Why do people look heaver on TV then they do in real life? I was on a TV show recently and, for some reason, I looked heaver. I've often heard that "...the camera adds 10 lbs." It appears to be true. Why?

The saying goes "The camera adds 10 pounds"
and that applies to photographs as well as tv, videos, and movies. But in all actuality, the camera really does not add 10 pounds. It shows your true weight. So why do we look larger?
The final product is produced on a flat surface. There is no depth, no dimension, to distribute the weight. So people look slightly larger than normal.

...Also, today's recording media makes people look more like 15 lbs heavier...not the 10 it used to be. So hopefully that's a bit of a comfort to you!

That's not always the case though.
Depending on the camera lense you can look heavier or any which way.

Being a tad overweight I have clips from my musician days where I appear to be slender.

I love those!

what about mirrors...do they really reflest our true appearance?

Nope Kitty - mirrors also reflect a flat image so it's not a true "reflection" of what we look like as 3 dimensional beings. Also, depending on the quality of the mirror or the way it was made will affect the way image is reflected. Have you ever noticed that some fitting room mirrors make you look a lot thinner than the mirrors you have at home? Some stores use misleading mirrors as a ploy to cause you to buy more outfits while making you think you look better in them than you really do.

I always heard it was 20, that's why models have to be so skinny. I told a friend that once, and he looked at me and laughed.

sniff, sniff