Nutrition and cancer common questions

The link between food and cancer is complex. There are many different types of cancer and many different causes of cancer, only some of which are understood.

Cancer starts when cells begin to grow out of control. The reason for this change is not always known. Poor eating habits combined with smoking, too little exercise, drinking too much alcohol, being overweight and too much sunlight exposure may, over a long period of time, increase the risk of developing some cancers.

Drinking alcohol increases the risk of developing some cancers, particularly cancers of the mouth, throat, oesophagus, stomach, bowel, liver and breast. Mouth cancers are six times more common in people who drink alcohol than non-drinkers. The type of alcohol you drink – wine, beer, spirits – doesn’t make a difference.

But drinking alcohol doesn’t mean that you’ll definitely get cancer. Your risk will depend on other factors, including your age and genetics.

Cancer Council recommends drinking less alcohol to reduce your risk of cancer. Drinking less alcohol has lots of other benefits too. It can help reduce your risk of accidents, high blood pressure and liver disease.

See NHMRC guidelines for their current health advice.

The World Health Organization (WHO) classifies processed meats such as bacon, ham and salami as Group 1 carcinogens because there is strong evidence that processed meats cause cancer. WHO puts processed meats in the same category as other proven causes of cancer such as tobacco, alcohol and ultraviolet (UV) radiation.

WHO classifies red meat as a Group 2A carcinogen because there is growing evidence that eating too much red meat increases the risk of bowel cancer but the evidence isn’t as conclusive as it is for processed meats.

These classifications do not indicate the risk of getting cancer from these foods; they describe the strength of the evidence that these foods are linked to cancer.

To reduce cancer risk, Cancer Council and the Australian Dietary Guidelines recommend that you:

• eat little, if any, processed meat such as bacon, ham and salami
• aim for no more than 455 g of cooked lean red meat (e.g. beef, lamb, pork, kangaroo, goat) per week. This could be one serve a day (65 g cooked) or 2 small serves at 3–4 meals a week.

You can swap a serve of red meat for fish, chicken, eggs or legumes (e.g. chickpeas or lentils) and get adequate amounts of the nutrients you need. If you are losing weight or finding it hard to eat enough during cancer treatment, ask your doctor or dietitian what foods to eat to help you get enough energy and protein.

Organic farmers and food producers grow and produce food without using synthetic pesticides or fertilisers. They also don’t expose food to radiation to extend shelf life, or use seeds, plants or animals that have had their genetic make-up altered in a laboratory.

Some people believe it’s better to eat organic foods because they don’t have extra chemicals. However, there is no strong evidence that organic food is better for you, or that it will help you recover faster or reduce the risk of cancer coming back.

Organic fruits and vegetables contain the same vitamins and minerals as those grown in the usual way and can be more expensive to buy. Wash all fruit and vegetables thoroughly before you eat them. Focus on eating a wide variety of fruits and vegetables, rather than whether or not they’re organic.

After a cancer diagnosis, you may think about changing what you eat. Improving your diet can help your body cope with the effects of cancer and its treatment, and speed up recovery. It can also give you a sense of control. Or you may need to adjust your diet to make sure you continue to eat the right balance of foods during or after treatment.

Some people claim that a particular diet or way of life can cure or control cancer on its own. Often these diets are promoted on social media or in the traditional media. There are no special foods, diets or vitamin and mineral supplements that have been scientifically proven to cure cancer. There’s also no research that shows any particular foods can lower the chance of the cancer coming back.

Many unproven diets encourage people to:

• cut one or more food groups (e.g. all dairy or all grains)
• eat large amounts of specific fruits and vegetables or their juices
• take special or high-dose supplements.

Following an unproven diet may mean you don’t get enough energy (kilojoules/calories), protein, fat, carbohydrates, vitamins and minerals. This may affect your energy levels, cause unwanted weight loss and fatigue, and weaken your immune system. This may make it harder for you to cope with treatment and lead to malnutrition. Buying large amounts of fruits and vegetables, or supplements can be expensive. Cutting out specific foods can also make it harder to eat meals with your family, at restaurants or other people’s homes.

See ‘Understanding Complementary Therapies’ for more information.

Vitamins and minerals are an essential part of a healthy diet and play an important role in the body’s immune system. It’s best to get your vitamins and minerals from eating whole foods, as these are easier for the body to absorb. If you are able to eat a wide variety of foods, you may not need to take vitamin and mineral supplements.

Some people may need to take vitamin and/or mineral supplements during and after treatment. For example, osteoporosis can be a side effect of treatment for prostate cancer and breast cancer, so you may need to take a calcium or vitamin D supplement. If you have had surgery to any part of your digestive system (e.g. gastrectomy), you will probably need to take nutritional supplements. A dietitian can give you more information.

