The plant chemical, resveratrol, is found in the skins of grapes and concentrated in red wine.
Scientists have long known that resveratrol has anti-cancer properties, as well as effects that might benefit diabetes and heart disease patients.
But a question mark remains over what dose of the compound it is best to take.
The new research suggests that for fighting bowel cancer it is very small -- around five milligrams per day.
That is about the amount of resveratrol typically found in one large glass of red wine, or two small glasses.
Scientists conducted tests on laboratory mice which showed that a dose of resveratrol in their food equivalent to five milligrams in humans halved the growth of bowel tumours.
The low dose proved more potent than a higher one.
Lead researcher Professor Karen Brown, from the University of Leicester, said: "Everybody thinks that more is better but we found that the low dose was more effective than the high one.
"We were amazed that it had any effect at all, and even more surprised by the effectiveness of the low dose."
Previous studies have shown that even tiny amounts of the compound can reach target tissues in humans.
But cancer trials involving resveratrol supplements were disappointing.
"People do take it as a supplement, but there's no clinical evidence that this is of any benefit," said Prof Brown.
"We're still trying to understand the mechanism behind the way resveratrol works and see if it translates to human tissues and cells.
"It's a fascinating compound because it does so much," Prof Brown added.