Organisms Added to Milk

Question: Until I read in your column that sweet acidophilus milk is of no value to individuals with lactose intolerance, I had never even heard of it. Later I noticed it in my supermarket and wondered what it is. Can you tell me?

Answer: Sweet acidophilus milk is basically a low-fat, pasteurized milk to which lactic acidophilus organisms are added. Like any organism used to sour milk, lactic acidophilus does it by converting the milk sugar, or lactose, into lactic acid. The resulting milk has a tart, unpleasantly sour taste.

Several years ago, Dr. Marvin Speck at North Carolina State University at Raleigh discovered that by growing the microorganisms outside the milk and then adding them, he could produce milk heavily stocked with these bacteria, which tasted sweet as long as it was kept cool. Thus was born sweet acidophilus milk.

Why would anyone want to consume this vast supply of microorganisms? The idea dates back to Elie Metchnikoff, the Russian Nobel Prize winner who suggested in 1908 that milk fermented with lactobacilli is beneficial to health, and that the longevity of Bulgarian peasants could be explained by their consumption of large amounts of lactic acid-rich, fermented dairy foods.

But does this milk actually promote good health? Numerous technical problems make it difficult to demonstrate clear advantages to humans. In the case of benefits related to gastrointestinal disorders, it is hard to define the "normal bacterial flora," and to decide whether the sample obtained is representative, since microbial populations along the gut vary widely. There is also great variability both in individuals and among groups.

These and other obstacles make it uncertain whether the bacteria in question can inhibit the growth of disease-causing and food-spoiling organisms in the intestine, or restore the normal bacterial population to the human intestine after it has been disrupted by prolonged antibiotic therapy.

Any possible relationship to lowered cancer risk remains similarly cloudy. In recent studies, the activity of fecal enzymes associated with an increased risk of bowel cancer was reduced by giving lactic-acid bacteria to humans eating a mixed diet. When the feedings were discontinued, enzyme activity returned to the original level. In laboratory animals, lactic cultures have been shown to cut the incidence of chemically induced tumors.

But it is important to point out that no cancer-causing organism has yet been identified, nor do we understand the significance of lowering bacterial-enzyme activity. So although the matter is under scientific investigation, so far no clear benefits may be attributed to sweet acidophilus milk.

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