Many people are firm believers that by smoking/vaporizing/eating marijuana will conjure up munchies so extreme that you will inevitably gain weight. While yes, sometimes you will get the munchies you must also realize that sometimes you may not. In my personal experience I will only acquire munchies if I have been lacking in calories for the day or week. This has led me to the belief, at least for my body, that if I'm lacking in nutrients/calories the marijuana stimulates my body to want to eat to make up for the deficit. Sometimes due to stress and life in general people become distracted from eating properly or at all. If you fall into this category where your eating schedule is a hot mess and you are not taking in proper nutrition requirements, then yes using marijuana is going to make you hungry! This is why people on chemo or AIDS therapy need marijuana to stimulate their appetite because otherwise they are too sick to eat.
I found that marijuana increases gym performance especially weight lifting. Vaporizing and eating edibles would be the way to go if you would like to incorporate it into your workouts. So far, I have measurably increased performance in the gym since the introduction of marijuana. I can lift heavier, lift longer, lift 100% in proper form, all with 100% mental focus on what I am doing. I feel that is it a great sport supplement, that really gets you the most out of your workout. So far I am reaping the benefits of increased strength, agility, stamina, focus and speed.
Of course, it is different for everyone. Each human body has unique chemistry and will react differently to substances. Some people may get insane munchies, some may get only slightly hungry and some will not get hungry at all. My advice if you get munchies, is to look at your eating and exercise habits. Maybe you are exercising too much and not eating enough calories? Or maybe you are too stressed out/sick to eat and you try to make up for it when your body is stoned? Try eating normally, and you may find yourself not getting the munchies anymore.
Overtime, I will see if this theory proves itself, but I know that the empirical data thus far is something to acknowledge and think about. I find this plant to be such a little gift and miracle form the earth.