Lactose Intolerance in Indians: Is It in Your Genes?

Have you ever wondered why some people can drink a full glass of milk without a problem, while others feel bloated or need to rush to the washroom soon after? The answer often lies in our genes. Most babies can digest milk easily, but as we grow older, many of us produce less lactase, the enzyme that helps break down milk sugar. This is what causes lactose intolerance, and how much lactase your body continues to make is largely influenced by the genes you inherit. In India, lactose intolerance also varies across regions and communities. That's why even people from the same family can react differently to milk and dairy products. So, how do you know if you're lactose intolerant or if something else is upsetting your stomach? Here's why it happens, how to recognise the symptoms and how to get enough calcium without giving up every dairy food you enjoy.

What happens when your body cannot digest lactose?

Lactose is the natural sugar found in milk. To digest it, your body needs an enzyme called lactase, which is produced in the small intestine. Lactase breaks lactose into two simpler sugars, glucose and galactose, so your body can absorb them. When your body doesn't produce enough lactase, some lactose passes into the large intestine without being digested. The bacteria living there break it down, producing gas and drawing extra water into the gut. That's why drinking milk can leave some people feeling bloated or uncomfortable. According to the NIDDK, symptoms can include gas, diarrhoea, stomach pain, nausea and rumbling sounds, usually within a few hours of having dairy.

There's also an important difference between two terms:

• Lactose malabsorption means your body doesn't fully digest lactose.

• Lactose intolerance means that difficulty digesting lactose actually causes symptoms.

Not everyone who has trouble digesting lactose feels unwell after drinking milk. Some people can still enjoy dairy without noticeable discomfort.

Why do so many adults lose the ability to digest milk?

Milk is a baby's food. For most of human history, adults did not drink it, so the body had no reason to keep making lactase once a child was weaned. That is still the default for most of the world. According to MedlinePlus Genetics, about 65 percent of people have a reduced ability to digest lactose after infancy. The lactase gene has a switch. It sits in a nearby stretch of DNA within a gene called MCM6 and works like a dimmer that slowly turns lactase down after childhood. Some people carry a small change in that switch that keeps lactase running for life. Scientists call this lactase persistence. Which version you have depends on the variants you inherited from your parents. This is also why the problem often shows up later. NIDDK notes that symptoms may not begin until later childhood, the teen years or early adulthood, because lactase falls gradually with age. So a person who drank milk happily as a child can start reacting to it in college.

Is lactose intolerance more common in South India?

Studies suggest that lactose intolerance is more common in South India than in North India, and genetics may help explain why. In one study, researchers in Lucknow tested 153 healthy adults from northern and southern India. They used breath tests to check how well participants digested lactose and genetic tests to understand the differences. The results showed that:

• 78.9% of South Indian participants had difficulty digesting lactose, compared with 57.1% of North Indian participants.

• The genetic pattern linked to reduced lactase production was found in 86.8% of the southern group and 67.5% of the northern group.

• After consuming lactose, 47.4% of southern participants experienced symptoms, compared with 15.6% of northern participants.

These findings come from a study published in 2009. Importantly, the results show that difficulty digesting lactose doesn't always mean someone will experience symptoms. A larger genetic study involving 2,284 DNA samples found a similar pattern. The gene variant that allows people to continue digesting lactose into adulthood was more common in northwestern India and became less common towards the southeast.

Interestingly, researchers found that this was the same genetic variant seen in European populations, suggesting a shared history linked to dairy farming and cattle herding. This helps explain why milk may be easier to digest for some people than others, even within India. However, where you come from doesn't determine whether you're lactose intolerant. Your individual genes, the amount of lactose you consume and how your body responds all matter.

How much milk can you still have?

Being lactose intolerant doesn't necessarily mean you have to stop drinking milk. Many people can still enjoy small amounts without feeling uncomfortable. In a small study involving 13 adults who had difficulty digesting lactose, researchers tested different amounts to see how much participants could tolerate. A 2 g dose caused no significant symptoms, and amounts up to 6 g were generally tolerated. That's roughly the lactose found in half a cup of milk. The NIDDK also notes that many people with lactose intolerance can tolerate up to 12 g of lactose, about the amount in one cup of milk, with few or no symptoms.

If milk tends to upset your stomach, a few simple changes may help:

• Drink milk with meals. Having it alongside food rather than on an empty stomach may make it easier to tolerate.

