Food types and bowel cancer

• A quick guide to what's on this page
• Fibre and bowel cancer
• Fruit, vegetables and bowel cancer
• Meat, fish, proteins and bowel cancer

• Fats and bowel cancer
• Body weight and bowel cancer
• Calcium and bowel cancer
• Alcohol and bowel cancer

Fibre is found mostly in fruit, vegetables and cereals (including flour and bread). A lot of research has looked at fibre and colorectal cancer. Until a few years ago there was quite consistent evidence that a diet high in fibre lowers the risk of bowel cancer. Then a few large studies reported that they did not find a protective effect from fibre intake. 

Recent research from the World Cancer Research Fund, including EPIC (the European study into the effect of diet on cancer risk), has suggested that fibre is likely to protect against bowel cancer. Information gathered from more than 100 studies showed that people who ate the most fibre had the lowest bowel cancer risk. And those who ate the least had the highest bowel cancer risk. The foods studied were all natural foods - fruit, vegetables and cereals - and not fibre supplements or foods with artificially added fibre.

Although the research results are not conclusive, intake of fibre is recommended as part of a healthy diet. This is because it probably does help protect against cancer - the evidence just isn't clear yet. And fibre intake can help to prevent other chronic diseases such as heart disease and diabetes. It is not clear whether the possible protective effect against bowel cancer is due to fibre itself or to other protective properties of fruit, vegetables and cereals that contain fibre. Another possible explanation is that people who eat a high fibre diet also tend to have a lower proportion of fat in their diets.

There are a couple of theories to explain the protective effect of fibre

• You need fibre to help waste products travel through the bowel
• Some types of fibre may reduce cancer risk by helping to carry bile acids that could potentially cause cancer through the bowel more quickly

People who do not eat enough fibre tend to be constipated. So any cancer causing agents are in contact with the bowel lining for longer and increase the risk of bowel cancer.

Eating more fruit and vegetables may lower the risk of bowel cancer at the lower end of the bowel whether you eat meat or not. But the evidence is not conclusive. Fruit and vegetables may be protective because they contain vitamins and minerals. Researchers think that antioxidant vitamins and minerals help prevent the cell damage which may lead to cells becoming cancerous. There is quite strong evidence that a diet rich in folate is linked to a lower risk of bowel cancer. Folate is a B vitamin found in green and leafy vegetables.

Fruit and vegetables may also be protective because of the fibre and lack of fat. Diets higher in fruit and vegetables tend to be lower in meat and fat. We do not really know whether it is this that makes the most difference or the antioxidant vitamin content.

If you take vitamin supplements instead of eating more fruit and vegetables, you miss out on the fibre and on other substances in plant foods that may help prevent cancers. These are called flavonoids, phyto-oestrogens and tannins. They have not been shown to specifically help prevent bowel cancer.

Protein foods are meats, fish, dairy foods and pulses (beans and lentils), soya products and tofu. There is reasonably consistent evidence that eating a lot of red meat (lamb, pork, veal and beef), particularly processed meat (sausages, salami, ham, bacon, paté, corned beef), could increase your risk of bowel cancer. Poultry meats, such as chicken and turkey, probably don't increase your risk of bowel cancer.

Recent results from the large European study (EPIC) showed that people who eat fish, at least every other day on average, lower their risk of bowel cancer by about a third compared with people eating a portion of fish about once a fortnight. Other studies have also found that the more fish people eat, the lower their risk of bowel cancer. But a review by the World Cancer Research Fund (WCRF) has found the results of these studies to be inconsistent. Fish might protect against bowel cancer because some types contain fats called long chain polyunsaturated fatty acids.

It is worth bearing in mind that cooking methods may increase the cancer risk of meat and fish. Foods cooked at very high temperatures can form chemicals called polycyclic hydrocarbons and aromatic amines. These chemicals are thought to increase cancer risk.

In some studies, diets that are high in fats have been linked with bowel cancer. But many researchers think this may be tied up with meat intake. Other researchers think that it is not fat that causes the problem so much as an unhealthy lifestyle in general. The studies have not generally looked at the different types of fats. But if you are trying to eat a healthier diet, it makes sense to use mainly monounsaturated and some polyunsaturated vegetable fats and to cut down on saturated animal fat.

There is a strong link between obesity and cancer of the large bowel (colon cancer), especially in men. Compared to men of a healthy bodyweight, overweight men (with a body mass index of 25 or higher) have a 25% increase in risk of colon cancer. Obese men (with a BMI of 30 or higher) have a 50% increased risk of colon cancer. There is a smaller risk increase for colon cancer in overweight and obese women. Body mass index (BMI) is a better measure of obesity than just your weight as it links weight and height. The link takes you to the glossary, which tells you how you can work out your BMI.

Calcium may protect against bowel cancer. The 2007 World Cancer Research Fund review of calcium and bowel cancer risk found that people with the highest amounts of calcium in their diets (over 1,300mg a day) had a lower risk of bowel cancer than people with the lowest amount (less than 500mg a day). But you only have to increase your calcium intake by a small amount and you will begin to lower your bowel cancer risk. Most of the calcium in our diets comes from milk and other dairy products. To give you some idea of how much calcium is in everyday foods

• A pint of milk has about 700mg
• A regular pot of plain, full fat yoghurt has about 300mg
• 100g of cheddar cheese (about 4oz) has about 700mg of calcium but also contains fats that can be harmful

Calcium may help because it prevents polyps from developing. Polyps are growths in the bowel that over a long period of time may develop into cancer. A research review in 2004 found that about 1g of calcium in your diet every day may help to prevent bowel polyps. You can read this review on dietary calcium in the Cochrane Library. It was written for researchers and specialists so it's not in plain English.

Researchers have brought together the results of several studies looking at alcohol intake and bowel cancer risk. The combined results show that you have a 40% increase in bowel cancer risk if you drink more than 5 units of alcohol a day on average. If you drink 3 to 4 units a day, there is a small increase in bowel cancer risk in both men and women.