Let's say you maintain a healthy weight in your twenties by eating about 2，000 calories a day and exercising vigorously for 45minutes four times a week.To stay at that weight in your thirties，you'll have to cut your daily food intake by about 100 calories (the equivalent of a medium banana) or boost your weekly workouts.After age 40，you'll have to continue adjusting your diet and exercise plan with each decade to balance out your falling calorie needs.According to one study，a man who runs an average of 10 miles a week at age 30 will have to put in 38 miles per week by age 50 to avoid age-related weight gain2.
注釋：
1.Longitudinal Study of Aging 年齡的縱向研究
2.age-related weight gain 由於年齡增長而引起的體重增加(肥胖)
譯文
為什麼隨著年齡的增長體重會增加，是如何增加的？
當你要三十歲時，肌肉開始慢慢地萎縮了。巴爾的摩年齡縱向研究專家傑弗裏·米特博士說，在二十歲到五十歲之間，這種削弱程度很小，大約隻有10%。同時塞繆爾·克林博士，聖路易斯華盛頓大學醫學院人類營養中心的主任說，問題在於脂肪取代了那些消失的肌肉組織，每天每磅隻消耗兩個卡路裏。因此，三十歲以後，你的身體隻需比以前少的卡路裏就可以完成每日的基本功能。
我們說，你在二十來歲時每天攝入2000卡路裏，每周積極鍛煉四次，每次45分鍾，保持了健康的體重。那麼，如果你要在三十幾歲時保持這一體重，則需要每日少攝入大約100卡路裏(相當於一隻中等大的香蕉)，或增加每周健身次數。四十歲以後，每十年你就得調整飲食和健身計劃，用以平衡身體對卡路裏日漸減少的需要。一項研究表明，一個人如果三十歲時每周平均跑10英裏，在50歲以前得每周跑足38英裏來避免因年齡增長而引起的肥胖。
(3)Learn How to Burn Fat—— Raising Your Metabolic Rate
學會燃耗脂肪——提高新陳代謝率
Nobody likes dieting1.But is there any really other choice for those who want to lose weight？ Yes，there is.Look at the data below to see how many calories you can burn if you replace some fat with muscle.
Let's face it.
You can't change your genes，your age or your gender2，so there are some parts of the metabolic equation that will stay constant no matter what you do.But with a few changes in your exercise and eating habits，you can boosts your metabolism by up to 10 percent，according to researcher R.Scott Van Zant，PH.D.，of Northern Arizona University's Department of Health，Physical Education，Exercise Science and Nutrition.If that doesn't seem like much，consider this： if a 150-pound woman changed her exercise habits and converted 10 percent of her body fat to muscle，she would be able to consume 300 extra calories a day without gaining weight.Looked at another way，the right change in your metabolism could mean you can eat three chocolate chip cookies every day，without gaining weight.