has been largely replaced by breath testing. after an overnight fast, blood is drawn and then 50 grams of lactose (in aqueous solution) are swallowed. blood is then drawn again at the 30-minute, 1-hour, 2-hour, and 3-hour marks. if the lactose cannot be digested, blood glucose levels will rise by less than 20 mg/dl. stool acidity test this test can be used to diagnose lactose intolerance in infants, for whom other forms of testing are risky or impractical. the infant is given lactose to drink. if the individual is tolerant, the lactose is digested and absorbed in the small intestine; otherwise, it is not digested and absorbed, and it reaches the colon. the bacteria in the colon, mixed with the lactose, cause acidity in stools. stools passed after the ingestion of the lactose are tested for level of acidity. if the stools are acidic, the infant is intolerant to lactose. stool ph in lactose intolerance is less than 5.5. intestinal biopsy an intestinal biopsy must confirm lactase deficiency following discovery of elevated hydrogen in the hydrogen breath test. modern techniques have enabled a bedside test, identifying presence of lactase enzyme on upper gastrointestinal endoscopy instruments. however, for research applications such as mrna measurements, a specialist laboratory is required. stool sugar chromatography chromatography can be used to separate and identify undigested sugars present in faeces. although lactose may be detected in the faeces of people with lactose intolerance, this test is not considered reliable enough to conclusively diagnose or exclude lactose intolerance. genetic diagnostic genetic tests may be useful in assessing whether a person has primary lactose intolerance. lactase activity persistence in adults is associated with two polymorphisms: c/t 13910 and g/a 22018 located in the mcm6 gene. these polymorphisms may be detected by molecular biology techniques at the dna extracted from blood or saliva samples; genetic kits specific for this diagnosis are available. the procedure consists of extracting and amplifying dna from the sample, following with a hybridation protocol in a strip. colored bands are obtained as result, and depending on the different combinations, it would be possible to determine whether the patient is lactose intolerant. this test allows a noninvasive definitive diagnostic. frequency lactose intolerance is most common in people of east asian descent, with 70 to 100 percent of people affected in these communities. lactose intolerance is also more common in people of west african, arab, and jewish descent, while only about 5 percent of people of european descent are lactose intolerant. management when lactose intolerance is due to secondary lactase deficiency, treatment of the underlying disease may allow lactase activity to return to normal levels. in people with celiac disease, lactose intolerance normally reverts or improves several months after starting a gluten-free diet, but temporary dietary restriction of lactose may be needed. people with primary lactase deficiency cannot modify their body's ability to produce lactase. in societies where lactose intolerance is the norm, it is not considered a condition that requires treatment. however, where dairy is a larger component of the normal diet, a number of efforts may be useful. there are four general principles in dealing with lactose intolerance: avoidance of dietary lactose, substitution to maintain nutrient intake, regulation of calcium intake, and use of enzyme substitute. regular consumption of dairy food by lactase deficient individuals may also reduce symptoms of intolerance by promoting colonic bacteria adaptation. dietary avoidance the primary way of managing the symptoms of lactose intolerance is to limit the intake of lactose to a level that can be tolerated. lactase deficient individuals vary in the amount of lactose they can tolerate, and some report that their tolerance varies over time, depending on health status and pregnancy. however, as a rule of thumb, people with primary lactase deficiency and no small intestine injury are usually able to consume at least 12 grams of lactose per sitting without symptoms, or with only mild symptoms, with greater amounts tolerated if consumed with a meal or throughout the day. typical lactose levels in dairy products dairy productserving sizelactose contentpercentage milk, regular 250 ml/g 12 g 4.80% milk, reduced fat 250 ml/g 13 g 5.20% yogurt, plain, regular 200 g 9 g 4.50% yogurt, plain, low-fat 200 g 12 g 6.00% cheddar cheese 30 g 0.02 g 0.07% cottage cheese 30 g 0.1 g 0.33% butter 5 g 0.03 g 0.6% ice cream 50 g 3 g 6.00% lactose is found primarily in dairy products, which vary in the amount of lactose they contain: milk – unprocessed cow's milk is about 4.7% lactose; goat's milk 4.7%; sheep's milk 4.7%; buffalo milk 4.86%; and yak milk 4.93%. sour cream and buttermilk – if made in the traditional way, this may be tolerable, but most modern brands add milk solids. butter – the process of making butter largely removes lactose, but it is still present in small quantities; clarified butter contains a negligible amount of lactose. yogurt – lactobacilli used in the production of yogurt metabolize lactose to varying degrees, depending on the type of yogurt. some bacteria found in yogurt also produce their own lactase, which facilitates digestion in the intestines of lactose intolerant individuals. cheese – fermentation also reduces the lactose content of cheeses and aging reduces it further; traditionally made hard cheeses might contain just 10% of the lactose found in an equivalent volume of milk. however, manufactured cheeses may be produced using processes that do not have the same lactose-reducing properties. there is no standardized method for measuring the lactose content of food. the stated dairy content of a product also varies according to manufacturing processes and labelling practices, and commercial terminology varies between languages and regions. as a result, absolute figures for the amount of lactose consumed (by weight) may not be very reliable. kosher products labeled pareve or fleishig are free of milk. however, if a "d" (for "dairy") is present next to the circled "k", "u", or other hechsher, the food product likely contains milk solids, although it may also simply indicate the product was produced on equipment shared with other products containing milk derivatives. lactose is also a commercial food additive used for its texture, flavor, and adhesive qualities. it is found in additives labelled as casein, caseinate, whey, lactoserum, milk solids, modified milk ingredients, etc. as such lactose is found in foods such as