First of all, some functions of protein powder in fitness training. Mainly to increase muscle and provide energy. As LZ said, training is mainly for muscle growth, so taking enough protein after training can help muscles recover quickly and avoid more muscle soreness.

Second, eating protein powder is also eaten by weight, not casually. Generally speaking, it is 0.8- 1.0g/ kg body weight. During bodybuilding training, the intake will double. There is nothing wrong with eating in this situation. Moreover, the pressure of protein powder on the kidneys is less than that of protein you consume from food.

As for the side effects on the body, it has not been found that drinking protein powder correctly has no side effects on the body. So you can eat it safely.