Alternative Diets for Patients with Cancer

Ketogenic Diet

The ketogenic diet is a low carbohydrate and high fat diet, causing the body to use ketones for energy. Claims that a ketogenic diet can “starve” cancer by depriving cancer cells of glucose are not supported by sufficient clinical evidence. Research is ongoing, and a ketogenic diet for cancer may increase the risk of nutritional deficiencies, increasing the risk of weight loss, malnutrition, and muscle loss during treatment. [1]

Alkaline Diet

An alkaline diet emphasises foods such as fruit and vegetables while limiting foods considered “acidic”. Although these plant foods can form part of a healthy diet, food cannot significantly alter blood pH. There is no evidence that an alkaline diet can prevent or cure cancer. [1]

Macrobiotic Diet

A macrobiotic diet is predominantly plant-based and focuses on whole grains, vegetables and legumes. Strict versions can be low in calories and certain nutrients, and there is no evidence that a macrobiotic diet treats cancer. [1]

Fasting and Calorie Restriction

Intermittent fasting and fasting around cancer treatment are being researched, including their possible effects during chemotherapy. Current human evidence is limited, however, and fasting may increase the risk of weight loss and malnutrition. It should not be undertaken during treatment without medical guidance. [1]

Organic and Whole Food Diets

An organic and whole food diet focuses on minimally processed foods and may reduce exposure to pesticides. While whole foods can support a healthy, balanced diet, there is no evidence that eating organic foods reduces cancer progression or treats cancer. 

Vegan and Plant-Based Diets

For the general population, a well-planned plant-based or vegan diet can ensure adequate nutritional intake, although a vegan diet requires careful planning to provide sufficient protein, vitamin B12, iron, calcium and other nutrients.

But there is no evidence that a plant-based or vegan diet can cure cancer, and for people with cancer experiencing weight loss, poor appetite, or treatment-related eating difficulties, such a diet may need to be adapted by an oncology dietitian to ensure you'll supply your body with all the nutrients it needs. 

Sugar-Free and Low-Carbohydrate Diets

The idea that removing sugar can “starve cancer cells” oversimplifies how the body uses glucose. Cancer cells use glucose, but so do healthy cells. Cutting out all sugar or carbohydrates does not selectively starve tumours and makes it harder to eat enough glucose. Reducing foods high in added sugars can be part of healthy eating, but extreme restriction is unnecessary.

Dairy-Free Diets

There is no general recommendation for people with cancer to avoid dairy products. If you remove dairy because of an allergy, intolerance or personal preference, ensure you obtain nutrients such as calcium, protein and iodine from other sources. [2]

Supplements and natural products are sometimes promoted alongside alternative diets, but “natural” does not necessarily mean safe during cancer treatment. Do not start high-dose vitamins, herbal products or 'immune-boosting' supplements without checking with your oncology team. Some can interact with chemotherapy, targeted therapy or immunotherapy. Oral nutritional supplements (also called ONS) are food products specifically designed to help patients who, due to their disease or medical condition, have different nutritional needs that cannot be met by their normal diet alone. ONS can provide additional calories, protein, and other key nutrients your body needs during cancer.

Your dietitian or other healthcare provider may recommend an oral nutritional supplement as part of your nutrition care plan if you're finding it difficult to meet your nutritional needs through food alone.

Vitamins and Minerals

Vitamin and mineral supplements may be recommended if you have a deficiency or cannot meet your needs through food. However, high-dose supplements can be harmful and some may interfere with cancer treatments, so check with your healthcare team before taking them. [2]

Probiotics and Diet during Cancer

If you consider adding probiotics to your diet, discuss this first with your healthcare professional as they may not be suitable for everyone.

“Superfoods”

Foods such as berries, turmeric and green tea when consumed as part of a balanced diet can participate in meeting your nutritional needs, but no "superfood" can prevent or treat cancer. Variety and overall dietary quality are more important. Your medical team can help you to elaborate a nutritional plan adapted to your needs.

Herbal and Alternative Products

Some herbal and alternative products are promoted for people with cancer, but their effectiveness and safety are not proven. 

• Essiac and Flor-Essence: These herbal mixtures are promoted as alternative cancer treatments, but there is no reliable evidence that they treat cancer or improve quality of life. [3]
• Amygdalin (Laetrile): Amygdalin, sometimes called laetrile or “vitamin B17”, has not been shown to treat cancer and can cause serious side effectsincluding risk of cyanide toxicity. [3]
• Cannabis-Based Products: Some prescribed cannabis-based medicines may help manage particular symptoms, but cannabis products have not been shown to cure cancer. They may also interact with medicines. [3]
• Black Salve: Black salve is promoted online as a treatment for some cancers but can destroy healthy tissue, cause serious injury and leave cancer untreated. It is not recommended. [3]

Nutritional needs can vary considerably according to cancer type, treatment and your general health. Always speak to your oncologist or dietitian before starting a restrictive diet.

Digestive Cancers (Colon, Rectal, Pancreatic)

Colon, rectal and pancreatic cancers and their treatments can affect digestion, absorption and appetite. Maintaining adequate energy and protein intake may therefore be particularly important. Your healthcare team can advise on an appropriate pancreatic cancer diet, diet for rectal cancer or dietary changes following bowel surgery.

Diet Considerations for Breast and Prostate Cancer

People with breast or prostate cancer may wonder whether changing their diet, such as eating more plant-based foods or avoiding certain foods, could affect their cancer. There is no need to eliminate specific food groups unless your healthcare team advises you to do so. A balanced eating pattern that provides enough energy, protein and other essential nutrients can support your overall health during and after treatment. If you are considering major dietary changes, discuss them with your doctor or dietitian. 

Advanced or Late-Stage Cancer

With advanced cancer, maintaining weight, strength, comfort and quality of life may take priority over dietary restrictions. Fasting and very low-carbohydrate diets can make it harder to obtain enough energy and protein and should not be attempted without professional advice.