The n-3 and n-6 polyunsaturated fatty acids (PUFA) are among the most studied nutrients in human metabolism. In the past few decades, prospective studies and controlled trials have supported the view that the effects of these essential fatty acids are clinically relevant. PUFA profiles in different blood compartments are reflections of both diet and metabolism, and their levels may be related to disease risk. Despite widespread interest, there is no consensus regarding which biomarkers best reflect PUFA status in the body. The measurement of PUFA levels is not straight-forward, and a wide variety of indices have been used in clinical studies, producing conflicting results. A major source of heterogeneity among studies is associated with research design, sampling, and laboratory analyses. To date, the n-3 index, n-6/n-3 ratio, and arachidonic acid (AA)/eicosapentaenoic acid (EPA) ratio are the most promising biomarkers associated with PUFA metabolism. Although hotly debated, these indices may be considered at least markers, if not risk factors, for several diseases, especially cardiovascular events and brain disorders. Here, we summarize the most updated evidence of n-3 and n-6 PUFA effects on human health, reviewing current controversies on the aforementioned indices and whether they can be considered valuable predictors of clinical outcomes.

中文翻译：

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多不饱和脂肪酸的代谢指标：当前证据，研究争议和临床实用性。

n-3和n-6多不饱和脂肪酸（PUFA）是人类代谢中研究最多的营养物质之一。在过去的几十年中，前瞻性研究和对照试验支持了以下观点：这些必需脂肪酸的作用与临床有关。不同血室中的PUFA谱是饮食和新陈代谢的反映，它们的水平可能与疾病风险有关。尽管有广泛的兴趣，但关于哪种生物标记物最能反映体内PUFA的状态尚未达成共识。PUFA水平的测量并非一帆风顺，在临床研究中已经使用了多种指标，产生了矛盾的结果。研究之间异质性的主要来源与研究设计，抽样和实验室分析有关。迄今为止，n-3指数，n-6 / n-3比率，花生四烯酸（AA）/二十碳五烯酸（EPA）的比率是与PUFA代谢相关的最有前途的生物标志物。尽管争论激烈，但这些指数至少可以视为某些疾病（尤其是心血管事件和脑部疾病）的标志，即使不是危险因素。在这里，我们总结了n-3和n-6 PUFA对人体健康的最新证据，回顾了当前对上述指标的争议以及它们是否可以被视为临床结果的有价值的预测指标。