Lactose: Milk Sugar, Lactase and Tolerance in Indian Adults

Lactose is the sugar found in milk. It is a disaccharide, one unit of glucose joined to one of galactose, and it has to be split by the enzyme lactase in the small intestine before it can be absorbed. The Indian Food Composition Tables 2017 give cow's milk 4.28 g of lactose per 100 g, which is about 8.6 g in a 200 g glass. Many Indian adults make little lactase, and the share differs between north and south. This entry belongs to the carbohydrates section of the handbook.

What is lactose and what does it do?

It is the main source of calories in milk and an essential nutrient in infancy. ICMR-NIN's Dietary Guidelines for Indians, 2024, lists it with sucrose as a disaccharide, and FSSAI's labelling regulations count it among the sugars on a nutrition panel, at 4 kcal per gram like any other digestible carbohydrate. Lactase sits at the tips of the villi lining the small intestine and cuts each lactose molecule into glucose and galactose, which are then absorbed.

Lactase activity is highest at birth. A 2019 review in the journal Gut describes how it falls during childhood in most of the world's people, while in some it stays high for life. Lactose that escapes digestion reaches the large intestine, where bacteria ferment it into hydrogen, carbon dioxide, methane and short-chain fatty acids. The result, after a large dose, can be bloating, cramps, wind and loose stools.

Lactase non-persistence, malabsorption and intolerance compared

Three terms are used loosely and mean different things. The Gut review calls low adult lactase a normal variant of human metabolism, not a disease. Malabsorption is a test result and intolerance is a set of symptoms, so a positive test does not by itself tell you to stop drinking milk.

How common is lactose malabsorption in India?

It is common everywhere in the country and more common in the south. A multicentre study published in 1981 found lactose intolerance in 66.6 per cent of healthy volunteers at two southern centres, Trivandrum and Pondicherry, against 27.4 per cent at a centre in New Delhi. A 2010 study tested 153 healthy volunteers three ways and found the same direction with higher figures.

Read the last row with care. Even in the south, fewer than half of the volunteers felt anything after the test dose, although about four in five had an abnormal breath test. These are small samples of volunteers from a few centres, not a national survey, and neither study covers the east or the north-east, so no figure for those regions is given here.

Is there an Indian requirement for lactose?

No. ICMR-NIN's Nutrient Requirements for Indians, 2020, sets no requirement and no upper limit for lactose, because an adult can make all the glucose and galactose the body needs from other foods. What the Indian guidelines do set is a place for dairy: My Plate for the Day in the 2024 dietary guidelines includes 300 ml of milk or curd. The nutrient that depends on it is calcium, for which the 2020 allowance is 1,000 mg a day for an adult man or woman, covered in the calcium entry.

Which Indian dairy foods carry the most lactose?

Per 100 g, khoa and paneer carry more than milk in IFCT 2017, because they are concentrated milk solids; per portion, a glass of milk is still the largest single dose most people take. The tables give cow's milk 4.28 g, buffalo milk 4.12 g, paneer 9.12 g and khoa 12.86 g of lactose per 100 g. IFCT has no entry for curd, lassi or chaas. The paneer figure is well above the 0.1 to 3.0 g per 100 g that the Gut review lists for European cheeses, so paneer should not be assumed to be free of lactose.

NNWA's food tables carry the full panels for whole milk, paneer per 100 g and khoa or mawa. Lactose also turns up outside the dairy shelf: the Gut review notes that lactose powder is added to processed foods such as sausages, gravies, sauces and bread.

Why is curd easier on the stomach than milk?

Curd brings its own lactase. In a 1984 study in the New England Journal of Medicine, lactase-deficient adults who ate 18 g of lactose as yoghurt breathed out only about one third as much hydrogen as after the same lactose in milk or water, and reported less diarrhoea and wind. A 2014 review explains why: the enzyme survives stomach acid inside the live bacteria and then works in the small intestine. The Gut review adds that yoghurt holds roughly half the lactose of the milk it was made from.

These studies used commercial yoghurt, not home-set dahi, and no trial read for this entry measured dahi, lassi or chaas directly. ICMR-NIN's 2024 guidelines still give the practical advice in one line: take less milk at a time, take it with a cereal and pulse meal, or take it as curd. The article on curd and yoghurt covers the difference between the two, and a glass of masala chaas is diluted curd.

How is lactose tolerance tested?

