How can intestinal health problems be prevented in babies and adults? Can increased fibre intake in our body alleviate stomach upsets? Paul Clayton explains how dietary fibre affects the digestive system.
Ever since Dr. Kellogg launched his breakfast cereals, a daily intake of dietary fibre has been considered a good thing. It is known that it helps to prevent constipation, haemorrhoids, diverticulosis and varicose veins. It is also common knowledge that some fibres can help to smooth out blood sugar levels in diabetes. And although the experts are still not in complete agreement, there is a reasonable amount of evidence that increasing the fibre in our diet will help to reduce the risk of heart disease, bowel cancer, and possibly even breast cancer.
But there is a problem with fibre that has caused a great deal of confusion and disagreement, among scientists as well as among the public. Until very recently, nobody could agree on what fibre actually was. It is now generally agreed that there are at least six types of fibre — more according to experts — which all have different properties, are handled differently in the body, and which all make a different contribution to our health. Some work within the gut, others have important effects elsewhere in the body. Until recently, only two types were used in medicine. These are the insoluble fibres which occur in bran, for example, and which are used to treat constipation. Then there are the soluble fibres in gums such as guar gum, which are used to slow down the absorption of sugar from the gut in diabetics. Both these fibre types are hardly broken down in the gut at all, and pass through the body basically unchanged. However, the emphasis is now switching to another type of fibre that is broken down in the body. This may seem a strange concept, because most people believe that dietary fibre by definition is indigestible. Nevertheless these new fibres are resistant to our digestive enzymes, but they are broken down by enzymes produced by bacteria that live in the colon. These fibres are knows as non-digestible oligosaccharides or pre-biotics.
A New Kind Of Fibre
The large bowel, which is where the majority of gastrointestinal cancer occurs, is full of four to five hundred different species of bacteria, known as the intestinal flora. Some of these can cause serious illness, while others are associated with positive health. Ever since the beginning of this century, doctors have experimented with different diets in an attempt to modify the gastrointestinal flora, and push it in a 'healthy' direction, without much success.
There are at least two types of health promoting bacteria, the lactobacilli and the bifidobacteria. Some of these are found in live yoghurt, and various scientists and nutritionists have used yoghurt to try to change the flora of the lower bowel. However, the bacteria have limited shelf-life, even when freeze-dried, and many of them are unable to survive the acid condition in the stomach. Even if the bacteria do arrive in the colon, they have to compete with the dense population of hostile bacteria that are already there. As long as one eats a daily helping of live yoghurt, some lactobacilli and bifidobacteria remain in the gut, but they disappear almost immediately when the yoghurt diet stops.
Pre-biotics have none of these disadvantages. They are stable, safe and have a long lasting effect on the gut flora. They encourage the growth of 'healthy' bacteria and put a check on other bacteria which can cause disease by overgrowth or by producing toxins. The two main types of natural pre-biotics are inulin and oligo-fructose. The general rule is that the fresher the vegetable, the higher its inulin content. When plants such as onions are stored for long periods of time, and particularly in cold or cool storage, their pre-biotic content declines dramatically. A low intake of pre-biotics leads to increased numbers of disease-causing bacteria in the gut —; which could be the cause of many gastrointestinal and other health complaints.
How Pre-biotics Work
Unlike most sugars and starches, pre-biotics cannot be digested and they pass into the colon intact. Once there, they act as a growth enhancer for the health promoting lactobacilli and bifidobacteria. As the 'good' bacteria multiply, they secrete enzymes, which break down pre-biotics into acids such as acetic and butyric acid. These inhibit the growth of disease-causing bacteria. The 'good' bacteria also secrete antibiotic substances, which restrain the 'unhealthy' bugs including most of those responsible for food poisoning. As a result, the balance of the flora of the gut tips in a healthy direction. The flourishing lactobacilli and bifidobacteria in the gut join gastric acid, the digestive enzymes and the immune system in 'crowding' out disease-causing bacteria.
Babies And Pre-biotics
Bifidobacteria are particularly important in the new-born, whose immune defences are not yet fully working. Breast milk contains substances which promote the growth of bifidobacteria, which is why these bacteria represent up to 95 per cent of the bacteria in the gut of breast-fed infants, but a mere 25 per cent in bottle-fed infants. This explains why breast-fed babies are more resistant to stomach upsets and diarrhoea. Recent studies show that live yoghurt cultures fed to infants significantly reduce their risk of contracting diarrhoea.
Fibre For The Heart
When reading the contents list on a carton of yoghurt one can see it contains significant amounts of thiamine, riboflavin and other vitamins. This is due to the fact that the lactobacilli and bifidobacteria make B vitamins, and are probably the major species of bacteria in the colon, which are able to do this. Vitamin B depletion is surprisingly common in the developed countries, and low B levels are a major risk factor for coronary artery disease. So pre-biotics, by increasing the good bacteria in the gut and vitamin B, will be cardioprotective by lowering homocysteine, and simultaneously raising HDL levels. This is one way in which oats and inulin contribute to a healthy heart, although LDL cholesterol reduction also plays a role.
Short chain pre-biotics (FOS) are rapidly fermented, stimulating the production of bifidobacteria in the proximal colon. As they grow they bind the bile acids present in this part of the gut and remove them from the body. This lowers LDL cholesterol levels and confers additional cardio-protection. The combination of bifidogenesis and bile acid binding is also likely to be cancer protective, especially if FOS is combined with long chain pre-biotics.
Long chain pre-biotics (i.e. inulin) are slowly fermented, stimulating bifidogenesis further down the gut in the lower colon and rectum. This is the main site of bowel cancer, and bifidogenesis here probably confers significant protection important against this type of tumour.
Bone Health And Dietary Fibre
Bifidobacteria produce vitamin K, which is essential for bone growth and repair. At the same time they help with the absorption of calcium and magnesium from food. These are two powerful anti-osteoporosis effects. Contrary to previous medical opinion, calcium is now known to be absorbed in the colon. One of the reasons why calcium in milk is better absorbed than from chalk-type supplements is because milk contains substances which promote bifidobacteria, which in turn boost the absorption of the calcium in the colon.
Excerpted from Health Defence by Dr Paul Clayton PhD
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