Does Drinking Milk Increase Lactobacillus? Exploring Fermented vs. Unfermented Dairy

October 17, 2025 •

4 min read

The human gut contains trillions of microorganisms, and the right balance of these can significantly impact overall health. But does drinking milk increase Lactobacillus, a key player in gut health, or is the answer more nuanced depending on how the milk is processed?

Quick Summary

The impact of milk on Lactobacillus levels depends on whether it's fermented or unfermented. Fermented varieties, like yogurt and kefir, directly introduce live bacteria, while unfermented milk can provide prebiotic nutrients that support existing populations.

Key Points

Fermented milk directly increases Lactobacillus: Products like yogurt and kefir contain live, active cultures of Lactobacillus, directly introducing them to your gut.
Unfermented milk does not contain live Lactobacillus: Standard pasteurized milk has undergone heat treatment that kills off any naturally occurring live bacteria.
Prebiotics in milk support existing gut bacteria: Unfermented milk's lactose and oligosaccharides act as food for your gut's existing beneficial bacteria, indirectly supporting a healthy microbiome.
Lactose tolerance is improved with fermented dairy: The fermentation process breaks down lactose, making yogurt and kefir more digestible for people with lactose intolerance.
Dietary diversity is key for gut health: For the best results, combine fermented dairy with other fiber-rich and fermented foods to cultivate a diverse and healthy gut microbiome.
Other fermented foods also provide probiotics: Non-dairy sources like sauerkraut, kimchi, and miso offer additional ways to get beneficial bacteria into your system.

The Basics of Lactobacillus and Gut Health

Lactobacillus is a genus of lactic acid bacteria (LAB) that plays a critical role in the human gut microbiome. These beneficial microbes help ferment complex carbohydrates, protect against pathogens, and produce beneficial short-chain fatty acids (SCFAs) that support the health of colon cells. A healthy gut microbiome, rich in diverse beneficial bacteria like Lactobacillus, is linked to numerous health benefits, including enhanced immune function, improved digestion, and even better mental well-being.

The composition of our gut microbiota is influenced by many factors, with diet being one of the most significant. The specific foods and beverages we consume can either nourish or harm our microbial populations. This is where milk comes into the picture, but its effect isn't as straightforward as it might seem.

The Role of Fermented Dairy

The most direct way to consume Lactobacillus via dairy is through fermented products. These foods are created by introducing live bacterial cultures into milk, which then ferment the lactose, or milk sugar, to produce lactic acid.

Yogurt: A classic example, yogurt is made by culturing milk with specific bacteria, typically Lactobacillus bulgaricus and Streptococcus thermophilus. Many brands also add other beneficial probiotic strains like Lactobacillus acidophilus. The presence of 'live and active cultures' on the label indicates it contains these beneficial microbes.
Kefir: This is a fermented milk drink made using kefir grains, which contain a mix of bacteria and yeasts. It is considered a functional food due to its high concentration and variety of probiotics. Research has shown that kefir can increase Lactobacillus populations and offer numerous health benefits.
Acidophilus Milk: Some milk is specifically cultured with L. acidophilus to create a probiotic-enriched product. This can be either fermented or non-fermented, so it is important to read the label carefully.

Fermentation offers additional advantages. For people with lactose intolerance, the fermentation process breaks down much of the lactose, making fermented dairy easier to digest than regular milk. The metabolic activity of the bacteria can also create bioactive peptides and enhance the bioavailability of certain nutrients.

Unfermented Milk and Its Indirect Impact

Plain, unfermented milk, especially if pasteurized, does not contain live Lactobacillus bacteria. Pasteurization is a heating process that kills harmful bacteria but also eliminates the beneficial ones naturally present in raw milk. Therefore, drinking a glass of standard pasteurized milk will not directly add Lactobacillus to your gut.

However, this doesn't mean unfermented milk has no role in promoting a healthy gut. It contains several components that can support the growth of beneficial bacteria already residing in your digestive tract. These are known as prebiotics.

Lactose: The primary carbohydrate in milk, lactose can act as a prebiotic, serving as a food source for existing friendly bacteria.
Oligosaccharides: Cow's milk, and especially colostrum, contains oligosaccharides that have prebiotic properties and can selectively stimulate the growth of beneficial bacteria like Lactobacillus and Bifidobacterium.
Proteins: Bioactive peptides released from milk proteins during digestion can also influence the gut microbiota.

