They ate protein moderately and only enough to satiate their appetite. But if they were using storage methods ranging from hot springs to drying and fermentation they were eating red meat daily for months. Remaining meat was given to dogs (which eat unlimited amounts of protein). Fat was what humans ate in vast quantities. They'd go to extreme lengths to eat all sources of fat and marrow.

Although this study though doesn't make quite the same point that you're making.

The researchers artificially caused IBD in the mice by injecting them with a compound that damages their mucosal layer in the gut.

So what they're saying is that once you have IBD you might want to eat a low protein diet. This is consistent with diets that were used to treat diarrhea (which suggests ibd) such as the BRAT diet.

Nowadays we have meat five times per day.

Who the hell is eating meat 5 times a day? Jordan Peterson??

Just cut down on the legumes and the gas will pass.