We know that athletes eating up to 3.3 grams of protein per kg of bodyweight each day for over a year have no negative effects and only positive ones. Lean mass increased, fat mass decreased. Kidney and liver function were fine. Blood lipids were good. Now, you could say that “a year of high protein dieting isn’t enough to show all the negative effects,” but you’d be pontificating about the future again. About unrealized potentialities. “Just you wait!”
There are caveats, of course.
Higher protein should always be paired with physical activity. Throughout human history, you couldn’t get protein without working for it. Meat and physical exertion have always been linked. You expend energy, engage your muscle fibers, obtain meat, eat the meat, activate muscle protein synthesis. It’s the same cycle. Only today, you can divest from that relationship. You can step out of the cycle. You can have a delivery guy drop off a crate of frozen steaks. You can stumble into the kitchen and whisk 40 grams of whey isolate into your water. It takes no physical effort, and that’s going to have ramifications.
One potential ramification of inadequate strength training is the buildup of ammonia, a toxic metabolite of protein digestion that we normally clear by converting to urea and expelling through the urine. If we “overload” the system, the ammonia may linger and cause health issues like brain fog. Resistance training has been shown to reduce serum ammonia in rats. They tied weights to their tails and had them climb ladders—the rat equivalent of lifting weights—and found that it reduced serum ammonia. If this holds true in people, then resistance training increases your protein “ceiling” by improving ammonia clearance and urea metabolism.
So make sure you’re lifting heavy things and moving around frequently—these activities increase your “protein ceiling.”
Another factor that increases your protein ceiling is dieting. The more calories you cut, the more likely your body is to start catabolizing muscle tissue. Eating a high-protein diet can mitigate this effect and stave off muscle loss.
And then there’s bed rest and injuries: both increase the amount of protein you should be eating. If you’re on bed rest or recovering from an injury or illness and can’t exactly make it to the gym, you should still eat extra protein to stave off lean mass attrition and improve healing. The binding principle is “protein ceiling.” Anything you can do to increase that protein ceiling and increase your “need” for protein, whether it’s physical activity or calorie restriction or injuries that require more healing, will make higher protein intakes safer and more effective.
Provided you get adequate physical activity, eat a nutrient-dense diet, and have good kidney health, there’s no reason not to try eating more protein if it appeals to you. The results may pleasantly surprise you—especially if you’re trying to lose weight and retain (or gain) lean mass.