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学过有机化学的人都知道,饱和脂肪是指含有一个甘油分子与3个饱和脂肪酸分子的有机化合物,而不饱和脂肪则是指含有一个甘油分子与3个不饱和脂肪酸分子的有机化合物。饱和脂肪酸的碳氢链中无双键,不饱和脂肪酸的碳氢链中却含有一个至多个双键。
那么,哪些动植物油脂属于饱和脂肪呢?黄油、牛奶、肉类、鲑鱼和蛋黄含有动物饱和脂肪,植物饱和脂肪则来自巧克力、可可脂、椰子和棕榈油。按现行食品指南,饱和脂肪的摄入量应限制在10%以内,否则将提高患心血管病的风险。
然而,《英国医学杂志》(BMJ)刚刚发表的一篇文章却指出,饱和脂肪与多病因死亡、心血管病(CVD)、冠心病(CHD)、缺血性中风和2型糖尿病均无关联(Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies)。
作者在原文的摘要中写道:
Saturated fat intake was not associated with all cause mortality (relative risk 0.99, 95% confidence interval 0.91 to 1.09), CVD mortality (0.97, 0.84 to 1.12), total CHD (1.06, 0.95 to 1.17), ischemic stroke (1.02, 0.90 to 1.15), or type 2 diabetes (0.95, 0.88 to 1.03). There was no convincing lack of association between saturated fat and CHD mortality (1.15, 0.97 to 1.36; P=0.10).
多病因死亡的相对风险为0.99(0.91-1.09),CVD死亡相对风险为0.97(0.84-1.12),总CHD相对风险为1.06(0.95-1.17),缺血性中风相对风险为1.02(0.90-1.15),2型糖尿病相对风险为0.95(0.88-1.03)。脂肪与CHD死亡相对风险之间尚无定论。
这项研究的意义在于间接否定了饱和脂肪与慢性炎症的关联,因为慢性炎症才是心血管病及糖尿病的诱因。由于饱和脂肪被消化后生成饱和脂肪酸,因此可以期待为饱和脂肪酸“平反昭雪”的日子已为期不远!
实际上,我前几天已经介绍过(为脂肪酸“平反”),导致2型糖尿病及非酒精性脂肪肝病的“元凶”是神经酰胺,而不是脂肪酸,尽管神经酰胺是由鞘氨醇与脂肪酸所组成的。否定脂肪酸诱导胰岛素抵抗,实际上已经排除脂肪酸导致炎症的可能性。
至于用碳水化合物代替饱和脂肪的问题,已有研究发现用高升糖指数的碳水化合物取代饱和脂肪,可以增大CVD风险,而用低升糖指数的碳水化合物(如水果、蔬菜、豆类和谷类)取代饱和脂肪,则能降低风险。
还有研究发现,用亚油酸替代饱和脂肪导致因CHD死亡的风险为1.33,导致CVD的风险为1.27,几乎没有好坏之分。用单不饱和脂肪或碳水化合物代替饱和脂肪,未发现明显降低CHD风险,只稍稍增大非致死性心梗风险。若用奶制品的饱和脂肪代替红肉的饱和脂肪,则CVD风险降低。
从这些结果可以进一步推论,过量食用动物食品的弊端不在于它们含有饱和脂肪及饱和脂肪酸,而是由于所含血红素、左旋肉碱、硫酸软骨素等成分,使得肠菌生态平衡被打破,肠道完整性受到破坏,肠粘膜细胞出现异常增殖。
另外,这项研究还谈到反式脂肪问题,只不过反式脂肪对健康有害已成为人们的共识,也就不会出现任何“闪光点”了。不过,仍然发现反式脂肪摄入与2型糖尿病及缺血性中风风险没有关联。
我有一个观点,既然动物来源的食品既有饱和脂肪酸,也有单不饱和及多不饱和脂肪酸,就表明它们各司其职,不可缺少。人类作为动物界的一员,其体内也是饱和、不饱和脂肪酸俱全,没有理由说明人体只需要不饱和脂肪酸,而不需要饱和脂肪酸。
总之,现代人应回归以“素食为主、肉食为辅、荤素搭配”的饮食习惯,毕竟人类进化的缓慢节奏赶不上饮食革命的飞快步伐,只有相向而行,才能平安无事,这大概就是“天人合一”的道理。
Trans fats, but not saturated fats like butter, linked to greater risk of early death and heart disease
Date:August 11, 2015
Source:McMaster University
Summary:Contrary to prevailing dietary advice, a recent evidence review found no excess cardiovascular risk associated with intake of saturated fat. In contrast, research suggests that industrial trans fats may increase the risk of coronary heart disease.
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A study led by researchers at McMaster University has found that that trans fats are associated with greater risk of death and coronary heart disease, but saturated fats are not associated with an increased risk of death, heart disease, stroke, or Type 2 diabetes.
The findings were published today by the British Medical Journal (BMJ). The lead author is Russell de Souza, an assistant professor in the Department of Clinical Epidemiology and Biostatistics with the Michael G. DeGroote School of Medicine.
"For years everyone has been advised to cut out fats. Trans fats have no health benefits and pose a significant risk for heart disease, but the case for saturated fat is less clear," said de Souza.
"That said, we aren't advocating an increase of the allowance for saturated fats in dietary guidelines, as we don't see evidence that higher limits would be specifically beneficial to health."
Guidelines currently recommend that saturated fats are limited to less than 10 per cent, and trans fats to less than one per cent of energy, to reduce risk of heart disease and stroke.
Saturated fats come mainly from animal products, such as butter, cows' milk, meat, salmon and egg yolks, and some plant products such as chocolate and palm oils. Trans unsaturated fats (trans fats) are mainly produced industrially from plant oils (a process known as hydrogenation) for use in margarine, snack foods and packaged baked goods.
Contrary to prevailing dietary advice, a recent evidence review found no excess cardiovascular risk associated with intake of saturated fat. In contrast, research suggests that industrial trans fats may increase the risk of coronary heart disease.
To help clarify these controversies, de Souza and colleagues analysed the results of 50 observational studies assessing the association between saturated and/or trans fats and health outcomes in adults.
Study design and quality were taken into account to minimise bias, and the certainty of associations were assessed using a recognized scoring method developed at McMaster.
The team found no clear association between higher intake of saturated fats and death for any reason, coronary heart disease (CHD), cardiovascular disease (CVD), ischemic stroke or type 2 diabetes.
However, consumption of industrial trans fats was associated with a 34 per cent increase in death for any reason, a 28 per cent increased risk of CHD mortality, and a 21 per cent increase in the risk of CHD.
Inconsistencies in the studies analysed meant that the researchers could not confirm an association between trans fats and type 2 diabetes. And, they found no clear association between trans fats and ischemic stroke.
The researchers stress that their results are based on observational studies, so no definitive conclusions can be drawn about cause and effect. However, the authors write that their analysis "confirms the findings of five previous systematic reviews of saturated and trans fats and CHD."
De Souza, a registered dietitian, added that dietary guidelines for saturated and trans fatty acids "must carefully consider the effect of replacement foods.
"If we tell people to eat less saturated or trans fats, we need to offer a better choice. Unfortunately, in our review we were not able to find as much evidence as we would have liked for a best replacement choice, but ours and other studies suggest replacing foods high in these fats, such as high-fat or processed meats and donuts, with vegetable oils, nuts, and whole grains."
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The above post is reprinted from materials provided by McMaster University. Note: Materials may be edited for content and length.
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