Re:
The rationale behind "30-40 g per meal" is that if you eat 6 meals a day, we're talking 180g to 240g per day.
180g x 4cal = 720cal
240g x 4cal = 960cal
It depends on your goal:
Maintaining
Losing
Gaining
The body can't store protein, it does store carbs, and fat, well if not used when consumed, is obviously stored in places we don't want it to be.
Aside from the essential protein/AA's, the body can CREATE the protein it needs from carbs.
It's not so much that excessive protein would kill your kidney, as it would be wasted, pissed out, or packed on as fat, since excess protein is burned or stored as fat. That's it.
But again, it isn't the macronutrient, it's the amount of calories. From there, storage is determined. If you have 40g of protein and it's the only macronutrient you consume, you'll likely LOSE weight. See all the women who eat 1 chicken breast. See all the guys who eat NO fat cottage cheese. Etc. Strick protein diets lead to massive weight loss. Generally because protein substances aren't calorie dense, but ARE large in quantity/size. Chicken, Cottage cheese. Eggs. Protein shakes, etc.
It's good to be in the RANGE of calories you need, not perfect, because life isn't perfect, so you can't perfectly determine calorie consumption. But you can be in the range. And that controls fat gain.
On the whole, you have to eat more calories period, but it's the FAT and Carbs people don't get enough of, and I mean GOOD fats. The carb's, too. They spare protein to be used for what they should. They power your workouts to keep lifting more. The inflate your muscles with water and sugar so they can keep an anabolic environment.
And healthy fats are helpful in hormone production and healthy body maintenance.
A-Unit