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 Some Facts About Protein
Second only to water, protein is the most abundant substance in the human body. In addition to forming collagen which is the “glue” that holds the body together, proteins are involved in every function in every cell in the body. Not surprisingly, protein has attracted the attention of so many people who are interested in nutrition. Here are some facts about protein:
Protein is the packaging for amino acids.
All proteins are composed of amino acids which are bonded together in long chains called polypeptides. The sequences of the amino acids, along with the folds in the protein structure, determine the type and function of the protein. 20 amino acids combine to form proteins, of which 9 cannot be manufactured in the human body and are therefore essential in the diet. This means that these 9 amino acids are the essential nutrients and that protein is nothing more than the packaging for them.
Here is a list of amino acids that form protein:
Very few if any protein sources are truly incomplete.
A protein is complete if it has all the essential amino acids. If it is missing an essential amino acid, it is an incomplete protein. Many plant-based foods have a relative scarcity of at least one essential amino acid. However, few if any have a total absence of any essential amino acid.
For example, the only scarce essential amino acid in brown rice is lysine. Also, brown rice has about 79% of the lysine necessary to match the proportions of essential amino acids needed by the body. So, although brown rice is not perfectly efficient for protein synthesis, it is not missing any of the essential amino acids. Also, some plant-based protein sources (such as wheat germ, spinach, and cashews) have amino acid profiles that match the essential amino acid profiles needed by the human body. You would be hard-pressed to find any protein source (plant or animal) that is completely missing any of the essential amino acids. Proteins are broken down before being absorbed.
Proteins are not digested whole from the digestive tract. They are denatured and broken down into tri-peptides, di-peptides, and amino acids before being absorbed. Proteins absorbed without being fully broken down can trigger the immune system and lead to allergies.
Your protein absorption is limited.
Protein digestion takes time. The amount of time it takes depends on many factors including stomach acidity, the protein source, and how it is prepared. So, the absorption rate from protein digestion is finite. For a quickly-digesting protein like whey protein, the absorption rate is about 10 grams/hour. For a more moderately digesting protein source like cooked eggs, the rate is about 4 grams/hour. If you multiply these numbers by 24, you get the amount you can absorb from the gastrointestinal tract per day. For whey protein, this limits your absorption to about 240 grams per day. For cooked eggs, the absorption rate will be about 96 grams per day.
Amino acids will be used for energy under some conditions.
Under healthy conditions, amino acids are used for protein synthesis to support muscle growth and other functions. However, if blood sugar or liver glycogen is low, your body will de-aminate amino acids to make glucose and ketone bodies. Also, preventing hypoglycemia (which can be lethal) is more important to survival than muscle growth. So, making glucose and ketones will take priority. If the amino acids absorbed from the diet are not enough, the body will start breaking down muscle tissue for the amino acids. This will cause you to lose muscle regardless of how much protein you are eating.
Protein is a very important nutrient. Understanding how it works can benefit you regardless of your goals. Other articles |
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