If we are what we eat, then in the Western world our diet has doomed us. Everything tasty seems to make you obese before it gives you diabetes, heart disease or cancer. We all know that eating a good diet is a significant part of any healthy person's lifestyle, but despite the variety and abundance of food available in supermarkets, it has never been harder to make the right choices.

In the fight against cancer, eating a healthy and balanced diet is important for people who are ill with the disease, as well as from those who want to protect themselves against it. But when you're up against an illness so deadly, could something as insignificant as an apple a day, really keep the doctor away? Strangely, yes.

"Apart from losing weight and maintaining it within the recommended range the most important thing that one would recommend is to eat lots of fruit and vegetables. That is because fruit and vegetables have been shown to be protective against cancers. Particularly cancers of the gastrointestinal tract (the stomach and colon principally, and the oesophagus), and also lung cancer, have been shown to be reduced by a high intake of fruit and vegetables", says Professor Ian Johnson of the Institute of Food Research at the Biotechnology and Biological Sciences Research Council (BBSRC).

It is notoriously hard to measure if a specific food is good or bad for you ? you cannot just make someone eat raw broccoli for 20 years to see if it kills or cures them. This means that researchers have to rely on big epidemiological studies: studying groups who have a low incidence of cancer to see what they eat, or making people keep food diaries. The one big trend that has emerged, is that people who eat a lot of fruit and vegetables (five portions or more a day), tend to be more immune to cancer than people who don't.

As Professor Johnson puts it: "You can measure total fruit and vegetable intake fairly well; what you can't really do is discriminate between the kinds of diet. It is very difficult to discriminate between people who eat a lot of fruit from a lot of vegetables ? and indeed even more difficult to say one fruit or vegetable is more important than another. The best thing, of course, is to hedge ones bets and eat five different fruit and vegetables."

The news is not all bad for fussy eaters who may like very few fruits or vegetables. "Given that a portion is 80 grams as a rule of thumb, I'm not going to say there is anything wrong with 160 grams of broccoli. If you happen to want to eat five apples a day I'm sure that is much better than eating one apple and then not bothering to eat anything else. I suspect that it is more important to eat the bulk, the 400 grams a day, but variety is probably better because it gives you the whole range of all compounds, vitamins and minerals," says Johnson.

Foods that help against cancer:

A diet rich in fruit and vegetables provides the body with phytochemicals, with could have an effect in reducing your chances of cancer. There are several groups of these plant chemicals:

* Antioxidants work by removing harmful free radicals from the body. They are found in vegetables like broccoli, cauliflower, Brussels sprouts and cabbage. Lycopene, which makes tomatoes, red peppers and red grapefruit red, can protect against prostate and lung cancer specifically.

* Carotenoids cause the orange colour in many fruits and vegetables, like carrots and apricots.

* *nthocyanins are found in grapes, aubergines and red cabbage

* Sulfides are found in garlic and onions

* Lutein and zeaxanthin found in spinach

* Polyphenols found in the skin and seeds of grapes, so red wine is a good source of this antioxidant. Red wine also contains a type of polyphenol called resveratrol, also found in raspberries, which has been shown to inhibit cancer cells growth.

Potatoes and nuts do not count as one of the five portions a day. Try to follow the "red, amber, green" rule: try to eat fruits and vegetables that are different colours, like beetroot, carrots and spinach.