The usual test is the hydrogen breath test. You drink a measured dose of lactose, then breathe into a collecting device every 30 minutes for a few hours. A rise in breath hydrogen of 20 parts per million or more over the starting level points to malabsorption, and symptoms that follow the rise point to intolerance. The older lactose tolerance test measures blood glucose at intervals after 50 g of lactose. A genetic test finds inherited non-persistence but misses secondary causes.

The dose matters. A study from Lucknow gave 50 g, 25 g and 12 g of lactose to three groups of 50 patients with irritable bowel syndrome. Those patients were drinking about 335 ml of milk a day, roughly 16.7 g of lactose. A positive breath test at 25 g predicted relief from stopping milk better than the 50 g or 12 g test did. Which test to order, and what the result means for you, is the doctor's call.

What does the evidence say about how much milk is tolerated?

More than most people expect. A systematic review in the Annals of Internal Medicine in 2010 covered 36 randomised studies and judged, on moderate-quality evidence, that 12 to 15 g of lactose is well tolerated by most adults with malabsorption or presumed intolerance. By IFCT's figure, 12 g is the lactose in about 280 g of cow's milk. The same review found the evidence insufficient to say that lactose-reduced milk, probiotics or gradual adaptation reduce symptoms.

Two blinded crossover trials sit behind that conclusion. In the first, 30 adults who described themselves as severely intolerant drank 240 ml of ordinary or lactose-hydrolysed milk with breakfast for a week each; 21 of them proved to be malabsorbers, and symptoms were minimal and no different between the two milks. In the second, adults with low lactase took 240 ml twice a day with food, again without a meaningful rise in symptoms. Both trials were small and American.

A worked example: the same 400 g of milk, taken differently

This case is invented to show the arithmetic; it is not a real person. A 31-year-old vegetarian accountant in Chennai drinks 250 g of cow's milk on an empty stomach at 7 a.m. and feels bloated by nine, then has 150 g more in two cups of filter coffee. At 4.28 g per 100 g, her day holds 17.1 g of lactose, with 10.7 g of it in one dose. Her 400 g of milk supplies about 472 mg of calcium at 118 mg per 100 g, close to half of her 1,000 mg allowance.

She keeps the 400 g and changes the form. She takes 100 g in coffee with breakfast (4.3 g of lactose), sets 200 g as curd for lunch with rice and sambar, and takes 100 g in coffee in the evening (4.3 g). The largest dose of lactose as plain milk falls from 10.7 g to 4.3 g, both taken with food, and the curd portion starts at no more than 8.6 g before fermentation lowers it. Nothing is drained away when milk sets, so her calcium stays at about 472 mg.

Keeping your calcium if you cut down on milk

Cutting milk without a plan removes one of the densest calcium sources on an Indian plate. Two glasses of cow's milk, 400 g, give about 472 mg. The foods below can cover that, using IFCT 2017 values, and all of them are vegetarian. NNWA's ranked table of calcium in Indian foods lists the rest, and the article on lactose intolerance on an Indian diet deals with plant milks.

Common mistakes and myths about lactose

The first mistake is diagnosing yourself from one bad morning. In the 1995 trial, 9 of the 30 adults who were sure they were severely intolerant turned out to absorb lactose normally. The second is treating all dairy as one food: a glass of milk, a katori of curd and the milk in a cup of chai deliver very different doses. The third is forgetting the lactose in khoa sweets and in paneer.

A related confusion is between intolerance and allergy. The United States' National Institute of Diabetes and Digestive and Kidney Diseases states that lactose intolerance is different from a milk allergy, which is a disorder of the immune system. Nothing in this entry applies to allergy.

When should you see a doctor about milk and your gut?

See one when symptoms are severe, new or do not follow the dose, because the same bloating and loose stools occur in conditions that need treatment. The Gut review lists infectious gastroenteritis, inflammatory bowel disease and coeliac disease among the causes of secondary malabsorption.

ICMR-NIN sets no upper limit for lactose. People with diabetes should count it with the rest of their carbohydrate, since it is digested to glucose and galactose; the diabetes nutrition course teaches how milk and curd fit into a day's carbohydrate.

Learning this subject at NNWA

How the body digests sugar, and how to read the Indian food tables, is taught at NNWA, a private skill academy in Kolkata that teaches online in English and Hindi. The Certification in Nutrition and the other programmes train people to coach healthy clients on food and to refer medical cases to a doctor. None is a degree or a dietitian qualification.