Protein turnover and nitrogen balance

Today i will speak a bit about protein synthesis and protein degradation. The protein balance, also known as nitrogen balance, is the balance between protein input and protein output. The Protein turnover consist mainly in changing the ingested proteins into aminoacids, and then using the aminoacids resulted to synthesize the proteins needed in our body. For some proteins the turnover is fast (less than 2 hours), for others can be slow (up to 12 months - structural proteins). But on average in 12 months our body is completely renewed.

When we talk about protein balance, we are thinking at the input and output in terms of carbon = energy and urea = nitrogen. Because most of the nitrogen in the body is on protein form, measuring the nitrogen intake and excretion results in finding the nitrogen balance, which is more or less equal with the protein balance.

In normal conditions the protein input is equal with the protein output. In some cases the input is bigger than the output, we are talking about a positive balance (this will happen in pregnancy, growing-up children, gaining weight through bodybuilding or in recovering patients). Negative balance (when the input is lower than the output) happen in case of illness, losing weight, low protein intake, burns or heavy trauma.

On average we will have 80 grams of dietary protein and 70 grams of residual protein, 150 grams of protein in total. The output will be 150 grams also, mainly urea and undigested proteins via stools with the carbon used for energy.

The aminoacid will divide in urea (the nitrogen part) and carbon dioxide CO2 and water (from the carbon part). Some aminoacids carbon part can be converted into glucose (gluconeogenic aminoacids). If they cannot be converted, they are called ketogenic aminoacids. The gluconeogenesis process will start during prolonged fasting to maintain the blood sugar levels. But except for this case, most people will increase the protein degradation if they increase the protein intake.