Some people believe that taking high doses of certain vitamins will boost the body’s immune system during cancer treatment. However, there is little evidence to support this claim. In fact, some vitamin and mineral compounds can be toxic at high levels, and may affect how radiation therapy, chemotherapy and other medicines work.

If your appetite is poor or if you’re concerned you’re not getting enough vitamins or minerals, check with your doctor or dietitian before taking any vitamin or mineral supplements.

Sugar is a type of carbohydrate found naturally in fruit and dairy products. It is also added to soft drinks and many processed foods. Our body uses  sugar for energy.

You may hear that because cancer cells use sugar to grow, cutting out all sugar and carbohydrates from your diet will stop the cancer growing. This is a myth and can be harmful. Cancer cells will get the energy they need to grow from other body tissues even if there are no carbohydrates available. The healthy cells in your body also use sugar to grow, so changing your diet in this way would mean missing out on the sugar that helps your vital organs work.

It’s a good idea to limit drinks with high amounts of added sugar such as soft drinks, cordials, fruit drinks, vitamin waters, and energy and sports drinks. Foods and drinks high in sugar may cause you to put on weight. If you are losing weight or struggling to eat enough, having foods with sugar in them may help to keep your energy levels up. Talk to a dietitian about what to eat after a cancer diagnosis.

Some people think that eating very little or no food for a specific period of time (fasting) helps treat cancer, but there is not enough evidence to support this idea, and it can be harmful. Not eating enough can leave you feeling tired, cause you to lose muscle and weight, weaken your immune system and affect your ability to cope with treatment. These outcomes may lead to treatment delays or a shorter course of treatment.

It is important to try to eat enough of a wide variety of foods to meet your body’s needs, so you maintain strength during treatment. Speak to your dietitian and treatment team before trying any fasting techniques.

Along with eating well, physical activity is important for general health and wellbeing. Any activity that gets your body moving and speeds up your breathing and heart rate can help you achieve or maintain a healthy body weight, improve your mood, and reduce the risk of several conditions, such as heart disease, type 2 diabetes and some types of cancer.

Australia’s Physical Activity and Sedentary Behaviour Guidelines for Adults encourage everyone to move more and sit less. Adults should aim to be active on most, preferably all, days of the week. Any physical activity is better than none. You don’t have to go to the gym or run; going for a walk or doing housework can also help. The aim is to be as physically active as your abilities and condition allow. For details on how active to be, visit health.gov.au/health-topics/physical-activity-and-exercise.

The advice used to be to rest during cancer treatment. But now exercise is recommended for most people during and after treatment. Research shows that regular physical activity can:

• help manage fatigue and other common side effects of treatment
• increase appetite
• speed up recovery
• strengthen muscles and bones, and improve circulation
• reduce the risk of the cancer coming back (for some cancer types) and of developing other health problems
• improve quality of life by reducing stress and improving mood.

According to the Clinical Oncology Society of Australia (COSA) position statement on exercise in cancer care, exercise should be prescribed to all cancer patients as a standard part of their cancer care to help manage the effects of cancer and its treatment. Talk to your treatment team or GP before starting an exercise program, and see a physiotherapist or exercise physiologist to develop an exercise plan that suits your situation. A  physiotherapist or exercise physiologist may be part of the team at your hospital or treatment centre, or your GP can refer you to one in private practice.

See our ‘Exercise for People Living with Cancer’ booklet for more information.

Cancer treatment often causes side effects that affect your mouth and teeth, such as dry mouth, mouth ulcers, tooth decay and mouth infections. These problems can make it hard to eat, and poor oral health can make them worse. This is why it is important to have a check-up with your dentist before treatment starts, especially if your treatment includes radiation therapy to the head or neck, some types of chemotherapy, or the drugs known as bisphosphonates (used to treat bone disease).

Your dentist can check the health of your teeth and find any problems early. You can also ask your dentist or your cancer treatment team for advice about caring for your teeth and mouth before, during and after treatment.

See our ‘Mouth Health and Cancer Treatment’ fact sheet for more information.

After cancer treatment, you might think about changing what you eat to reduce the risk of cancer coming back. There’s no research that shows any particular foods or eating plan can lower the chance of the cancer coming back.

To reduce your risk of cancer, follow the Australian Dietary Guidelines and Australia’s Physical Activity and Sedentary Behaviour Guidelines for Adults. These are similar to the World Cancer Research Fund International’s cancer prevention recommendations. For more information, visit wcrf.org/diet-activity-and-cancer/cancer-prevention-recommendations.