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Diet causing cancer

Nurse and patients talking about cancer

This page tells you about how diet can affect your risk of getting cancer. There is information about

 

Diet, cancer risk and research

Our diets are made up of hundreds of different types of food, containing thousands of nutrients and chemicals. Some of these protect us against cancer, while others increase risk. We all eat different things in different amounts, which confuses the picture even more. As well as that, there are more than 200 types of cancer. So trying to find out how diet affects cancer risk is extremely complicated.

A review of how lifestyle affects your risk of developing cancer was published in 2011. This review included diet. It found that around 1 out of 10 cancers (10%) may be linked to diet. Over half of these were caused by eating less than 5 portions of fruit and vegetables a day. Other factors include eating too much red meat, not eating enough fibre and eating too much salt.

An international research study is going on at the moment across Europe to try to answer more questions about diet and cancer. The study, called EPIC, involves 500,000 people in 10 countries. EPIC stands for European Prospective Investigation into Cancer and Nutrition. Over many years, the researchers are recording people's food intake, monitoring their health records, and noting who gets cancer and who doesn't. Then they may be able to link certain factors in the diet with the risk of getting particular cancers. It is the largest study into diet and cancer ever carried out.

The results of EPIC could have huge implications for the prevention of cancer. To start with, the researchers are looking into common cancers such as breast, lung, bowel, prostate and stomach cancer. But the size of this study means that researchers will also be able to look into the possible role of diet in rarer cancers. 

The results of the study will have implications for cancer prevention everywhere. The results will be presented at international conferences and published in journals available to researchers and health officials throughout the world. The results already available helped to inform the Cancer Research UK study looking into lifestyle factors.

 

Being overweight

There is information about how to work out the right weight for you on this website. It is measured by comparing your weight with your height.

Overweight or obese people have an increased risk of bowel cancer and pancreatic cancer and this could be because they tend to have higher insulin levels.

Obese means being more than about 25% overweight. Obesity can also increase your risk of

  • Oesophageal cancer, kidney cancer and gallbladder cancer
  • Breast or uterine (womb) cancer if you are a woman

Researchers are not sure exactly why obesity increases the risk of these cancers. Breast cancer is hormone linked. Its development is affected by amounts of the sex hormones oestrogen and testosterone. Fatty tissue produces an enzyme called aromatase. Aromatase affects the balance between these hormones and this may explain why being obese affects your risk of breast cancer.

Although obesity increases breast cancer risk if you are post menopausal, it lowers breast cancer risk if you are pre menopausal. But the risk of breast cancer increases strongly with age, and being obese increases the risk of several cancers as well as other diseases. So it is important to maintain a healthy body weight throughout your life.

 

Alcohol and cancer

We now know that alcohol can increase your risk of a number of cancers. A review in 2011 by Cancer Research UK suggests that around 4 out of 100 cancers (4%) are linked to alcohol. It increases the risk of mouth cancer, liver cancer, breast cancer, bowel cancer, and throat cancer, which includes pharyngeal cancer, laryngeal cancer and cancer of the food pipe (oesophagus).

Even moderate alcohol intake increases your risk of cancer. A recent UK study showed that women who drink 1 or 2 drinks a day have a slightly increased risk of cancer.

 

Foods that might be protective

There has been a lot of interest in whether eating certain foods might reduce the risk of certain types of cancer. Despite a great deal of research, we haven't found any convincing links.

There is some evidence that eating plenty of fruit and vegetables can protect against cancer. The evidence is strongest for cancers of the upper digestive system, such as the mouth, food pipe (oesophagus) and stomach.

Fruit and vegetables contain a wide variety of nutrients and are high in fibre. Scientists are working to find out about which of these nutrients protect against cancer. So far they are fairly sure that vitamins A and C, and folate play an important role in protecting against cancer. It's a complicated picture, but as far as we know, it is not enough to take vitamin supplements. You have to eat the fruit and vegetables. There is something about eating fresh, vitamin rich foods, that is protective.

Bowel cancer is less common in people who eat lots of fibre. One EPIC study showed that people who ate the most fibre had a 40% lower risk of bowel cancer than those who ate the least. A review of 25 studies in 2011 also found that people who eat a lot of fibre in their diet (particularly from whole grains and cereals) had a lower risk of bowel cancer.

