evidence: A review of 17 cancer studies from 1966 to 2020 shows that eating just 18 grams of mushrooms (equal to about a 1/8-cup or two medium mushrooms) a day may lower your risk of cancer by as much as 45%. Mushrooms are a powerful source of ergothioneine, an amino acid and antioxidant that prevents or slows cellular damage. Some mushroom varieties (such as shiitake, oyster, maitake and king oyster) have higher amounts of ergothioneine. But researchers found that incorporating any variety of mushrooms into your daily diet will lower your risk of cancer.