I went to the gym five times and gained a kilo. What is the reason?

It is directly related to your physique. If your body aches, it may be fibromuscular transformation. ....

Of course, after exercise, the body will lose a lot of water and drink water unconsciously.

More appetite than usual, these are all weights. Fitness doesn't require weight control like some competitive sports.

And if you don't plan and train systematically, you will definitely get fat and your figure may be better than before.