The amount of carbohydrates in your diet is important for determining if your muscle is preserved or degraded. High carb diets preserve the muscles better than low carb diets. Low carb diets can cause muscle breakdown , while high carb diets support protein synthesis, muscle building and repair . The effects of low and high carb diets are mediated through insulin.
Anabolic and Catabolic Effects of Insulin
The anabolic action of insulin is characterized by increased synthesis of various substances including proteins and glycogen. The catabolic action of insulin is characterized by the breakdown of various tissues and substances, including the muscles, proteins and glycogen. The anabolic activity of insulin increases when the plasma level of insulin rises. A decline in insulin level produces the catabolic effects of insulin. Factors that raise the plasma level of insulin, such as high carbs, stimulate the synthesis of glycogen and proteins, and the building and repair of muscles. Low carb diets lower the level of insulin and promote the breakdown of the muscles.
Plasma Glucose
Under low carb diets, plasma glucose levels tend to decrease. Muscles are broken down to obtain amino acids which are converted to glucose to maintain the plasma glucose level. The plasma glucose is maintained at a steady-state level within the normal range of 90 to 100 mg/dl. When a low carb diet lowers the plasma glucose level, the body synthesizes glucose from other metabolites to maintain the normal plasma glucose level. The muscles are frequently broken down for their amino acids which are used by the liver to synthesize glucose by a process called gluconeogenesis. Glucose from the liver is used primarily for maintaining the plasma glucose level. The utilization of plasma glucose by the muscles declines under low carb diets because adequate levels of insulin are needed for transporting glucose into the muscle cells. The simultaneous increase in glucose production by the liver and diminished utilization by the muscle cells help to maintain adequate plasma glucose level during low carb diets. The maintenance of normal plasma glucose level is important for the functional integrity of the brain.
The Brain Needs Glucose
Adequate plasma glucose level is important for the brain to function properly. The brain uses only glucose for energy metabolism under most conditions. Under some conditions such as prolonged starvation, the brain can gradually switch to using other metabolites such as ketone bodies for energy metabolism. Some adverse effects of a low plasma glucose include confusion, seizure and death. If a low carb diet impairs brain function, muscle preservation would become a minor concern because life itself may be threatened.
Muscle Preservation and Good Health
Although high carb diets preserve the muscles better than low carbs, high carb diets can raise the risk of chronic diseases such as ischemic heart disease, type-2 diabetes, hypertension and ischemic strokes. Therefore, carbs should be consumed in moderation. The degradation of muscles in the low carb diet can be minimized if protein and fat are maintained at normal or near-normal levels.
References
- "Endocrinology and Metabolism"; Mechanism of Insulin's Anabolic Effect on Muscle: Measurements of Muscle Protein Synthesis and Breakdown Using Aminoacyl-tRNA and Other Surrogate Measures; Lisa S. Chow, et al.; May 2006
- "Journal of Clinical Investigation"; Effects of Brief Starvation on Muscle Amino Acid Metabolism in Nonobese Man; T. Pozefsky, et al.; February 1976
- "Neuropsycopharrmacology: The Fifth Generation of Progress": Brain Energy Metabolism
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