It may not sound very appetising, but an edible powder made from waste excreted by bacteria in our guts may help people to avoid gaining weight.
Stabilising a person's weight could have a major health impact, says Gary Frost of Imperial College London, because as people on Western diets grow older, they tend to put on between 0.3 and 0.8 kilograms per year on average.
A fatty acid called propionate is released when the bacteria in our gut digest fibre. Propionate makes people feel full by activating cells in the large intestine that produce the satiety hormones GLP-1 and PYY: these tell the brain that it's time to stop eating.
But to trigger a big enough dose of this appetite-suppressing signal from gut bacteria alone, people would have to eat extremely large amounts of fibre. To get around that, Frost and his team made the molecule in a concentrated form called inulin-propionate ester (IPE). "That gives you eight times the amount of someone following a typical Western diet," he says.
Pass the IPE
To test its appetite-stemming properties, the team gave powdered IPE, mixed in with fruit juice or a milkshake, to a group of overweight volunteers every day for six months. A type of ordinary fibre was given to another set of people, who acted as controls.
Only one of the 25 volunteers taking IPE put on more than 3 per cent of their body weight over that time, compared with six of the 24 controls. One reason for this might be that the IPE recipients ate around 9 per cent less over the six months.
A second experiment on 20 healthy volunteers also supported the effects of IPE. When the volunteers were invited to eat as much as they liked from a buffet, they ate 14 per cent less when given IPE than when given ordinary fibre. Levels of the satiety hormones GLP-1 and PYY were higher in recipients of IPE.