Animal protein tied to higher circulating trimethylamine N-oxide

An increased circulating trimethylamine N-oxide (TMAO) is consistently associated with animal protein consumption, whereas TMAO associations with fish, shellfish, eggs, and red meat intakes vary among populations, according to a study. TMAO is a diet-derived, gut microbial-host cometabolite that has been linked to cardiometabolic diseases.

The authors included 32,166 adults (16,269 White, 13,293 Asian, 1,247 Hispanic/Latino, 1,236 black, and 121 others) without cardiovascular disease, cancer, chronic kidney disease, or inflammatory bowel disease in the analysis. They computed for the linear regression coefficients (β) for standardized TMAO with harmonized variables.

Random-effects meta-analysis was conducted to combine study-specific results. A false discovery rate <0.10 was considered significant.

After adjustment for potential confounders, circulating TMAO correlated with intakes of animal protein and saturated fat (β, 0.124 and 0.058, respectively, for a 5-percent energy increase) and with shellfish, total fish, eggs, and red meat (β, 0.370, 0.151, 0.081, and 0.056, respectively, for a 1 serving/d increase).

Plant protein and nuts were inversely associated with circulating TMAO (β, –0.126 for a 5-percent energy increase from plant protein and –0.123 for a 1 serving/d increase of nuts).

The association between animal protein and TMAO was consistent across populations, but fish and shellfish associations were more robust in Asians (β, 0.285 and 0.578, respectively), while egg and red meat associations were stronger in Americans (β, 0.153 and 0.093, respectively).

In addition, circulating TMAO positively correlated with creatinine (β, 0.131 SD increase in log-TMAO), homocysteine (β, 0.065), insulin (β, 0.048), glycated haemoglobin (β, 0.048), and glucose (β, 0.023) but was inversely associated with high-density lipoprotein cholesterol (β, –0.047) and blood pressure (β, –0.030).

Each association between TMAO and biomarkers remained significant after adjusting for creatinine and was robust in subgroup/sensitivity analyses.

“The adverse associations of TMAO with certain cardiometabolic biomarkers, independent of renal function, warrant further investigation,” the authors said.