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Many nutritionists, having known for decades that saturated fat, fou

游客2024-01-11  29
问题             Many nutritionists, having known for decades that saturated fat, found in
       abundance in red meat and dairy products, raises blood cholesterol levels that
       are in turn associated with a high risk of coronary heart disease, have fallen
Line    victim to the temptation of simplifying dietary recommendations to facilitate
(5)     public nutrition education. After decades of promoting the consumption of all
       complex carbohydrates and eschewing all fats and oils, much of this theory has
       been discredited.
           Controlled feeding studies in which the participants eat carefully prescribed
       diets for several weeks substantiated that saturated fat increases cholesterol
(10)    levels, and that polyunsaturated fat-found in vegetable oils and fish-reduces
       cholesterol. Dietary advice should therefore emphasize the replacement of
       saturated fat with polyunsaturated fat, not total fat reduction. The subsequent
       doubling of polyunsaturated fat consumption that this advice might inspire could
       potentially contribute to a halving of coronary heart disease rates.
(15)         Indeed, the argument that fat in general is to be avoided has been hastily
       extrapolated from observations that affluent Western countries have both high intakes
       of fat and high rates of coronary heart disease. This correlation is limited to saturated
       fat, however, for societies in which people eat relatively large portions of
       monounsaturated and polyunsaturated fat (whose health benefits are nearly identical)
(20)    tend to have lower rates of heart disease. On the Greek island of Crete, for
       instance, where the traditional diet contained much olive oil, a rich source of
       monounsaturated fat, and fish, a source of polyunsaturated fat, fat constituted
       40 percent of the calories in this diet, but the rate of heart disease was lower
       than the rate for those who followed the traditional diets of Japan, where fat
(25)    composes only 8 to 10 percent of the calories. Furthermore, international
       comparisons of overall fat intake can be misleading: many negative influences
       on health, such as smoking, physical inactivity and high amounts of body fat,
       are also correlated with Western affluence. Many nutritionists decided it would
       be too difficult to educate the public about these subtleties, instead advocating a
(30)    clear, simple message that fat was insalubrious.
           The wisdom of this practice has further come into question as researchers
       discover that the two main cholesterol-carrying chemicals, low-density
       lipoprotein (LDL), and high-density lipoprotein (HDL), have very different
       effects on the risk of coronary heart disease, such that increasing the ratio of
(35)    LDL to HDL in the blood raises the risk, whereas decreasing the ratio has the
       opposite effect. Unfortunately, certain controlled feeding studies have shown
       that when a person replaces calories from saturated fat with an equal amount of
       calories from carbohydrate-rich polyunsaturated fats, not only the levels of LDL
       and total cholesterol diminish, but also the level of HDL, and thus in only a
(40)    limited reduction in risk accrues from shifting to a polyunsaturated fat diet. [br] According to the passage, which of the following is characteristic of lipoproteins?
选项 A、The dangers of lower density lipoproteins and the dangers of higher density lipoproteins are remarkably similar in the case of coronary heart disease.
B、A higher ratio of higher density lipoproteins to lower density lipoproteins has a salubrious effect on heart disease.
C、A shift from a polyunsaturated fat diet to a saturated fat diet tends to increase the risk of coronary heart disease stemming from high-density lipoproteins.
D、A shift from a polyunsaturated fat diet to a saturated fat diet tends to decrease the risk of coronary heart disease stemming from low-density lipoproteins.
E、Controlled feeding studies have yet to establish the feasibility of attempting to manipulate lipoprotein ratios through dietary change.
答案 B
解析
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