This next section will briefly describe normal protein metabolism and the cellular metabolism of proteins instead of glucose for energy in diabetes. Protein metabolism is very complex; therefore, this section focuses only on topics that are relevant to your understanding of type-2-diabetes.
As noted earlier, when insulin action is normal, glucose is used for energy. However, abnormalities in glucose metabolism in patients with type-2-diabetes lead to problems of meeting the body’s energy needs, and the body (at times) turns to proteins for its fuel source.
Proteins fulfill a variety of key roles in the body;
- Proteins can form the structure of organs and muscles.
- Proteins can function as enzymes to facilitate the chemical reactions of metabolism.
- Proteins can be broken down for energy production when glucose is not available.
Proteins are synthesized from molecules called amino acids. Much like beads in a necklace, amino acids are linked together in long chains called peptides. Proteins are formed when one or more peptide chains are coiled and folded in configurations specific to each protein.
Normal protein metabolism consists of following steps;
- Following a meal containing proteins (such as meat, fish, chicken, etc.), the proteins are broken down into amino acids in the digestive tract in a process termed proteolysis.
- The amino acids are absorbed into the blood. A
fterentering the bloodstream, amino acids are taken up by cells of the entire body, especially the liver.
- Within the cells, amino acids are used to synthesize other proteins that cells need.
- In the liver, proteins can be broken down later to amino acids that can be used to produce energy or be converted to glucose (Gluconeogenesis).
Insulin affects protein metabolism by promoting protein synthesis and storage and inhibiting protein breakdown.
Protein metabolism and Diabetes
In type-2-diabetes, glucose cannot transported readily into muscle, fat, and liver cells because of beta cell dysfunction and insulin resistance. These cells must find another source of energy. While fat is usually the next choice for energy production, some cells, particularly muscle cells, turn to proteins as sources of energy.
The following steps of protein metabolism in diabetes are highlighted below;
- When the body needs energy, and glucose and/or fat are not available, the breakdown of proteins for energy results in the generation of amino acids.
- Amino acids can be used to produce more glucose, thereby contributing to hyperglycemia.
- Amino acids can also be used directly for energy production.
- Because insulin is not available to promote protein storage, new proteins are not created to replace the one that is being broken down into amino acids for energy. Without enough proteins to maintain and rebuild the required tissues of body, cachexia – a loss of essential body tissue – will occur. before insulin became available for the treatment of type-1-diabetes, profound cachexia was commonly seen in patients with type-1-diabetes and was frequently fatal. While patients with type-2-diabetes are often overweight, patients with uncontrolled type-2-diabetes experiencing progressive beta cell failure can suffer the loss of essential body tissue leading to weakness and loss of well-being.