How do you break down lactose? A complete guide

December 30, 2025 •

4 min read

Approximately 65% of the human population has a reduced ability to digest lactose after infancy. Normally, a person's body breaks down lactose, the sugar found in milk, using an enzyme called lactase. For those with lactose intolerance, this process is incomplete, leading to digestive discomfort.

Quick Summary

The body primarily breaks down lactose using the lactase enzyme in the small intestine. When there is a deficiency, undigested lactose moves to the large intestine where it is fermented by bacteria, causing symptoms like bloating and gas. Management strategies include dietary changes, lactase supplements, and consuming fermented dairy products.

Key Points

Lactase Enzyme is Key: The body naturally breaks down lactose using the lactase enzyme, which is produced in the small intestine and splits lactose into glucose and galactose for absorption.
Lactase Deficiency Causes Intolerance: When lactase is deficient, undigested lactose ferments in the large intestine, causing gas, bloating, and other digestive discomforts.
Prevalence Varies: Lactose intolerance affects a large portion of the global population, with prevalence varying significantly by ethnicity and increasing with age.
Dietary Management is a Solution: Strategies include limiting or avoiding high-lactose foods, consuming low-lactose products like aged cheeses, and opting for fermented dairy like yogurt with live cultures.
Supplements Aid Digestion: Over-the-counter lactase supplements can be taken with dairy to assist with lactose digestion.
Lactose-Free Options Exist: Many lactose-free dairy alternatives are available, where the lactase enzyme has been added during production to pre-digest the lactose.
Hidden Lactose is Common: Check food labels for hidden lactose in ingredients like whey, milk solids, and milk powder.

The role of the lactase enzyme

To understand how the body breaks down lactose, it is essential to first understand the role of lactase. Lactase is a crucial enzyme produced by the cells lining the small intestine, specifically within the 'brush border'. Its primary function is to hydrolyze, or split, the disaccharide lactose into its two constituent, simpler sugar molecules: glucose and galactose. These simpler sugars can then be easily absorbed by the intestinal lining and enter the bloodstream to be used for energy. This digestive process is efficient in healthy individuals who produce sufficient lactase.

However, in people with lactose intolerance, there is a shortage or absence of this enzyme. This means that when they consume dairy products, the lactose remains undigested as it passes through the small intestine. It continues its journey to the large intestine, where it is fermented by the gut bacteria. This fermentation process produces gases like hydrogen, methane, and carbon dioxide, as well as short-chain fatty acids. These byproducts are what cause the uncomfortable gastrointestinal symptoms associated with lactose intolerance, including bloating, gas, stomach pain, and diarrhea.

Factors influencing lactase deficiency

Lactase deficiency is not a one-size-fits-all condition. There are several contributing factors that can lead to its development, and its prevalence varies significantly among different populations.

Primary Lactase Non-Persistence: This is the most common type and results from a genetically programmed reduction in lactase production after infancy. It is widespread, affecting about 65% of the world's population, and its prevalence is particularly high in people of East Asian, African, and Hispanic descent.
Secondary Lactase Deficiency: This type occurs due to damage to the small intestine, which impairs lactase production. Conditions such as celiac disease, Crohn's disease, or gastroenteritis can cause this temporary or long-term damage. Treating the underlying condition may restore lactase levels over time.
Congenital Lactase Deficiency: This is a very rare genetic disorder where infants are born with a complete inability to produce lactase, leading to severe diarrhea from birth if not managed with a lactose-free diet.
Developmental Lactase Deficiency: This can occur in premature infants whose small intestines are not fully developed to produce adequate lactase. The condition typically improves as they mature.

Strategies for breaking down lactose

For individuals with lactose intolerance, several effective strategies can help manage symptoms and ensure adequate nutrient intake from dairy products.

