Lactose is the main sugar in mammalian milk. It is a disaccharide composed of a molecule of glucose bound to a molecule of galactose. Digestion of the lactose sugar in milk requires the presence of the enzyme lactase, which cleaves the glucose and galactose at the glycosidic bond. The glucose and galactose are then absorbed, with the galactose being converted to glucose in the liver. Most infants possess the ability to synthesis the lactase enzyme in order to allow consumption of their mother’s milk. However, the vast majority of the World’s human adult population is lactose intolerant, which means that they are unable to synthesise the lactase enzyme. This is because during adolescence, the ability to synthesise lactase declines, and only a relatively small percentage of the total population are able to digest lactose into adulthood. Those individuals that remain able to digest lactose are located mainly in Western countries such as Australian, Western Europe, The United States and Canada.
Lactose malabsorption therefore affects most of the World’s population. In general this is not problematic because the traditional diets of most populations reflect this lactose malabsorption and milk in its unfermented form is not a large part of the diet. However, some Westerners do not retain the ability to digest lactose and these people may find it difficult to adapt to diets devoid of milk because of its widespread use in Western nations. If those with lactose intolerance consume milk, the undigested lactose passes to the colon, where the gut bacteria ferment the sugars, producing hydrogen gas. It is this gas production that causes the bloating and intestinal discomfort associated with milk malabsorbers who consume milk. Fermentation of the milk into yoghurt is effective at allowing correct digestion of milk products in lactose malabsorbers. The reason for this is not clear, but may relate to the presence of bacterial lactase in yoghurt.
The effects of various fibres have also been tested for their effects at improving the symptoms of lactose malabsorption. In one study1, investigators assessed the ability of cellulose, pectin and psyllium fibre to reduce the symptoms of lactose malabsorption as measured by a hydrogen breath test (a measure of the degree of fermentation of lactose in the colon). Addition of psyllium to a lactose solution and milk significantly reduced the amount of hydrogen produced in breath and symptoms experienced compared to a control drink. Pectin provided some benefits when added to a solution of lactose, but cellulose showed no benefits when added to either a lactose solution or milk. The authors then assessed if the gastric emptying rate was the reason for the improvement in symptoms. The addition of cellulose and psyllium to the liquid test meal reduce gastric emptying rates, but pectin did not. Therefore the beneficial effects of the fibre were likely not related to changes in gastric emptying, but occurred by some other mechanism.
Dr Robert Barrington’s Nutritional Recommendation: In this study the addition of psyllium fibre to a lactose solution or milk drink was beneficial at reducing the amount of hydrogen in the breath and the symptoms of lactose malabsorption in the subjects. The effects of the fibre on the gastric emptying rate did not match the reductions in symptoms seen in the subjects suggesting that gastric emptying is not the reason for the effects. One alternative is that the fibre slows the passage of the lactose to the colon in the small intestine. However, whatever the mechanism these result suggest that psyllium fibre may be a useful tool for those with lactose malabsorption in order to reduce the symptoms derived from the over consumption of lactose.
RdB
