Willett Walter C
Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts 02115, USA.
J Cardiovasc Med (Hagerstown). 2007 Sep;8 Suppl 1:S42-5. doi: 10.2459/01.JCM.0000289275.72556.13.
n-6 Fatty acids, like n-3 fatty acids, play essential roles in many biological functions. Because n-6 fatty acids are the precursors of proinflammatory eicosanoids, higher intakes have been suggested to be detrimental, and the ratio of n-6 to n-3 fatty acids has been suggested by some to be particularly important. However, this hypothesis is based on minimal evidence, and in humans higher intakes of n-6 fatty acids have not been associated with elevated levels of inflammatory markers. n-6 Fatty acids have long been known to reduce serum total and low-density lipoprotein cholesterol, and increases in polyunsaturated fat intake, mostly as n-6 fatty acids, were a cornerstone of dietary advice during the 1960s and 1970s. In the United States, for example, intake of n-6 fatty acids doubled and coronary heart disease (CHD) mortality fell by 50% over a period of several decades. In a series of relatively small, older randomized trials, in which intakes of polyunsaturated fat were increased (even up to 20% of calories), rates of CHD were generally reduced. In a more recent detailed examination of fatty acid intake within the Nurses' Health Study, greater intake of linoleic acid, up to about 8% of energy, has been strongly related to lower incidence of myocardial infarction or CHD death. Because n-3 fatty acids were also related inversely to risk of CHD, the ratio was unrelated to risk. n-6 Fatty acids reduce insulin resistance, probably by acting as a ligand for peroxisome proliferator-activated receptors-gamma, and intakes have been inversely related to risk of type 2 diabetes. Adequate intakes of both n-6 and n-3 fatty acids are essential for good health and low rates of cardiovascular disease and type 2 diabetes, but the ratio of these fatty acids is not useful. Reductions of linoleic acid to "improve" this ratio would likely increase rates of cardiovascular disease and diabetes.
n-6脂肪酸与n-3脂肪酸一样，在许多生物学功能中发挥着重要作用。由于n-6脂肪酸是促炎性类二十烷酸的前体，因此有人认为较高的摄入量是有害的，并且有人提出n-6与n-3脂肪酸的比例尤为重要。然而，这一假设所依据的证据极少，而且在人类中，较高的n-6脂肪酸摄入量与炎症标志物水平升高并无关联。长期以来，人们已知n-6脂肪酸可降低血清总胆固醇和低密度脂蛋白胆固醇，在20世纪60年代和70年代，多不饱和脂肪摄入量的增加（主要是n-6脂肪酸）是饮食建议的基石。例如，在美国，在几十年的时间里，n-6脂肪酸的摄入量增加了一倍，冠心病（CHD）死亡率下降了50%。在一系列相对较小的、较早的随机试验中，多不饱和脂肪的摄入量增加了（甚至高达卡路里的20%），冠心病的发病率总体上有所降低。在护士健康研究中最近对脂肪酸摄入量进行的一项更详细的研究中，亚油酸摄入量增加至约占能量的8%，与心肌梗死或冠心病死亡的较低发病率密切相关。由于n-3脂肪酸也与冠心病风险呈负相关，因此该比例与风险无关。n-6脂肪酸可能通过作为过氧化物酶体增殖物激活受体-γ的配体来降低胰岛素抵抗，其摄入量与2型糖尿病风险呈负相关。摄入足够的n-6和n-3脂肪酸对于保持良好健康以及降低心血管疾病和2型糖尿病的发病率至关重要，但这些脂肪酸的比例并无实际意义。降低亚油酸摄入量以“改善”这一比例可能会增加心血管疾病和糖尿病的发病率。
