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expert reaction to study of lactose intolerance, milk intake and type 2 diabetes

A study published in Nature Metabolism looks at lactose intolerance and the association between milk intake and type 2 diabetes. 


The comment below was provided by our friends at SMC Germany.


Dr Lonneke Janssen Duijghuijsen, Researcher Nutrition & Health, Wageningen University & Research, Wageningen Food and Biobased Research, Wageningen, The Netherlands, said:

“Lactase non-persistence does not necessarily preclude the ability to consume some amount of lactose. Research has shown that many lactase nonpersistent individuals can still consume up to 12 grams of lactose per day, comparable to the amount in a large glass of milk, without suffering from intolerance symptoms. The ability to tolerate lactose varies among individuals; some can consume more than 12 grams without issues, while others may experience symptoms with lower doses.”.

“It is highly plausible that milk consumption can influence the composition and, consequently, the metabolomic profile, particularly in lactase nonpersistent individuals. Since lactose from milk remains undigested in the small intestine of those with lactase non-persistence, it serves as an energy source for intestinal microbiota.

“In our recently published study (JanssenDuijghuijsen et al., 2023, ), we demonstrated that the ingestion of incremental amounts of lactose by individuals with the lactase non-persistent genotype leads to changes in the microbiota, including an increase in bifidobacteria. Also a significant increase in fecal β-galactosidase activity was shown, in line with the current study. Given the close connection between the composition of the gut microbiota and the metabolome profile, it is likely that changes in one can affect the other.

“It is currently premature to draw conclusive relations to type 2 diabetes. The publication suggests a statistical association without implying a causal relationship. The study proposes statistical associations  between milk consumption, a specific metabolite, and type 2 diabetes incidence. However, it is crucial to note that these associations do not provide definitive evidence of causation. The suggested links are indirect, leaving room for other influencing factors. Further research is imperative to delve deeper into these associations and determine their significance.

“The primary difference lies in how lactose is digested, as previously mentioned. In general, lactase persistent individuals efficiently digest lactose and absorb the resulting galactose and glucose molecules in the small intestine. Individuals with lactase non-persistence lack the lactase enzyme expression in the brush border of their small intestine, preventing the digestion of lactose from milk in this particular location. Consequently, the lactose remaining undigested in the small intestine, can serve as an energy source for the intestinal microbiota. This process, as demonstrated in our recent publication (JanssenDuijghuijsen et al., 2023,, can influence the composition of the microbiota, which may in turn change the levels of circulating metabolites.

“The study does not explicitly provide dietary recommendations but rather highlights potential effects of milk consumption by a specific population on gut microbiota and its metabolites and the potential relation with a specific health outcome. They are transparent that it is an observational population-based epidemiological study unable to make causal inferences.

“Addressing the sensitive topic of milk consumption by adults, it is worthwhile to note that being lactase non-persistent does not necessarily compare to lactose intolerance and gastrointestinal discomfort. Research indicates that many lactase non-persistent individuals can still tolerate up to 12 grams of lactose per day. Gastrointestinal discomfort, often associated with lactose intolerance, might be mitigated by changes in the gut microbiota, allowing for lactose digestion without the production of gases that lead to intolerance symptoms. Therefore, the study sheds light on the intricate relationship between milk consumption, the gut microbiota and its metabolites, and health outcomes. However, specific dietary recommendations would necessitate further research, considering individual tolerances, health effects, and cultural contexts.”


‘Variant of the lactase LCT gene explains association between milk intake and incident type 2 diabetes’ by Luo K et al. was published in Nature Metabolism at 16:00 UK time on Monday 22nd January. 


DOI: 10.1038/s42255-023-00961-1


Declared interests

Dr Lonneke Janssen Duijghuijsen: No conflicts of interest


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