Bowel Cancer Prevention

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Overview -
copied directly from the Cancer Research page :

What we know about diet and bowel cancer:
Researchers think that more than 4 out of 10 cancers (40%) could be prevented by lifestyle changes, such as eating a healthy balanced diet and keeping active. Diet is a difficult area of research because we all eat such a range of different foods in such different amounts.

No single diet can guarantee you won't get bowel cancer. But changing your diet could help to reduce your risk of cancer in general, as well as improving your overall health.

If you have been diagnosed with bowel cancer, your dietary needs may be different because of your illness or treatment. If you have bowel cancer and are concerned about your diet, ask your doctor to refer you to a dietician.

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Fibre and bowel cancer
(again copied directly from the Cancer Research site, linked in the title)

Fibre is found mostly in fruit, vegetables and cereals, including flour and bread. A lot of research has looked at fibre and bowel cancer.

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 protects against bowel cancer. More than 8 separate 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, such as fruit, vegetables and cereals, and not fibre supplements or foods with artificially added fibre.

In November 2011 a large meta analysis looked at fibre and bowel cancer risk. It included 25 studies and the findings supported the EPIC study. In people who had a high intake of dietary fibre, in particular cereal fibre and whole grains, there was a lower risk of colorectal cancer.

So, fibre is recommended as part of a healthy diet. It can help to prevent other chronic diseases such as heart disease and diabetes. It is not clear whether the protective effect against bowel cancer is due to fibre itself or to other protective properties of fruit, vegetables and cereals. Another possible explanation is that people who eat a high fibre diet also tend to have less food in their diets that increase the risk, such as red and processed meat.

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 help 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 bowel cancer risk.

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Meat and Fish
(again copied directly from the Cancer Research site, linked in the title)

There is strong evidence that eating a lot of red meat and processed meats increases bowel cancer risk. In 2011, it was estimated that around 1 in 5 bowel cancers were linked to eating these types of meat. Red meats include lamb, pork, veal and beef. Processed meats include sausages, salami, ham, bacon, paté and tinned meat.

Poultry meats, such as chicken and turkey, probably don't increase your risk of bowel cancer.

Results from the EPIC study showed that people who eat fish at least every other day on average, lower their risk of bowel cancer by about a third compared to people eating fish about once a fortnight. Other studies show that the more fish people eat, the lower their risk of bowel cancer. But a review by the World Cancer Research Fund (WCRF) 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.

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, but studies have not linked them specifically to bowel cancer.

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Fruit and Vegetables
(again copied directly from the Cancer Research site, linked in the title)

Eating more fruit and vegetables may lower the risk of bowel cancer, according to results from the EPIC study. But the evidence is not conclusive.

A meta analysis in 2011 found that increasing fruit or vegetable intake from very low levels up to about 100 to 200 grams a day reduced bowel cancer risk by about 10%. But there was no further reduction in risk with higher amounts of fruit and vegetables.

Fruit and vegetables may be protective because they contain vitamins and minerals. Researchers think that antioxidant vitamins and minerals help prevent cell damage that 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 their fibre content. Diets higher in fruit and vegetables tend to be lower in meat and fat. We do not really know whether it is the fibre or the antioxidant vitamins that make the most difference.

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. We don't know whether these help to prevent bowel cancer.

The World Cancer Research Fund report in 2010 concluded that garlic probably protects against bowel cancer. But more studies are needed.

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Alcohol and Smoking
(again copied directly from the Cancer Research site, linked in the title)


Alcohol increases the risk of bowel cancer. It has been estimated that about 11% of bowel cancers are linked to drinking alcohol.

A 2011 systematic review showed a 21% increase for both colon and rectal cancers with an alcohol intake of around 1.6 to 6.2 UK units a day, compared to non drinkers or occasional drinkers. 1.6 units is less than one standard glass of red wine or around half a pint of beer. The risk increases further if you drink more than this.

Several large reviews of research into smoking and bowel cancer show that smoking also increases bowel cancer risk. It seems to have a greater effect on rectal cancer risk than colon cancer risk.

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Dairy / Calcium / Vitamin D  
(again copied directly from the Cancer Research site, linked in the title)

Calcium may protect against bowel cancer, according to the World Cancer Research Fund. A 2004 meta analysis showed that people with the highest levels of calcium intake (from food and supplements) reduced their risk of bowel cancer by 22% compared to people with the lowest calcium intake. However 2 meta analyses in 2010 found that calcium supplements had no effect on bowel cancer risk in the general population. But they did find a link between calcium intake and a reduced risk of polyps coming back in the bowel after previous treatment. Polyps are growths in the bowel that may develop into cancer over a long period of time, if left untreated.

To reduce bowel cancer risk, it may be better to take vitamin D and calcium together. We need vitamin D to be able to absorb calcium. A large randomised controlled trial in 2006 showed that only the people with high intakes of both calcium and vitamin D had a reduced risk of bowel cancer. Other studies have shown that people with the highest intakes of vitamin D have a lower risk of bowel cancer and bowel polyps.

There is some evidence that drinking milk reduces the risk of bowel cancer. A review in 2011 showed that the benefit of dairy in reducing bowel cancer risk was only seen at levels over 100 grams (g) a day. Having 500 to 800g milk a day reduced bowel cancer risk by 20 to 30%. One pint, or 0.5 litres, of semi skimmed milk weighs about 550g. The effect of milk on lowering bowel cancer risk may be partly due to the calcium. But milk contains many other substances which may also play a role.

There is limited evidence that eating cheese may increase the risk of bowel cancer. It is not clear how cheese may increase the risk, but it may have something to do with the saturated fatty acids.

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Obesity and Exercise  
(again copied directly from the Cancer Research site, linked in the title)

There is a strong link between obesity and cancer of the large bowel (colon cancer), especially in men. Body mass index (BMI) is a better measure of obesity than just your weight as it links weight and height.

Compared to men of a healthy bodyweight, overweight men (with a body mass index of 25 or higher) have a 25% increase colon cancer risk. 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.

People who are more physically active are at lower risk of colon cancer. But being active appears to have no effect on the risk of developing rectal cancer.