• Try smaller portions. Instead of drinking a large glass at once, spread your intake throughout the day. For example, a little milk in your morning and evening chai may suit you better.

• Choose lactose-free milk. It's available in many Indian supermarkets and provides similar nutrients to regular milk, including calcium and protein.

Everyone's tolerance is different, so start with an amount you're comfortable with and pay attention to how your body responds.

Why does curd sit better than milk?

Have you noticed that milk upsets your stomach, but curd doesn't? There's a reason why some people with lactose intolerance can enjoy curd without the same discomfort. Yoghurt contains live bacteria that produce lactase, the enzyme that helps break down lactose. A review published in the American Journal of Clinical Nutrition found that these bacteria can help digest lactose in the intestine, making yoghurt easier to tolerate for many people with lactose intolerance. Homemade curd also contains live bacterial cultures, which may explain why some people can enjoy curd rice even when a glass of milk causes bloating or gas. However, the amount of lactose and the types of bacteria can vary between products. The NIDDK also notes that yoghurt and hard cheeses are often easier to tolerate than milk.

Also read: Probiotics vs Prebiotics: What's the Difference and Why Do You Need Both?

How do you know it is really lactose?

Bloating after meals has many causes. Before you give up milk for good, look at the pattern.

1. Symptoms come within a few hours of milk, milkshakes, ice cream or kheer.

2. They ease when you skip milk for a while and come back when you have it again.

3. Curd, buttermilk or hard cheese bother you much less than plain milk.

If that sounds like you, mention it to your doctor. They may suggest a hydrogen breath test, in which you drink a measured amount of lactose and breathe into a bag every 30 minutes over a few hours. Extra hydrogen in your breath shows lactose is being fermented in the gut instead of being digested.

Lactose intolerance is not the same as a milk allergy. NIDDK explains that a milk allergy is the immune system reacting to milk protein and most often appears in the first year of life. Lactose intolerance is a digestion problem and usually appears later. If your bloating does not follow the milk pattern, other causes are worth a look. These articles on morning bloating vs evening bloating and whether constipation can cause bloating can help you narrow it down. The NHS advises seeing a GP if you feel bloated regularly, keep feeling bloated after changing your diet, or have bloating with weight loss you did not intend or with blood in your poo.

Keep your calcium when you cut back on milk

Milk is one of the easiest sources of calcium in the Indian diet. NIDDK warns that if you avoid all milk products, you may get less calcium and vitamin D than you need. Over years, that matters for your bones. You do not need a lot of milk to get enough calcium. Lean on curd, buttermilk, paneer in moderate portions, ragi, sesame seeds, rajma, green leafy vegetables such as methi and amaranth and lactose-free milk. Get some morning sun and ask your doctor about a vitamin D test if you spend most days indoors. Our guide to vitamin D deficiency covers the signs. If bone strength is on your mind, read can you increase bone density.

Your genes are not the end of the story

Your genes may affect how well you digest milk, but that doesn't mean you have to give up dairy altogether. Many people with lactose intolerance can still enjoy their morning chai, a bowl of curd or an occasional milk-based sweet without much discomfort. What matters is understanding how much lactose your body can tolerate and choosing dairy foods that suit you. You can also explore lactose-free options to make sure you're getting enough calcium. So, even if your grandfather could drink a full glass of milk without a second thought and you can't, there's no need to give up everything you enjoy. A few small changes can help you keep dairy in your diet without the discomfort.

Sources

• Frequency of lactose malabsorption among healthy southern and northern Indian populations by genetic analysis and lactose hydrogen breath and tolerance tests (American Journal of Clinical Nutrition, 2010)

• Herders of Indian and European cattle share their predominant allele for lactase persistence (Molecular Biology and Evolution, 2012)

• How much lactose is low lactose? (Journal of the American Dietetic Association, 1996)

• Lactose digestion from yogurt: mechanism and relevance (American Journal of Clinical Nutrition, 2014)

• MedlinePlus Genetics: Lactose intolerance

• NIDDK: Symptoms and causes of lactose intolerance

• NIDDK: Eating, diet and nutrition for lactose intolerance

Medical Disclaimer: This article is for general information and is not a substitute for advice from your doctor. Speak to a qualified healthcare professional before starting any supplement, especially if you are pregnant, breastfeeding or taking medication.