Physiological changes due to mild cooling in healthy lean males of white Caucasian and South Asian descent: A metabolomics study.

During mild cold exposure, non-shivering thermogenesis increases to maintain core body temperature by increasing utilization of substrates, especially fatty acids (FA), ultimately affecting lipid-associated metabolites. We aimed to investigate whether mild cooling induces changes in other metabolites and whether this response differs between white Caucasians and South Asians, who have a disadvantageous metabolic phenotype. 12 lean male Dutch white Caucasians and 12 matched Dutch South Asians were exposed to mild cold. Before and after 100 min exposure, serum samples were collected for analysis of 163 metabolites and 27 derived parameters using high throughput metabolomics. The overall response to mild cooling between both ethnicities was not different, therefore the data were pooled. After Bonferroni correction, mild cooling significantly changed 44 of 190 (23%) metabolic parameters. Specifically, cooling increased 19 phosphatidylcholine (PC) species, only those containing very long chain FAs, and increased the total class of PC containing mono-unsaturated FAs (+12.5%). Furthermore, cooling increased 10 sphingomyelin species as well as the amino acids glutamine (+18.7%), glycine (+11.6%) and histidine (+10.6%), and decreased short-chain (C3 and C4) acylcarnitines (-17.1% and -19.4%, respectively). In conclusion, mild cooling elicits substantial effects on serum metabolites in healthy males, irrespective of white Caucasian or South Asian ethnicity.