What are the best foods and exercise for quick weight gain? what are BMI increasing diets?
Well, BMI is based on weight and height. and since you can't really increase height, you need to gain weight as you say. You also say in a "healthy" way, I'm going to assume this means max muscle gain with minimal to no fat increase.
Depending on your fitness history, this will determine how "quick" the weight gain is. For example, if you haven't weight trained at all previously, then your body has no idea what weight training stimulus is and as a result, it will have to immediately adapt as a survival mechanism to this external stress. Basically, you'll gain weight faster regardless at this stage. If you have some weight training history, it'll be a little bit slower but since you're asking this question, it's safe to assume you're still at the beginning stages.
Technically speaking, you can only add on weight if you consume more calories than your spend, i.e you eat more than what you burn off during exercise or due to your resting metabolic rate. Since you said "healthy" weight gain, it's a little bit more complicated since you want minimal fat gain. Well, a guideline is you would consume around 14-15x your bodyweight in lbs to maintain the weight you are at, so, depending on how quick you want results and how much fat gain you want to limit, you're going to want to consume around 15-20x your bodyweight in lbs. Of these calories, you need at the very minimum 1g of protein per lbs of bodyweight. We need protein because when you breakdown your muscles during weight training, proteins are the main way your body builds them back up, and back up stronger and bigger (given you ate enough). The rest of your calories will come from carbs and fat obviously...how much will depend on your carb tolerance. Generally, you don't want to eat too many sugary foods as they will make you become insulin resistant, and insulin is one of the most anabolic, if not the most, hormones in the body (anabolic means building the muscles back up, whereas catabolic is the opposite, together these two constitute your metabolism). Anyways, there are lots of great weight gain diet articles out there but this should point you in the right direction, it's always better to do your own research and your own experiments on your own body, since noone will know your body and your habits better than you. Everyone is unique, and genetics do play a role, so just keep that in mind. If you are VERY new, then you could argue that you don't even need to keep these tips in mind, and that you should just eat..eat alot, eat often, then eat more...just keep eating until you can't...then do it again.
I'll quickly mention that sleep is CRUCIAL since rest is when your body builds itself back up, therefore if you don't get enough sleep (AT LEAST 6 hours at the very very minimum), you will halt your weight gain.
In terms of exercise, PLEASE don't be one of the people that weigh 100lbs of all bone and go to the gym only to work arms...this is one of the dumbest things I've ever seen and yet it happens every day. Just think, if you want to become larger, WHY would you train the smallest muscles in your body? I'm not saying don't train them at all, but definitely not anything more than twice a week for now, as you get more advanced you can play around and see what works. Now, the easiest way then, to add mass, is to work your larger muscles...makes sense right? This means start doing compound movements, i.e your squats, your deadlifts, bench, rows, pullups, overhead press, dips...etc. Not only are these movements going to recruit more overall muscle fibres, they also release more hormones due to their recruitment patterns, this is CRUCIAL for lifters who do not supplement with hormones (steroids and hgh). You don't need to over complicate things, just go to the gym 3,4, or 5 times a week (make sure to get at least 2 rest days since your muscles wont grow unless they recover), lift some weights...have a training plan, train certain groups of muscles on certain days or do full body or split into lower and upper. You don't need to do the "bro" split, which is when the entire universe does chest & triceps, back & biceps, legs, shoulders & arms if you don't want. Just go to the gym and train hard. For optimal growth, grab a weight that you can barely get 12 reps with and do that for 3-4 sets of 8-12 reps, and NEVER forget to progress in the gym... This means if you benched 135lbs for 4 sets of 8 reps last week, try 140-145 for 4 sets of 8 now, try to improve, try to overload the muscles, this is the only way they will grow. Once again there are lots of training articles, way more than I can cover here, so just go look them up, experiment yourself, do your research, and most of all just stay dedicated...at the end of the day, the people that you see that are more muscular, stronger, leaner, bigger, just wanted it more, and they did the work to get there.
What you should take from this:
- Eat a lot and then some more.
- Train big movements not calf raises and forearm curls.
- Sleep...a lot.
- Don't believe in these online scams and magic diets and pills, and gain "50lbs in 4 weeks" claims.
- Put in the work and stay dedicated.
- Most importantly, always try to progress, beat your previous self.