Mushrooms may help increase the immune system's ability to fight tumors.

Mushrooms could give the immune system a hand in attacking foreign invaders, if the effects in mice translate to humans.

What's more, the common white button mushroom had stronger immune-boosting effects than more exotic -- and more expensive -- fungi such as oyster and shiitake mushrooms, Dr. Keith Martin of Arizona State University in Mesa and his colleagues found.

"What really stood out is that the white button mushrooms seemed to be the most effective," Martin told Reuters Health. "That's good, because those probably are the most affordable in the supermarket."

One probably wouldn't suspect, he added, that these humble fungi are actually "powerhouses for boosting the immune system."

Mushrooms have long been used in traditional medicine, and mushroom extracts are popular as dietary supplements today, Martin and his team point out in their report in the online journal BMC Immunology. Studies of individual components of mushrooms in lab dishes and animals suggest they may help increase the immune system's ability to fight tumors.

To investigate whether whole mushrooms might offer a similar benefit, the researchers performed a series of experiments using crimini, maitake, oyster, shiitake, and white button mushrooms added to the diets of mice.

The team found that the effects on healthy animals were much weaker than the effects seen in isolated immune cells in lab studies. Rodents that ate a diet consisting of 2% white button mushrooms for four weeks showed no changes in their immune system, and no signs of toxicity.

However, when the researchers fed the animals a chemical that triggers colon inflammation and can promote the growth of colon tumors, the rodents that had mushrooms in their diet were protected from weight loss and colon injury

"We should expect beneficial effects in humans, with the key being that the mushrooms alone are not setting off the immune system," Martin commented.

To get the equivalent amount of mushrooms consumed by the mice in the study, Martin added, a person would need to eat about 100 grams or 3.5 ounces -- roughly 2.5 cups of raw mushrooms -- daily.