The Cancer Council's message, like that of its international peers, is clear: diet can play a role in preventing cancer - too much red meat or alcohol has been shown to increase the risk of breast and bowel cancer, for example - but there is no scientific evidence to prove any one food or diet can treat, control or cure cancer.

Yet many of the 114,000 Australians diagnosed each year - most commonly with prostate, bowel, breast and lung cancers - reject this advice. It defies logic, they say, that if eschewing a Western diet high in saturated fat, salt and red meat can reduce the risk of some cancers, that food becomes irrelevant after diagnosis?

Paul Reid challenged mainstream medicine's prognosis with a regime of colonic cleansing, a 75 per cent raw fruit and vegetable diet, and chewing on apricot pits - rich in amygdalin, an extract also known as B17, which doctors say is a ''phoney'' vitamin, but which supporters claim kills cancer cells. He is convinced that his diet was the cornerstone of his recovery. The fact that no robust research supports his restrictive diet, or that there is evidence high doses of of amygdalin can cause cyanide poisoning and, in some cases death, is of little consequence to the Berwick father of two.

''So what if there's no scientific proof? What has a person to lose by going on an organic diet?'' he asks. ''I don't think my journey has been unscientific, it's just that there's been no science in a big way applied to it.''

The substances we ingest undoubtedly affect the body's metabolic processes. Drinking alcohol can lead to slurred speech and loss of balance, while eating too much fat and sugar causes weight gain. But food's effect on cancer is less clear. Some practitioners in both the medical and alternative communities point to research that certain foods can either promote or inhibit cancer cell growth. Others say the disease is caused by a build-up of toxins that must be flushed from the body with nutrient-rich produce, or that cancer feeds on sugar.

Evidence is flimsy, cautions Jenelle Loeliger, senior dietitian at the Peter MacCallum Cancer Centre. The findings are often from small, observational studies that lack the scientific rigour of large-scale clinical trials, she says, or are based on laboratory results on animals, not humans.

The most reliable nutritional advice for those with cancer is to maintain a balanced diet, she says, warning that those undergoing chemotherapy, radiotherapy and surgery are particularly at risk if following restrictive diets. ''They [diets] eliminate essential food groups, so you're eliminating good quality protein sources. It can exacerbate or accelerate malnutrition in a group already at risk of malnutrition. If someone's losing weight, it can have a big impact on their tolerance and even their ability to get through the treatment.''

Dr Hordern has received many calls from relatives of cancer sufferers who have followed unorthodox diets with tragic results. ''I remember a man whose wife had recently died from very advanced breast cancer. He said to me with absolute agony and desperation in his voice, 'My wife was so sure that this wonder treatment was going to work.' It was a really extreme, alternative therapy with coffee enemas and a cleansing detoxifying diet recommended by a naturopath. In the end she was so wasted, had lost so much weight and he was really angry. He felt that he had been robbed of the last month of her life.''

Ruth Gawler, who supports cancer patients through the foundation she runs with husband Ian - author of bestseller You Can Conquer Cancer - insists they never use the word ''cure'', preferring ''heal'' in relation to the no-salt, no-sugar, plant-based vegan diet provided in conjunction with meditation and ''mind training'' at their $3000, 11-day residential retreats. Dr Gawler says countless patients have had ''spontaneous remissions'' after undergoing their programs, which have a two-month waiting list. She believes the rise in demand - 1000 people are treated each year, a 50 per cent increase in two years - is proof of a growing dissatisfaction with the perceived limits of orthodox medicine.

If dietary treatments attracted the same research dollars as pharmaceutical regimens, she argues, stronger evidence would exist. ''No one's going to be able to make a big buck from selling people carrots and beans and onions. Who's going to invest the huge money these trials require into proving the point?'' she asks.

Doctors acknowledge there is emerging evidence that some foods could have an effect on cancer cells - antioxidant-rich foods such as berries and leafy green vegetables, for example - but say the limited research is not enough to recommend dietary changes to patients.

But with studies showing between 22 per cent and 52 per cent of Australian cancer patients use one or more complementary therapies - those in the booming $2.3 billion alternative health industry say it is as high as 80 per cent - clearly, there is a growing demand for adjuncts to or alternatives to drug treatment. For many, diet is the first and most simple way to regain control of a body that has defied them.

Sally White, 41, was diagnosed with a brain tumour in 2007. She enrolled in a Gawler program after being left frustrated by doctors. ''I wasn't given any direction about whether to change my diet or not and the inference was it doesn't matter what you do, it's not going to change the outcome or your survival chances,'' she says.

The mother of two boys, aged 13 and 11, was told by Melbourne surgeons who removed a part of the tumour, that it was only a matter of time before it began to grow again. She sought a second opinion from controversial Sydney neurosurgeon Charlie Teo, who said he could remove substantially more of the tumour, giving her a better shot at survival. Despite the 50 per cent risk of a speech deficit and left-side paralysis, she emerged from theatre unscathed.

Since her diagnosis she has largely stuck to the Gawler diet, cutting out red meat, ensuring 90 per cent of her produce is organic and eating foods rich in antioxidants such as broccoli, beetroot, chickpeas, lentils and green tea.

Her tumour has started to grow again but she believes the diet will increase her survival chances. ''Potentially it has stopped the tumour growing back more aggressively and quickly. It has put me in a position to have this treatment [she is set to undergo radiotherapy and chemotherapy] and hopefully have the best outcomes from it, because I've already reduced the toxic load on my body over the last three years.''

Dr Ian Haines, medical oncologist at Cabrini Health, is open to his patients making changes to their diet if they are not too extreme, and says it can provide a placebo effect. He says confusion about what to eat is a big problem: ''Once someone gets diagnosed with cancer they get six or 10 different books on curing cancer from all variety of sources, so they're absolutely flooded with mixed messages. There is no magic solution out there, moderation is probably the best answer we have in 2010.''

Former Australian Medical Association president Kerryn Phelps believes many doctors are dismissive of nutritional regimes, which can leave patients feeling hopeless. ''If they're not getting the answers from their cancer specialists they're going somewhere else to get that information,'' she says. ''It's really important that people are given careful guidance. It will protect them from going down the path of something faddish, which is potentially dangerous.''

Dr Phelps, a GP and president of the Australasian Integrative Medicine Association, says most alternative practitioners operate ethically, and many work collaboratively with mainstream doctors.

However, she says there is a pressing need for greater attention to be paid to nutrition in medical schools and for more funding to research potential links between food and cancer.

''Just because we haven't got the whole picture yet doesn't mean there isn't something in it,'' she says. ''We are gathering [information] gradually, which is the way you gather evidence. You don't suddenly have eureka moments where you think, 'that's the answer, we can cure cancer'.''

Breast cancer survivor Melanie Meehan, 38, wants stronger evidence before she makes radical changes to her diet. The Preston mother of boys aged two and five is in remission after having a mastectomy and chemotherapy. During treatment she met many women who had a very healthy diet but still got cancer.

She has decided to have her remaining healthy breast removed.

''If someone could demonstrate statistically that cutting out certain things in your diet would eliminate or greatly reduce the risk of recurrence, I would put up my hand and do it. But the way that I feel like I'm going to prevent recurrence is to take off the other breast,'' she says.

''You can have a very healthy life by having everything in moderation and just going out and enjoying yourself.''

But for Sally White, who is preparing to undergo more medical treatment on her brain tumour, taking control of her eating habits is the most practical way she can help herself. She rejects the notion that putting faith in food creates false hope.

''From my perspective there's no such thing. Hope is hope.''