Dietary Adjustments: This involves limiting or avoiding high-lactose foods based on individual tolerance. Some individuals can tolerate small amounts of lactose, especially when consumed with other foods to slow down digestion. Many can also tolerate fermented dairy products like yogurt and hard cheeses, as the fermentation process and bacteria consume much of the lactose.
Lactase Supplements: Over-the-counter lactase enzyme supplements (available as tablets or drops) can be taken just before consuming dairy to help the body break down lactose. This effectively adds the missing enzyme to the digestive system.
Lactose-Free Products: Many food manufacturers produce lactose-free versions of milk, ice cream, and other dairy products by adding the lactase enzyme during production. These products are widely available in supermarkets and provide the nutrients of dairy without the lactose.
Probiotics: Some yogurts and supplements contain live and active probiotic cultures that can produce lactase, aiding in the digestion of lactose and potentially improving symptoms.

Comparison of lactose management strategies


Strategy	Mechanism	Pros	Cons
Dietary Adjustment	Limits or eliminates lactose intake by avoiding certain foods.	Natural and cost-free approach. Builds personal understanding of tolerance.	May require strict monitoring and elimination of many food items. Potential for nutrient deficiencies.
Lactase Supplements	Adds exogenous lactase enzyme to digest lactose.	Provides flexibility to consume dairy products. Easy to use (tablets/drops).	Needs to be timed correctly with meals. Not always effective for everyone. Recurring cost.
Lactose-Free Products	Lactase is added during manufacturing to pre-hydrolyze lactose.	Convenient and widely available. Provides a safe, symptom-free dairy option.	Can be more expensive than regular dairy. Does not address the underlying issue.
Probiotic-Rich Foods	Probiotic bacteria produce lactase, aiding digestion.	Can improve overall gut health. Tolerated by many with lactose intolerance.	Efficacy varies depending on the strain and product. Not all yogurts contain sufficient live cultures.

Food label knowledge

Understanding food labels is crucial for anyone managing lactose intake. Lactose is often a hidden ingredient in processed foods. Watch for these terms on ingredient lists:

Milk solids
Whey or whey protein
Milk powder or skim milk powder
Casein
Margarine
Artificial cream

Conclusion

Understanding how to break down lactose is key to managing lactose intolerance effectively. For most people, the process relies on the lactase enzyme in the small intestine, but a deficiency can cause uncomfortable digestive symptoms. Fortunately, a variety of strategies can help. From adjusting your diet to include fermented products or smaller portions, to using lactase supplements and opting for lactose-free products, there are many ways to enjoy dairy without discomfort. For those with persistent issues, dietary alternatives and a consultation with a healthcare provider can help ensure a balanced and nutritious diet while mitigating symptoms. A personalized approach, guided by an understanding of your body's specific tolerance, is the most successful path to managing lactose intolerance.

Frequently Asked Questions

When your body breaks down lactose, the lactase enzyme in the small intestine splits it into two simpler sugars, glucose and galactose. These simple sugars are then absorbed into the bloodstream and used for energy.

The fastest way to aid your body in breaking down lactose is by taking a lactase enzyme supplement in tablet or drop form just before or with your first bite of a dairy-containing meal. The enzyme immediately begins to digest the lactose in the food, preventing it from reaching the large intestine undigested.

You can't increase your body's natural production of lactase if it's genetically declining, but you can build tolerance by gradually consuming small amounts of lactose. Additionally, incorporating probiotics from sources like yogurt with active cultures may help, as some of these bacteria produce their own lactase.

Hard, aged cheeses (like cheddar and parmesan) and yogurt with live, active cultures are often easier to digest. The aging and fermentation processes significantly reduce the lactose content, making them more tolerable.

When lactose isn't broken down properly, it ferments in the large intestine. Common symptoms include bloating, gas, stomach cramps, nausea, and diarrhea, typically appearing within 30 minutes to 2 hours after eating.

Infants with congenital lactose intolerance require a specialized lactose-free formula. For premature infants with temporary developmental lactase deficiency, the condition often improves as their digestive system matures. Any decision regarding infant formula should be made under the guidance of a healthcare provider.

In the large intestine, lactose is broken down not by human enzymes but by resident bacteria through a process of fermentation. This process produces gases and acids that lead to symptoms like bloating and pain.