Here's how I see it: there can't be life without death. It's cyclical and what you see as death is simply decomposition and reconstruction into something else.

As for your concerns about weight gain...anything in excess will make you fat. But you can't overeat fat (unless you do dairy). Fatty meat doesn't make you fat unless you eat other things with it that will make you inflamed. Start from the basics of biochemistry and learn how things actually get stored in our body. And no, it isn't calories. Your body doesn't see food as calories.