Can Drinking Milk “Cure” Lactose Intolerance?

Most of us treat lactose intolerance like a genetic quirk: either you tolerate dairy or you don’t. But symptoms aren’t determined only by how much lactase (the lactose-digesting enzyme) you produce in your small intestine; they also depend on what happens to undigested lactose after it reaches the colon, where gut microbes ferment it and draw water into the bowel.

Your large intestine is home to trillions of bacteria that break down leftover carbohydrates, and if you regularly consume a specific carbohydrate, the microbes that can use it tend to become more active and more abundant, which can change how much gas and irritation you get from the same dose over time.

A classic stool-composition study in the Journal of Medical Microbiology found that bacteria made up about 55% of fecal solids in their controlled-diet sample. In other words, a meaningful slice of what comes out of you is, quite literally, microbial biomass and its byproducts. That’s one reason diet can change not just how you feel, but what your gut does.

Some researchers even argue that gut microbes may be under evolutionary pressure to influence host eating behavior, nudging cravings toward foods that help them thrive. You don’t have to accept that whole thesis to take the practical point that microbes respond to repeated exposure.

That brings us to lactose intolerance, or, more precisely, lactose maldigestion.

What is Lactose Intolerance?

Lactose is the sugar in milk. To absorb it, you need the enzyme lactase in your small intestine. When lactase is low, lactose slips through to the colon, where microbes ferment it. The fermentation process produces gas and acid, and the osmotic pull of unabsorbed sugar can produce those classic symptoms of bloating, cramps, and diarrhea.

In nearly all mammals, lactase production is a limited feature of infancy. During nursing, the small intestine produces abundant lactase, but after weaning, lactase gene expression typically plummets, and enzyme levels drop accordingly. Roughly 65–70% of adults globally produce insufficient lactase to comfortably digest significant amounts of lactose, making lactose intolerance remarkably common.

As it turns out, lactose intolerance isn’t a defect or disease; it’s the ancient mammalian baseline. The ability to drink milk as an adult is the fascinating exception.

Using Microbial Adaptation to Digest Lactose

This invites a key question: can the body break down lactose without producing lactase enzymes?

A frequently cited paper in the American Journal of Clinical Nutrition explored whether the gut microbiome could adapt to process lactose more effectively with repeated exposure—a phenomenon known as colonic adaptation.

The paper reports two complementary studies: an initial mechanistic investigation of microbial lactose-splitting capacity and a subsequent randomized, blinded crossover trial assessing physiological and symptom outcomes.

Study 1 (mechanism): Nine lactose maldigesters consumed an ever-increasing dose of lactose daily for 16 days. Researchers measured fecal β-galactosidase activity (a marker tied to microbial lactose-splitting capacity) and saw it rise about threefold.

In other words, regular lactose exposure was associated with a measurable increase in the microbiome’s ability to break lactose down.

Study 2 (real-world test): Twenty lactose maldigesters then did a blinded crossover: 10 days of lactose supplementation versus 10 days of dextrose (control sugar), with a 1-day break, and the lactose dose gradually increased and split into three daily doses. After each period, everyone took the same standardized lactose “challenge,” and the team measured breath hydrogen for 8 hours and noted symptoms.

The breath hydrogen result was dramatic. After the lactose-feeding period, breath hydrogen over 1–8 hours was near baseline (~9 ± 38 ppm·h) compared with after the dextrose period (~385 ± 52 ppm·h, P < 0.001). That’s an objective signal that lactose was being handled very differently after regular exposure.

Probiotics, Prebiotics, & Fermented Foods

If drinking straight milk feels daunting, fermented dairy offers a gentler entry point. The European Food Safety Authority (EFSA) reviewed the evidence and concluded that the live cultures in yogurt—specifically Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus—actively improve lactose digestion in people with lactose maldigestion.

A 2023 meta-analysis in the Journal of Dairy Science found that probiotic supplementation improved common lactose intolerance symptoms like abdominal pain, diarrhea, and flatulence across pooled trials. Dig into the underlying research, however, and the evidence quickly becomes muddied by small sample sizes, varied methodologies, and incomparable interventions.

In a systematic review published in Clinical Nutrition, the authors screened 830 records and ended up with only five randomized, placebo-controlled adult trials that fit their criteria. That small evidence base is part of the problem; the bigger issue is how different the studies were from each other.

On the prebiotic side, just two studies used the same product—a galacto-oligosaccharide (GOS) supplement, and RP-G28—and those two trials (together 462 participants) reported symptom improvement during treatment and even up to 30 days after stopping.

On the probiotic side, there were three different strains across three small studies (total 117 participants): Bifidobacterium bifidum 900791, Limosilactobacillus reuteri DSM 17938, and Lactobacillus acidophilus DDS-1—and results varied by strain (e.g., L. reuteri improved symptoms and reduced expired hydrogen; B. bifidum did not show significant symptom improvement).

Because the trials used different strains and often measured outcomes differently, the review concludes a pooled meta-analysis couldn’t be performed due to lack of comparable strains or common outcomes.

A separate systematic review in Nutrients makes a similar point more broadly: it found “varying degrees of efficacy,” but emphasized wide heterogeneity across trials and noted that only one study in their included set examined a prebiotic intervention.

Ultimately, this means we still don’t have enough apples-to-apples data to confidently say which specific probiotics are useful for lactose intolerance.

Raw Milk, A2 Milk, and When It's Not Actually Lactose

Despite popular claims, raw milk offers no advantage for lactose digestion. A randomized crossover pilot study in Annals of Family Medicine tested this directly in people with confirmed lactose malabsorption. In this study, raw milk performed no better than pasteurized milk at reducing symptoms or improving lactose digestion.

If gradual lactose exposure doesn't help your symptoms, the culprit may not be lactose. Some milk intolerance actually stems from reactions to milk proteins or other components.

The most extensively studied difference among cow’s milk proteins is between the A1 and A2 variants of β-casein. These two common forms of milk protein account for roughly a third of milk’s total protein. A Nutrients study found that lactose-intolerant individuals experienced fewer digestive symptoms when drinking milk containing exclusively A2 β-casein compared to conventional milk (which contains both A1 and A2).

A more recent randomized crossover study in the Journal of Dairy Science went further, comparing A2 milk with protein-hydrolyzed, lactose-free milk in people who reported milk sensitivity. Researchers tracked both GI symptoms and inflammation markers, reinforcing that milk sensitivity often involves factors beyond lactose alone.

If lactose adaptation strategies aren't working, consider that your issue might be with milk proteins rather than milk sugar.

Conclusion: Can You “Cure” Lactose Intolerance?

If by "cure" you mean your small intestine will start producing lactase again, the answer is almost certainly no—adult lactase levels are genetically determined and won't rebound simply because you want them to. Yet if by “cure” you mean enjoying dairy without suffering, the answer is more hopeful. For many people, lactose tolerance is something you can potentially improve by training the gut microbiome that processes the lactose your body doesn't break down.

Practically speaking, this leaves you with a fairly low-stake strategy: start small, stay consistent, and build slowly. For most people, fermented dairy is a gentler starting point than liquid milk. Probiotics or prebiotics may help certain individuals, though the research remains strain-specific and inconsistent enough that no single "take this pill" recommendation holds up across the board.

And if none of these approaches work, consider the possibility that the problem might not be lactose at all. Some symptoms attributed to lactose intolerance may actually stem from reactions to milk proteins or other components.

Drinking milk won't rewrite your genes—but with a measured, evidence-based approach, it might help you reclaim dairy on your own terms.

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