TMAO, creatine and 1-methylhistidine in serum and urine are potential biomarkers of cod and salmon intake: a randomised clinical trial in adults with overweight or obesity.

To identify biomarkers to assess participants' compliance in an intervention study with high intake of cod or salmon, compared to a fish-free diet.In this randomised clinical trial, 62 healthy overweight/obese participants consumed 750 g/week of either cod (N = 21) or salmon (N = 22) across 5 weekly dinners, or were instructed to continue their normal eating habits but avoid fish intake (Control group, N = 19) for 8 weeks.After cod intake, serum concentrations of trimethylamine N-oxide (TMAO, p = 0.0043), creatine (p = 0.024) and 1-methylhistidine (1-MeHis, p = 0.014), and urine concentrations (relative to creatinine) of TMAO (p = 2.8 × 10), creatine (p = 8.3 × 10) and 1-MeHis (p = 0.016) were increased when compared to Control group. After salmon intake, serum concentrations of 1-MeHis (p = 2.0 × 10) and creatine (p = 6.1 × 10), and urine concentrations (relative to creatinine) of 1-MeHis (p = 4.2 × 10) and creatine (p = 4.0 × 10) were increased when compared to Control group. Serum and urine concentrations of TMAO were more increased following cod intake compared to salmon intake (p = 0.028 and 2.9 × 10, respectively), and serum and urine 1-MeHis concentrations were more increased after salmon intake compared to cod intake (p = 8.7 × 10 and 1.2 × 10, respectively). Cod and salmon intake did not affect serum and urine concentrations of 3-methylhistidine, and only marginally affected concentrations of free amino acids and amino acid metabolites.TMAO measured in serum or urine is a potential biomarker of cod intake, and 1-MeHis measured in serum or urine is a potential biomarker of salmon intake.