Hardly a day goes by without a different type of food or drink being linked to or blamed for causing cancer.

But what should you eat when you've been diagnosed and are undergoing treatment?

It is not, as many might think, about eating organic, avoiding red meat or even taking supplements.

Cancer and the various ways of treating it have a profound effect on your body. As part of that, the sense of taste, smell and appetite can be dramatically altered.

For some patients, all food tastes of metal or their daily cup of tea or coffee becomes a complete turn off.

For others it can be even worse; they find their mouths dry up or ulcers form making eating very painful.

Taste changes

Bitterness is the taste most affected by cancer and its treatment, meaning familiar food and drink often becomes unpalatable.

Taste changes may be due to a number of other factors including damage or desensitisation of taste buds or interference with a patient's sense of smell, which is intricately linked to taste.

And a metallic taste is experienced when chemotherapy drugs get into saliva and the chemicals come into contact with taste buds.

A common side effect patients report is going off tea and coffee.

Dr Clare Shaw, consultant dietician at the Royal Marsden Hospital in London, has edited The Royal Marsden Cancer Cookbook, which contains recipes and tips intended to help cancer patients overcome such difficulties, and offers advice on how to adapt recipes - perhaps adding a dash of Tabasco sauce or chilli powder to alter the flavour.

As well as recipes, it has advice on exactly what kinds of foods might be palatable - and provide the right balance of nutrients - for people during and after treatment experiencing various side effects - ie dry mouth, nausea or taste change.

Half of the royalties from the book will go to the hospital's charity.

Cravings

Emma was diagnosed with breast cancer just after her 40th birthday. She then underwent six rounds of chemotherapy, a lumpectomy and radiotherapy.

The cycles of chemotherapy - and other medication she had to take - had dramatic effects on her appetite.

Emma says: "I was prescribed steroids to take on the day before, the day of and the day after having chemo. I woke up at 2am after the first dose and ate several huge slices of cake. This continued for about 20 hours a day for three days during each cycle. My appetite was insatiable."

But the chemo also affected her sense of taste which "totally disappeared" on the second day after the first dose.

Apart from the three days of steroid treatment, Emma saw her appetite plummet during the rest of the treatment cycle.

"I only craved salty foods - even though I couldn't taste. I ate lots of salty mashed potato and gravy."

Ditch the soup

Those patients who lose their appetite are likely to lose weight - but the same can be true even if a high calorie diet is being eaten, due to changes in the body.

That's because cancers can produce molecules that change the way the body functions.

For example, cytokines are proteins normally produced by the immune system to help your body fight infections. Cancers are known to produce these in large numbers. This abnormal release leads can cause weight loss by making the body break down proteins and fat.

High energy foods can help people to maintain their weight, but Dr Shaw notes that it is sometimes hard to know what to eat.

Many of her patients eat a lot of soup.

"It's liquid, it goes down easily, it's a prime choice. But, as a dietician, I will often talk to them about the fact that soup is often low in energy, and it's often low in protein.

"So people might be using it as a replacement for a meal, but it's not providing the same nourishment as a meal.'

Other high energy meals such as roasted chicken, or more nutritious soups, are advised.

Soft is best

People being treated for cancer often find it difficult to eat due to a sore or dry mouth or throat and difficulty swallowing whilst undergoing treatment

That's because the digestive system is lined with a soft layer of tissue called the mucous membrane. This tissue is susceptible to damage during some cancer treatments such as chemotherapy,

The resulting inflammation and ulceration is called mucositis. Oral mucositis leads to the pain and difficulty of swallowing.

Emma says that was a real problem.

"My nurse told me the sore mouth was a possible side effect so I was sort of expecting it but it was far worse than I imagined.

"My oncologist suggested fresh pineapple to help soothe and cleanse my mouth. It was the only thing I really ate that felt like it was giving me any goodness."

Recipes for soft or moist foods, such as elderflower jelly or pea and pancetta risotto, are also recommended in the cookbook.

'I missed eating'

Keeping up with the changes and challenges of eating is very emotional for many. "I loved food, eating and cooking and not to be able to derive any pleasure from food was really hard," said Emma.

"I really missed eating and enjoying simple things like going out for lunch."

The advice from Dr Shaw and other leading cancer charities is to be flexible with meals and to eat what you can when you can.

Most people fully recover their sense of taste - including Emma.

"About three weeks after my final chemo, my taste came back over a couple of weeks. Such a happy feeling!"