisely soy helps in losing weight. "We wanted to compare the effects of soy protein hydrolysates and soy peptides with those of leptin because we hypothesized that soy might behave in the body in a similar way. Leptin is a hormone produced in our adipose tissue that interacts with receptors in the brain and signals us that we're full so we stop eating," said co-researcher Elvira de Mejia, an assistant professor of food science and human nutrition.

"And we found that soy did have an effect on these mechanisms and hormones that are induced in the body to help us degrade lipids and reduce body weight, but it did so by boosting metabolism and not by reducing food intake," she said.

The researchers implanted in the brain of lab rats some cannulas for the injection of leptin, as a positive control. On the functional models of rats, they experimented with two formulations of hydrolyzed soy protein and soy peptides to assess their effects on food intake and weight loss. The rats were injected 6 times in 2 weeks and had unlimited access to food and water.

All individuals exercised similarly and all lost weight. But following the third injection, the researchers detected a great weight loss in the animals receiving soy hydrolysates, even if their food intake was the same with that of the other rats.

Soy protein induced weight loss without decreasing the rats' food consume, but by changing their metabolism and affecting brain receptors.

More importantly, this research shows that weight loss is not always linked to less food intake. "Weight loss is a complex physiological event. It's not always as simple as 'Eat less or exercise more,'" said de Mejia. "Losing weight is a cascade of many steps, beginning with the production of certain hormones and continuing with their action in the brain. Some people are resistant to these hormones, just as other people are insulin-resistant. These people never receive the message from the brain that tells them they're full," she added.

Team's next goal is to isolate the active peptide in soy and describe how it acts.