Almost half the world's peoples, including an estimated 40 per cent to 70 per cent of black Americans, suffer digestive distress of one sort or another if they drink milk or eat cheese, ice cream or any other dairy product.

According to Massachusetts Institute of Technology nutritionist Paul Newberne, it is impossible to arrive at an accurate estimate of the number of persons who suffer from lactose intolerance -- the failure of the digestive system to produce enough lactase, the enzyme that digests lactose, "milk sugar."

What is known is that those persons suffering from the condition, many of whom live on protein deficient diets, are deprived of one of the best, cheapest, forms of natural protein.

Newberne has just completed a study at MIT that may make it possible, perhaps in the next few months, for persons suffering from lactose intolerance to drink milk.

". . . there is now a reasonably economical supply of lactase and it will be possible to provide it to people who need it, so it can be added to milk, in the near future," said Newberne.

Those particularly affected by lactose intolerance include western Africans, Indochinese, Malaysians, Japanese and Chinese -- when did you last see a dairy dish on a Chinese menu, which may list more than 100 dishes?

Most Caucasians have little trouble digesting lactose, but according to Newberne, "even in the Caucasian population there is considerable evidence that a reasonably large segment" -- particularly among the elderly -- "has some problem with lactose intolerance. But these data are generally taken from epidemiological studies (studies of disease and its spread) and are not all that accurate.

There are studies currently under way, said Newberne, some sponsored by the World Health Organization and some by the Dairy Council, attempting to determine the exact extent of lactose intolerance.

"One who has this problem and learns that it is related to milk quite clearly is going to avoid milk," said Newberne. 'People who need this as a source of protein lose it as a good source of food." This would include many poor black children who spend their milk money for soda, because the milk makes them sick.

Those who suffer from the condition "don't digest (lactose), they don't break it down and it stays in the GI (gastrointestinal) tract. Then two things happen," said Newberne. "One, the lactose molocule attracts water so it holds water in the gut or draws it back from the body tissue.

"Secondly, lactose stays in the gut and passes on down to the lower tract" where it interferes with normal breakdown of food stuffs and causes stomach rumblings, gas and diarrhea said Newberne.

There seem to be two basic causes of the intolerance, he said, one genetic and one related to the normal aging process.

The genetic problem is that some people simply aren't able to produce the normal levels of lactase, the enzyme that digests lactose.

"Another (cause) is not understood at all, but there seems to be with age a loss of enzyme activity, so from adolescence into adulthood there seems to be a slow decline of lactose tolerance in some people," said Newberne.

The condition does not seem to affect infants born to lactose intolerant mothers, he said, because there appear to be sufficient amounts of the enzyme in almost all infants. There are some infants, however, unable to digest milk for other reasons.

"We have to find out whether or not school age children can drink and digest an 8-ounce glass of milk without running into problems," said Newberne. "He said, "most of the data we have is from studies of adults."

Trying to determine exactly what causes the genetic intolerance to lactose is a bit like attempting to answer the proverbial question: which came first, the chicken or the egg?

In most of those areas where people are lactose intolerant, cattle are unknown as a source of food. They are not milked, and are only eaten when they become useless as draft animals.

In western Africa, for example, many cattle are lost to sleeping sickness carried by the tsetse fly. The majority of American blacks are descended from western Africans, and scientists believe that is why such a large proportion of them are also lactose intolerant.

The question arises, if western Africans were able to raise cattle, and then began drinking milk, would they over generations develop a tolerance for lactose?

While that question may never be answered fully, nor the problem solved, Newberne contends he has found a relatively simple way to allow the lactose intolerant to drink milk.

Lactase, he explained, can be derived from a common, easily grown form of yeast "That is generally regarded as safe."

Newberne and his associates conducted a three-month study in which 180 rats were given 100 times the amount of the yeast-derived lactase a human would be expected to consume, and according to Newberne, there were not side effects.

"The question arises, since this is a food additive, is the Food and Drug Administration going to generally consider it as safe, or are they going to require elaborate human and animal testing?" Newberne asks.

Newberne said that the lactase produced from yeast already is being marketed in some parts of Europe by a European drug firm. All one who is lactose intolerant has to do, he said, is add some of the lactase to a glass of milk before drinking it.

If the FDA requires more elaborate testing, it could be an unpredictably long time before the product is marketed here.

"But if there are no FDA problems, I see it within a few months," said Newberne.