Dr Kiran Thakur
Food intolerance is the buzzword among the scientific fraternity nowadays with researchers spending considerable time and resources to determine various types of food intolerances and their solutions. Lactose intolerance, one of the most common food intolerances, is estimated to affect about three quarters of the world’s population. As milk and dairy products are used extensively in the food industry, many people are also intolerant to a wide range of foods.
Almost 60 to 70 per cent of people in India are lactose intolerant. The frequency is higher among healthy populations from southern India than from northern India. The lower frequency in the north Indians is apparently due to the fact that they are descendants of the Aryans who have been dairying for long and are known to be lactose tolerant. So, the genetic mixing is responsible for greater lactose tolerance amongst them.
Not all people can survive well at high altitude or under intense ultraviolet radiation. Similarly, there are major differences around the world in how effectively our bodies process particular foods. In addition, some people live well on daily diets that would be at a starvation level for others. Different human populations not only eat different foods, but their digestive systems often use them in somewhat different ways. The adaptation to local nutritional opportunities has led to the evolution of related genetic differences among the populations of the world.
The best documented differences in nutritional adaptation relates to milk sugar, or lactose, which is commonly found in uncooked dairy products. Most human adults have moderate to severe difficulty in digesting lactose. They experience bloating, stomach cramps, belching, flatulence, and even diarrhoea when they drink milk. Not surprisingly, this commonly results in a decision to remove dairy products from their diet.
The ability to produce lactase is genetically controlled. The gene that codes for it (LCT) is on chromosome 2. A vast majority of babies throughout the world can digest their mother’s milk. However, there is a decline in lactase production as people grow older. This decline usually begins by two years of age, which is shortly after the time when babies are weaned in most societies. More rarely, lactase continues to be produced at sufficient levels to consume milk throughout life.
Milk drinking is pronounced in north-west India but is relatively rare in the northeast, with per capita consumption on the state-level varying by well more than an order of magnitude where the vast majority of people are lactose tolerant. Due to religious restrictions, vegetarianism is widespread in India. But very few Indians follow a vegan diet in which all animal products are avoided. Milk and other dairy products, derived from both cows and water buffalos, are avidly consumed across a large portion of the country. Indeed, India is the largest milk producer in the world. Milk is India’s leading agricultural commodity, produced on some 75 million dairy farms, most of which are quite small.
But milk drinking and the consumption of other dairy products is by no means uniformly distributed across India. On the basis of milk consumption, the major difference between the urban and rural population is that urban dwellers, being wealthier on average, tend to drink more milk than rural dwellers. At one level, the east/west dairy disparity in India is easily explained on a genetic basis.
In north-western India, the vast majority of people are lactose tolerant, and hence can drink milk without digestive problems into adulthood. In eastern India, on the other hand, most adults are lactose intolerant. (Some dairy products, however, are generally digestible by those with lactose intolerance; this is particularly the case with ghee, or clarified butter, an essential component of many Indian dishes.) In non-milk-drinking north-eastern India, the lack of protein in the diet is generally made up by the consumption of meat, eggs and fish.
Vegetarian precepts are much weaker among Hindus in north-eastern India than among those in the west. The high levels of meat consumption in such Indian states as Goa, Mizoram, Meghalaya and Kerala is rooted in the fact that many or most of their inhabitants are non-Hindu (Christian in the first three cases; Christian and Muslim in the last). Lactose tolerance in western India may be connected to the Bronze-Age movement of Indo-European-speaking people into South Asia.
