Don't know why you are putting on so much weight? Blame the stress at work and at home.

In a study to show how stress has a direct effect on fat accumulation, body weight and metabolism, scientists have demonstrated that neuropeptide Y (NPY), a molecule the body releases when stressed, can unlock Y2 receptors in the body's fat cells, stimulating the cells to grow in size and number.

According to Professor Herbert Herzog, director of the neuroscience research programme at Garvan Institute of Medical Research, blocking these receptors will prevent fat growth or make fat cells die.

Herzog said the finding basically showed that when we have a stress reaction, NPY levels rise in our bodies, causing our heart rate and blood pressure to go up. Chronic stress therefore has damaging effects.

Researchers have now figured out how to remove fat from one part of the body and make it grow in another part at least in mice and say their findings could benefit health as well as beauty.

"We have known for over a decade that there is a connection between chronic stress and obesity. We also know that NPY plays a major role in other chronic stress-induced conditions, such as susceptibility to infection. Now, we have identified the exact pathway, or chain of molecular events, that links chronic stress with obesity," Herzog said.

Interestingly, the study which Herzog has conducted along with scientists from the US and Slovakia shatters myths that stress-mediated fat gain is brain instigated and shows that it is actually just a physiological response of their fat tissue.

Dr Anoop Misra from Fortis Hospital said, "Obesity has been known to be a disease not due to diet but because of stress. Stress increases cortisol level secreted from the adrenal gland which has direct connection to fat accumulation."

For the study, scientists at Georgetown University fed normal diets and high calorie (high fat and high sugar) diets to stressed and unstressed mice. The mice on normal diets did not become obese. However, stressed mice on high calorie diets gained twice as much fat as unstressed mice on the same diet.

The unexpected finding was that when stressed and non-stressed animals ate the same high calorie foods, the stressed animals utilised and stored fat differently.

"Our findings suggest that we may be able to reverse or prevent obesity caused by stress and diet, including the worst kind of obesity the apple-shaped type which makes people more susceptible to heart disease and diabetes," said senior author of the Nature Medicine paper, Professor Zofia Zukowska of Georgetown University.

Zukowska's team also made NPY into a slow-release pellet. When they placed this pellet under the skin of thin rhesus monkeys, they grew pockets of fat around the pellets. Such treatments may help replace the fat lost in people's faces as they age.