Initial tests showed it helped people to eat less and slow weight gain.
It harnessed the power of a proprionate, which naturally makes us feel full when it is produced by breaking down fibre in the gut.
Writing in the journal Gut, the UK researchers said their chemical would have to be eaten regularly to have an effect.
The ingredient is a foul-tasting soluble powder, but the team, from Imperial College London and the University of Glasgow, are trying to incorporate it into bread and fruit smoothies.
The tricky part of the research was finding a way to deliver the proprionate into the colon, where it triggers the release of hormones that control appetite.
Adding it on its own to food would not work because it would be absorbed by the intestine too early.
So the team found a way to bind it to a natural carbohydrate found in plants, called inulin.
Once bound, the proprionate can safely make its way through the digestive system before being freed from the inulin by bacteria in the colon.
In initial tests, 20 volunteers were either given inulin on its own or the new ingredient, known as IPE, and then allowed to eat as much as they liked from a buffet.
Those who had been given IPE ate about 14% less food.
In the next part of the study, 49 overweight volunteers were either given IPE or inulin in powder form and asked to add 10g (about a spoonful) to their food every day.
After 24 weeks, six of the 24 volunteers given inulin had gained more than 3% of their body weight while only one of the 25 given IPE had done so.
Study leader Prof Gary Frost, from Imperial College London, said: "We know that adults gain between 0.3kg and 0.8kg [1lb 12oz] a year on average, and there's a real need for new strategies that can prevent this.
"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."
Dr Douglas Morrison, from the Scottish Universities Environmental Research Centre at the University of Glasgow, said the experiments had shown that propionate may play an important role in weight management.
Prof David Haslam, chair of the National Obesity Forum, said: "If they have brought this about without affecting taste or the bowels, then I would welcome it."
Scientists have created a chemical that can be added to food to make people feel full.