Pro-vitamins

Naturally-occurring substances such as beta carotene, which the body can convert into vitamins.

Proanthocyanidins (see Flavonoids)

Probiotics

Dietary supplements which provide bacteria and other factors to encourage a good balance of intestinal microflora. It has been estimated that over 400 bacterial species inhabit our digestive tract, amounting to three or more pounds in weight. Some of these species are 'symbiotic', or 'friendly', producing vitamins, short-chain fatty acids and other helpful substances, assisting bowel function, forming part of our immune defence system and preventing harmful species from taking up residence. Others are not so friendly. While not necessarily pathogenic (disease-causing) they are undesirable in large amounts because they produce endotoxins which can be absorbed into our bloodstream and significantly add to our toxic load.

Within a few days of birth, an infant's gastrointestinal tract is colonized by bacteria. Breast-feeding has been shown to favourably influence the balance of these bacteria. The main two types of friendly bacteria found in the gut are known as Lactobacillus acidophilus and Bifidobacteria; many probiotic supplements will provide a balance of these. In addition Lactobacillus bulgaricus and Streptococcus thermophilus are also friendly, and are found in some yoghurt cultures. Some examples of undesirable putrefactive bacteria commonly found in the gut are Clostridium and E coli. The yeast Candida albicans is also highly undesirable in large amounts.

Antibiotics. The friendly bacteria are much more easily destroyed by antibiotics than their more undesirable cousins, so probiotic or prebiotic (see below) supplements or the frequent consumption of live acidophilus yoghurt is often recommended to ensure that the friendly species are replaced during oral antibiotic or herbal antibacterial therapy, otherwise the gut may become overrun with undesirable species.

Sex hormones have an important relationship with the intestinal flora. Normally over 60 per cent of circulating oestrogen is excreted into the intestines through the bile, to be deconjugated by bacterial enzymes. Some of the oestrogen is reabsorbed and excreted in the urine. However, when antibiotics are used, oestrogen reabsorption drops, lower levels are found in the urine, and the quantity found in faeces may be up to 60 times greater than normal. Because of this excessive loss of oestrogen, antibiotics can lead to breakthrough bleeding in women.

A number of studies have shown that probiotic supplements are often a safe, effective treatment for infant diarrhoea.

Prebiotics: The friendly bacteria thrive on a type of fibre known as fructo-oligosaccharides (FOS), (also known as bifido growth factor (BGF) or vegetable inulin). This occurs naturally in certain vegetables such as jerusalem artichokes. When isolated and made into a commercial product, it has a sweet taste and dissolves in liquid. It can be used as a sugar substitute, although it is rather more expensive than sugar. Because the addition of FOS to the diet can result in a several-fold increase in friendly bacteria within a few days, these products are known as 'prebiotics'.

Quality assurance. It is best to purchase probiotic products from a manufacturer who gives certain quality assurance guarantees and has a known reputation for quality in this area, since product quality can be extremely variable. On testing, it is not unknown for some products to contain no viable friendly bacteria at all, because of poor manufacturing expertise, poor strain selection, or poor storage conditions. Probiotic products consist of delicate live organisms which require refrigeration or vacuum packing during storage. (Also see Dysbiosis).