A new food additive that suppresses the appetite and prevents weight gain may one day be used in slimming bread.
The ingredient, IPE (inulin-propionate ester) makes food more filling by stimulating the gut to release hormones that act on the brain.
IPE contains propionate, a natural compound produced when dietary fibre is fermented by gut microbes.
In tests, overweight volunteers given IPE as a powder to add to their food were much less likely to pile on extra pounds than those not using the additive. The IPE group also had less fat in their abdomens and livers.
Scientists are now investigating ways of incorporating IPE into common foods.
Study leader Professor Gary Frost, from the Department of Medicine at Imperial College London, said: "Molecules like propionate stimulate the release of gut hormones that control appetite, but you need to eat huge amounts of fibre to achieve a strong effect.
"We wanted to find a more efficient way to deliver propionate to the gut.
"This small, proof-of-principle study shows encouraging signs that supplementing one's diet with the ingredient we've developed prevents weight gain in overweight people. You need to eat it regularly to have an effect.
"We're exploring what kinds of foods it could be added to, but something like bread or fruit smoothies might work well."
In one study, 20 volunteers were given either IPE or inulin, a dietary fibre, and allowed to eat as much as they liked from a buffet.
Those given IPE ate 14% less on average and had higher levels of appetite-reducing hormones in their blood.
Next, 60 overweight individuals took part in a 24 week study in which half were given IPE and half inulin.
Just one member of the IPE group gained the equivalent of more than 3% of body weight compared with six from the inulin group.
None of those given IPE, but four of the volunteers taking dietary fibre, put on more than 5% of their body weight, the research published in the journal Gut showed.
Co-author Dr Douglas Morrison, from the University of Glasgow, said: "There is significant interest in how food components like dietary fibre interact with gut microbes to influence health, but much of the evidence we rely upon comes from laboratory and animal studies.
"It is often difficult to translate these findings directly into successful human interventions.
"Packaging propionate up to more efficiently deliver it to the large intestine has allowed us to make direct observations in humans that propionate may play an important role in weight management.
"These exciting findings could at last open up new ways to manipulate gut microbes to improve health and prevent disease."
The research was funded by the Biotechnology and Biological Sciences Research Council's (BBSRC) Diet and Health Research Industry Club (DRINC), which aims to help the food industry develop health-enhancing products.
Dr Celia Caulcott, BBSRC director of innovation and skills, said: "This is an excellent example of the exciting discoveries being made thanks to DRINC funding that can help to improve our health and benefit society.
"By working closely with industry to identify research priorities, we are investing in discoveries that have a much better chance of moving out of the lab and into our lives."