Lactose intolerance

Some people cannot digest the sugar in milk. This sugar is called lactose.

Our bodies use a tool to break this sugar down. If we do not have enough of this tool, we feel sick. Our bellies may feel full of gas or hurt. This can happen soon after we drink milk.

Most people lose this tool as they grow up. Some people are born without it. This is very rare.

This is not a milk allergy. It does not hurt the body for a long time. You can still eat if you choose foods without this sugar.

Many people in the world can still drink a little milk. It helps to eat it with a meal.

Some people have a hard time digesting milk. Milk contains a sugar called lactose. To break this sugar down, our bodies use a tool called lactase. This lactase is an enzyme, which is a tiny part that helps cause changes in our bodies.

If you do not have enough lactase, the sugar cannot be absorbed. Instead, it moves into the colon. Bacteria there eat the sugar and make gas. This can cause belly pain, bloating, or diarrhea. These feelings often start thirty minutes to two hours after eating dairy.

There are different types of this condition. Primary lactose intolerance happens as people grow up. In this way, the body makes less lactase over time. Secondary lactose intolerance happens if the small intestine is hurt by an illness. A very rare type is congenital lactase deficiency. This means a person is born without any lactase at all.

Lactose intolerance is not a milk allergy. An allergy is an immune response. This condition is just a lack of an enzyme. Most people can still drink a little milk. Eating it with a meal might help too.

Some people have a hard time digesting milk. This happens because of lactose intolerance. Lactose is a sugar found in dairy products. To use this sugar, the body needs a tool called lactase. Lactase is an enzyme that breaks lactose into two smaller sugars. These are called glucose and galactose. If you do not have enough lactase, the sugar cannot be absorbed. It moves into the colon instead.

When the sugar stays in the colon, things change. Bacteria in the gut eat the sugar. This process is called fermentation. It creates gases like hydrogen, carbon dioxide, and methane. These gases cause bloating, cramps, and flatulence. The sugar also pulls water into the bowels. This can lead to diarrhea. These feelings usually start thirty minutes to two hours after eating. The severity often depends on how much lactose was eaten.

There are four different types of this condition. Primary lactose intolerance happens as people grow up. The body simply makes less lactase over time. Secondary lactose intolerance comes from an injury to the small intestine. This might happen because of an infection or diseases like celiac disease. Developmental lactose intolerance can happen to premature babies. Finally, congenital lactase deficiency is very rare. It is a genetic disorder where a person has no lactase from birth.

History shows us how humans have changed. Most mammals lose the ability to digest lactose after weaning. For a long time, all humans were likely lactose intolerant. About 10,000 years ago, people began domesticating dairy animals. Some humans developed a mutation in the MCM6 gene. This mutation keeps the LCT gene turned on. This allows them to digest milk into adulthood. This is called lactase persistence. Scientists found this mutation spread in Europe about 4,300 years ago.

Today, how much lactose people can handle varies by region. About 65% of adults worldwide have trouble with lactose. In East Asia, 90% of people are lactose intolerant. In Northern Europe, tolerance is much more common. Many cultures have adapted to this. In Mongolia, people drink kumis. This is a fermented milk product with very little lactose. You can manage intolerance by eating less dairy or taking lactase supplements.

Lactose intolerance is a condition where a person has a reduced ability to digest lactose. Lactose is a disaccharide, which is a type of sugar found in milk and dairy products. This condition is not a milk allergy. A milk allergy is an immune response to milk proteins like whey. Instead, lactose intolerance is a sensitivity caused by a deficiency of the enzyme lactase. This enzyme is produced in the lining of the duodenum, which is part of the small intestine. When there is not enough lactase, the body cannot properly process dairy sugars.

The digestive process fails when lactase is missing. Normally, lactase breaks the lactose molecule into two smaller sugars: glucose and galactose. These smaller sugars can then pass through the wall of the small intestine into the bloodstream. Without enough lactase, the lactose remains intact. It travels through the small intestine and enters the colon. Once in the colon, bacteria begin to metabolize the sugar through a process called fermentation. This fermentation produces large amounts of gas, including hydrogen, carbon dioxide, and methane. These gases cause symptoms like bloating, flatulence, and abdominal cramps. Additionally, the unabsorbed sugars increase the osmotic pressure in the colon. This causes water to flow into the bowels, resulting in diarrhea. Symptoms usually appear between thirty minutes and two hours after eating.

There are four distinct types of lactose intolerance. Primary hypolactasia is a genetic form where lactase production declines as a person grows up. This is the most common type and is linked to the absence of a lactase persistence allele. Secondary hypolactasia, or acquired lactase deficiency, is caused by an injury to the small intestine. This injury might result from infections, celiac disease, or inflammatory bowel disease. Developmental lactose intolerance can occur in premature babies but often improves quickly. Finally, primary congenital alactasia is an extremely rare genetic disorder. In this case, a person has little to no lactase from birth due to mutations in the LCT gene. About 40 cases have been reported worldwide, mostly in Finland.

History shows that lactose intolerance was once the ancestral state for all humans. Most mammals lose the ability to digest lactose after they are weaned from milk. However, humans began domesticating dairy animals roughly 10,000 years ago. This change likely led to the evolution of lactase persistence. This is a condition where the LCT gene remains active into adulthood. This persistence is caused by mutations in a nearby gene called MCM6. The MCM6 gene helps control whether the LCT gene is turned on or off. Analysis of 94 ancient skeletons suggests this mutation spread through Europe about 4,300 years ago. This allowed certain populations to gain nutrition from dairy animals.

The prevalence of lactose malabsorption varies significantly across the globe. A 2016 study of 60,000 participants showed that roughly 65% of adults worldwide are affected. In East Asia, the rate of lactose intolerance is as high as 90%. In contrast, Northern Europe has much higher levels of lactose tolerance. Other regional data shows 70% malabsorption in the Middle East and 66% in Northern Africa. In the United States, intolerance is more common among Asian Americans, African Americans, Mexican Americans, and Native Americans. These numbers show how much human biology has changed based on local environments and diets.

Different cultures have found clever ways to manage low levels of lactose tolerance. Many societies developed traditional foods that contain much less lactose than fresh milk. For example, in Mongolia, people drink kumis. Kumis is a fermented milk product that contains little to no lactose. This allows people to receive dairy nutrition without the discomfort of intolerance. People can also manage their symptoms by reducing dairy intake. Some choose to take lactase supplements to help break down the sugar. The amount of supplement needed usually depends on how much lactose is being consumed.

Understanding lactose intolerance requires looking at how genes and environments interact. The LCT and MCM6 genes are both located on chromosome 2 at the locus 2q21. While many thought a single mutation caused tolerance in different regions, scientists now know that lactase persistence evolved independently multiple times. Different alleles have developed at least three times in East African populations. This shows how human biology adapts to the food available in a specific culture. By studying these genetic patterns, researchers can better understand the history of human nutrition and health.