Many people eat a lot still they rarely gain weight and are less bothered about calories. Some people gain weight very quick.
Ectomorphs, mesomorphs and endomorphs are three different body types.
Ectomorphs are skinny people. They have high basal metabolic rate. It is hard for them to gain weight. They lose weight very easily if they skip their meals. Less exhaustive basic exercises like sit ups are beneficial to them.
Mesomorphs have good muscle mass and have athletic look. They have broad shoulders and medium to large body. They also tend to lose weight easily due to their fast metabolism. Yoga, jump rope is sufficient to maintain good shape and weight.
Endomorphs have bigger bones, large thighs and hips. They have short arms and legs. They gain weight easily and it is very difficult for them to lose weight. They also have pear shaped body. Regular weight maintaining exercises are required for them. Treadmill, walking are best exercises for endomorphs.
There are also combinations of body types in some people.
Every person has a natural body type or shape. It is essential to know you body shape and type and exercise accordingly to gain weight or lose weight. Understanding your body type and shape helps in planning a successful fitness program. To maintain proper weight it is essential that the weight is distributed all over the body according to your body type.