A study conducted in 2000 found that 69% of cancer patients had used at least one complementary alternative medicine (CAM) as part of their cancer treatment. Most CAM treatments for cancer have not been rigorously studied or tested. Some CAM treatments are used to make the patient feel better, but may not have any effect on eliminating or eradicating the cancer but can improve quality of life, others such as improved diet are being increasingly associated with a reduction in cancer risk.

Vitamins
Some believe that cancer can be prevented through effective vitamin supplements and this thought stems from earlier observations linking human disease to vitamin deficiency (such as scurvy with Vitamin C deficiency).

More recent research findings indicate that many foods have cancer-fighting components, so patients are being advised on a more frequent basis to consume fresh, organic, unprocessed fruits and vegetables for maximum health benefits.

Epidemiological studies have illustrated that low vitamin D levels, are correlated to increased cancer risk. The results, however, do not directly indicate whether a correlation between these two factors means that one causes the other.

Diet
The overall consensus on diet and cancer is that obesity (being 1/3 or more above your recommended body weight for your age, height & sex) causes an increased risk of developing cancer. Supporting evidence includes the fact that certain cancers are more prevalent in certain countries, for example, colon cancer is more common in the US, whereas gastric cancer is more common in Japan.

Interestingly enough, studies also indicate that immigrants tend to develop the cancer risk of their new country, typically within only one generation, which suggests a substantial link between diet and cancer risk.

Some proposed dietary interventions for cancer risk reduction have gained support from epidemiological studies, examples include those that report that reduced meat consumption is associated with a decreased risk of colon cancer, and that consuming coffee is linked to a decreased risk of liver cancer.

Even the way you eat your food can make a difference. Grilled meat consumption has been linked to an increased risk of stomach cancer, colon cancer, breast and pancreatic cancer. This may be due to the presence of carcinogens such as benzopyrene in foods that are cooked at high temperatures.

A reduction in cancer markers in a group of men with prostate cancer (who were using no conventional cancer treatments at the time) was attributed to consumption of a plant-based diet and lifestyle changes in a study conducted in 2005. Another study conducted on 2400 women in 2006, concluded that when ½ were randomly assigned a normal diet, and ½ were on a low fat diet (< 20% calories from fat), the women on the low-fat diet had a markedly lower risk of breast cancer recurrence (confirmed in an interim report released in December, 2006).

In November 2007, the American Institute for Cancer Research (AICR) combined with the World Cancer Research Fund (WCRF) published “Food, nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective”. This is the most comprehensive analysis on diet, physical activity and cancer. The report lists the following 10 recommendations that people can follow to help to reduce their risk of developing cancer:
1. Reduce your intake of foods and drinks that promote weight gain, i.e. energy-dense, fatty foods, and sugary drinks.
2. Eat mostly foods of plant origin (reduce your intake of meat proteins and starches).
3. Limit how much processed and red meat you consume.
4. Limit how much alcohol you consume.
5. Cut down on your sodium (salt) intake, and avoid mouldy cereals (grains) or pulses (legumes).