Is weight gain really as simple as calories in vs. calories out? I really want to gain about 15 lbs over the next year or so but since I train muay thai 3 hours per week and jiu jitsu 3 hours a week plus I spend about 2 hours a week in the gym lifting and doing cardio, I know it will be difficult. If I just start eating a lot more, will I gain weight? I weigh about 155 lbs right now and was thinking if I started doubling what I eat in a day (over time), I would have to gain weight, correct? I eat very healthy and eat mostly lean, whole foods so I'm hoping the weight won't be fat. Basically, I just want to really ramp up the amount I'm eating in hopes to gain some muscle. Will grappling and muay thai with a bit of weight training provide the resistance I need to build the muscle? What do you guys think?