If there is one aspect to nutrition that I think is underrated..it is fibre. Fibre can come in many different forms but essentially it is the indigestible part of plant foods, such as vegetables, fruits, grains, beans, legumes, nuts and seeds. Fibre is structured in a way that it passes relatively unchanged through the digestive tract because it is resistant to digestion and absorption in the stomach and small intestine, which is what allows it to have the beneficial effects that it does on our health.
Benefits of fibre:
Gut health: As mentioned, fibre passes through the stomach and small intestine unchanged, and when it reaches the large intestine it is metabolised/fermented by the bacteria present there and forms short chain fatty acids and other metabolites. These acids provide fuel for the cells in the large intestine, improve the integrity of our gut lining and can stimulate the growth of further bacteria. Basically fibre is food for our gut bugs and is what allows them to thrive. Studies have indicated that diets low in fibre can actually lead to bacteria eating the mucosal layer of our gut lining (because it is starved off fibre) and this can lead to ‘leaky gut’ or permeability in the gut barrier where toxins and undigested food can pass in and out - not ideal! Hence my concern around the paleo and keto movements where fibre sources are limited - definitely not the best diets for gut health.
Cardiovascular and bowel health: There are different types of fibre and each has been shown to have positive effects on cardiovascular and bowel health. For example, soluble fibres have been shown to lower blood cholesterol and blood glucose levels, and insoluble fibre has been shown to decrease intestinal transit time, reducing the risk of constipation and diverticulitis and colon cancer.
Satiety and weight management: fibre helps to keep us feeling full without extensive energy intake. Certain types of fibre can absorb water and expand in the GI tract which is believed to give us a feeling of fullness and hence, we are less likely to overeat and gain weight. In contrast, refined carbohydrates which have little to no fibre can be eaten in much higher quantities until we feel full.
Types of fibre:
Soluble Fibre – Includes pectins, gums and mucilage which come from fruits, vegetables, legumes, plant seeds and plant extracts. This type of fibre is soluble in water and forms a gel like material. This helps to slow down the food moving in our digestive systems and also the emptying process which helps us stay fuller for longer. The best sources of soluble fibre are fruits, vegetables, oat bran, barley, seed husks, flaxseed, psyllium, dried beans, lentils, peas and soy.
Insoluble Fibre – This includes cellulose, hemicelluloses and lignins from the plant wall. This type of fibre is not soluble so instead it absorbs water to help soften the contents of our bowels and support regular bowel movements. Insoluble fibre is found in wholegrain breads and cereals, nuts, seeds and the skin of fruits and vegetables, hence why you should leave those skins on!
Prebiotics: are molecules that resist digestion and fermented in the large intestine, stimulating the growth of bacteria. Food sources include bananas, Jerusalem artichokes, oats, wheat, barley, garlic, flaxseeds, legumes, and green vegetables. Resistant starch is a particular type of prebiotic and is found in lentils, peas, beans, oats, barley, cashews, green bananas, cooked and cooled potatoes and al dente (slightly undercooked) pasta and rice.
How much fibre do we need:
The recommendations are 25g/day for females, 30g/day for males, 28g/day for pregnancy and 30g/day for lactation. To show you an example of how much fibre is in particular foods (total fibre in 100g):
Wholegrain bread: 7-8g
Wholegrain pasta: 6g
Brown rice: 2g
Sweet Potato: 3g
Variety of fibre is important!
Something I talk about a lot is food diversity and having a diverse range of fibre sources in your diet is really important. For example, bananas contain resistant starch but apples are a good source of pectin so including both is ideal. The more types of fibre we have, the more diverse bacteria composition we have which is most beneficial for gut health. If you only have certain types of fibre in your diet and this fiber is a highly fermentable type of fibre, it can result in unpleasant side effects such as gas, bloating, and diarrhea.
So hopefully this article has encouraged you to include more fibre sources in your diet, but do note that if you significantly increase your fibre intake you may experience some gas, bloating or bowel movement changes initially - this is normal and can it just take a while for your body to adjust (if it continues it is best to see a practitioner). Always ensure you are consuming lots of water when increasing or regularly consuming good amounts of fibre.