Lactose is a disaccharide that consists of the monosaccharides glucose and galactose linked together by a beta-1,4 glycosidic bond and is only found in mammalian milk. The mammalian enzyme lactase produced in the human small intestine hydrolyzes lactose to release glucose and galactose. However, this conversion is not always absolute; one seminal report that measured lactose in ileal aspirations of healthy human adults found that  approximately 0-8% of lactose consumed was not broken down and absorbed. Therefore, upon consumption of bovine milk, a small amount of lactose may be available for use by the colon gut microbiota. In particular, lactic acid bacteria and <i>Bifidobacteria</i>, which are ubiquitous members of the gut microbiota, produce the enzyme beta-galactosidase, which is also able to metabolize lactose into glucose and galactose and produce metabolic byproducts such as short chain fatty acids (SCFAs). To fully understand how the dairy component lactose may serve as a mediator of the gut microbiota, we analyzed the effects of lactose on the gut microbiota of donors from healthy adults and elderly adults, through application of the short term, batch incubation culturing platform. Changes to the community function were determined through quantification of short chain fatty acids and gas production. To elucidate the effect of lactose on community structure, 16S rRNA sequencing was performed to provide information on changes to diversity and relative abundance of community members and qPCR analysis was used to specifically analyze the impact of lactose on <i>Bifidobacteria</i>. Together, these results demonstrate the potential for lactose to serve as a mediator of the gut microbiota structure and function for adults and elder adults. These results are  important to understanding the contribution of dietary milk to human health through promotion of a healthy gut microbiome.

Lactose as a modifier of the gut microbiota

ACS Spring 2022

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