“I don’t recommend that people eat in excess of about two grams of protein per kilogram of bodyweight” per day, says Dr. Nancy Rodriguez, professor of nutritional sciences at the University of Connecticut. That’s about 136 grams of protein per day for a 150-pound person.
Eating any more than that isn’t proven to build more muscle, Rodriguez says. In fact, she’s observed that athletes with healthy kidneys who ate more than three grams per kilo per day (more than 204 grams for a 150-pound person) for about three weeks started to show signs of impaired kidney function.
That’s because the kidneys are responsible for removing toxins from the body. Nitrogen is a toxic byproduct of protein metabolism that the kidneys must remove from your blood, so eating too much protein for too long can start to tax your kidneys.
The International Society of Sports Nutrition recommends athletes keep their daily protein intake between 1.4 and 2 grams of protein per kilogram per day, or 95 to 136 grams for a 150 pound person.
The two important things to remember, Rodriguez says, are to eat your protein throughout the day, not all at once, and to drink plenty of water, particularly if your protein intake is at the high end of the spectrum since water helps the kidneys flush out toxins.
Rodriguez recommends drinking one milliliter of water for every calorie you eat. So if you’re eating a 2,000 calorie diet, you should be drinking a liter (four cups) of water a day, more if you exercise.
The bottom line: Current science suggests you should eat no more than two grams of protein per kilogram of bodyweight daily (136 grams for a 150-pound person). Eating more has not been proven to help build more muscle. Consuming more than three grams of protein per kilogram of bodyweight per day for more than a few weeks may adversely affect your kidneys.