The benefits of "live" yoghurt containing helpful strains of bacteria persist - even when the bacteria it contains are dead.
Probiotic foods are popular, and have been found to help conditions such as inflammatory bowel disease.
Researchers from California and Israel irradiated their probiotics to kill the "friendly" bacteria.
In the journal Gastroenterology, they report that the product's effect on inflammation remained the same.
The use of probiotics dates back thousands of years - it is reported that people in ancient Babylon drank sour milk to help problems in the gut.
They can be added to yoghurt and a small number of other dairy-based products - as well as taken in capsule form.
However, in most foods, adding bacteria would lead to fermentation within hours, changing the taste and texture of the product.
The finding from the University of California San Diego School of Medicine and the Shaare Zedek Medical Center in Jerusalem potentially opens the door for probiotics to be added to a far wider range of foods.
They gave irradiated probiotics to mice with gut inflammation induced in the laboratory.
The treatment reduced the inflammation in a similar way to giving "live" bacteria, and the researchers concluded that irradiated probiotics were just as effective.
Professor Eyal Raz, one of the study authors, said: "Our goal was to address whether the metabolic activity of probiotics was mandatory for their protective effect."
The team believes that part of the body's immune system called the "innate" immune system responded to the bugs, regardless of whether they were dead or alive.
This immune response might be damping down the overactive response within the gut.
However, experts say that the presence of live rather than inactivated bacteria in the gut has several advantages.
Firstly, the simple fact that they are occupying space and attached to the gut wall denies that space to harmful bacteria, particularly if their numbers increase over time.