Let's say you're an 18 year old male who runs every other day, logging 12 miles a week.
假设你是一个18岁的男性，每隔一天就会跑步，算下来每周会跑12英里。
Now fast-forward to your late 40's.
现在，把你的年龄快速往后推到40多近50岁。
Your eating habits are the same.
你的饮食习惯不变。
To maintain your high school weight, how many miles a week would you need to run?
为了保持你高中时的体重，你一周需要跑多少英里呢？
Believe it or not, you'd have to multiply your weekly mileage 4 and 1/2 times, increasing it from 12 to 54 miles a week!
信不信由你，你得把每周的英里数乘以4.5，也就是从每周的12英里增加到54英里！
Unless you take up weekly double marathons in middle-age, it's impossible simply to “out run”middle-age spread.
除非你在人到中年时，每周进行两次马拉松长跑，否则绝不可能轻易逃脱中年发福。
That's because metabolism decreases with age.
这是因为，新陈代谢的过程随年龄而逐渐放缓。
At 50 you just don't burn as many calories as you did at 18.
到了50岁，你就不能像18岁时一样燃烧同样多的卡路里。
Luckily, there are other factors in this equation.
幸运的是，在这个等式中还有其他的影响因素。
Gradually eatingless is one way to make up the difference, since metabolism slows by about 100 calories every ten years.
减少食量是一种弥补差额的方法。因为新陈代谢的过程每隔十年就会降低100卡路里的消耗。
That's equivalent to a tablespoon of butter.
这个数字相当于一大匙黄油的热量。
To keep pace with metabolic changes, your daily menu at 40 could include everything you ate at 30, minus that tablespoon of butter!
为了跟上新陈代谢过程的不断变化，你在40岁时的每日菜单必须在30岁时的食谱里减少一大匙黄油。
However, cutting more calories every ten years gets trickier, and limiting food intake alone isn't the healthiest approach, anyway.
然而，每隔十年减少更多的热量摄入越来越棘手，并且，不管怎样，仅仅限制食物摄取并不是一条健康的途径。
Between our 20th and 70th birthdays, most of us lose about 30%of our muscle cells.
在我们20岁生日和70岁的生日之间，我们中大多数人丧失了大约30%的肌肉细胞。
Loss of muscle mass is the main reason metabolism slows down in the first place, since resting metabolic rate is directly related to lean body mass that's mostly muscle.
本来，肌肉数量的减少是新陈代谢减缓的主要原因。这是由于停滞的新陈代谢率与大部分为肌肉的“瘦肉组织”直接相关。
Maintaining or increasing muscle mass through strength training ups your metabolism and burn smore calories, even while you're sitting on the couch!
通过体能训练来维持或增加瘦肉组织，能提高你的新陈代谢和增加更多热量消耗，甚至当你坐在沙发上时也可以做到！
Two or three sessions a week, using free weights or equipment at a gym, will do the trick.
一周花上两到三次时间，利用好健身房里的力量训 练器材或装备，你就能获得理想的效果。