Ultimately, unfermented milk acts as a fuel for the existing good bacteria, while fermented milk is a direct source of new, live bacteria.

A Closer Look: Fermented vs. Unfermented Milk


Feature	Fermented Milk (Yogurt, Kefir)	Unfermented Milk (Pasteurized)
*Direct Source of Lactobacillus?*	Yes, contains live, active cultures.	No, pasteurization kills live bacteria.
Effect on Gut Microbiota	Directly introduces beneficial bacteria, increasing population size and diversity.	Supports existing beneficial bacteria by providing prebiotics like lactose and oligosaccharides.
Lactose Content	Lower due to fermentation, often easier for lactose-intolerant individuals to digest.	Standard lactose content, may cause digestive issues for those with intolerance.
Processing	Involves introducing specific bacterial starter cultures.	Involves heat treatment (pasteurization) to ensure safety.
Nutritional Profile	Contains all the nutrients of milk, plus unique bioactive compounds created during fermentation.	Excellent source of protein, calcium, vitamins B12 and D, but lacks live probiotics.

Other Dietary Influences on Your Gut

While milk, especially in its fermented form, is a powerful tool for modulating the gut microbiome, a holistic approach is key. The diversity and health of your gut bacteria are influenced by many other dietary and lifestyle factors.

Fiber-Rich Foods: Prebiotic fibers found in fruits, vegetables, legumes, and whole grains act as food for beneficial gut bacteria. Combining these with probiotic-rich foods can create a powerful synergistic effect.
Other Fermented Foods: Besides dairy, foods like sauerkraut, kimchi, miso, tempeh, and kombucha are excellent sources of diverse probiotic organisms.
Stress and Sleep: Chronic stress and poor sleep can negatively impact the gut microbiome. Managing these factors is crucial for maintaining microbial balance.
Antibiotics: These medications can disrupt the delicate balance of gut bacteria by killing off beneficial strains along with the harmful ones. In such cases, consuming probiotics can help repopulate the gut.

Conclusion

Simply drinking standard, pasteurized milk will not directly increase Lactobacillus because the bacteria are killed during processing. However, it can provide prebiotic nutrients that nourish existing beneficial bacteria in your gut. The most effective way to increase Lactobacillus through milk consumption is to choose fermented dairy products like yogurt and kefir, which contain high concentrations of live, active cultures. For a truly healthy gut, it is best to combine fermented dairy with a diverse, high-fiber diet and a healthy lifestyle, providing both the probiotics and the prebiotics needed to thrive. For personalized nutrition advice, consider consulting with a registered dietitian.

BDA - British Dietetic Association

Frequently Asked Questions

No, regular pasteurized milk does not provide probiotics. The pasteurization process involves heating the milk to a high temperature, which kills the live bacteria, including Lactobacillus.

Fermented milk products are made by adding live, active bacterial cultures to milk. These bacteria ferment the milk, resulting in a product that is rich in live probiotic strains, which are then introduced to your gut when consumed.

A probiotic is a live microorganism, while a prebiotic is a type of non-digestible fiber that acts as food for the beneficial bacteria already in your gut. Fermented milk contains probiotics, whereas unfermented milk contains prebiotics (like lactose and oligosaccharides) that nourish your existing gut flora.

Raw, unpasteurized milk can contain naturally occurring Lactobacillus and other beneficial bacteria. However, its consumption is associated with food safety risks, and it is not recommended for everyone.

Other excellent sources of Lactobacillus include fermented foods like sauerkraut, kimchi, tempeh, and miso. Some non-dairy beverages like kombucha also contain beneficial microbes.

For lactose intolerant individuals, fermented milk products are often easier to digest than regular milk because the fermentation process breaks down much of the lactose. The live probiotics may also assist with lactose digestion in the small intestine.

If your goal is to introduce new, live probiotic bacteria like Lactobacillus into your gut, consuming yogurt or kefir is more effective. Both products offer valuable nutrients, but fermented dairy provides a direct probiotic boost.