The breakthrough by the Sydney team could help cancer patients with wasted bodies put on the weight they need to survive chemotherapy and radiotherapy.
Conversely, spurring on the MIC-1 molecule in overweight people would help them rapidly shed weight.
The research team declared that discovering the role of MIC-1 was an enormous breakthrough after more than 15 years of multi-disciplinary effort. They found that the MIC-1 molecule is a protein that targets the receptors in the brain that switch appetite on or off.
"It's very exciting to be able to work on a therapy that could change lives the way this will," lead researcher Herbert Herzog told The Sydney Morning Herald. "We think that a cancer patient will only have to be injected with the (MIC-1) antibody every three weeks and a person can put on a significant amount of weight in that time which would really help them."
Herzog said a large amount of MIC-1 was produced by cancers and that this was a cause of the dramatic weight loss seen in cancer patients.
Sam Breit, a member of the team, said experiments in mice showed the more advanced the cancer, the stronger the don't-eat message conveyed to the brain.
"This is a very exciting discovery because we have effectively found a new appetite pathway we didn't know existed," Breit said. "It's a breakthrough that could directly improve quality of life for many people."
He said the next step was to find a commercial sponsor and run clinical trials with humans using a synthetic MIC-1 protein.
The findings are published in the journal Nature Medicine.