Why does a human radiate more energy than they consume from food?

[Xalkias]

Homework Statement

If we assume that a human radiates like a black body, calculate the luminosity in watts, then compare it to the daily energy a human gets from eating. (The area of a human A=1.3 m²)

The Attempt at a Solution

The temperature of a human is 310K so L=AσT⁴ = 1.4*5.6*10^-8*(310)⁴=733 watts and the average energy of a human gets from eating is about 3000 calories=12500 joules.
So in one day a human seems to radiate too much energy compared to the daily energy he gets. What is going on?

 

[Bandersnatch]

What is going on?

Let's say you're not looking at a human, but at a rock. It gets zero Joules from eating. How come it stays at a comfy 30-ish degrees centigrade on a warm day?

 

[OmCheeto]

...3000 calories=12500 joules.
... What is going on?

Along with paying attention to Bandersnatch's comment, you might also want to look into the sciency vs laymanish use of the word "calorie".

hint: They have two different values.

ps. I'm going to ignore your "area" typo, as it's not that big a deal.