Do Vegans Stop Producing Lactase? The Surprising Truth

January 1, 2026 •

4 min read

Worldwide, over 60% of adults are naturally lactase non-persistent, meaning their ability to digest lactose declines after childhood. For those who go vegan, this genetic trait is the primary factor, not the diet itself; vegans do not stop producing lactase due to their lifestyle.

Quick Summary

A vegan diet does not genetically halt lactase production. Any change in dairy tolerance is likely due to the gut microbiome adapting or pre-existing lactase non-persistence.

Key Points

Genetics, Not Diet, Determines Lactase Production: An adult's ability to produce the lactase enzyme is determined by their genes, not by whether they follow a vegan diet.
Lactase Production Naturally Declines for Most Adults: For most of the world's population, lactase production naturally decreases after infancy, a condition known as lactase non-persistence.
Dietary Changes Impact Gut Microbiome: Eliminating dairy from a vegan diet can reduce the population of lactose-digesting bacteria in the gut, which can lead to intolerance symptoms upon reintroduction.
Lactose Intolerance Can Be a Coincidence: Developing symptoms after quitting dairy may be a coincidence, as an individual's genetically programmed decline in lactase production can happen at any time.
Tolerance Can Be Re-Established: For most, tolerance can be re-established through gradual reintroduction of dairy to allow the gut microbiome to adapt, a process called colonic adaptation.
Lactase Supplements Offer an Alternative: For those who cannot tolerate dairy, even after adaptation, lactase enzyme supplements are available to help digest lactose.

Understanding Lactase Persistence vs. Non-Persistence

Lactase is the enzyme responsible for breaking down lactose, the sugar found in milk. In almost all mammals, and most of the human population worldwide, the production of lactase decreases significantly after infancy, a condition known as lactase non-persistence. In these individuals, undigested lactose travels to the large intestine, where it is fermented by bacteria, causing the uncomfortable symptoms of lactose intolerance.

However, a significant portion of the global population, particularly those of Northern European descent and some groups in Africa and the Middle East, have a genetic mutation that allows for continued lactase production into adulthood. This trait is called lactase persistence and allows them to digest dairy comfortably throughout their lives.

Genetics, not diet, is the primary determinant of whether an individual will be able to produce lactase as an adult. While a vegan diet naturally excludes lactose, it does not alter the underlying genetic programming that governs lactase enzyme production.

The Role of Gut Microbiota in Lactose Tolerance

If the lactase gene isn't affected by a vegan diet, why do some former dairy consumers report experiencing lactose intolerance symptoms after reintroducing dairy? The answer often lies with the gut microbiome.

How Gut Bacteria Influence Digestion

The bacteria residing in your gut play a vital role in digestion. For individuals who regularly consume dairy, certain beneficial bacteria that assist in breaking down lactose thrive in the gut. When a person follows a vegan diet and eliminates dairy, these specific lactose-digesting bacteria may decrease in population over time. When dairy is reintroduced, the gut microbiome is no longer equipped to efficiently handle the lactose load, leading to classic intolerance symptoms.

This process is known as colonic adaptation. The good news is that this adaptation can work both ways. By slowly and gradually reintroducing small amounts of lactose, it is possible to re-establish a gut flora that can process it more effectively.

Why a Vegan Diet Might Seem to Affect Dairy Tolerance

There are several reasons why a person might mistakenly attribute new-onset lactose intolerance to their vegan diet:

Coincidental Timing: Lactase non-persistence is a gradual process that can happen at any time after childhood. Some individuals may start a vegan diet coincidentally around the same time their body's natural lactase production was already programmed to decline. The vegan diet doesn't cause the decline; it simply removes the symptom-causing trigger (lactose) until dairy is reintroduced.
Lowered Tolerance Threshold: Even for people who are genetically lactase persistent, extended periods without consuming a particular food can lower the body's overall tolerance. When dairy is absent from the diet, the digestive system is not regularly exposed to lactose, and the gut can become less efficient at processing it.
Other Digestive Changes: Adopting a vegan diet involves significant changes in fiber intake and overall gut environment. This shift can influence how the digestive system reacts to different foods, including the reintroduction of dairy.

