Too much of anything can be harmful. Drinking too much water can lead to death (called hyponatremia); pushing past your limits during exercise, even if you’re extremely fit, can lead to a fast death (called rhabdomyolysis); and too much protein converts to fat, or may even cause a distended-looking belly.
If you look at the photos of many of the competitive bodybuilders today, they have massive muscles and firm, but fat-looking midsections, which is a disturbing combination, and not at all healthy. The big bellies of these bodybuilders are sometimes due to taking growth hormones, but, it is also appears to be caused by excessive protein consumption over a long period of time.
Weight lifters in a 2019 study were consuming about 2.4 grams of protein per kilogram, (which is much higher than the .8 grams per kg of the RDA) where the conclusion came from that eating too much protein may cause organs to grow, pushing out the belly. If you want flat abs, exercise daily, eat nutrient-dense foods, and don’t exceed 35% of your calories from protein.
Source: TC Luoma, TNation, “Tip: A Scary Effect of Too Much Protein.” On-line. Retrieved May 3, 2020. https://www.t-nation.com/diet-fat-loss/tip-a-scary-effect-of-too-much-protein?utm_source=tnation&utm_medium=email&utm_campaign=weekly_dose-200503