As autumn approaches, seasonal change reminds us that our biology is continuously evolving throughout life. Aging is accompanied by measurable shifts in metabolism, many of which reflect the complex relationship between the human host and the gut microbiome.
This season, we highlight the TMAO/choline ratio, a promising metabolomics biomarker that provides insight into host-microbiome interactions and age-related metabolic processes. Emerging research suggests that this ratio may serve as a valuable indicator of healthy aging, helping researchers better understand the biological mechanisms that contribute to longevity and metabolic health (Kanitsoraphan et al. 2018; Janeiro et al. 2018).
Metabolic Biomarkers Reveal the Biology of Aging
Just as changing leaves signal the transition of the seasons, metabolite profiles can reveal important biological signatures of aging.
The TMAO/choline ratio combines two biologically linked metabolites:
- Choline, an essential nutrient involved in cell membrane synthesis, lipid metabolism, and neurotransmission (Sanders and Zeisel 2007)
- Trimethylamine N-oxide (TMAO), a host-microbiome co-metabolite associated with cardiometabolic health and age-related metabolic changes (Janeiro et al. 2018; Kanitsoraphan et al. 2018)
Accurate quantification of both metabolites enables researchers to gain deeper insight into age-associated metabolic processes and the dynamic crosstalk between the gut microbiome and the host.
Understanding the Choline-TMA-TMAO Pathway
The biological significance of the TMAO/choline ratio lies in the pathway connecting dietary nutrients, microbial metabolism, and host physiology.
After dietary intake, choline is metabolized by specific gut microorganisms into trimethylamine (TMA). TMA is then absorbed into the bloodstream and oxidized in the liver to produce TMAO (Janeiro et al. 2018).
Because it relates a metabolic precursor to its downstream product, the TMAO/choline ratio serves as a functional indicator of activity within the choline-TMA-TMAO pathway. The ratio reflects the combined influence of:
- Nutrient availability
- Gut microbial metabolism
- Host metabolic function
As a quantitative measure of host-microbiome crosstalk, the TMAO/choline ratio can provide more mechanistic insight than either metabolite alone.
Healthy Aging Spotlight: Metabolomics and Age Prediction
The relevance of this pathway is highlighted in our recent whitepaper, Metabolic Age Calculation with Plasma and Dried Blood.
Notably, most evaluated age-prediction models demonstrated improved performance when metabolic indicators were included, with TMAO synthesis markers such as the TMAO/choline ratio ranking among the most informative predictors of chronological age.
These findings suggest that microbiome-dependent metabolism contributes measurable information to biological aging beyond traditional clinical biomarkers. As a result, host-microbiome metabolism may play an increasingly important role in metabolomics-driven approaches to biological age assessment.
Evidence from Longevity Research
Additional support comes from the New England Centenarian Study, which identified the ergothioneine/TMAO ratio among metabolite signatures associated with age, survival, and exceptional longevity (Monti et al. 2026).
Together, these observations reinforce the growing importance of TMAO-related metabolic pathways as indicators of age-associated changes in host-microbiome interactions and healthy aging.
Importantly, the study combined deep untargeted metabolomics with data from multiple independent cohorts and analytical platforms, including standardized targeted metabolomics using the biocrates Quant 500 kit in the Baltimore Longitudinal Study of Aging.
Today, the Biognosys Group brings together the strengths of both approaches, enabling researchers to combine high-confidence targeted quantification with comprehensive untargeted metabolite discovery in a single hybrid metabolomics workflow.
- Explore MetaboINDICATOR tool
- Discover biocrates pathway coverage
Publication bibliography
Janeiro, Manuel H.; Ramírez, María J.; Milagro, Fermin I.; Martínez, J. Alfredo; Solas, Maite (2018): Implication of Trimethylamine N-Oxide (TMAO) in Disease: Potential Biomarker or New Therapeutic Target. In Nutrients 10 (10). DOI: 10.3390/nu10101398.
Kanitsoraphan, Chanavuth; Rattanawong, Pattara; Charoensri, Suranut; Senthong, Vichai (2018): Trimethylamine N-Oxide and Risk of Cardiovascular Disease and Mortality. In Current nutrition reports 7 (4), pp. 207–213. DOI: 10.1007/s13668-018-0252-z.
Monti, Stefano; Lustgarten, Michael S.; Huang, Ziwei; Song, Zeyuan; Li, Mengze; Ellis, Dylan et al. (2026): Metabolomic signatures of extreme old age: findings from the New England Centenarian Study. In GeroScience. DOI: 10.1007/s11357-026-02174-2.
Sanders, Lisa M.; Zeisel, Steven H. (2007): Choline: Dietary Requirements and Role in Brain Development. In Nutrition today 42 (4), pp. 181–186. DOI: 10.1097/01.NT.0000286155.55343.fa.