I like to smoke weed, and I'm in decent shape. It's been "said" that smoking weed makes you lose confidence, which triggers physical activity, but that's not true. I've been smoking for well over a year now, and it hasn't once made me lose confidence. If anything, I've gained more confidence and evens self-motivation while smoking it. The only time you'll ever really gain weight is when you eat a whole shit load from smoking it, which is also known as the munchies.