What we choose to eat is one of the factors involved in cancer risk. It’s estimated a third of cancers could be prevented by making healthier food choices, being physically active and having a healthy body weight.

What is cancer?

The growth and function of all the cells in our body are carefully controlled by many processes. The term cancer is used when these control systems go wrong and our cells start to grow out of control. The process usually involves damage to the DNA in cells, which can be caused by chemicals found in cigarette smoke, radiation and even some viruses. The food we eat also affects DNA function, but the exact mechanisms are unclear.

In most cases, cancer is caused by many different factors, with several processes being involved in DNA damage in cells.

Food and the prevention of cancer

The link between diet and cancer is complicated, and scientists have not yet unravelled the exact mechanisms involved. This is because diets are made up of different foods containing many nutrients that interact in different ways in individuals.

Nutrition scientists need to study very large groups of people over many years to give us more specific answers to how and what foods increase the risk of cancer. These studies are ongoing, but the World Cancer Research Fund has examined all the existing evidence.

It has produced recommendations on food, nutrition and physical activity to help reduce the risk of cancer, based on current scientific evidence.

Achieve and maintain a healthy weight

Aim to stay in the healthy body mass index range of 18.5kg/m2 to 25kg/m2.

Excess body fat is a particular risk factor for cancer of the oesophagus, pancreas, colon, rectum, endometrium and kidney, as well as postmenopausal breast cancer.

Cut calorie by reducing dietary fat and eating plenty of fruit and vegetables, and foods rich in fibre. Avoid sugary drinks and keep a check on portion sizes.

Develop regular physical activity habits

Aim for at least 30 minutes of moderate activity a day, then build up to either 60 minutes of moderate activity or 30 minutes of intense activity every day.

Activity not only helps protect against weight gain but also decreases the risk of colon cancer and possibly endometrium and postmenopausal breast cancer.

Moderate activity should raise your heart rate and breathing, but not make you completely breathless and unable to talk. Examples of moderate activity include brisk walking, gardening and dancing. Examples of intense activity include jogging and swimming.

Moderate alcohol intake

Men should not exceed two drinks a day and women no more than one. Check up on the risks of alcohol and find out about sensible drinking limits.

Over the past few years, research has shown alcohol increases the risk of cancer, especially of the breast and colon.

Limit intake of red meat and avoid processed meat

Try to eat no more than 500g (18oz) each week and have very little, if any, processed meat such as bacon and salami.

Red meat is an important source of nutrients, especially iron, but we only need to eat red meat in modest amounts, probably no more than two to three times a week.

Eat foods that mostly come from plants

This means eating more fruit, vegetables and unrefined cereal foods and pulses, as they are mostly rich in fibre, low in calories and packed with the nutrients that lower the risk of cancer.

Limit consumption of salty foods

Salt and salt-preserved foods are linked to an increased risk of stomach cancer. Avoid salty snacks and don’t add salt at the dinner table or during cooking – use herbs and spices to flavour food instead.

Use supplements wisely

Following the principles of healthy eating should provide most individuals with the nutrients they need to minimise the risk of cancer. There’s no good evidence to show supplements will protect the general population from cancer. Some studies have shown beneficial effects of supplements in groups of people who have a high risk of developing certain cancers, but these findings can’t be applied to the general population.

Cancer patients and dietIf you’ve been diagnosed with cancer, it’s vital you continue to eat well during treatment, as it will help you to

• cope with your treatment
• withstand infections
• reduce the risk of nutritional deficiencies
• generally improve your quality of life

 

Maintaining a good dietary intake can be challenging because tumour growth can increase energy needs. Also, physical symptoms such as difficulty swallowing, sore mouth, taste changes, nausea, vomiting or diarrhoea make it difficult to eat well and maintain a good weight.