Can You Re-Build Lactose Tolerance?

For those who are genetically lactase non-persistent, it's not possible to permanently increase endogenous lactase production. However, tolerance to dairy can be improved through colonic adaptation. This involves a controlled, gradual reintroduction of dairy to allow the gut microbiota to repopulate. Starting with fermented dairy products like yogurt or kefir, which contain beneficial lactase-producing bacteria, is often recommended.

Symptoms of Lactose Intolerance

Abdominal bloating
Gas (flatulence)
Diarrhea
Stomach cramps
Nausea

Lactase Persistence vs. Non-Persistence: A Comparison


Feature	Lactase Persistence (LP)	Lactase Non-Persistence (LNP)
Genetic Basis	Presence of a gene variant that keeps lactase production 'turned on' past infancy.	Absence of the LP gene variant, leading to a natural decline in lactase production.
Enzyme Levels in Adulthood	High levels of the lactase enzyme.	Very low or minimal levels of the lactase enzyme.
Tolerance to Dairy	Typically able to consume dairy products without significant digestive issues.	Often experience symptoms of lactose intolerance after consuming more than a small amount of lactose.
Geographic Prevalence	High frequency in populations with a long history of dairying, such as Northern Europeans and some Middle Eastern/African groups.	The global default, with high prevalence in populations of Asian and African descent.
Dietary Effect	Diet does not affect the genetic expression of lactase, but prolonged avoidance can alter gut bacteria.	Diet does not affect the genetic downregulation of lactase production.

Conclusion: Diet Doesn't Control Your Genes

In summary, the notion that a vegan diet causes an individual to stop producing lactase is a misconception. The ability to produce lactase as an adult is determined by a person's genetic makeup, a trait called lactase persistence. The common experience of reduced dairy tolerance after a vegan diet is primarily a consequence of changes in the gut microbiome, which adapts to the absence of lactose. Reintroducing dairy can lead to temporary intolerance symptoms until the gut bacteria that assist in digestion have time to repopulate. The temporary nature of this intolerance highlights that the underlying genetic ability remains unchanged.

For more information on the genetic basis of this condition, visit the MedlinePlus resource on lactose intolerance genetics.

Frequently Asked Questions

A vegan diet does not trigger lactose intolerance because it does not affect the genes responsible for lactase production. Any change in dairy tolerance is likely due to pre-existing lactase non-persistence or shifts in the gut microbiome after dairy is removed from the diet.

This is likely due to changes in your gut bacteria. When dairy is removed from the diet, the bacteria that help digest lactose can decrease. When you reintroduce dairy, the lack of these bacteria can cause intolerance symptoms, a temporary condition known as colonic adaptation.

Yes, for many people it is possible to improve tolerance through gradual reintroduction. This allows the gut microbiome to adapt and repopulate with beneficial lactose-digesting bacteria.

Lactase persistence is the genetic trait that allows individuals to continue producing lactase into adulthood. Lactase non-persistence is the natural, genetically programmed decline of lactase production after infancy, which is the norm for most adults globally.

No, a reduced intake of dairy does not permanently stop your genetically determined lactase production. However, it can temporarily reduce the efficiency of your digestive system in handling lactose due to shifts in gut bacteria.

The primary risks are the uncomfortable digestive symptoms associated with lactose intolerance, such as bloating, gas, and diarrhea. Lactose intolerance is not dangerous but can be unpleasant. Consuming dairy with a lactase supplement is an option.

Yes, lactase supplements provide the necessary enzyme to break down lactose in the gut. Taking one with a dairy-containing meal can help prevent the symptoms of lactose intolerance without relying on the body's own lactase production.