 

Foods that might increase risk

It is also possible that other foods and nutrients might increase risk. Again it has proved difficult to show any firm links, apart from alcohol. The strongest evidence we have is probably for high intakes of red or processed meat increasing risk.

Bowel and stomach cancer are more common in people who eat lots of red and processed meat. Red meat includes all fresh, minced and frozen beef, pork, lamb or veal. Processed meats have been preserved in some way other than freezing and include bacon, ham, salami, sausages, spam, corned beef, black pudding, pâté and tinned meat.

The way you cook meat may increase cancer risk. Certain chemicals are made when red and processed meats are cooked at high temperatures, such as on a barbeque. These chemicals can damage our cells, making them more likely to become cancerous.

There are other aspects of diet where the evidence is much less clear. Some studies have shown that milk may reduce bowel cancer risk. This may be partly due to the calcium in milk. But other research shows that diets high in calcium and dairy proteins may increase the risk of prostate cancer. It is too early to be sure.

 

Food additives and cancer

Many different substances are added to commercially prepared foods. But these are not all bad. Some additives stop food from going off and so can help to keep us healthy. A good example of this is a toxin called aflatoxin that comes from a mould. It grows on stored food in hot and humid countries, especially on peanuts. Aflatoxin is known to help cause liver cancer so anything that stops the mould from getting into the nuts is helping to prevent cancer.

Most additives are not thought to affect cancer risk. Colours, flavours and sweeteners are constantly investigated by researchers and if any are thought to be a real risk, they are withdrawn. Sometimes there is a scare about a particular additive.

Some years ago saccharin was claimed to be a carcinogen. Researchers had found that when it was fed to rats in huge quantities, the rates of cancer in the rats increased. We are very unlikely to eat that much saccharin and so it is unlikely to cause cancer in people, but far fewer foods contain it now than did a few years ago.

Other additives can be a cancer risk. Pickled foods may increase risk of cancer of the stomach, particularly if they are very salty. This may explain why there are such high rates of stomach cancer in Japan, where salty, pickled foods are popular.

 

Contaminants

This means chemicals in foods or drinks that are not meant to be there. For example, they could form as an unwanted effect of the manufacturing process.

Nitrosamines are chemicals found in cured meats (bacon and ham, for example) and in very small amounts in beer. Nitrosamines have been shown to be carcinogenic so the amount in foods has been cut as much as possible. In brewing, one cause of nitrosamines is a reaction between pollution in the atmosphere and the malted barley that is a main ingredient of the beer. The brewing industry has tried to cut the levels of nitrosamines in beer as much as possible. Levels are now much lower than they used to be, but it hasn't been possible to get rid of them completely.

Smoking and barbecuing foods so that they are slightly burnt on the outside causes chemicals called polycyclic aromatic hydrocarbons to form. These chemicals are known to help cause cancer. So in theory barbecuing or cooking meat and fish over a high heat could increase cancer risk. But few research studies have shown this.

Frying and baking meat at high temperatures can also create chemicals called heterocyclic amines. These may increase the risk of some cancers such as cancer of the food pipe (oesophagus), but this isn't certain. Acrylamide, another chemical that may cause cancer, has been found in foods such as crisps and chips. But there isn't proof yet that these chemicals cause cancer in humans and so there are no grounds for telling people to change cooking or eating habits because of these chemicals.

 

A healthy diet

Apart from obesity and alcohol, there isn't much specific evidence at the moment that diet can reduce cancer risk. But a healthy diet may help and it will also lower your risk of other diseases, such as heart disease. To eat healthily

  • Eat less red meat and animal fats (butter, cream, cheese)
  • Eat at least 5 portions of raw or lightly cooked fruit and vegetables every day (see below for examples)
  • Eat more fibre
  • Eat more oily fish (eg salmon, trout, mackerel)
  • Eat less salt and salty foods
  • Eat less sugar and sugary foods
  • Eat more whole grain cereals and bread, brown rice and pulses
  • Don't fry foods and if you use fats in cooking, choose vegetable oils or olive oil not lard or butter
  • Drink less alcohol

Examples of a portion of fruit or veg include an apple, pear, orange or banana, about 5cm of cucumber, a medium tomato, a handful of grapes or strawberries, 3 tablespoons of vegetables, or a heaped tablespoon of dried fruit.

There is information about diet and healthy eating in the healthy living section of the Cancer Research UK website.

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Updated: 19 February 2014