Can a diet high in fibre reduce my breast cancer risk?

Fibre has long been suggested to lower the risk of developing various conditions and diseases, including heart disease, obesity, diabetes and constipation. But what about breast cancer – can eating a diet high in fibre reduce your risk of breast cancer?

What is fibre, and where is it found?

Fibre is a type of carbohydrate that your body cannot digest. Though most carbohydrates are broken down into sugar molecules called glucose, fibre cannot be broken down; instead, it passes through your body undigested. Dietary fibre occurs in its natural form, almost exclusively in plants. Sources of fibre include wholewheat pasta, wholegrain bread, oats, peas, beans and pulses, nuts and seeds and fruits.

Why does the body need fibre?

Fibre affects your body in several ways, most notably gut health. For example, it influences the time it takes your food to travel through your gut, the size and consistency of your stools, the frequency of your bowel emptying and controlling how hungry you feel. It is also associated with preventive health effects. For example, it may reduce the risk of coronary heart disease and stroke, as well as type 2 diabetes, obesity and cholesterol concentration.

Can eating a diet high in fibre reduce my breast cancer risk?

We looked at several observational studies (single studies and reviews summarising single studies) conducted over the last 13 years. They all suggest that an increased fibre intake may reduce the risk of breast cancer. For example, a 2018 umbrella review, which is among the highest levels of evidence currently available in medicine, looked at 19 different meta-analyses (an examination of data from several independent studies to determine overall trends) based on dietary surveys, which compared the highest vs lowest daily dietary fibre consumption on the incidence of developing breast cancer. The researchers concluded that women consuming the highest amounts of dietary fibre may benefit from a small reduction in the incidence of breast cancer.

Although these observational studies do not prove a protective effect (due to the nature of the study design), they do show an association between increased fibre intake and a decreased breast cancer risk. So eating whole grains more often is recommended because of the other many health benefits.

How could fibre reduce my risk?

Scientists have suggested different mechanisms for how fibre in your body could reduce the risk of breast cancer. For example, a high-fibre diet decreases activity in certain intestinal enzymes, leading to less oestrogen being absorbed in the colon. Oestrogen is a well-established risk factor for breast cancer. Dietary fibre can also promote the formation of short-chain fatty acids, especially butyrate, propionate, and acetate, which can have a protective effect against breast tumour development. It has also been proposed that dietary fibre can bind to oestrogens in the colon and increase their faecal excretion, releasing more oestrogen from your body. Lastly, a high intake of dietary fibre may also prevent weight gain. Being overweight or obese is an established risk factor for postmenopausal breast cancer.

How much fibre do you need?

The British Nutrition Foundation recommends 30g a day of fibre for adults in the UK. For children, the following recommendations apply 2–5-year-olds: 15g per day; 5–11-year-olds: 20g per day; 11–16-year-olds: 25g per day; 17 and over 30g per day. The average intake of UK adults is 20g of fibre per day. Eating dietary fibre from different sources, e.g., vegetables, cereals and beans, is recommended.

Tips to increase the amount of fibre you eat:

• Eat whole fruits instead of drinking fruit juices
• Replace white rice, bread, and pasta with bulgur and whole-grain products
• Choose a high-fibre breakfast cereal, for example, porridge with some fresh fruit
• Go for wholemeal bread. You can also try baking your own bread and trial versions that combine white and wholemeal flour as a start
• Cook with wholegrains like wholewheat pasta or bulgur wheat
• Snack on raw vegetables (e.g., red bell pepper, carrot sticks, and cucumber with houmous), whole fruit, nuts (without added salt) or dried fruits (without added sugar)
• Include plenty of vegetables with meals – either as a side dish/salad or added to sauces, stews or curries
• Keep a supply of frozen vegetables for quick meals
• Add pulses like beans, lentils, or chickpeas to stews, curries, and salads

For more fibre and breast cancer information, look at our fibre, the gut microbiome and breast cancer key facts sheet.

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