Although lactose tolerance has evolved separately in at least four different areas of the world, it appears that Europeans and Indians share the same genes that allow milk digestion into adulthood. Europeans have higher percentage of lactose absorption in the whole world. People of African, Asian, African-American have lower frequency of lactose absorption and are most likely to be affected at an earlier age. The common ability of people in Europe and some other areas of the world to continue producing lactase as adults is very likely a relatively recent evolutionary development. Prior to the domestication of cattle, sheep, goats, and horses, which occurred after about 9000 years ago, milk was most likely only consumed by babies and very young children. That milk was human milk. Dairy products such as cow’s milk, yoghurt, and cheese did not exist. When nutrient rich nonhuman milk became widely available in pastoralist societies, the rare genetic variations that allowed some adults to easily digest lactose were selected for and this trait became more common. In other words, natural selection gradually shifted to favour lactose tolerant people, resulting in the progressive evolution of the gene pools of these populations in Europe.
Lactose intolerance is lactase deficiency, due to a person’s inability to produce enough of the lactase enzyme in the small intestine. Lactase breaks down the lactose into a pair of simpler sugars: glucose and galactose. Both sugars absorb quickly through the small intestine and release into the bloodstream. If someone doesn’t have enough lactase, however, the small intestine can only digest a portion of the lactose. The undigested lactose continues down through the small intestine and into the colon where bacteria work on the sugars in a process known as fermentation. Most people with lactose intolerance can digest at least some lactose, but how much depends on the amount of lactase in their bodies. As many people age, they begin to lose some of their lactase enzymes, making them less able to digest foods containing lactose. The condition is more common in those of Asian and African descent than Caucasians, as well as in Jewish people over people who are not Jewish.
Lactose intolerance is also more common in those with Crohn’s disease than those without, but doesn’t cause the illness. For some people, the lactase enzyme may be inducible. This means that if a person regularly exceeds the amount of lactose they can normally tolerate, their body may respond by increasing the amount of lactase it produces. The easiest way to diagnose lactose intolerance is to avoid dairy products such as milk, cheese, yogurt, and ice cream and see if the symptoms go away. If, after one week, you consume a glass of milk and the cramps and diarrhoea return, it’s highly likely you are lactose intolerant. Another more objective way to test for lactose intolerance is to have a doctor order a lactose breath test. When lactose metabolizes in the colon, the bacteria will release hydrogen into the bloodstream that can then be measured in the breath.
Currently, there are only two ways to treat lactose intolerance. You can avoid dairy products completely, or you can consume additional lactase enzymes in the form of an over-the-counter supplement such as Lactaid. Additionally, people who give up dairy may need to supplement their diets with vitamin D and calcium, by taking supplemental tablets. Way back in 80s, a multicenter study had that intolerance was found to be 66.6% in the subjects from two South Indian centers at Trivandrum and Pondicherry. In contrast, the incidence in the subjects from a North Indian center in New Delhi was much lower, i.e., 27.4% (p less than 0.001). The lower incidence in the North Indian subjects may perhaps be due to the fact that they are descendants of the Aryans who have been dairying for long and are known to be lactose tolerant.
The type of lactose intolerance that occurs in infants (congenital lactase deficiency) is inherited in an autosomal recessive pattern, which means both copies of the LCT gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition. The ability to digest lactose into adulthood depends on which variations in the regulatory element within the MCM6 gene individuals have inherited from their parents. The variations that promote continued lactase production are considered autosomal dominant, which means one copy of the altered regulatory element in each cell is sufficient to sustain lactase production. People who have not inherited these variations from either parent will have some degree of lactose intolerance. Gradually introducing small amounts of milk or milk products may help some people adapt to them with fewer symptoms.
Often, people can better tolerate milk or milk products by having them with meals, such as having milk with cereal or having cheese with crackers. People with lactose intolerance are generally more likely to tolerate hard cheeses, such as cheddar or Swiss, than a glass of milk. However, people with lactose intolerance are also more likely to tolerate yogurt than milk, even though yogurt and milk have similar amounts of lactose.
