Fish is widely endorsed as a food that should be regularly included in our diet. Besides being low in fat and high in protein and essential nutrients, it is hailed as a means of lowering cardiovascular risk. The cardiovascular health benefits have been inferred from the fact that fish, especially oily fish, is a source of long-chain omega-3 polyunsaturated fatty acids (3-PUFAs).
The beneficial cardioprotective effects of fish have indeed been reported in numerous studies. Data from observational studies, however, have not shown a clear link between dietary fish intake and cardiovascular disease risk factors, such as blood pressure and body mass index (BMI). Some have observed reductions in blood pressure with increased fish intake, whilst others report that there was no effect.
1H-NMR Metabolic profiling investigations have aimed to identify objective biomarkers of fish intake to facilitate consistency. Furthermore, the study of such biomarkers could help elucidate the underlying mechanisms of the positive cardiovascular health outcomes associated with fish intake.
3-PUFAs and polychlorinated biphenyls, amongst others, have been identified as serum biomarkers for fish intake. Research on urinary biomarkers is less advanced but trimethylamine-N-oxide (TMAO), taurine, and 1-methylhistidine appear to be likely candidates. Urinary biomarkers of fish intake are particularly desirable since this would allow non-invasive monitoring in observational studies.
The latest analysis of data from the INTERMAP study (International Study of Macro-/Micronutrients and Blood Pressure; NCT00005271) has identified three predominant metabolites associated with fish intake —TMAO, homarine, and taurine. Urine samples from almost 5000 participants were prepared and analyzed by proton nuclear magnetic spectroscopy (1H-NMR) using a Bruker Avance IVDr system and following the standardized SOPs for urine analysis.
Homarine is a novel potential urinary biomarker of shellfish intake. Although validation of this finding is needed through further studies, it may contribute to the development of new objective dietary biomarkers.
In addition, investigations of the relationships between fish consumption and these urinary metabolites with blood pressure and body mass index (BMI) revealed that the associations between fish intake and health outcomes appear to be region-specific. This may be a consequence of cultural differences in dietary patterns and/or gut microbiota.
There was a direct association between fish intake in Japanese participants but not in Western participants. In contrast, urinary TMAO was directly associated with BMI for Western participants but not for Japanese participants. Similarly, an association was observed between TMAO and diastolic blood pressure in Western populations but not in those from Japan.
This study has provided new insights into the metabolites of fish intake, which may enable the development of new urinary biomarkers by 1H-NMR metabolic profiling. It has also highlighted the possibility that health outcomes may be determined by ethnicity or region, and the need for more in-depth research in this area.
Gibson R, et al. Am J Clin Nutr 2020;111:280–290. https://academic.oup.com/ajcn/article/111/2/280/5645625