Dietary fibre has many effects on the body, especially on digestion and the composition of the microorganisms in your gut.
More and more studies show that a diet high in fibre is linked to a decreased breast cancer risk.
Fibre may help prevent breast cancer through several mechanisms. It could prevent the reabsorption of oestrogens from the gut into the blood (long-term exposure to oestrogen exposure is a well-established risk factor for breast cancer); it could bind oestrogen and thus increase faecal excretion (release more oestrogen from the body through faeces); and it could help to reduce the risk of becoming overweight or obese.
The British Nutrition Foundation recommends that the average adult consumes at least 30g of fibre daily.
A varied diet rich in fibre, such as the Mediterranean diet – which includes high consumption of whole grains – supports a diverse and stable gut microbiome (the total population of gut microorganisms) and contributes significantly to gut health.
Fibre is a type of carbohydrate that your body cannot digest. 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.
There are two types of fibre, soluble and insoluble. Each has important health benefits and plays a different role in the body.
Soluble fibre dissolves in water and forms a gel-like substance in your stomach, slowing digestion. It may help control your blood sugar and cholesterol. It is found in apples, oats, peas, beans, brussels sprouts, and avocados.
Insoluble fibre does not dissolve in water. It adds bulk to the stool and appears to help food pass quickly through the stomach and intestines. Insoluble fibre is found in whole wheat flour, bran, nuts, seeds, and the edible skins of many fruits and vegetables.
Various vegetables and legumes, e.g., artichokes, beans, soybeans and chickpeas, nuts and seeds (for example, ground linseed with 24 g fibre per 100 g), have a high fibre content. Whole grains and products made from them, such as bread, pasta, and bran, are also rich in fibre. Cooked wholemeal pasta provides about 5 g of dietary fibre per 100 g, while cooked white pasta made from durum wheat semolina provides only about 2 g per 100 g. Other sources of dietary fibre include sweet peppers, carrots, broccoli, rhubarb, mushrooms, berries and pears.
Dietary fibre affects your body in many ways, most notably digestion, but it is also associated with preventive health effects. For example, it influences the transit time of food in your digestive system, the mass and consistency of your stool, the frequency of bowel emptying, how hungry or full you feel, and how your body absorbs nutrients.
Dietary fibre also serves as “prebiotics”, which are special plant fibres that help healthy bacteria grow in your gut. The fermentation of prebiotics produces short-chain fatty acids. They act as an energy source for the cells in the intestine and promote mucus formation. At the same time, they strengthen the intestinal barrier and positively affect blood sugar and fat metabolism and appetite regulation. Eating enough fibre helps good microorganisms in your gut grow.
Increased dietary fibre intake also shows protective effects on conditions like heart disease or strokes and diabetes, obesity, cholesterol concentrations, hypertension and colorectal cancer.
Getting fibre from different food sources, such as cereals, fruit and vegetables, is important for maximum health benefits.
Many observational studies, including one umbrella review, among the highest evidence currently available in science, find high fibre consumption associated with a decreased breast cancer risk.
High fibre consumption may also play a role in survival after a breast cancer diagnosis. A 2021 systematic review and meta-analysis of several studies concluded that a higher dietary fibre intake decreases the risk of dying after a breast cancer diagnosis.
Many actions in the body may explain how dietary fibre might reduce the risk of breast cancer. Some of these include preventing oestrogen reabsorption from the gut into the blood. Long-term exposure to oestrogen is a well-established risk factor for breast cancer. They promote the making of short-chain fatty acids, which can have a protective effect against tumour development—gathering oestrogens in the colon and increasing their excretion and preventing overweight and obesity, which is an established risk factor for postmenopausal breast cancer.
For more information on fibre and breast cancer, see our science review.
For more prevention tips, visit our Prevention Hub.
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