Abstract Background Elevations in the gut metabolite trimethylamine-N-oxide (TMAO) have been linked to cardiovascular and metabolic diseases. Whether elevated TMAO levels reflect early mechanistic involvement or a sequela of evolving disease awaits elucidation. The purpose of this study was to further explore these potential associations. Methods We investigated relationships between circulating levels of TMAO and its pre-cursor substrates, dietary factors, gut microbiome profiles and disease risk in individuals with a Healthy BMI (18.5 &lt; BMI &lt; 25, n = 41) or key precursor states for cardiometabolic disease: Overweight (25 &lt; BMI &lt; 30 kg/m 2 , n = 33), Obese (BMI &gt; 30, n = 27) and Metabolic Syndrome (MetS; ≥ 3 ATPIII report criteria, n = 39). Results Unexpectedly, plasma [TMAO] did not vary substantially between groups (means of 3–4 µM; p &gt; 0.05), although carnitine was elevated in participants with MetS. Gut microbial diversity and Firmicutes were also significantly reduced in the MetS group ( p &lt; 0.05). Exploratory analysis across diverse parameters reveals significant correlations between circulating [TMAO] and seafood intake ( p = 0.007), gut microbial diversity ( p = 0.017–0.048), and plasma [trimethylamine] (TMA; p = 0.001). No associations were evident with anthropometric parameters or cardiometabolic disease risk. Most variance in [TMAO] within and between groups remained unexplained. Conclusions Data indicate that circulating [TMAO] may be significantly linked to seafood intake, levels of TMA substrate and gut microbial diversity across healthy and early disease phenotypes. However, mean concentrations remain &lt; 5 µM, with little evidence of links between TMAO and cardiometabolic disease risk. These observations suggest circulating TMAO may not participate mechanistically in cardiometabolic disease development, with later elevations likely a detrimental sequela of extant disease.

Circulating TMAO, the gut microbiome and cardiometabolic disease risk: an exploration in key precursor disorders