Find out what we know about diet and how it might affect breast cancer risk.
Researchers estimate that we might be able to prevent as many as 9 out of every 100 cancer cases (9%) by changing our diets. But it is difficult to be exact about this. Research also suggests that about 5 out of 100 cancers (5%) could be avoided by maintaining a healthy body weight.
There has been a lot of research into the effect of dietary factors on the risk of breast cancer. So far most findings have been inconclusive and inconsistent. But there is some evidence for the following factors.
Fats include oils, butter and margarine as well as the fat in meats, fish and nuts. Remember there are also hidden fats in sweets, biscuits, cakes and other foods that you buy ready made.
An overview study has reported that women had an increased risk of breast cancer if they had more fats in their diet after the menopause. Another study has shown that women who ate higher levels of saturated fats had a higher risk of breast cancer compared to those eating lower levels.
Foods high in saturated fat include:
- fatty cuts of meat
- meat products, including sausages and pies
- butter, ghee and lard
- cheese, especially hard cheese
- cream, soured cream and ice cream
- some savoury snacks and chocolate products
- biscuits, cakes and pastries
Based on the evidence we have, it appears that saturated fats play a role in increasing breast cancer risk. But it is probably a combination of this as well as other things that causes breast cancer.
People who eat a lot of foods containing fish oils (marine omega-3 polyunsaturated fatty acids) seem to have a lower breast cancer risk than people who only eat small amounts.
There is no strong evidence of a direct link between sugars and carbohydrates and breast cancer. But a large study of Chinese women in the USA reported in 2009 that for women younger than 50 a high carbohydrate diet slightly increased the risk of developing breast cancer. High carbohydrate diets are linked to an increased risk of a type of breast cancer called oestrogen receptor negative breast cancer.
Eating too much sugar can make you put on weight and we know that being overweight increases the risk of breast cancer in post menopausal women.
Dairy products have been studied for their effect on breast cancer risk. Some recent studies have shown that premenopausal women with a high intake of dairy products have a lower risk of breast cancer. But we need results from more studies before we can be sure about this.
Dairy products are high in calcium, and several studies show a lower risk of breast cancer for women with high calcium intakes or calcium blood levels.
Fibre is found mostly in fruit, vegetables and whole meal cereals (including flour and all kinds of bread, particularly whole grain). There is some evidence that women who have a high fibre diet have a lower risk of breast cancer than women whose diets don’t have so much fibre.
Researchers aren't quite clear about why dietary fibre seems to reduce breast cancer risk. But it might be because wheat fibre reduces oestrogen levels. Or it might be that high fibre diets contain less fat and more antioxidants than low fibre diets.
An overview study found that women who ate more fruit had a lower risk of breast cancer. This may be due to the fibre and antioxidants that they contain. Anti oxidants are molecules that prevent a chemical process called oxidation, which occurs when oxygen molecules join with another chemical. Oxidation can cause gene damage in cells that may lead to cancer. Antioxidants include vitamins A, C and E and selenium.
If you change your diet to include more fruit and vegetables and more starchy carbohydrates, you will almost certainly eat less fat. So you will be more likely to keep your weight within a healthy range.
Scientists have been looking into whether eating soya foods or other phyto oestrogens could affect the risk of getting breast cancer.
Phyto oestrogens are chemicals found in plants (phyto means plant). So they can also be called plant oestrogens. They have a similar structure to the female sex hormone oestrogen.
There are different types of phyto oestrogens. Some are found in soya bean products (isoflavones). Others are found in the fibre of whole grains, fruit, vegetables and flax seed (lignans). Milk sometimes contains phyto oestrogens, depending on which plants the cows have been eating.
Soya in the diet
Soy (or soya) products such as tofu and soy milk are made from soybeans. They contain chemicals called isoflavones, which are plant-based oestrogens. They have a similar structure to human oestrogen and laboratory studies have shown that they can mimic the effects of oestrogen in the body. Scientists think this could reduce the risk of some cancers that depend on oestrogen to grow.
But in humans the effect of soy on the body is less clear. Some studies have shown that diets high in soy could reduce the risk of prostate cancer, but it’s not clear if this is really the case. There is no strong evidence for a link between soy and any other cancer type.
Many studies which look at the effect of soy on cancer risk take place in Asian countries, where people generally have more soy in their diets than in Western countries. This means that the results might not be relevant to people in the UK.
More studies are needed to understand if there is a link between soy and cancer.
Carotenoids are organic colourings (pigments) found in some plants. Foods that are good sources of carotenoids include carrots, sweet potatoes, spinach, kale, greens, papaya, bell peppers, and tomatoes. A summary of published studies has shown that women with higher levels of carotenoids in blood samples might have a lower risk of breast cancer.
Flavonols and flavones are substance found in plants and are also called flavonoids or bioflavonoids. Flavonols are found in high levels in:
- black tea, green tea and oolong tea
Flavones are found in:
- aromatic herbs (such as parsley)
- camomile tea
Studies have shown that people who have high levels of some flavonoids in their diet have a lower risk of breast cancer than people with lower levels.
A lot of research has looked into coffee drinking and cancer risk. Breast cancer is one of the cancers investigated. A recent analysis of 37 studies seemed to show that drinking coffee might slightly reduce breast cancer risk in post menopausal women.
Preventing breast cancer with diet
Read about what you can do to have a healthy diet and reduce the risk of cancer.
Researching diet and breast cancer
Researching diet and breast cancer is very difficult because we all eat such a range of different foods in such differing amounts. A large study called EPIC (the European Prospective Investigation into Cancer) is looking at the links between lifestyle and cancer. It involves around 520,000 people in 10 European countries.
EPIC is producing reports on diet and a variety of cancers and will continue over the next 10 to 20 years, including breast cancer. If you would like to keep up to date with the findings from the EPIC study you can look online at the EPIC website.