For a lot of us, fibre is thought of as that cardboard-tasting powder your nanna sprinkles on her cereal, or wholemeal bread your dad tried to make you eat as a kid. It is well known that fibre is good for you, but it is poorly understood why. Yes, it has something to do with the bowels, and yes, it comes from whole grains, fruit and veg. Let’s try to deepen our understanding of fibre, past the basics.
What is Fibre?
Fibre is a carbohydrate. It consists of long strands of glucose, arranged in a way that the body’s digestive enzymes are unable to break down. Fibres’ resistance to digestion is due to how to it is organised in the grain, or, the way glucose is chemically bonded to itself. Either way, your enzymes are unable to breakdown the long strands into molecules small enough for the body to absorb. Unlike other nutrients, fibre moves through the gastro-intestinal system un-digested and un-absorbed until it reaches the large intestine. Here, gut bacteria ferment fibre into by-products that are healthful and absorbed.
Where is it found?
Nuts, fruit, vegetables and whole grains are all good sources of fibre. Fibre makes up the cell wall of plants as cellulose and hemi-cellulose. This fraction of fibre makes up the structural component of fruit, vegetables and nuts, giving apples and carrots their signature crunch. Liquefying fruits and vegetables, in the form of juice and smoothies’ break down these structural carbohydrates, reducing fibre content. In whole grains, fibre is found in the outer coating of the grain. This is known as the bran or seed coat. Not only does it contain fibre, but it also protects carbohydrates deeper within the grain from digestion. This is known as resistant starch which is a type of fibre. Note that in whole grains where the bran has been removed, ground down and then recombined with the remainder of the grain, deeper carbohydrates are exposed, no longer protected from digestion. Furthermore, fibre within the bran has been at least partially broken down. Hence, decreasing fibre content of the food.
What does it do?
Fibre makes it all the way to the intestine intact, as a long chain molecule. Here, insoluble fibre (found in cereals, nuts and the skin of fruit and vegetables) exerts a pressure that draws water in the intestine. This stretches the walls of your bowel, stimulating rhythmic contractions that propel the mass through your system and out the end. The results in more frequent and regular defecation, offering relief to those suffering constipation and reducing the risk of diverticulitis and other bowel diseases.
Unlike non-fibrous foods that are easily and quickly digested, fibre offers a slow and gradual delivery of glucose to the blood. The pancreas and liver are responsible for maintaining blood glucose levels within acceptable levels. A slow, gradual delivery of glucose to the blood stream makes the liver and pancreases’ job very easy. Decreasing the strain on these organs helps prevent type 2 diabetes. Therefore, to avoid type 2 diabetes, consume a diet high in fibre and pair it with regular exercise. Furthermore, a slow delivery of glucose prolongs the sensation of fullness after eating. In this respect, fibre has a role to play in the fight against obesity.
Soluble fibre (found in fruit, vegetables, oats and legumes) also aids in satiation. It slows gastric emptying by forming a gelatinous mass with fluid in the stomach. This further sustains the sensation of fullness after a meal. Hence, reducing the risk of over-eating.
Beta-glucan is a special type of soluble fibre found primarily in oats. It has unique blood cholesterol lowering capabilities. B-glucan binds bile and dietary cholesterol, promoting their excretion, which helps lower cholesterol. Bile, without the presence of B-glucan, is reabsorbed by the body. In the presence of B-glucan, the body needs to make new bile to replace what is excreted. To achieve this, the body removes cholesterol from the blood and incorporates it into new bile. Therefore, a transfer of cholesterol from the blood to the bile occurs. Hence, plasma cholesterol is lowered. Through this mechanism, a diet high in oats is conducive to better health.
We already know that fibre travels to the large intestine, undigested. Here, gut bacteria ferment the fibre to produce by-products that are extremely healthful e.g. butyrate. The type of bacteria that ferment fibre is the type of bacteria we want to stick around. By feeding such bacteria, we can ensure the good bacteria not only survive, but thrive. A healthy gut bacteria profile is associated with a variety of health benefits, with more and more links to health being discovered with further research. Currently, it is understood a healthy microbiome is associated with better mental health, decreased inflammation and decreased risk of cancer.
Fibre cannot be under-estimated. Its health benefits are wide-spread and multi-factorial. We could all benefit from incorporating more fibre into our daily diet. Choose a diet high in whole grains, fruits, vegetables, and nuts to reap the health benefits of this super nutrient.