I'm 16 yrs old my body is gud from the upper part but it is not gud below waist and waist size is 28 what do i do to increase waist size and my wt too?

Eat a good diet and: You gain weight by eating a good balanced diet and you perform a reasonable exercise exercise program. You don't have to join a local gym. Gym routines are awfully boring. But if you do at least you will be with other people who are doing the same thing and the boredom factor may decrease. You may meet a coach there and a dietician.

See below: If you are otherwise healthy, there is no need to increase your weight. As you grow older, you will gain weight and look back at this time with fondness, when you could eat and not gain weight. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, low fat milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form.