Growth hormone is a protein hormone involved in several physiological processes such as building muscle and regulating metabolism. Other hormones, such as elevated insulin in response to carbohydrate consumption, can impair its secretion. Since your pituitary gland secretes the majority of growth hormone during deep-stage sleep, eating carbohydrates at night may be particularly detrimental for your growth hormone secretion. This may lead to reductions in muscle building and fat-burning capacity, hindering your athletic progress and leading to unhealthy abdominal fat storage.
Growth Hormone Function
The anterior pituitary gland in the brain secretes growth hormone in several pulses, about 85 percent of which occur while you are sleeping. This growth hormone helps facilitate tissue repair, increase breakdown of stored fat and maintain blood glucose. Growth hormone secretion is especially prominent in children and adolescents, who are undergoing rapid growth and development, but it decreases thereafter in adulthood. Too much or too little growth hormone can negatively impact your metabolism by disrupting the levels of other hormones and lead to an imbalance between tissue building and breakdown.
Carbohydrate Consumption and Insulin Response
When you eat food containing carbohydrate, your blood glucose rises. This triggers your pancreas to secrete insulin into the blood, which shuttles the glucose to your body tissues. Insulin also increases fat storage and the building of muscle mass to some extent. Simple carbohydrates—such as white bread, many baked goods and candy—raise blood sugar quickly, resulting in a rapid insulin increase to clear the glucose out of the blood. Complex carbohydrates—such as whole grains and beans—result in a slower rise in blood sugar and a more gradual insulin response.
Elevated Insulin Levels Inhibit Growth Hormone
Growth hormone and insulin have antagonistic effects: Elevated growth hormone levels will reduce insulin's effectiveness, and high insulin levels will suppress the secretion of growth hormone. Therefore, repeatedly eating carbohydrate-rich food immediately before going to sleep may impair growth hormone secretion during your deep-sleep phase. Additionally, your body is more resistant to the effects of insulin at night, meaning that you must produce more insulin to move a given amount of glucose to your body tissues. This may lead to even further suppression of growth hormone secretion.
Possible Consequences of Reduced Growth Hormone
A primary function of growth hormone secretion during deep sleep is to build and repair damaged tissues. Therefore, if this growth hormone production is interrupted, you may have diminished muscle recovery and reductions in bone mineral density if reductions in growth hormone are chronic. Growth hormone also activates insulin-like growth factor 1, which increases production of several hormones such as estrogen, testosterone and thyroid hormones that regulate metabolism and tissue repair. Furthermore, reduced growth hormone levels are associated with increased abdominal fat and insulin resistance.