eat smart

Mike Lean believes if your gut instinct is to eat yoghurt, go ahead

UNTIL the Seventies, yoghurt was virtually unknown in Britain. I used to eat it as a child, in Switzerland and knew it by the Arabic/ French term, yaourt.

Now millions of yoghurt tubs are consumed each day in the UK in its natural form alone, with cereals and fruit at breakfast, as a snack or as dessert, and with salads or main courses, such as raita with cucumbers on curries.

Just as yoghurt was rare in Britain, milk was scarce in Mediterranean and particularly Eastern countries. Their cows made cheese and yoghurt.

There are many practical reasons to prefer yoghurt in these parts. Milk goes off more rapidly and can harbour pathogenic (food poisoning) bacteria. Yoghurt is made by heating milk, to sterilise it, then infecting it with a pure strain of safe bacteria which breeds rapidly and prevents other contamination. So it keeps better, and helps avoid food poisoning, as long as the culture is living.

When the bacteria (lactobacillus acidophillus, bifidus or bulgaricus) grow to make yoghurt, they do so by fermenting the normal milk sugar, lactose, into absorbable products. This gives yoghurt its sharp refreshing taste. It also makes the yoghurt digestible and safe for people with lactase deficiency, who cannot tolerate the lactose in milk.

We are all born with the enzyme lactase in our small intestine, to digest lactose human milk. It falls away with age (reminding us that milk is primarily a food for baby cows) but enough remains in most European guts to digest quite large amounts of milk.

Adults from Eastern countries have, for genetic reasons, much lower levels of lactase, and so lactose intolerance, rather than milk intolerance is really the normal state. Yoghurt-making seems to have developed as a natural solution to allow adults to benefit from the calcium, proteins and other nutrients in milk.

Lactase drops rapidly during bowel upsets, so "secondary lactose intolerance" can occur for a time, and yoghurt may be useful in this instance There are many unsubstantiated health claims (such as longevity), but more plausible is the suggestion that yoghurts top up the normal bowel flora with safe bacteria.

This is the principle behind "pro-biotic" foods, now a major food industry. Bacteria firstly may modify a food to make it more nutritionally valuable, by fermenting out unwanted nutrients, or by synthesising vitamins; secondly they colonise the gut to help suppress unwanted bacteria.

Probiotics have been used extensively in the cattle and poultry industries to reduce infections, such as salmonella, but still largely lack evidence for benefit in humans.

Hi-tech micro-encapsulation may be necessary to avoid destruction by stomach acid. The variety of "new" health claims is bewildering, but there is plenty to be said for natural, living yoghurt. It is even easy to make in the comfort of your own home.

Mike Lean is Professor of Human Nutrition at the University of Glasgow

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