The phrase "kg body" refers to the weight of a person or an object measured in kilograms. It is a way to describe how heavy something is. Full definition
Regardless of exercise mode, the adult body needs 0.8 g of protein per kg body weight per day. (aimworkout.com)
If that effect were to last for a whole year, then people with high caloric requirements could lose 3.7 kg body fat in that amount of time. (ergo-log.com)
The standard formula is 0.8 g protein per kg body weight. (heynutritionlady.com)