Research performed on smokers at rest indicates that nicotine (尼古丁) itself can increase basal metabolic (新陈代谢的) rates, meaning smokers burn more energy than nonsmokers during periods of inactivity. But surveys suggest most smokers smoke not while completely at rest, but while performing light activities such as desk work that can increase metabolic rates by two or three times. Unless nicotine’s metabolic effects increase proportionally with metabolic rates, its influence on weight might be insignificant.Now a study shows that nicotine’s effects on body-fuel consumption indeed increase proportionally with increases in activity. “These results indicate that the metabolic effect of nicotine may play a greater part in accounting for body-weight differences between smokers and nonsmokers than was previously believed,” says Kenneth

Why do smokers tend to weigh less than nonsmokers and gain weight when they give up the habit?Contrary to “common knowledge”, nonsmokers do not generally eat more than smokers, nor do they exercise less, studies find. Research performed on smokers at rest indicates that nicotine (尼古丁) itself can increase basal metabolic (新陈代谢的) rates, meaning smokers burn more energy than nonsmokers during periods of inactivity. But surveys suggest most smokers smoke not while completely at rest, but while performing light activities such as desk work that can increase metabolic rates by two or three times. Unless nicotine’s metabolic effects increase proportionally with metabolic rates, its influence on weight might be insignificant.Now a study shows that nicotine’s effects on body-fuel consumption indeed increase proportionally with increases in activity. “These results indicate that the metabolic effect of nicotine may play a greater part in accounting for body-weight differences between smokers and nonsmokers than was previously believed,” says Kenneth A. Perkins and his colleagues at the University of Pittsburgh School of Medicine.The researchers gave a nicotine nose spray to individuals performing light work — in this case riding an exercise bicycle modified to allow easy riding while subjects   remain seated in a comfortable armchair. The activity raised resting metabolic rates two to three times.By analyzing air breathed out, the researchers calculated energy consumption in the armchair bicyclists before and after giving the nose spray and compared the relative changes with subjects in the control group given placebo (（试验药物用的）无效对照剂) nose sprays. Relative to their baseline bicycle expenditures, individuals in the nicotine group expended considerably more energy than did those in control group while doing the same amount of work. With nicotine, Perkins says, “It’s as if the body is becoming much less efficient in using its stored energy.”While the results may seem discouraging to smokers who’d like to quit without gaining weight, Perkins notes that walking an extra mile a day should make up for the difference in metabolic efficiency. And he says smokers would have to gain “well more than 50 pounds” to counterbalance the health risks of continued smoking.1. What might “common knowledge” say about smokers and nonsmokers?A)  Smokers eat more and exercise less than nonsmokers.B)  Smokers eat less and exercise more than nonsmokers. C)  Smokers eat more and exercise more than nonsmokers.D)  Smokers eat less and exercise less than nonsmokers.2. When might nicotine influence smokers’ weight significantly?A)  While smokers are at rest.B)  While smokers are exercising.C)  When Nicotine’s metabolic effects and metabolic rates increase at the same rate. D)  When Nicotine’s metabolic effects increase proportionally with the amount of light activities.3. The word “subjects” in the fourth paragraph means ________.A)  researchersB)  addicted smokersC)  people under medical treatmentD)  people undergoing an experiment 4. What have the researchers found out in their study?A)  People in the nicotine group consumed more energy. B)  People in the control group breathed out more air.C)  People without nicotine nose spray are becoming much less efficient in using energy.D)  People in the armchair expended more energy than people doing desk work.5. Why do the study results seem discouraging to some smokers according to the passage?A)  Because they want to keep fit without having to quit smoking.B)  Because they want to quit smoking and still keep fit. C)  Because they want to gain weight to tackle the health risks of continued smoking.D)  Because they want to walk an extra mile a day to lose some weight.