No sugar food, no body fat. This is the principle of the high-fat, low-carbohydrate Atkins diet. But how does this work?

Two new researches link this to a hormone that regulates fat burning when the body turns from carbohydrates to its own fat reserves for getting energy, a discovery crucial for treating metabolism conditions like type 2 diabetes or obesity.

When the body consumes lots of fat and few carbohydrates, it enters a starvation metabolism. Having no glucose (sugar), the body starts using stored fats, sending fat molecules from the fatty tissue to the liver, where they are degraded into ketones (hence the name of ketogenic diet for Atkins).

A team led by Eleftheria Maratos-Flier, an endocrinologist at Beth Israel Deaconess Medical Center in Boston, put mice on either a ketogenic or a regular diet for 30 days.

Liver levels of FGF21, rose in mice fed on a ketogenic diet, but dropped back once they were put to eat a normal meal. The team engineered mice lacking the hormone and put them on the Atkins diet.

"Their liver blew up with fat. Without the ability to burn triglycerides, cholesterol, or free fatty acids, the result was "mouse foie gras," said Maratos-Flier.

In another approach, a team led by Steven Kliewer, a molecular biologist at the University of Texas Southwestern Medical Center in Dallas, put normal mice and engineered mice that overproduce the hormone to a regular diet, then starved them for a day. Normal mice behaved normally but body temperature of engineered mice dropped and they entered a hibernationlike torpor.

"All of this was completely unexpected. They looked like they were starved, even when they were fed. The hormone's knack for revving up fat metabolism and weight loss, added to earlier evidence that it makes blood sugar levels drop, may lead to treatments for people with type 2 diabetes or obesity," said Kliewer.

Maratos-Flier's team will investigate if obese mice could get lean when administered the hormone.

"Studies like these two will eventually help tailor diets to people based on their physiology and genes," said obesity researcher Randy Seeley of the University of Cincinnati, Ohio.

Still, he is skeptical, as Atkins diets work on people because they eat less, while mice get slimmer through exercise; moreover, the mouse and human livers work differently.