zits? o.O Not really sure that's the correct wording right there.
But no, masturbating does not cause acne. Most acne and skin problems experienced by teenagers is caused by excess hormones (released during puberty), and while fatty foods and soda are not the cause (of acne), they certainly don't help.
Basically, teenage acne caused by excess hormones works a bit something like this: during puberty and your teenage years, your body produces more hormones than it's used to (to cause the changes you see in puberty), creating what is technically a hormonal imbalance in the body (and also, if you aren't a very healthy person, eating fatty foods all the time etc, those toxins also build up in the body, which really
doesn't help this, either). Once you've got this build up of toxins and excess hormones (hormones which send "messages" back and forth in your body, such as to your organs and cells, telling them what to do), you get all the extra hormone sending the wrong "message" to the oil glands in your skin. This causes a build up of excess oil, causing a blockage in the skin pore. The body reacts with swelling, and sometimes infection, and that's the pimple or "zit" that you see on your skin.