I've gone through this myself a few years back. I'm 6'4" and was only 70kg. Managed to put on +10kg, which isn't huge, but made a big difference to my physique and health.
The main things you need to do... lift weights and eat lots of protein and healthy carbs. Don't think you're going to gain healthy weight just by changing your eating habits. You need to pump iron too.
There are more details than that, but those are the basics you need to get started on. For a bit more detail:
- Sign up at a gym and start lifting weights
- If you haven't lifted weights before seek help or do your research. Lifting weights are very good for you, but if you do it wrong you can seriously injure yourself. That being said, don't let that warning scare you away from it. You just need to be smart about it
- Pay for a personal trainer for 1 or 2 sessions to teach you proper lifting technique, or read guides online if you don't want to pay for it. The work of Mark Ripptoe, "Starting Strength", is considered the defacto standard: http://www.muscleandfitness.com/workouts/workout-routines/4-week-guide-starting-strength
- You have to do the right types of exercises at the gym. Deadlifts, squats, and bench press are the most important, but you want to balance it out with resistance exercises for your arms, back, and shoulders too
- Free weights are a better exercise for your body, but if you're a beginner you might want to start with guided weights to build up a base level of strength, before moving onto free weights
- Go to the gym at least 3 times a week, maybe 4-5 times. You want to have some rest days, but not too many
- Incrementally increase weights and track your progress with a pen and paper
- The key here is higher weights, lower reps. That is you want to lift lots of iron fewer times. Good way to do this is just pick a weight you think you can lift and lift it as many times as you can, till failure
- If you lifted it more than 10 times, you need to increase the weight. You're aiming for about 8 reps until failure (i.e. you can't lift it one more time), that's when you know you've got the sweet spot
- Keep lifting that weight until you can break 10 reps consistently
- Ususally you want to do 3 sets per exercise i.e. for a set you lift weight 8 times (reps), take a 30-60 second break, lift it 8 times again, take a break, lift it 8 times once more. Then move onto the next exercise
- Drink protein shakes, with milk, immediately after training. Maybe blend some fruit into it too, like bananas
- Eat lots of protein e.g. chicken, beef, pork, fish, eggs etc.
- Eat lots of carbs e.g. pasta, rice (brown), potatoes, sweet potatoes etc.
- Supplement your carbs and protein with vegetables such as leafy greens, broccoli, sprouts etc.
- Between major meals snack healthily. Things like nuts (almonds, walnuts, macadamias etc.), legumes (peanuts, lentils, chickpeas), dairy (yoghurt, milk, cheese).
Don't expect fast results. You need to keep at it for at least 3 months before you'll notice a change. And you WILL get sick of eating. Your jaw will ache from chewing so much, but you just need to push through it. You're re-training your body to absorb more mass from your food by eating more and doing exercises that demand it.
Good luck OP. It's worth the effort.