Ask to see a dietitian if you’re struggling to eat well – you’ll receive support and specific advice for maintaining your nutritional intake. Some of these practical solutions may also be helpful:

• Try to regain any weight lost during acute treatment periods
• Keep ready-meals in the freezer for when you’re too tired to cook
• Eat regularly – keep nutritious snacks to hand
• Add an extra dash of olive oil in cooking or on salads and don’t worry too much about sugar intake
• Try a glass of wine to stimulate your appetite

Alternative diets for cancer prevention and treatment

There are many so-called anti-cancer diets that claim to prevent or even cure cancer. They often recommend excluding whole groups of foods or eating only a few specific foods. These diets are not supported by robust scientific evidence and tend to be based on anecdotal reports of success, so be wary of those that:

• suggest excessive food restrictions
• are based on eating raw foods only
• recommend single large doses of supplements

The right nutrition can not only enhance physical activity and athletic performance but also aid recovery from training.

How many people follow these diets?

Many individuals exercise at different levels. Recommendations for competitive sport are very specialised but individuals who are ‘exercising’ rather than training regularly can get all the nutrients they need from following a balanced diet.

As well as carbohydrate for energy and some protein for muscles, vitamins and minerals play an important role in helping your body to function properly. For example, a lack of calcium and magnesium may lead to muscle cramps. A good iron status is important to prevent exercise-induced anaemia. A varied, well-balanced diet that includes all the major food groups will normally ensure an adequate intake of vitamins and minerals (see the eatwell plate).

EnergyDepending on the duration and intensity of the exercise you do, your body needs some extra energy. The amount of additional calories required will also vary greatly depending on your body size, age, gender and external factors such as climate, ground or air resistance. For example, male Tour de France cyclists may need up to 7,000 calories a day. However, an average man weighing 70kg would only need about 350 calories when jogging for 30 minutes or 400 calories for swimming (3km/h) for 30 minutes.

Which nutrients are best for providing energy?Muscles use two main fuels – carbohydrate and fat. Carbohydrates provide rapidly available energy and are therefore the most important energy source for short, intense exercise like sprinting. When exercising at full capacity, the energy requirement is so great and needed so quickly, that only carbohydrates can produce energy fast enough. The body stores limited amounts of carbohydrates – enough for approximately 20 to 30 minutes of moderate exercise. After this, if fat can’t be converted to energy during high intensity exercise, the body becomes fatigued.

The body can use fat for supplying energy during longer periods of exercise at a more moderate pace. For those people exercising to help lose weight, it’s best to exercise for longer periods at a moderate level to burn fat, ie walking or jogging for longer than 30 minutes.

Whatever the intensity of the exercise, some carbohydrates are always used, and it’s important to replenish stores before the next session. It‘s best to top up carbohydrates straight after exercising by eating bananas or drinking high-energy fruit juice-water mixes or sport drinks.

‘Carbo-loading’Athletes preparing for competition sometimes follow a ‘carbo-loading’ diet, which increases carbohydrate stores and their availability during an event. This can improve sports performance for these athletes and delay the onset of fatigue. Exercise time can be increased by 50 per cent following carbo-loading, which is extremely important for endurance athletes. However, these extreme diets are only suitable for serious athletes and should only be used with advice from a qualified coach or sports nutritionist.

Fluid intakeFluid intake is extremely important for exercise to prevent dehydration and to compensate for the loss in minerals and carbohydrates. Fluids should be consumed before and during long periods of exercise so choose a drink that you like and that satisfies your needs.

Water is not the best choice. Salts will be lost during sweating and it’s important to replace these. The addition of carbohydrate also provides fuel for the muscles, although too many carbohydrates are not good either.

Isotonic drinks can be used for refuelling as they contain an ideal amount of carbohydrates. For rehydrating, hypotonic drinks are ideal as they also provide the body with a lot of fluid. Plan ahead what you will drink during exercise and drink small amounts regularly.

Alcohol should be avoided when exercising and in the days leading up to a period of prolonged exercise as these beverages may lead to dehydration.

Top Tips

• Carefully plan the amount of food and fluids, the number of meals, and the timing of meals (before, during and after exercise) to get the most out of your performance.
• The intensity, duration, mode of exercise, level of conditioning, and how efficiently you move all influence how many calories you’ll need.
• Start re-fuelling as soon as you can after training as the muscles’ capacity to refuel is greatest over the first hour after training.
• If you have high energy needs don’t restrict yourself to traditional mealtimes – eat smaller but more frequent meals, plus several snacks.
• Take a positive interest in food. Take care in planning meals and choosing and preparing food. Enjoy your food!