If I only take fruits in daily diet,then what is the effect of diet on my weight and energy.

Long term it will seriously hurt your health.

There is a lot that won't be able to get nutrition wise from JUST fruits. You will probably not get your proper caloric intake so your body could go into starvation mode. That will cause you to gain weight and lose energy. A balanced diet is the best for you, but you can tweak it to be what you want but make sure you consult with a professional before you do ANYTHING like this. It could be detrimental to your health.

Fruits typically have very low Protein, no muscle build, lower strength. Balanced diet is the only way.

The loose runny bowels ain't no fun either.