Milk and other dairy products may offer greater health benefits than previously recognized, thanks to the sugars they contain naturally. That is because lactose and its breakdown products may act as prebiotics that feed our gut microbiota and therefore play a role in modulating the host health, researchers have discovered.
It is yet another reason to include dairy in our diet, on top of the established health benefits gained from its rich nutrient content.
Rethinking lactose: from problem to potential
When we think of lactose, we often see it in a negative light due to its association with lactose intolerance – a condition causing sufferers to have digestive discomfort after consuming dairy foods. But nutrition researchers from Brazil and France decided to investigate how lactose consumption might benefit people who don’t have this intolerance (1).
Their focus? The gut microbiome – a community of trillions of bacteria living in our digestive tract, playing a key role in everything from digestion to immunity. Scientists have long known that what we eat can influence the balance of these microbes, but this study is one of the first to explore how lactose itself might act as a prebiotic – a compound that boosts beneficial gut bacteria.
Investigating the gut-friendly role of lactose
Lactose – the natural sugar found in dairy foods – is a vital nutrient in infants and has been shown to have health benefits in adults. It raises blood glucose levels less than other sugars and is associated with a lower risk of cancer (2). Recent studies suggest that lactose intake may also impact the composition and metabolism of the gut microbiome, stimulating the growth of beneficial bacteria and increasing the production of their metabolites (3-5).
In a new study, nutrition researchers set out to assess the effects of lactose on the gut microbiome of healthy adults, considering the impact of different amounts of lactose for the first time. The research team ran two types of lab-based experiments using models that simulate the human gut. The first looked at the short-term effects of lactose intake, while the second studied long-term impacts using a dynamic system that mimics daily digestion over time.
In both experiments, the researchers used a mixture of lactose and its digestion products – galactose, and glucose – to mimic how our bodies absorb milk sugars. They tested three doses: equivalent to drinking half a glass, one glass, or two glasses of milk. Here’s what they discovered…
Lactose consumption can enhance our gut microbiome
The researchers found that lactose consumption significantly altered the composition of the gut microbiome – in a good way. Lactose improved the gut microbiome’s structure in healthy adults over both the short-term and the long-term.
- In short-term studies, lactose consumption significantly increased the Prebiotic Index compared with control studies. The Prebiotic Index is a tool used to evaluate the prebiotic effects of different carbohydrates on gut bacteria – it assesses the extent to which a prebiotic promotes the growth of beneficial bacteria versus potentially harmful bacteria
- All doses of lactose significantly increased populations of beneficial Bifidobacterium bacteria and reduced populations of potentially harmful Clostridium and Bacteroides bacteria
- Long-term studies confirmed these findings, with all doses of lactose increasing the relative abundance of beneficial Lactobacillus bacteriaand decreasing the relative abundance of Clostridium bacteria
Lactose consumption can support the gut metabolism
The study also found that lactose consumption led to a boost in short-chain fatty acids (SCFAs) – acetate, propionate, and lactate – produced by gut bacteria. These SCFAs have roles in maintaining gut health, supporting energy metabolism and influencing overall health.
- In short-term studies, all doses of lactose resulted in significant increases in acetate, although the production of propionate and butyrate decreased compared with control studies
- In long-term studies, lactose consumption appeared to increase the production of lactate and propionate, although acetate production decreased
What does this mean for milk drinkers?
For people who are lactose-tolerant and enjoy eating dairy foods, this study offers another reason to keep milk in the diet. It suggests that regular lactose intake may nourish the gut bacteria in ways that support overall digestive health.
The results of this study support the role of lactose as a prebiotic that exerts health benefits through selective stimulation of gut Bifidobacteria and Lactobacilli (4,6,7).Previous studies have highlighted the positive impact of such bacterial strains on gut health, as they play a crucial role in maintaining a balanced gut microbiome (8).
Of course, this research is still in its early stages and was done in lab models, not people. The authors suggest that clinical trials should be the next step for establishing a better understanding of the prebiotic effects of lactose. In the meantime, these results reveal the prebiotic potential of drinking a glass of milk for healthy, lactose-tolerant people.
“Lactose ingestion could positively modulate the gut microbiota in healthy lactose-tolerant adults, thereby promoting gut health and shedding light on the dietary benefits of consuming milk.”
