A New Source of Protein?
This is an odd and interesting bit of research. It relates to reaborption of nitrogen . . . and presents the possibility that more protein is conserved than previously thought. First dietary nitrogen 101: Nitrogen is a major component of amino acids. Amino acids are needed to form proteins. We can synthesize some amino acids ourselves, but others need to be obtained through diet. Dietary protein provides nitrogen and amino acids from plant or animal sources which are resynthesized into human proteins. Unused nitrogen is converted into Ammonia and Urea and excreted.
Can nitrogen be reabsorbed from the intestines?
The answer is a shocking “maybe.” A new nutritional study (published ahead of print in the Journal of Nutrition) has found that nitrogen appears to be reabsorbed. This makes little sense at first glance. Until we consider the vast populations of microorganisms that reside in the gut. Until recently, they were all thought of as “germs” that needed to be quashed. That has changed. We are learning more and more about how important they are for our health and even our survival.
The study is titled:
Nonprotein Nitrogen Is Absorbed from the Large Intestine and Increases Nitrogen Balance in Growing Pigs Fed a Valine-Limiting Diet.
Valine is an essential Amino Acid, so these animals were fed a protein-deficient diet. Then researchers administered urea or casein into the cecum of pigs. Let’s consider this research a step toward greater understanding of how nitrogen may be recycled in living animals. Not a new way to increase protein for strength. (Although who knows. It might work.) The urea was synthesized using Nitrogen-15. Dietary nitrogen is Nitrogen 14. Using nitrogen-15 lets the team know where the cecum-delivered nitrogen ended up.
Researchers found that more than 80% of the cecum delivered nitrogen was absorbed. Some of it was excreted in urine, but some was retained. This is a shocker. I know. Humans cannot synthesize protein using nitrogen. So WTF? The researchers propose that urea traveled through the bloodstream and into to the small intestine. Bacteria (some of which can make amino acids using urea or plain nitrogen) in the small intestine then used the extra urea to make amino acids. Amino acids produced by bacteria could then be absorbed the host (animals).
More research would need to be done to confirm that this happens. But it is very interesting. Humans vary in the types of bacteria they host. Bacterial populations vary according to diet, environment, chance (?) and who knows what else. Do people get extra protein from bacteria? Does this happen under normal circumstances (i.e. not piped in through the back end.)? One thing is sure: there is a lot to learn.
Columbus DA, Lapierre H, Htoo JK, & de Lange CF (2014). Nonprotein Nitrogen Is Absorbed from the Large Intestine and Increases Nitrogen Balance in Growing Pigs Fed a Valine-Limiting Diet. The Journal of nutrition PMID: 24647394