MUSHROOMS are easy to overlook in the so-called rainbow colours we are advised to eat to get a full range of nutritional benefits from fruit and veg. But research increasingly reveals why they are now qualified to join the ranks of so-called super foods such as broccoli and blueberries. Numerous studies reveal that mushrooms may help reduce the risk of heart disease and cancer. 'Mushrooms may seem plain, but they really are a superfood,' says dietician Dr Sarah Schenker. 'They contain virtually no fat, sugar or salt and are a valuable source of dietary fibre as well as the five B vitamins thiamine (B1), riboflavin (B2), niacin (B3), pyridoxine (B6) and folate. 'They also contain the essential minerals potassium, copper, phosphorous and iron. 'Most significant among their mineral content is selenium, which you don't find in many fruit and vegetables.' With more than 90 per cent water content, adding mushrooms to dishes such as stews can make us feel fuller without boosting calorie content. More than 2,500 different varieties grow in the wild, but until now most research has focused on the exotic types. Active antiviral compound lentinan, present in the shitake, has been found to boost the immune system. The shitake may also help lower blood cholesterol and reduce the harmful effects of saturated fat. The maitake is a rich source of beta-glucans, which have potentially anti-tumour effects. Even in small amounts, the tree ear - or wood ear - mushroom, can thin the blood, helping prevent heart disease and stroke. The humble white button mushroom could also carry significant health benefits. Researchers at Pennsylvania State University found that just a handful has about 12 times more of the powerful antioxidant, L-Ergothioneine than wheatgerm and four times more than chicken liver, previously thought to be the best sources. L-Ergothioneine works on cell-damaging substances known as free radicals and protects the body's DNA from damage. As a result of this research, the university advocated that white mushrooms be elevated to 'super food' status. Meanwhile, Hanyang University in South Korea found mushrooms may lower the risk of breast cancer. Dr Schenker says most of us don't realise that mushrooms count as one of our five-a-day fruit and vegetables: an 80g serving provides one portion. - Mail