Researchers may have discovered why people who lose large amounts of weight often put it back on.
Studies at the University of Adelaide have shown that the way the stomach detects and tells the brain how full we are becomes damaged in obese people and does not return to normal once they lose weight.
PhD student Stephen Kentish investigated the impact of a high-fat diet on the gut's ability to signal fullness.
His results show show that the nerves in the stomach that send signals to the brain appear to be desensitised after long-term consumption of a high-fat diet and don't return to normal when food intake is reduced.
Study leader, Associate Professor Amanda Page, said the leptin hormone could also change the sensitivity of nerves in the stomach of obese people that signal fullness.
"These two mechanisms combined mean that obese people need to eat more to feel full, which in turn continues their cycle of obesity," she said.
Prof Page said while the studies showed that the nerves remained desensitised after weight loss, it was unclear whether that condition was permanent or just long-lasting.
"We know that only about five per cent of people on diets are able to maintain their weight loss and that most people who've been on a diet put all of that weight back on within two years," she said.
"More research is needed to determine how long the effect lasts and whether there is any way, chemical or otherwise, to trick the stomach into resetting itself to normal."