processed meats (sausages/hot dogs, sliced meats, pâtés), gravy stock powder, margarines, sliced breads, breakfast cereals, potato chips, processed foods, medications, prepared meals, meal replacements (powders and bars), protein supplements (powders and bars), and even beers in the milk stout style. some barbecue sauces and liquid cheeses used in fast-food restaurants may also contain lactose. lactose is often used as the primary filler (main ingredient) in most prescription and non-prescription solid pill form medications, though product labeling seldom mentions the presence of 'lactose' or 'milk', and neither do product monograms provided to pharmacists, and most pharmacists are unaware of the very wide scale yet common use of lactose in such medications until they contact the supplier or manufacturer for verification. milk substitutes plant-based milks and derivatives such as soy milk, rice milk, almond milk, coconut milk, hazelnut milk, oat milk, hemp milk, macadamia nut milk, and peanut milk are inherently lactose-free. low-lactose and lactose-free versions of foods are often available to replace dairy-based foods for those with lactose intolerance. lactase supplements when lactose avoidance is not possible, or on occasions when a person chooses to consume such items, then enzymatic lactase supplements may be used. lactase enzymes similar to those produced in the small intestines of humans are produced industrially by fungi of the genus aspergillus. the enzyme, β-galactosidase, is available in tablet form in a variety of doses, in many countries without a prescription. it functions well only in high-acid environments, such as that found in the human gut due to the addition of gastric juices from the stomach. unfortunately, too much acid can denature it, so it should not be taken on an empty stomach. also, the enzyme is ineffective if it does not reach the small intestine by the time the problematic food does. lactose-sensitive individuals can experiment with both timing and dosage to fit their particular needs. while essentially the same process as normal intestinal lactose digestion, direct treatment of milk employs a different variety of industrially produced lactase. this enzyme, produced by yeast from the genus kluyveromyces, takes much longer to act, must be thoroughly mixed throughout the product, and is destroyed by even mildly acidic environments. its main use is in producing the lactose-free or lactose-reduced dairy products sold in supermarkets. rehabituation to dairy products regular consumption of dairy foods containing lactose can promote a colonic bacteria adaptation, enhancing a favorable microbiome, which allows people with primary lactase deficiency to diminish their intolerance and to consume more dairy foods. the way to induce tolerance is based on progressive exposure, consuming smaller amounts frequently, distributed throughout the day. lactose intolerance can also be managed by ingesting live yogurt cultures containing lactobacilli that are able to digest the lactose in other dairy products. epidemiology an estimate of the percentage of adults that can digest lactose in the indigenous population of the old world worldwide, about 65% of people experience some form of lactose intolerance as they age past infancy, but there are significant differences between populations and regions. as few as 5% of northern europeans are lactose intolerant, while as many as 90% of adults in parts of asia are lactose intolerant. in northern european countries, early adoption of dairy farming conferred a selective evolutionary advantage to individuals that could tolerate lactose. this led to higher frequencies of lactose tolerance in these countries. for example, almost 100% of irish people are predicted to be lactose tolerant. conversely, regions of the south, such as africa, did not adopt dairy farming as early and tolerance from milk consumption did not occur the same way as in northern europe. lactose intolerance is common among people of jewish descent, as well as from west africa, the arab countries, greece, and italy. different populations will present certain gene constructs depending on the evolutionary and cultural pre-settings of the geographical region. history greater lactose tolerance has come about in two ways. some populations have developed genetic changes to allow the digestion of lactose: lactase persistence. other populations developed cooking methods like milk fermentation. lactase persistence in humans evolved relatively recently (in the last 10,000 years) among some populations. around 8,000 years ago in modern-day turkey, humans became reliant on newly-domesticated animals that could be milked; such as cows, sheep, and goats. this resulted in higher frequency of lactase persistence. lactase persistence became high in regions such as europe, scandinavia, the middle east and northwestern india. however, most people worldwide remain lactase non-persistent. populations that raised animals not used for milk tend to have 90–100 percent of a lactose intolerant rate. for this reason, lactase persistence is of some interest to the fields of anthropology, human genetics, and archaeology, which typically use the genetically derived persistence/non-persistence terminology. the rise of dairy and producing dairy related products from cow milk alone, varies across different regions of the world, aside from genetic predisposition. the process of turning milk into cheese dates back earlier than 5200 bc. dna analysis in february 2012 revealed that ötzi was lactose intolerant, supporting the theory that lactose intolerance was still common at that time, despite the increasing spread of agriculture and dairying. genetic analysis shows lactase persistence has developed several times in different places independently in an example of convergent evolution. history of research it is not until relatively recently that medicine recognised the worldwide prevalence of lactose intolerance and its genetic causes. its symptoms were described as early as hippocrates (460–370 bc), but until the 1960s, the prevailing assumption was that tolerance was the norm. intolerance was explained as the result of a milk allergy, intestinal pathogens, or as being psychosomatic – it being recognised that some cultures did not practice dairying, and people from those cultures often reacted badly to consuming milk. two reasons have been given for this misconception. one was that early research was conducted solely on european-descended populations, which have an unusually low incidence of lactose intolerance and an extensive cultural history of dairying. as a result, researchers wrongly concluded