来自《耶鲁大学开放课程：有关食物的心理学、生物学和政治学第5集第5集》

is to weigh people under water

就是检测水下体重
which is what you see in the upper left.

就是你们在左上角看到的
A person sits on a chair,

一个人坐在椅子上
is submerged in water for just a very short time,

很快的潜入水中
and their body fat can get estimated from that

以此来估测体内脂肪含量
because lean tissue and fat tissue have different densities

因为瘦肌肉组织和脂肪组织的密度不同
and that can be determined through calculations.

可以通过计算得出结果
Of course you could imagine

当然你可以想象
how this is difficult to do with large numbers of people

要对大批量的人群进行测试有多困难
and if you have to have the right equipment.

而且你必须要有相应的装置
The same would be true of the Dexa machine,

用骨密度仪也面临同样的问题
which provides a pretty good estimate of body fat as well,

尽管它也可以很好的评测体内脂肪