During the darkest years
在经济大萧条
of Great Depression - 1929 to 1933
最黑暗的1929至1933年间
life expectancy increased by a remarkable six years.
人均寿命显著增加 延长了六年
Now, on the face of it, that is really surprising,
乍看之下 这实在令人惊讶
and yet, clues as to why could also be found
然而 关于这种现象的原因
from research done back in the 1930s.
在三十年代的研究中就已经发现
Nutritionists at Cornell University working with animals
康乃尔大学的营养学家进行动物试验
discovered that if you severely restrict
发现如果严格限制
the amount they eat, they live longer.
动物的摄入量 它们寿命更长
Much, much longer.
且长寿很多
So the next obvious question -
那么下一个显而易见的问题
if you do the same with humans,
如果在人类身上进行
will it have the same effects?
会有相同的效果吗
Well, it's been eight decades since that observation,
那项实验距今已过了八十年
and only now are scientists really beginning to understand
现在科学家们才真正开始了解
the link between calorie restriction and longevity in humans.
低热量饮食与人类长寿之间的联系

重点解释：

1.on the face of 从 ... 外表判断

例句：On the face of it, you are right.
由此可见，你是对的。

2.as to 关于

例句：As to the author of the book, I will hazard a guess.
关於这本书的作者，我来试猜一下。