Researchers found seaweed fibre could reduce the body's fat uptake by more than 75 per cent.
A fibrous material in sea kelp called alginate was better at preventing fat absorption than most slimming treatments, laboratory tests showed.
Dr Iain Brownlee, who co-led the University of Newcastle team, said: "This suggests that if we can add the natural fibre to products commonly eaten daily – such as bread, biscuits and yoghurts – up to three quarters of the fat contained in the meal could simply pass through the body.
"We have already added the alginate to bread and initial taste tests have been extremely encouraging. Now the next step is to carry out clinical trials to find out how effective it is when eaten as part of a normal diet."
The scientists used an "artificial gut" to test the effectiveness of 60 different natural fibres by measuring the extent to which they affected the digestion of fat.
They presented their findings today at the American Chemical Society's spring meeting in San Francisco, US.
Dr Brownlee said the aim was to see if the same effects modelled in the laboratory could be reproduced in living volunteers.
"Our initial findings are that alginates significantly reduce fat digestion," he said.
The research is part of a three-year project funded by the Biotechnology and Biological Sciences Research Council.
It addresses new European regulations that insist on scientific evidence backing any health claims made on a food label.
"There are countless claims about miracle cures for weight loss but only a few cases offer any sound scientific evidence to back up these claims," said Dr Brownlee.
"Alginates not only have great potential for weight management – adding them to food also has the added advantage of boosting overall fibre content."