A study led by Imperial College London and the Medical Research Council has helped unpick a long-standing mystery about how dietary fibre suppresses appetite – and could play a crucial role in the fight against obesity.

The researchers discovered an anti-appetite molecule, called acetate, which is naturally released when fibre is digested in the gut.

Once released, the acetate is transported to the brain where it produces a signal to tell us to stop eating. The molecule reduces appetite when directly applied into the bloodstream and colon, as well as the brain itself.

The research confirms the natural benefits of increasing the fibre in our diets to control over-eating, and may help develop methods to reduce appetite.

"The average diet in Europe today contains about 15 g of fibre per day," said lead study author Professor Gary Frost, of Imperial College London. "In stone-age times we ate about 100g per day but now we favour low-fibre ready-made meals over vegetables, pulses and other sources of fibre."

The researchers analysed the effects of a form of dietary fibre called inulin, which comes from chicory and sugar beets.

Researchers demonstrated that mice fed on a high fat diet with added inulin ate less and gained less weight than mice fed on a high fat diet with no inulin. Further analysis showed that the mice fed on a diet containing inulin had a high level of acetate in their guts.

Using positron emission tomography scans, researchers tracked the acetate through the body and showed that it eventually ended up in the hypothalamus region of the brain, which controls hunger.

In collaboration with researchers in Madrid, the team then investigated the effects of acetate in the hypothalamus using a cutting-edge scanning technique called High Resolution Magic Angle Spinning.

""From this we could clearly see that the acetate accumulates in the hypothalamus after fibre has been digested," said Sebastian Cerdán, a professor at Consejo Superior de Investigaciones Científicas.

"The acetate then triggers a series of chemical events in the hypothalamus leading to the firing of pro-opiomelanocortin (POMPC) neurons, which are known to supress appetite."

Professor Jimmy Bell, co-author on the study, added: " In the context of the growing rates of obesity in western countries, the findings of the research could inform potential methods to prevent weight gain."

Yet Frost said the next challenge was to develop an approach that will deliver the necessary amount of acetate in a safe dosage for humans.

"It's a good challenge to have and we're looking forward to researching possible ways of using acetate to address health issues around weight gain."

The research was published in Nature Communications.