Lactose is the main sugar found in mammalian milk. Lactose intolerance is characterised by a deficiency of the lactose digesting enzyme, lactase, that normally hydrolyses the glycosidic bond in lactose to produce galactose and glucose. Following digestion by lactase, these two sugars are then absorbed to the circulation where the glucose contributes to blood sugar and the galactose is sent to the liver for conversion to glucose. Most people in the World are lactose intolerant, losing their lactose digesting ability shortly after being weaned. Consumption of lactose without the necessary lactase enzyme results in fermentation of the lactose in the colon by gut bacteria and this leads to the production of hydrogen gas which causes bloating and discomfort. Only those of white origin in Western nations retain the lactase digesting enzyme into adulthood, and being able to consume dairy products throughout life is not the norm. As a result of their lactose intolerance, the vast majority of the World can only consume fermented dairy products.
Fermentation of dairy products by bacteria reduces the lactose content and this prevents the gastrointestinal symptoms. In addition, some fermented dairy products possess inherent β-galactosidase enzyme activity because this enzyme is present in the bacteria used for fermentation. Evidence suggests that this enzyme survives the acid environment of the stomach and is able to allow some small intestinal digestion of the lactose in lactose deficient individuals. Researchers have used measurements of breath hydrogen to assess the digestibility of fermented dairy products in lactose intolerant individuals. In one such study1, researchers fed lactose intolerant subjects either pasteurised yoghurt, cultured milk (buttermilk) or sweet acidophilus milk. Of the foods tested, the pasteurised yoghurt was the only product that enhanced the digestion of lactose, as measured by a hydrogen breath test. In fact eight of the nine subjects reported no gastrointestinal discomfort when consuming pasteurised yoghurt.
These results are interesting because pasteurisation kills the bacteria within the yoghurt and removes the lactase activity. In previous studies by the same authors, unpasteurised yoghurt did not cause large increases in breath hydrogen, however, in this study the use of pasteurised yoghurt elevated breath hydrogen somewhat. This suggests that other factors within the yoghurt are beneficial at preventing gastrointestinal distress, and the unique tolerance of yoghurt by lactase deficient individuals is not dependent on its inherent lactase activity. Such factors were tentatively suggested by the authors of this study to include the effects of the yoghurt on the stomach emptying rates, organic products of the bacteria present in the yoghurt which may interact with the intestine and slight nuances in the gases produced during fermentation in the gut of the subjects. It is also possible that it is not the total gas production is not the overriding factor in discomfort, but the rate of gas production. Whatever the reason, yoghurt is well tolerated by lactase intolerant individuals.
Dr Robert Barrington’s Nutritional Recommendation: Yoghurt appears unique amongst dairy products in that although it contains lactose, it is tolerated by lactose intolerant individuals. Lactase tablets and pre-digested dairy products such as milk are available, but studies show they are inferior to yoghurt in terms of preventing the symptoms of lactose malabsorption.
RdB
