No area of oncology is more complex and controversial than the relationship of cancer and diet. Everyone would like to believe that there is some diet which can substantially affect the likelihood of cancer, or better still to cure it once contracted. But to date, the evidence of the effect of diet is unclear and often inconsistent.

All reputable sources agree that no diet outright cures cancer. Nor is there strong evidence to support the view that any particular diet prevents contracting it. But there are many studies that suggest that occurrence, recurrence and survivability may be affected by the foods we choose.

Though far from certain, many studies examined by researchers at Cornell University were able to correlate lower death rates - an increased five or ten year survivability, with certain dietary choices.

In one study examined (the Nurses Health Study), 1,982 women who had already developed breast cancer were followed for an average of 13 years. Over 1,200 had cancers that had not metastasized (spreading of a primary tumor to other areas producing secondary tumors of the same type). Survival rates of cancer patients whose disease has spread are known to be much lower (21% five-year survival, as contrasted to 86% for those whose cancer has not metastasized).

Some in the first group ate larger amounts of poultry and fish, containing protein and omega-3 fatty acids. They had significantly lower risk of death than women in the group who did not consume as much. Further, women who ate large amounts of hydrogenated oils had a significantly higher death rate.

Another study was carried out by the National Cancer Institute of more than 2,400 individuals. A subset, 975 women, who had contracted breast cancer consumed a low fat diet (33.3g per day) for five years. Another 1,462 consumed 51.3 g per day. The low fat group experienced a 42% reduction in recurrence.

The difficulty with all these studies is they are looking only at associations, not causation. It's unclear from the data what is relevant. Do these dietary choices reflect only the fact that women who focus on maintaining a healthy diet are making healthier lifestyle choices overall? Or, are the foods themselves actually helpful or harmful, and to what degree?

As with many studies involving fruits and vegetables, the answer is unclear. Apart from those which contain antioxidants, any beneficial effect is simply not known with confidence. In this case, however, the evidence is strong that foods high in antioxidants do help reduce the chances of contracting breast cancer.

Free radicals in the blood stream are ionized atoms that are known to be able to harm cells. Antioxidants 'gobble them up' - reduce the amount by combining with the free radicals, rendering them harmless.

But fat studies are less clear. The leading theory says, since high estrogen levels are known to highly correlate with higher breast cancer risk, and fat efficiently stores estrogen, then lowering fat lowers the risk.

The flawed conclusion that is sometimes drawn however is the belief that eating fat makes you fat. But it isn't the consumption of fat that causes higher body fat, per se. Eating more calories than are used causes the body to store the excess in fat, leading to a higher body fat percentage. And, fat contains more calories per unit weight than other foods. The route is indirect.

Despite difficult to interpret or incomplete evidence, there is one thing all experts can readily agree on: maintaining a healthy diet and lifestyle are wise choices. Whether they lower the risk of contracting breast cancer or not, for the 1 in 12 women who will get it sometime in their life, being in optimal health helps combat it before, during and after.