Fibre-rich foods. Cereal grains have a high fibre content and are are found in muesli (bowl, lower centre), cereal bars (lower left) along with nuts and seeds from other plants. Cereal grains can be processed to form flakes (bowl, upper left). Bread is made from ground cereal grains, and can contain more fibre if unground parts are added back to the flour. Fibre is not digestible by humans, but it is an essential part of the diet as it helps keep a healthy muscle tone in the digestive tract. This helps food pass faster through the intestines, and so reduces contact with carcinogens that can lead to cancer.