Main food groups and breast cancer

There has been quite a lot of research into diet and breast cancer. Researchers have looked at fat in our diets, fibre, fruits and vegetables, as well as other dietary factors.

There has been a great deal of research about fat and breast cancer. We first thought that diets containing a lot of fat greatly increased the risk of breast cancer. In countries where people ate high fat diets, there was a higher rate of breast cancer. But we didn't know if this was due to the fat itself or to another risk factor that happened to be common in these countries.

Some older large studies found no link between total fat intake and risk of breast cancer. When several studies were looked at together, no important link was found with any particular type of fat. But the researchers from a large UK study (part of the European EPIC Study) wondered whether we weren't finding a link because of the way we ask people what they've eaten. They asked people to fill in detailed food diaries for 4 years and found that people who ate a lot of saturated fat had higher rates of breast cancer.

Another study, from October 2003, looked at many studies on fat and breast cancer and found a small increased risk of breast cancer in people who have a higher total fat intake. Saturated fat and high meat intake were also associated with a small but significant increased risk of breast cancer in this study.

The Women's Health Initiative is a trial running in the USA that is looking into whether eating less total fat and saturated fat, more whole grains and more fruit and veg will lower breast cancer risk. Results from this study in 2006 showed that women who ate a low fat diet had a slightly lower risk of breast cancer.

Since then, a very large American study has shown an increase in breast cancer risk for women who get more of the energy in their diet from fat. (In other words, a higher percentage of the calories in their diet came from fat.) But the risk increase was small. An overview study in 2009 also showed a higher risk of breast cancer in women who ate higher amounts of fat in their diet.

Based on the evidence we have, it appears that saturated fat does 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. The most sensible approach to reducing your risk is to follow general advice about choosing a healthier lifestyle. It will help to lower your risk of many chronic diseases, including cancer and heart disease if you

• Eat a healthier diet
• Stay at a healthy weight
• Don't smoke
• Cut down on alcohol
• Take more exercise

There is detailed information about eating a healthy diet in this section.

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. 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 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.

Protein foods are meats, fish, dairy foods and pulses (for example, beans, lentils, or dahl), soya and tofu. There is some evidence that eating a lot of red meat or fried meat increases the risk of breast cancer. But some studies show no increase in risk from eating these foods and so it probably doesn't play a large role.

It is better to eat white meat and fish instead of red meat, for a variety of health reasons. Lots of vegetable proteins, beans, lentils and soya may be the healthiest choice.

Fibre is found mostly in fruit, vegetables and wholemeal cereals (including flour and all kinds of bread, particularly whole grain). There is some evidence that diets containing more than 20g of fibre per day reduce the risk of breast cancer in pre-menopausal women. Fibre from cereals seems to have the most protective effect and fibre from fruit does not seem to make much difference.

Eating wheat bran fibre has been found to lower the levels of oestrogen in the blood in women who have not yet had their menopause. Lower levels of oestrogen may help to reduce the risk of breast cancer. Researchers aren't quite clear about why wheat fibre reduces oestrogen levels. It may not be an effect of the fibre itself. Instead it may be that high fibre diets contain less fat and more antioxidants than low fibre diets.

Although fruit and vegetables seem to reduce the risk of some types of cancer, research has not so far found much good evidence that a diet high in fruit and vegetables can reduce breast cancer risk. But a study in China in 2009 found that the people who ate the most fruit and vegetable in their diet had a lower risk of breast cancer. Individual types of vegetable and fruit groups such as dark green leafy vegetables, cruciferous vegetables (like cauliflower), carrots and tomatoes, banana, watermelon and papaya and cantaloupe all seemed to reduce cancer risk. It is not clear whether this lowering of risk also happens in other ethnic groups.

The Chinese study also seemed to show that vitamin A, carotene, vitamin C, vitamin E, and fibre may reduce the risk of breast cancer. There is some other evidence that the anti-oxidant vitamin A in fruit and vegetables may protect against breast cancer. This includes the plant substances it is made from - retinol and carotenoids, including lycopenes and beta-carotene. If you get enough vitamin A in your diet, taking extra doses is unlikely to reduce your risk. But taking too much vitamin A can be dangerous. It is not recommended that you take vitamin A supplements if you are expecting a baby.

Some studies seem to show that women who take high amounts of the B vitamins folic acid and B12, have a slightly reduced risk of breast cancer but other studies have not shown the same effect. So we need more studies before we can be sure of the effect of B vitamins on breast cancer risk.

Some other substances in plant foods may help to prevent cancers. Researchers have looked at flavenoids, plant oestrogens, (phyto-oestrogens), and tannins. There is detailed information about these diet compounds on our page about dietary factors and breast cancer.

If you do change your diet to include more fruit and vegetables, as well as more starchy carbohydrates, you will almost certainly eat less fat. So you will be more likely to keep your weight within a healthy range. This will help to reduce your risk of breast cancer.

Remember that some of the links with diet and breast cancer are not certain at the moment, so the best thing to do is to eat a generally healthier diet. It will not only help you keep to a healthy weight, but also help toprotect you from many other chronic health conditions such as diabetes, other cancers and heart disease.