Food and nutrients that may affect breast cancer risk

Dietary factors may be protective against breast cancer or increase risk. These factors may take a long period of time to exert their effects. Diets are made up of the following components.

1. Fats

Fats have many essential functions in the body and help with the absorption of vitamins.

Some studies suggest a higher intake of polyunsaturated fats reduces breast cancer risk and a higher intake of trans fatty acids, saturated fats, and dietary cholesterol may increase risk (see table 1) (1, 2).

A diet high in fat can lead to obesity, which significantly increases breast cancer risk in postmenopausal women and men (3).

Although it contains the highest calorie content of all nutrients, consuming some fat is part of a healthy diet.

Tips

A diet that includes essential unsaturated fats, which cannot be made by your body, helps maintain healthy cholesterol levels.

Less than 30% of your total energy intake should come from fats.

Choose food containing a high content of unsaturated fats, avoid saturated fats, and limit your intake of trans fats.

Try to replace saturated fats with unsaturated ones (4).

Table 1: Types of fats and where they are found

* Unsaturated fats have one or more double or triple bonds and are usually liquid at room temperature. Saturated fats have single bonds only; they are “saturated” with hydrogen and usually solid at room temperature.  Trans fats are unsaturated fatty acids that contain at least one double bond in the trans configuration and are made artificially using heat and pressure which adds hydrogen to vegetable oil.

2. Carbohydrates and glycaemic index

Carbohydrates provide your body with our primary energy source. Carbohydrates may be simple e.g. glucose or sucrose (table sugar), or complex e.g. starch (found in foods like potatoes, legumes, tubers, fruits, and seeds), which need to be broken down before they can be absorbed (5).

It is unclear whether there’s a link between breast cancer and a diet high in sucrose or other carbohydrates, although some studies suggest there may be (6, 7, 8).

However, there is increasing evidence that a diet high in fibre reduces breast cancer risk (9).

Consuming too much sugar can promote weight gain, and being overweight increases breast cancer in men and post-menopausal women (3).

Tips

Consume higher amounts of complex carbohydrates, which allow you to stay full for longer and help you maintain a healthy weight.

Eat around 30g of fibre/day, found in whole-grain foods, fruit, and vegetables, especially pulses such as lentils.

Fruit and, to a lesser extent, vegetables contain simple carbohydrates (e.g. fructose), but also vital vitamins, as well as fibre, so make these part of your five-a-day.

Soft drinks, biscuits, and cakes high in simple carbohydrates, provide lots of energy with little nutritional value. Try to have these less often, in moderation.

3. Fruit and vegetables

A diet high in fruit and vegetables may help reduce the risk of breast cancer.

In particular, high quantities of non-starchy vegetables (see table 2) decrease the risk of oestrogen receptor-negative (ER-) breast cancer; and consuming plenty of food high in carotenoids (orange pigments found in certain fruits and vegetables) decreases breast cancer risk (10).

Tips

No single fruit or vegetable provides all the nutrients you need to be healthy, so you should eat plenty of different varieties every day.

Eat at least three portions of non-starchy vegetables and two portions of fruit (in total 400g) each day.

Put special emphasis on vegetables high in carotenoids.

Vegetables, with their usual high water and low sugar content, are a great low-calorie substantial dish and can help to control body weight.

Fruit usually has more calories than vegetables, so eat more vegetables than fruit.

Vegetables should be steamed or lightly fried in olive oil at low temperatures rather than deep-fried.

Table 2: Vegetables and fruits

4. Red and processed meat consumption

Some studies suggest processed meat (e.g. ham, sausages, bacon, tinned meat) slightly increases breast cancer risk (2, 11).

Although red meat is a good source of protein, high consumption can be unhealthy. Some studies suggest increased red meat consumption may increase breast cancer risk, but evidence remains inconclusive (12, 13).

Tips

Avoid processed meat or consume small quantities infrequently.

Try to limit intake of red meat to no more than about three portions – 350–500g (12–18oz) cooked meat per week.

