What proportion of the population are making Big Gainz? And what proportion are just getting fat? Because excess protein will just end up as fat.
It's nearly impossible to choke down enough protein to get fat on that macronutrient. I mean I'm sure someone has done it but that's just not a practical concern. The issue with gaining adipose tissue is typically caused by consuming excess carbohydrates and (to a lesser degree) fats that come along with the protein.
Most Americans consume more than enough protein and engage far too little exercise. Beans and some walks would do them well.