Fibre intake and health
Dietary fibre (also called roughage) is the part of your food that cannot be broken down by your own digestive enzymes. It consists of non-starch polysaccharides – inulins, lignins, pectins, beta-glucans, oligopolysaccharides and dextrins.
It is important to understand that the colourful Mediterranean Diet, or Rainbow Diet as we like to call it, is a naturally high fibre diet. That is one of its major qualities. All those vegetables, nuts, seeds and fruit could not be anything else.
And fibre has important health benefits.
Fibre consumption, immune response and inflammation
Fibre is ‘divided’ into soluble or insoluble fiber. Both are carbohydrate based but neither can be broken down by your normal personal digestive processes. However, your gut bacteria love them and feed off them, as long as the commensal bacteria (the good guys) are present in sufficient numbers.
Not surprisingly then, research has shown that a high fibre diet rapidly increases the numbers of good bacteria. And in turn this increases the immune system strength because about 85% of your immune response and immune memory, is produced in response to the bacteria in your microbiome.
Research has shown that people who consume the highest levels of soluble fibre have the strongest immune systems.
Examples of soluble fibre? Oats, vegetables, pulses, nuts and seeds, psyllium. The foods of the Rainbow Diet.
These foods are all ‘soluble’ in water and found in water pockets in the gut where they are viscous and form a gel much loved by commensal bacteria, which eat, thrive, grow and multiply. Hence you will hear the term ‘Prebiotics’.
Prebiotics are foods that feed ‘Probiotics’ (your bacteria).
The good and bad news – you can change the composition of your whole gut microbiome in just 24 hours. One day you can eat lots of bread and pasta containing gluten plus lots of cows’ dairy. The next you will have large numbers of bacteria in your gut, producing high levels of inflammatory compounds.
Alternatively you can have high soluble fibre days and 24 hours later know that you have made many more commensal bacteria that will be making anti-inflammatory molecules.
That’s life. You are what your gut bacteria eat!
Fibre consumption and cholesterol
Research shows that people who eat higher levels of soluble fibre tend to have lower levels of cholesterol. One of the main reasons is the gut bacteria. The fibre feeds them, they grow and multiply, and they make short-chain esters. Certain of these are short-chain fatty acids that can block the formation of cholesterol in the blood stream. Not surprisingly, people who consume more fibre tend to have less cardiovascular and heart disease.
Fibre consumption and weight loss
Most importantly, soluble fibre bulks up and makes you feel full. It also slows down the emptying process, so you feel fuller and eat less – and people who eat high soluble fibre diets tend to lose weight.
One study found that people who added more fibre to their diets felt fuller and lost more weight that people who went on ‘slimming diets’.
Fibre and glucose
A high fibre diet also reduces the level of plasma glucose, and people who indulge in high fibre diets live significantly longer than average. Weight loss can also be a benefit. One finding in the Human Microbiome Project was that we actually have a strain of Clostridium in our intestines which binds to fibre and helps clear excess glucose from our bodies. How clever is that; a protective bacterium. Unfortunately 5 days of antibiotics can make it extinct. Poor gut bacteria can equal poor sugar control and obesity.
All types of soluble fibre slow the digestion process, whereas only insoluble fibre helps move the waste through the intestines.
Fibrous cell membranes prevent the rapid release of sugar from the cells, but over-cooking destroys these cellulose membranes, which is why (for example) raw carrots have a very low Glycemic Index, but cooked carrots have a high GI – the sugar is much more readily available when the cell walls have been broken down. Whole brown rice is good for you but eating refined white rice is like eating neat sugar. Ditto pasta, breakfast cereals and various grains.
Glucose rushes can have two disastrous effects, for example glucose can directly feed (and even cause) cancer cells and high plasma glucose can heighten insulin levels, which in turn stimulate an enzyme (Cox-2) present throughout the body, causing chronic inflammation.
Dr. Chauncey Crandall and the UK’s Dr. Aseem Malhotra have both argued that without this glucose-insulin-inflammatory effect, arteries would not inflame and fat would not stick to them.
Soluble fibre seems to be able to bind to fats before they are absorbed, reducing plasma cholesterol levels.
Gut bacteria use fibre to bind chemicals, heavy metals and hormones to them, and then take them effectively out from the body.
Insoluble fibre moves through the gut unchanged. It cannot be attacked by your digestive enzymes. Its benefit is that it helps push your food remains through the gut. Many vegetables and fruits contain both soluble and insoluble fibre.
Examples of insoluble fibre? Bran (oat bran and wheat bran), beans (legumes, pulses), vegetables, whole grains.