Lactose-free and lactose-reduced milk and milk products are available at most supermarkets and are identical nutritionally to regular milk and milk products. Manufacturers treat lactose-free milk with the lactase enzyme. This enzyme breaks down the lactose in the milk. Lactose-free milk remains fresh for about the same length of time or, if it is ultra-pasteurized, longer than regular milk. Lactose-free milk may have a slightly sweeter taste than regular milk. People can use lactase tablets and drops when they eat or drink milk products. The lactase enzyme digests the lactose in the food and therefore reduces the chances of developing digestive symptoms.
People should check with a health care provider before using these products because some groups, such as young children and pregnant and breastfeeding women, may not be able to use them. Ensuring that children and adults with lactose intolerance get enough calcium is important, especially if their intake of milk and milk products is limited. The amount of calcium a person needs to maintain good health varies by age.
Many foods can provide calcium and other nutrients the body needs. Non-milk products high in calcium include fish with soft bones, such as canned salmon and sardines, and dark green vegetables, such as spinach. Manufacturers may also add calcium to fortified breakfast cereals, fruit juices, and soy beverage—also called soy milk. Many fortified foods are also excellent sources of vitamin D and other essential nutrients, in addition to calcium.
No matter how much ancient wisdom emphasizes its importance, three out of four Indians have no tolerance for milk. Besides the large population of milk mal-absorbers, the study found Indians more sensitive than their European or American counterparts. The most important long-term health consequence of lactose intolerance is calcium deficiency that leads to osteoporosis. Less commonly, vitamin D deficiency may occur and compound the bone disease. Both these health issues can be prevented easily by calcium and vitamin D supplements. The researchers also relate milk intolerance to poor bone health. The real problem is that many lactose intolerant people who consciously or unconsciously avoid milk do not realize that they need a supplement. The finding reasons out why one out of three Indian women above the age of 30 suffer from osteopenia which is a pre-osteoporosis condition.
Probiotics can compensate for lactase insufficiency by the hydrolysis of lactose in the milk product and in the small intestine at the level of colonic fermentation. The hydrolytic capacity of probiotic strains can be used to reduce the actual amount of lactose in the product, as occurs in yogurt. It can also be used to increase the overall hydrolytic capacity in the small intestine. The probiotic strain can be alive or can be lysed in the intestinal tract for its effect. Lactobacillus acidophilus is a bile-salt tolerant bacterium which hardly increases lactose digestion. However, sonication of Lactobacillus Acidophilus milk weakens their membranes and improves lactose intolerance symptoms. Lactobacillus delbrüeckii in a milk product can deliver â- galactosidase activity. These microorganisms do not have to be alive as long as their
Membranes are intact which helps to protect â-galactosidase during gastric passage. Yogurt improves the lactose intolerance due to the presence of a group of lactobacillus bacteria it contains, i.e., Lactobacillus acidophilus. The consumption of yogurt containing Lactobacillus bulgaricus and Streptococcus thermophiles alleviate the lactose intolerance through their enzyme lactase when the product reaches the intestinal tract.
From these findings it is inferred that lactose intolerance can be reduced by regularly consuming the fermented dairy products due to the production of â-galactosidase enzyme by lactic acid bacteria present in them. In general, it can be stated that in yogurt several probiotic strains are present which results in a better tolerance of lactose in lactose intolerant persons. Research is going on to prove that the application of probiotics to manipulate the colonic fermentation not only has an effect at the level of the colon but also at the level of the small intestine.
There is evidence that probiotics can alleviate symptoms of lactose intolerance. This can occur by increased hydrolysis of lactose in the dairy product and in the small intestine. It can also be achieved by manipulation of the colonic metabolism. However, the precise mechanism on how colonic metabolism influences lactose intolerance symptoms is not yet known. The diagnosis of lactose maldigestion and the relation to complaints is highly complex. For an effective treatment of lactose intolerance and a correct interpretation of the effects of an intervention, knowledge of the underlying mechanisms of lactose intolerance is essential. Development of new strategies concerning the treatment with probiotics should therefore include an analysis of the relevant intermediate endpoints. In this way applications of probiotics for treatment of lactose intolerance could lead to a promising strategy.