Thanks for your attention to this matter.
It depends on what you mean by excess protein. Protein should comprise 10 – 15% of total calories. So if you eat 1,200 calories a day, you only need 30 – 45 grams, but if you are eating 3,000 calories because of your regular activities and exercise program, then you need 75 – 113 grams.
Protein contributes 4 calories per gram. Take your calorie intake and multiply by 10% or 15%, then divide that number by 4 to get the grams of protein you should eat. Protein grams are listed on the new foods labels or you could use nutrition analysis software to track it for you.
Another consideration is what is your age and sex, which determines your RDA for protein. Studies have shown that most healthy persons can stay in positive nitrogen balance (body protein broken down equals body protein being built) on as little as 20 grams of high-quality protein per day. Less than that, your body starts breaking down protein structures like internal organs and muscles which reduces your body’s ability to function normally and resist disease.
Excess protein, above body needs, is used for fuel or converted to body fat. Any protein excreted is filtered out by the kidneys which usually retains proteins because they are large molecules in the blood. If you have a kidney infection though, protein will show up in your urine. So depending upon how much protein you are eating, you can stress your kidney function.
If you are weight lifting and concerned about increasing muscle mass, then focus on eating a balanced diet with the above amount of protein. If you want to gain weight, then increase calories with a proportionate amount of protein as above.