Steve Levitt is my free economics friend and co-author.

He stands about 5'11, weighs 160 pounds, so he does not have a weight problem.

But he has been thinking about our collective weight problem, but not thinking about it in

a way that most people think about it.

In fact, not even close.

What we've learned over time, which is one of the most surprising things about obesity,

is that the body has a very strong homeostasis device, which makes it both hard to gain weight

and hard to lose weight.

So the calculation I did was a simple one.

I probably 2800 calories a day, and I like eating.

So let's just say I decided I wanted to go up to 3300 calories a day, an extra 500 calories

a day.

I wanted to do that for the rest of my life.

Now you might think, well, if you did that, that I would my weight would essentially go

to infinity, that extra 500 calories would pile up and pile up and pile up.

And the rough real thumb people use is that every maybe 3500 calories turns into a pound.

And so you would think, you know, my god, you're going to gain a pound a week for the rest

of your life.

It turns out I wouldn't, because of the way the body works, I would only gain 40 pounds.

So if I started this one a little younger when I was 20, then I could have basically,

instead of being 160 pounds of my whole life, I could have been 200 pounds of my whole

life, and I could have had an extra 8.7 million calories over the course of my life.

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