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Definition
定义
Different medical organizations, governments, and diet plans define "low fat" in slightly different ways. In general, a low-fat diet is one where 30% or less of the total daily calories come from fats. A very low-fat diet is one where 15% or less of the total daily calories come from fat. By comparison, in the average American diet about 35%-37% of calories come from fat.
不同的医疗机构、政府和饮食计划都对"低脂"有不同的定义，但差别不大。总的来说，低脂饮食是指每天摄入的卡路里总量只有30%或以下来源于脂肪。脂肪量很低的饮食是指每天摄入的卡路里总量只有15%或以下来源于脂肪。相比之下，美国人平均饮食中有35%-37%的卡路里来源于脂肪。
Origins
起源
When metabolized in the body, fats provide 9 calories per gram compared to 4 calories per gram from proteins and carbohydrates. Because of this, diet plans repeatedly target reduction in fats as a good way to lose weight. Examples of low-fat diets include the Pritikin diet and Scarsdale diet, both popular in the 1970s, Rosemary Conley's Hip and Thigh Diet (late 1980s), and the Dr. Dean Ornish Diet (2000s). Research into preventing cardiovascular disease also stimulated interest in low-fat diets as a preventative health measure.
当在身体中代谢时，每克脂肪提供9卡，而每克蛋白质和碳水化合物提供4卡。因此，饮食计划反复将减少脂肪作为减肥的好方法。低脂饮食包括在20世纪70年代十分风靡的普里特金低脂饮食和斯卡斯代尔低脂饮食、罗斯玛丽臀部和大腿饮食（20世纪80年代末）以及欧尼许节食法（21世纪初）。有关预防心血管疾病的研究也推动了人们对低脂饮食的兴趣，可将其作为预防性的健康措施。
Description
描述
Fats are described as either saturated or unsaturated based on their chemical structure. Saturated fats are found in animal fats such as butter, the fats in milk and cream, bacon fat, the fat under the skin of chickens, lard, or the fat on a piece of prime rib of beef. These fats are usually solid at room temperature. Exceptions are palm oil and coconut oil, which are both liquid saturated fats. Saturated fats are often referred to as the "bad" fats. When consumed in high amounts, they raise the level of LDL cholesterol ("bad" cholesterol) in the blood. High LDL cholesterol levels are associated with an increased risk of heart disease.
基于脂肪的化学构造，人们将其描述为饱和脂肪或不饱和脂肪。黄油等动物类脂肪、牛奶和奶油中的脂肪、培根脂肪、鸡肉皮下脂肪、猪油或是牛上肋的脂肪都属于饱和脂肪。通常这些脂肪在室温下呈固体状态。饱和脂肪经常被称为"坏"脂肪。当摄入大量饱和脂肪时，血液中低密度脂蛋白胆固醇（"坏"胆固醇）的水平会升高。高水平的低密度脂蛋白胆固醇与心脏病风险增加相关。
Unsaturated fats have a slightly different chemical structure that makes them liquid at room temperature. Unsaturated fats, especially monounsaturated fats, are considered "good" fats that can help lower cholesterol levels. Olive oil, canola oil, and peanut oil are high in monounsaturated fats. Corn oil, soybean oil, safflower oil, and sunflower oil are high in polyunsaturated fats. Fish oils are a rich source of two particular polyunsaturated fats termed long-chain omega-3 fatty acids, which have beneficial health effects.
不饱和脂肪的化学构造与其略有不同，使它们在室温下呈液体状态。不饱和脂肪，尤其是单一不饱和脂肪被认为是"好"脂肪，能有助于降低胆固醇水平。橄榄油、菜籽油和花生油富含单一不饱和脂肪。玉米油、大豆油、红花油和葵花籽油富含多元不饱和脂肪。鱼油是两种特别的称为长链欧米茄3脂肪酸的多元不饱和脂肪的丰富来源，这种脂肪有健康益处。
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