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Scientists have pinpointed exactly why obese people don't lose much weight when they diet.
Researchers at Sydney's Garvan Institute of Medical Research have found that a chemical known as the Neuropeptide (NPY), which stimulates appetite, plays a major role in controlling whether the body burns or conserves energy.
The study, published in the journal Cell Metabolism, shows that when the body takes in less energy or is on a diet, high levels of NPY signal to the body that it's in starvation mode, and the body subsequently starts storing as much energy as possible.
"Evolution provided us with these mechanisms to help us survive famine," co-author Professor Herbert Herzog told AAP.
"But now we're eating more than we should because food is always available, so in many cases additional energy is stored as fat," he said.
"When you try to lose the extra weight, NPY will trigger and it defeats the purpose of quickly lowering your calorie intake."
Professor Herzog said with obesity being a major epidemic in the community, researchers have found it challenging to find ways of tricking the body into losing weight because of NPY.
"Now that we have identified the exact brain circuitry, drugs can be developed to target and control these types of neurons," he said.
Professor Herzog said it was important to note that the study showed that fad diets simply did not work.
"Weight loss needs to be done over a long period of time and that's what people underestimate," he said.