Obesity is linked to a range of health problems
The discovery of another way in which the body appears to control how much it eats could shed fresh light on obesity.
US researchers said poor diets may trigger a signalling system which prompts the body to consume even more.
When the signals - involving a protein linked to inflammation - were blocked in mice, they maintained normal weight.
A UK expert warned that the finding, in the journal Cell, may not lead to an effective anti-obesity drug because it could interfere with the immune system.
The complexity of the controls governing the human metabolism, appetite and the laying down of fat has become clear over recent years.
Despite some promising experiments in animals, none has yet produced a breakthrough in the battle against obesity.
The latest "pathway" under investigation, by scientists at the University of Wisconsin-Madison, is normally associated with the immune system, and inflammation, one of the body's defence systems.
The link to obesity was made when scientists investigated "metabolic inflammation", a chronic, low-level condition often seen in obesity-related diseases.
In mice, a protein connected to inflammatory reactions appeared to be switched on when the animals were given a high fat, high sugar diet.
Not only this, but once the protein was switched on, the mice started eating more, suggesting that it was part of a pathway involving the regulation of food intake.
Closer examination of the a part of the brain called the hypothalamus, which is known to be involved in energy regulation, revealed the protein present there too.
In mice genetically altered to block the pathway, even with a high fat diet available, they were able to maintain a healthy weight.
Dr Dongsheng Cai, who led the research, said that that the pathway could possibly be used in anti-obesity drugs.
He said: "The ultimate goal will certainly be to identify a selective and effective suppressor of the pathway to target related neurons."
However, Professor Fran Ebling, from the University of Nottingham, said that other potential targets might prove more fruitful.
He said: "It's certainly interesting, but if we have some drugs that target this pathway, they may well interfere with some other part of the immune system."