Patients with lactose intolerance are usually advised to avoid milk. However, many still consume dairy products despite experiencing gastrointestinal symptoms. Surprisingly, this “unreasonable” strategy may have the benefit of reducing the risk for type 2 diabetes, as shown in a recent American study.

“At first glance, the statement of the study seems counterintuitive,” said Robert Wagner, MD, head of the Clinical Studies Center at the German Diabetes Center-Leibniz Center for Diabetes Research at Heinrich Heine University Düsseldorf, Düsseldorf, Germany. “However, lactose intolerance has different manifestations.” Less severely affected individuals often consume milk and tolerate discomfort such as bloating or abdominal pain. “It is precisely these individuals that the study clearly shows have a lower incidence of diabetes associated with milk consumption,” said Wagner.

Milk’s Heterogeneous Effect

The effect of milk consumption on diabetes, among other factors, has been repeatedly studied in nutritional studies, with sometimes heterogeneous results in different countries. The reason for this is presumed to be that in Asia, most people — 60%-100% — are lactose intolerant, whereas in Europe, only as much as 40% of the population has lactose intolerance.

The authors, led by Kai Luo, PhD, research fellow in the Department of Epidemiology and Population Health at Albert Einstein College of Medicine in Bronx, New York, did not mention lactose tolerance and intolerance in their paper in Nature Metabolism. Instead, they divided the study population into lactase-persistent and non-lactase-persistent participants.

“Not being lactase-persistent does not necessarily exclude the ability to consume a certain amount of lactose,” said Lonneke Janssen Duijghuijsen, PhD, a nutrition scientist at Wageningen University, Wageningen, the Netherlands. “Studies have shown that many individuals who lack lactase can still consume up to 12 g of lactose per day — equivalent to the amount in a large glass of milk — without experiencing intolerance symptoms.”

Gut Microbiome and Metabolites

Luo and his colleagues analyzed data from 12,653 participants in the Hispanic Community Health Study/Study of Latinos, an ongoing prospective cohort study involving adults with Hispanic backgrounds. It collects detailed information on nutrition and the occurrence of diseases.

The authors examined whether the study participants were lactase-persistent or non-lactase-persistent and how frequently they consumed milk. They also analyzed the gut microbiome and various metabolites in the blood over a median follow-up period of 6 years.

The data analysis showed that higher milk consumption in non-lactase-persistent participants — but not in lactase-persistent participants — is associated with about a 30% reduced risk for type 2 diabetes when socioeconomic, demographic, and behavioral factors are accounted for. Comparable results were obtained by Luo and his colleagues with data from the UK Biobank, which served as validation.

A higher milk consumption was associated not only with a lower diabetes risk in non-lactase-persistent individuals but also with a lower body mass index. “This could be one of the factors behind the diabetes protection,” said Wagner. “However, no formal mediation analyses were conducted in the study.”

Luo’s team primarily attributed the cause of the observed association between milk consumption and diabetes risk to the gut. Increased milk intake was also associated with changes in the gut microbiome. For example, there was an enrichment of Bifidobacterium, while Prevotella decreased. Changes were also observed in the circulating metabolites in the blood, such as an increase in indole-3-propionate and a decrease in branched-chain amino acids.

These metabolites, speculated the authors, could be more intensely produced by milk-associated bacteria and might be causally related to the association between milk consumption and reduced risk for type 2 diabetes in non-lactase-persistent individuals. “The authors have not been able to provide precise evidence of these mediators, but one possible mediator of these effects could be short-chain fatty acids, which can directly or indirectly influence appetite, insulin action, or liver fat beneficially,” said Wagner.

Bacteria in the Colon

For Janssen Duijghuijsen, the conclusion that milk consumption can influence the composition of the microbiome and thus the metabolic profile, especially in individuals without lactase persistence, is plausible.

“Individuals with lactase persistence efficiently digest lactose and absorb the resulting galactose and glucose molecules in the small intestine. In contrast, in non-lactase-persistent individuals, lactase is not expressed in the brush border of the small intestine. As a result, lactose remains undigested in the colon and can serve as an energy source for gut bacteria. This can influence the composition of the microbiome, which in turn can alter the concentration of circulating metabolites,” she said.

Janssen Duijghuijsen has investigated the effect of lactose intake on the microbiome. In a recently published study, she also showed that increasing lactose intake by non-lactase-persistent individuals leads to changes in the microbiome, including an increase in Bifidobacteria.

“In line with the current study, we also found a significant increase in fecal β-galactosidase activity. Given the close relationship between the composition of the gut microbiome and the metabolite profile, it is likely that changes in one can affect the other,” said Janssen Duijghuijsen.

Nutritional Recommendations

The nutrition scientist warned against concluding that milk consumption can protect against type 2 diabetes in non-lactase-persistent individuals, however. “The study suggests a statistical association between milk consumption, certain metabolites, and the frequency of type 2 diabetes. These associations do not provide definitive evidence of a causal relationship,” she said. Any dietary recommendations cannot be derived from the study; much more research is needed for that.

This story was translated from the Medscape German edition using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.