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Fueling Sleep

Fuels used in sleep


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Energy utilization during a fast or sleep1.

  • The liver has approximately 100 g of glycogen stores in a 70 kg individual [~ 400 Cals of energy stores]
  • Muscle has 3x this amount with 300 g of glycogen [~ 1200 Cals of energy stored] – however, skeletal muscle lacks glucose-6-phosphatase to enable these muscle stores to break down glycogen to supply glucose for metabolism and thus it is liver glycogen that supplies the brain and other tissues with glucose during the first few hours after a fast or sleep.
  • Within a few hours of fasting [while asleep], the liver is almost depleted of its glycogen stores as the central nervous system [and in particular the brain], has a great demand for glucose as an energy source.
  • Gluconeogenesis actually occurs constantly in the background. The depiction in the graphic is more to suggest that gluconeogenesis increases while glycogen stores are being utilized and in particular after glycogen stores are depleted. 
  • Gluconeogenesis is where glucose is formed from certain substrates including gluconeogenic amino acids. However, after glycogen stores are depleted, gluconeogenesis is the main source of glucose for the energy needs of the brain in particular.

Negative nitrogen balance in the morning1: Have Protein Always at Breakfast!

  • Skeletal muscle is used as the main source for gluconeogenic amino acids especially alanine and as a result you wake up in negative nitrogen balance.
  • Your skeletal muscle is being ‘robbed’ of amino acids to meet energy needs in the form of glucose. This is a good reason to ensure you consume good quality protein at breakfast.
  • As the night progresses towards the end of the sleep, insulin levels drop to their lowest and fatty acids now become a source of fuel for the liver, heart and muscle.
  • The fatty acids are released from visceral fat stores and not peripheral fat.
  • This is a good reason to eat early and nothing 3 hours before sleep to enable fat ‘burning’ to occur for as long as possible. Sleeping for as long as possible [at least 8 hours a night] will also ensure you tap into these abdominal fat stores for a longer period before you eat your breakfast and stop this fat burning process. The carbohydrate you consume at breakfast will now be used for energy and the increased insulin level will dampen fat burning [lipolytic] enzymes and stimulate the production of fat accumulating [lipogenic] enzymes.


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Energy Matters References