The bacteria lives in the gastrointestinal tract
Eating a daily portion of broccoli sprouts could help tame the H. pylori bacteria, linked to stomach ulcers and even cancer, research suggests.
The study in Cancer Prevention Research of 50 people in Japan found eating 2.5 ounces of broccoli sprouts each day for two months may confer some protection.
They contain sulforaphane, previously found to act as an antibiotic.
UK experts said while sprouts may have an effect on the bug, they were likely to make "no difference" to cancer risk.
In the study, an international team of scientists gave half the group a daily portion of broccoli sprouts and the rest alfalfa sprouts, which do not contain sulforaphane.
In those who ate broccoli sprouts, levels of a marker of H. pylori in human stools called HpSA was cut by over 40%.
There was no HpSA level change in those who ate alfalfa sprouts.
In people who ate broccoli sprouts, HpSA levels had returned to pre-treatment levels eight weeks after people stopped eating them.
The researchers say this suggests that although the sprouts can dampen down H. pylori, they do not eradicate it.
Dr Jed Fahey, of Johns Hopkins University in the US who led the study, said: "The fact that the levels of infection and inflammation were reduced suggests the likelihood of getting gastritis and ulcers and cancer is probably reduced."
It was Dr Fahey who discovered the sprouts contained sulforaphane early this decade. He is a co-founder of a company licensed by The Johns Hopkins University to produce broccoli sprouts. A portion of the proceeds is used to help support cancer research.
His team also carried out tests on mice infected with H. pylori, giving them broccoli-sprout smoothies for eight weeks.
The number of H. pylori bacteria in the mice's stomachs fell significantly - but did not change in infected mice that only drank plain water.
A second group of H. pylori-infected mice were genetically engineered to lack the Nrf2 gene that activates protective enzymes.
They failed to respond in the same way to the sprout-smoothie diet.
Nell Barrie of Cancer Research UK said: "This small study shows that eating broccoli sprouts might reduce levels of H. pylori infection.
"We know that H. pylori is a major risk factor for stomach cancer but only three in a 100 people with the infection will develop the disease, so there are clearly other factors at work.
"This means we can't conclude that eating broccoli sprouts makes any real difference to the chance of getting stomach cancer. "