A new study by scientists in the U.S. has found that red and blue foods are the best when it comes to fighting cancer.
They say the natural pigments which give some fruit and vegetables a rich red, purple or blue colour act as powerful anti-cancer agents.
The researchers say compounds, found in foods such as aubergines, red cabbage, elderberries and bilberries, restricted the growth of cancer cells and in some cases killed them off entirely, leaving healthy cells unharmed.
The researchers from Ohio State University conducted a study which combined laboratory tests on human cancer cells with experiments on animals.
The study was designed to examine whether a diet rich in the foods made a difference to the risk of developing cancer.
The researchers led by Dr. Monica Giusti, an expert in plant nutrients, extracted anthocyanins from a variety of exotic and more common fruits and vegetables which all had a deep red, blue or purple colour and added them to flasks containing a suspension of human colon cancer cells.
They found that foods with the highest levels of the compounds were most effective at slowing cancer growth; in particular the exotic purple corn and chokeberries stopped the growth of colon cancer cells and also killed 20% in lab tests.
Foods with less of the pigments, such as radishes and black carrots, slowed the growth of colon cancer cells by 50% to 80%.
The pigments belong to a class of antioxidant compounds known as anthocyanins which are not easily absorbed by the bloodstream.
In their passage through the stomach to the gastrointestinal tract, they are taken up by surrounding tissues.
The scientists believe it is their survival through to the lower part of the intestine which may be the key to their role in preventing cancers.
While the team calculated purple corn to be the most potent, chokeberries and bilberries were almost as effective, and radish anthocyanin required nine times as much to cut cancer cell growth by half.
For the second study, the researchers fed rats with colon cancer a diet of anthocyanin extracts from bilberries and chokeberries, which are most often used as flavourings in jams and fruit drinks.
They found the colon tumours in the rats fell by 60% to 70% compared with a control group that were not given anthocyanin.
Dr. Giusti says all fruits and vegetables that are rich in anthocyanins have compounds that can slow down the growth of colon cancer cells, whether in experiments in laboratory dishes or inside the body.
The research was presented at the annual meeting of the American Chemical Society in Boston and is part of a long-term investigation aimed at a greater understanding of the 600 anthocyanins found in nature.
Dr. Giusti says scientists have just begun to scratch the surface of understanding how the body absorbs and uses different structures.
Chokeberries (Aronia) are two species of deciduous shrubs in the family Rosaceae, and are native to eastern North America and are most commonly found in wet woods and swamps.