'Superfoods' - science or fiction?

31 May 2008

Superfoods science or fictionA growing body of evidence suggests that certain foods may cut cancer risk, protect against heart disease and preserve mental faculties. But just how do these "superfoods" improve our health, and should we be including them in our everyday diet?

"Diets rich in fruits and vegetables are generally associated with lower disease risks, in particular cardiovascular disease and some cancers," says the British Nutrition Foundation, which adds, "The search is on for the components of fruits and vegetables that convey these health benefits."

Scientists all over the world are hard at work trying to identify these components. An enormous amount of medical research is underway examining links between diet and disease. There is already a large volume of evidence suggesting that certain foods have significant protective effects against illnesses ranging from cancer to heart disease and Alzheimer's. In this article, we highlight a selection of foods that studies to date suggest may have particular health-giving properties.

Cruciferous and dark green vegetables: can they cut cancer risk?

Cruciferous vegetables - including broccoli, kale, cauliflower, cabbage and sprouts - contain isothiocyanates, which are thought to stimulate the body to break down potential carcinogens, and thus prevent normal cells from becoming cancerous. Several recent studies have produced evidence that cruciferous vegetables may protect some people against prostate and certain other types of cancer.

For example, scientists from the International Agency for Cancer Research in France reported that eating a weekly helping of cruciferous vegetables might reduce the risk of developing lung cancer in individuals with a particular genetic make-up. The researchers found that people with a certain genetic mutation who ate the most broccoli, cabbage and brussels sprouts were around one-third less likely to develop the disease than those with the same mutation who ate these vegetables less often.

In another recent study, published in the British Journal of Cancer, a research team from Georgetown University in the USA showed that a naturally occurring compound in cruciferous vegetables (indole-3-carbinol), when added to cells, significantly boosted the activity of the genes BRCA1 and BRCA2, which play a vital role in detecting damaged DNA and triggering a cell's response to repair it.

In their study of more than 400 Chinese men, meanwhile, Professor Colin Binns and his colleagues at Curtin University of Technology in Australia found that men who regularly consumed spinach - as well as other fruit and veg such as tomatoes, watermelons and citrus fruit - significantly reduced their risk of developing prostate cancer compared with men who did not eat much of these foods. In their report in the International Journal of Cancer, the authors say that eating extra portions of dark green vegetables might cut the risk of developing prostate cancer by up to 50 per cent.

Prof Binns stated, "We recommend eating more yellow, orange, and red vegetables and fruits such as tomatoes, watermelon, citrus and pumpkin, plus dark green vegetables such as spinach, because the risk of prostate cancer declines with increased consumption of the lycopene and other carotenoids found in these fruits and vegetables."

Pomegranate - a cure for all ills?

Recent research has suggested an array of potential benefits of consuming pomegranate or its juice - from cutting the risk of heart disease to protecting against brain damage in babies undergoing traumatic birth. Pomegranate juice contains flavonoids, which are also found in red wine, green tea and cranberry juice, and is high in vitamins A, C and E.

According to Dr Hasan Mukhtar of the University of Wisconsin Medical School in the USA, pomegranate juice may have the potential to prevent and slow the progress of prostate cancer. Dr Mukhtar's team found that mice given a concentration of pomegranate extract in their drinking water experienced a significant slowing of cancer progression and a decrease in the levels of prostate-specific antigen (a marker used to indicate the presence of prostate cancer in humans). In contrast, the tumours in the mice that received only water grew much faster than those in the animals treated with pomegranate extract.

The researchers say their findings add to a growing body of evidence that pomegranates contain powerful agents to fight cancer, especially prostate cancer. Dr Mukhtar adds, "There is good reason now to test this fruit in humans both for cancer prevention and for treatment."

A glass of pomegranate juice each day might also be effective at fighting heart disease, according to other research conducted in Israel. Biochemical tests revealed that pomegranate juice reduced the size of atherosclerotic lesions by half and helped combat "bad" cholesterol. The juice was also found to reduce blood pressure and double the amount of antioxidants in the blood. Biochemist Dr Michael Aviram claims that high-risk patients could potentially be spared bypass surgery "simply by drinking pomegranate juice".

Yet another potential benefit of consuming pomegranate juice might be protection against brain damage in unborn babies. US researchers at the Washington University School of Medicine found that pregnant women who drank pomegranate juice in the third trimester helped protect their unborn babies against hypoxia ischaemia - a reduction of blood flow and oxygen to the baby's brain. The researchers suggest that the high levels of antioxidant compounds contained in pomegranates can give babies an increased chance of coping with hypoxia ischaemia.

Fish and blackcurrants: can they help stave off mental decline?

"A human is truly what he or she eats," says Dr John E Morley, director of the division of geriatric medicine at Saint Louis University in the USA and one of a team of researchers who recently demonstrated a direct link between the stomach and the brain. In a report in the journal Nature Neuroscience, Dr Morley's group showed that high levels of ghrelin - the hormone that regulates appetite - triggered activity in the part of the brain responsible for learning and memory.

The authors of another recent US study found that consuming fish at least once a week was associated with a 10-13 per cent per year slower rate of cognitive decline in elderly people, compared with their peers who ate fish less often. "The rate reduction is the equivalent of being three to four years younger in age," the researchers concluded in a report in the journal Archives of Neurology.

Fish is a direct source of omega-3 fatty acids, which a considerable body of research has shown to be vital for neurocognitive development and normal brain functioning. Several studies have produced evidence that a diet high in the omega-3 fatty acid docosahexaenoic acid (DHA) helps lower the risk of Alzheimer's disease and slow progression of the disease in its later stages. Omega 3 fatty acids are found primarily in oily cold-water fish such as tuna, salmon and mackerel, while other sources include walnuts, flaxseed oil and rapeseed oil.

Blackcurrants might also have a role to play in preventing dementia, according to researchers at the Horticulture and Food Research Institute in New Zealand. This team recently found that antioxidants (called anthocyanins) contained in blackcurrants could protect brain cells and delay or prevent the onset of Alzheimer's. The study, published in the Journal of the Science of Food and Agriculture, showed that anthocyanins were able to block the cell damage that causes Alzheimer's - although the antioxidants could not cure the disease once it developed.

Other culinary heroes: apples, cocoa and cranberries

Among other foods to have been singled out recently as providing specific health benefits are apples - scientists suggested that they might reduce the incidence and number of breast cancer tumours when eaten daily; cocoa - research has shown that drinking a cup at night-time may help to lower blood pressure and reduce the risk of death from cardiovascular disease; and cranberries - several studies have demonstrated a protective effect in conditions ranging from urinary infections to preventing plaque forming on teeth.

Much more research will be needed confirm or challenge the health benefits claimed for these and other "superfoods". However, one thing all of the foods above have in common is that they can be readily incorporated into a healthy, balanced diet. At best, they may indeed provide some degree of protection from certain illnesses - and at worst, they are unlikely to do you any harm!

Further information:

Nature Neuroscience - www.nature.com/neuro/index.html

British Nutrition Foundation - www.nutrition.org.uk

British Journal of Cancer - www.nature.com/bjc/index.html

International Journal of Cancer - www3.interscience.wiley.com/cgi-bin/jhome/29331

Archives of Neurology - archneur.ama-assn.org

Journal of the Science of Food and Agriculture - www.soci.org/publications/journal-of-science