The vast majority of the adult population of the World is lactose intolerant. Humans tend to lose their ability to digest lactose as they are weaned onto solid food and as a result cannot digest cow’s milk. Interestingly, it is only those populations that are mainly of European descent that have maintained their ability to digest lactose into adult life, including Western Europeans, Australasians, North Americans and white South Africans. In most of the World then, lactose intolerance is the norm, whereas within ‘Western’ populations lactose intolerance is quite rare. Avoidance of milk is an obvious solution to the problem of lactose intolerance and this can be an effective strategy for those most affected with severe lactose intolerance. However, in reality, lactose intolerant individuals can usually digest some milk. This is because although lactose intolerant individuals are reported to not possess any lactase enzyme in the brush border of the small intestine, they do in fact retain some residual activity.
While avoidance of milk by those with lactose intolerance appears at first sight to be an effective solution, dairy products including milk are an important source of calcium. An increased prevalence of osteoporosis amongst those with lactose intolerance has been reported, but the reason for this association is not fully understood. If it is due to the lower intakes of calcium in this group of individuals then alternative sources of calcium or alternative strategies need to be implemented to ensure optimal calcium intakes. Calcium supplements might seem beneficial in this regard, but generally people do not reliably take dietary supplements. Yoghurt may be a suitable alternative to milk because it is partially fermented and so contains lower amounts of lactose, and also because the bacterial cultures it contains produce the β-galactosidase enzyme. For the consumption of yoghurt to be an effective strategy the bacteria must be in live cultures, or at least partially intact. This provides active forms of the enzyme to the gut and allows the digestion of lactose.
Because yoghurt could be an alternative source of calcium for those with lactose intolerance, researchers have investigated the calcium absorption from yoghurt compared to milk. In one study1, subjects were given 147.5 grams of yoghurt containing 270 mg calcium or 250 grams of milk containing an equivalent amount of calcium spaced two weeks apart. The calcium absorption was measured by use of radioactive calcium (45C) at 8 μCi (micro Curies) and blood radioactivity was assessed over 24 hours. The results showed that lactase deficient and healthy controls absorbed calcium equally well from both milk and yoghurt. Further the lactase deficient subjects absorbed calcium equally well as the healthy controls. Yoghurt therefore remains an excellent source of calcium and those with lactose intolerance could use yoghurt as an alternative source of calcium if milk is to be avoided in the diet. Combining milk with yoghurt would also provide adequate calcium with the added bonus of allowing better digestion of the milk component.
The use of lactase tablets has also been shown to be an effective way to prevent the symptoms associated with lactose intolerance. Tablets are widely available and contain enzymes capable of digesting lactose. Tablets can be added directly to milk to pre-digest the lactose to glucose and galactose, which sweetens the milk somewhat due to the sweeter taste of glucose and galactose compared with lactose. In this regard cow’s milk becomes more similar to the sweeter goats milk. However, there are discordant results seen between studies investigating the use of lactase tablets and this likely relates to the fact that lactose digesting enzymes from different organisms (yeast or bacteria) can show different efficiencies at hydrolysing lactose2. In addition, the residual lactase activity present in some individuals with lactose intolerance may affect results from studies. Anecdotal evidence supports the contention that lactase tablets may provide increase lactose hydrolysis for some time, perhaps days, although this has not been researched scientifically.
RdB
