Do you grab a candy bar when you feel tired? Do you soothe your weary mind with adoughnut? These quick fixes offer a temporary high that could actually be fueling your fatigue,sending you on a blood-sugar roller coaster. For example, researchers at Kansas State Universitymeasured mood in 120 college women who drank twelve ounces of water or beverages sweetenedwith either aspartame (NutraSweet) or sugar. Within 30 minutes the women who drank the sugarsweetened beverage were the drowsiest. Some people are so sensitive to sugar or caffeine that theyfeel tired, irritable, or depressed within an hour of eating even two cookies or drinking one cup ofcoffee. Others can tolerate large sugar doses before symptoms develop.
         Sugar is a good source of carbohydrate—the energy fuel—so why do sweets bring you down?For one thing, unlike starch, which slowly releases carbohydrate units called glucose into the blood,sugar dumps rapidly into the bloodstream, causing a rapid rise in blood sugar. To counteract thisrise, the pancreas quickly releases insulin, which shuttles excess sugar from the blood into the cells.Consequently blood sugar drops, often to levels lower than before the snack.
         Sugar also increases tryptophan levels in the brain and triggers the release of the brainchemical serotonin, which in turn slow you down. A researcher and a professor of psychology at theMIT report that people feel sleepier and have “less vigor” for up to three and a half hours aftereating a highly refined carbohydrate snack, as compared to a snack that contains more protein.
          Finally, people who frequently snack on sweets are likely to consume inadequate amounts ofthe energizing nutrients. Researchers in Australia report that the more sugar people consume, thehigher their fat and calorie consumption and the lower their intake of vitamins and minerals.
        Consuming sugar as a quick fix for dwindling energy merely results in a temporary high, but inthe long run, it can initiate a vicious energy cycle.
【題組】38. Excess sugar is brought from the blood into the cells by _____.
(A) insulin
(B) carbohydrates
(C) glucose
(D) caffeine