Combination of balanced diet and regular exercise can help you to gain your body weight in a healthy way. By exercising you will gain weight from increase in size of your muscles and not just from body fat. Such a weight gain is considered healthier since the ratio of body fat to lean body mass (muscles, cartilage, bones etc) remains within a specified range.
If you are not used to exercising daily you can start with simple aerobics exercises for 20-30 minutes for first few days.
This will make you a bit active and will not cause any strain on your body. Once you get used to aerobics you can gain momentum and switch to strain exercises. In the initial phase you can work-out for the same amount of time i.e., about 30 minutes. Then you can increase the time span for an hour and then 1 hour twice a day.
When you exercise really hard, there is breakdown of your body muscles. Amino acids present in the muscle proteins are released in blood. These are again reused during repair of muscles. When you have your meals, the process of building new muscles begins. Proteins are very essential for muscle synthesis process in the body. It has been evident that the new muscle building process accelerates after you exercise. Thus those people who exercise gain more muscles than those who just eat and remain idle.
Simple exercises like walking or just moving your hands and legs to and fro would not help. You should opt for strength training exercises that put a lot of stress and strain on your muscles. Such workouts target larger muscles in your body and hence weight gain is faster. Pull ups, barbell rows, bench press, bar dips are some of the exercises you can start with.
You need to have a balanced diet to supplement your exercise program. There is arises a need of proteins to build new muscles after you exercise. Hence your meals should have adequate protein content to fulfill your body needs.
An average person should consume daily 1 gram proteins per kilogram of body weight. When you do strength training exercises you should consume about 1.3 to 2 grams of protein per kilogram. Eggs are the most preferred food items which provide proteins. Along with it whole grains, fish, meat, milk and milk products are rich sources of protein. Dried fruits and nuts also help to increase weight.
Starchy vegetables, especially potatoes are preferred by bodybuilders who do strain exercises.
Hence a balanced combination of exercises and steady increase in food intake will both increase your muscles and weight in a healthier way.