US scientists have hailed a new weight loss vaccine as the latest weapon in the fight against obesity but Australian experts warns it's not the Holy Grail.
Researchers from US company Braasch Biotech in South Dakota have been testing the "flab jab", an injection that makes the immune system attack a hormone that slows our metabolism and makes us gain weight.
After feeding obese mice a high-fat diet, they injected them with the vaccine and saw a 10 percent drop in body weight in four days, the UK's Telegraph reported.
The mice maintained the weight loss after booster injections were administered three weeks later.
"This study demonstrates the possibility of treating obesity with vaccination," lead researcher Dr Keith Haffer said.
"Although further studies are necessary to discover the long-term implications of these vaccines, treatment of human obesity with vaccination could provide physicians with a drug- and surgical-free option against the weight epidemic."
But Professor Michael Cowley, director of the Monash Obesity & Diabetes Institute at Monash University, said the study was flawed.
"It wasn't a particularly well-controlled study; the experiment wasn't well done," he told ninemsn.
The vaccine uses a peptide protein molecule called somatostatin, which suppresses the growth hormones that speed up metabolism and help weight loss.
When somatostatin is used as a vaccine, the immune system sees it as a threat and the body releases antibodies to neutralise it.
In the study, the mice's body weight was reduced but their normal growth hormones weren't affected.
A control group of mice were injected with a saline solution, but Professor Cowley said that was not an adequate control model.
"They should have used a vaccination against something else, or a scramble of hormones, rather than giving the animals nothing," he said.
"It could be that it wasn't to do with somatostatin at all, it was simply that the animals felt crook after getting the injection. It could be correct, but what they've done doesn't enable us to prove that point."
Professor Cowley also warned using growth hormones to control weight loss could have dangerous side effects.
"It causes the heart to thicken, and a raft of other side effects. That's why human growth hormone is not used except for in patients who have low levels of growth hormone," he said.
"The side effects of using growth hormone for weight loss would outweigh the benefits, and certainly the US Food and Drug Administration has never let a company use growth hormone supplementation as a weight loss aid."
More than 4 million Australians are obese, which is defined as having a body mass index (BMI) greater than 30.
Obesity is the leading cause of premature illness and death in Australia, and if weight gain continues at current levels, 80 percent of adult Australians will be overweight or obese by 2020.
Professor Cowley said a new drug, lorcaserin, is a much better breakthrough, because the comprehensive study on thousands of people who took it found they lost an average of 5.8 percent of their body weight.