Abstract
The metabolic health benefits of fermented milks have already been investigated using clinical biomarkers but the development of transcriptomic analytics in blood offers an alternative approach that may help to sensitively characterise such effects. We aimed to assess the effects of probiotic yoghurt intake, compared to non-fermented, acidified milk intake, on clinical biomarkers and gene expression in peripheral blood. To this end, a randomised, crossover study was conducted in fourteen healthy, young men to test the two dairy products. For a subset of seven subjects, RNA sequencing was used to measure gene expression in blood collected during postprandial tests and after two weeks daily intake. We found that the postprandial response in insulin was different for probiotic yoghurt as compared to that of acidified milk. Moreover changes in several clinical biomarkers were associated with changes in the expression of genes representing six metabolic genesets. Assessment of the postprandial effects of each dairy product on gene expression by geneset enrichment analysis revealed significant, similar modulation of inflammatory and glycolytic genes after both probiotic yoghurt and acidified milk intake, although distinct kinetic characteristics of the modulation differentiated the dairy products. The aryl hydrocarbon receptor was a major contributor to the down-regulation of the inflammatory genesets and was also positively associated with changes in circulating insulin at 2h after yoghurt intake (p = 0.05). Daily intake of the dairy products showed little effect on the fasting blood transcriptome. Probiotic yoghurt and acidified milk appear to affect similar gene pathways during the postprandial phase but differences in the timing and the extent of this modulation may lead to different physiological consequences. The functional relevance of these differences in gene expression is supported by their associations with circulating biomarkers.
Highlights
Fermentation is a widely used method for processing dairy milk that results in the transformation of the milk by the action of lactic acid bacteria
Postprandial responses to dairy intake for clinical biomarkers and appetite sensations Yoghurt intake induced a significantly greater postprandial insulin response compared with acidified milk whilst no differences between the products were observed for the glycemic
Little differences were observed for the responses in circulating inflammatory parameters a non-significant trend towards a lower response after yoghurt compared to acidified milk was noted for TNFα (p = 0.10)
Summary
Fermentation is a widely used method for processing dairy milk that results in the transformation of the milk by the action of lactic acid bacteria. The many health benefits that have been described for fermented milks may be attributed to the effects of the fermentation-specific changes of the milk on digestion and metabolism, and/or the interactions of the bacterial strains with the gut microbiota [4]. The wider consequences of milk fermentation on host metabolism have been investigated; in postprandial studies differential effects of fermented compared to nonfermented dairy milks have been observed for glycemia and insulinemia [7] as well as lipidemia [8] and protein flux [9]. The health benefits of fermented dairy intake are not limited to effects on postprandial metabolism; the daily intake of fermented dairy foods (in particular those containing probiotic bacteria) has been associated with lowering lipid parameters [12], regulation of glycemia [13,14,15,16] and a reduction in circulating parameters of inflammation [17,18,19,20,21]
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