Consider replacing red meat with organic poultry, sustainably sourced fish, or non-meat protein such as soybeans, nuts, eggs, tofu, or mycoprotein (a meat substitute).

A vegetarian diet can be healthy but make sure you are getting enough protein, vitamins, and minerals from food such as yogurt, eggs, lentils, or beans and omega-3-fatty-acids from foods such as salmon, chia seeds, or flaxseed oil.

5. Dairy and Calcium

There is some evidence that dairy products (milk, cottage cheese, yogurt), which contain high levels of calcium, might be beneficial in reducing the risk of pre-menopausal breast cancer (2, 14).

Probiotics (live microorganisms) and products of fermentation found in yogurt or kefir may also be beneficial in helping to reduce breast cancer risk (15).

Tips

Choose natural products with no added sugar, e.g. (organic) natural yogurt, cottage cheese, and reduced-fat milk. These contain high-quality protein and lots of calcium, zinc, and iodine as well as vitamins B₂, B₁₂, A, and D.

Yoghurt also contains beneficial bacterial cultures, making it a source of probiotics that are beneficial for gut health.

Avoid sweetened yogurts, and milk drinks, as they are high in calories and contain large amounts of sugar.

6. Soy

Currently, it is unclear if a soy-rich diet might protect healthy women against breast cancer, although quite a few studies suggest it may (16, 17).

The soybean is a legume rich in isoflavones, compounds that have properties that can be both protective and cancer-promoting. There is no convincing evidence that the consumption of soy increases risk (18).

Moderate consumption of soy (one to two portions of soy food per day) is generally considered positive for our health.

Soybeans are easily digested and a good source of unsaturated fats, plant-based protein, B vitamins, iron, calcium, zinc, and other compounds beneficial to your health (19).

Tips

Choose natural soy products such as tofu, (natural) soy yoghurt, and tempeh (fermented soybeans). They are often low in fat as well as high in protein.

Certain highly processed soy products contain high fat and salt content and numerous additives. Choose those with lower fat, salt, and additives. Seek medical advice before taking isoflavone supplements.

7. Micronutrients and supplements

Micronutrients are vitamins and minerals needed by the body in very small amounts (20).

Although some studies have found a protective effect for breast cancer of certain micronutrients (e.g. vitamin D₃, folate, vitamin B₆) (21, 22), there is a lack of high-quality scientific evidence that demonstrates nutritional supplements reduce breast cancer risk.

Low levels of vitamin D are correlated with an increased risk of breast cancer (23). The World Cancer Research Fund recommends meeting nutrient needs exclusively through food and does not recommend supplements for cancer prevention (24).

The Harvard School of Public Health lists five specific situations in which it might be useful to take multivitamin tablets; for example, if you are on a strict diet or have a very low appetite (25).

Tips

Your main source of vitamin D is sunlight, but you can also find it naturally present in foods, for example, oily fish such as salmon or supplements.

8. Alcohol

Drinking alcohol is a serious risk factor for breast cancer (see also our key facts sheet on alcohol and breast cancer risk).

The more you drink the greater the risk with no lower limit.

UK government guidelines recommend drinking less than 14 units of alcohol (e.g. 6 glasses of wine) per week and limiting the amount you drink on any one occasion.

Tips

To reduce breast cancer risk even more we recommend not drinking or drinking as little as possible (23).

Which diet is the right one for breast cancer prevention?

There is no ideal diet for breast cancer prevention. However, a diet high in fruit and non-starchy vegetables has been shown to reduce breast cancer risk. A balanced, diet with moderate calorie intake is important.

We also recommend organic fruit and vegetables if possible. Many diets can be healthy and help reduce risk. For example, studies suggest the Mediterranean diet reduces the risk of breast cancer, as compared to a more traditional Western-style diet with a higher intake of meat.

A Mediterranean diet is high in vegetables, fruits, nuts, beans, cereals, grains, fish, and unsaturated fats such as olive oil and includes only a small amount of meat (26, 27).

For more prevention advice and tips visit our Prevention Hub.