Human Fuel Status: From Fasting to Overeating

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A mixed meal contains the macronutrients carbohydrate, protein and fat, which are processed in the stomach and intestines and delivered to the bloodstream as glucose, amino acids, triglycerides, and free fatty acids. Adjustment to the blend of macronutrients and regular exercise can affect body composition, body building, food energy storage, and hormone regulation related to future body development. Adjustments to the blend of macronutrients related to exertion status, fatigue and hunger status can also affect mood, energy level and alertness on a real-time basis.

Here are some simplified pointers to remember about macronutrients:
Simple sugars, such as sucrose and glucose, are important for energy storage as glycogen in freshly exerted muscles when ingested within 45 minutes after exertion. Glucose causes a rise in serum insulin and a fall in glucagon and serum GH (growth hormone). Sugar that is ingested immediately after exertion is more likely to be stored as glycogen in muscles and the liver than sugar that is ingested without previous exertion, which is more likely to be converted to triglycerides via glycerophosphate synthesis in adipose tissue and the liver. Excess sugar is also stored via fatty acid synthesis in the liver with the action of insulin.

Proteins are important for supplying muscles with amino acid structural units and regulating hormones — anabolic hormones — that build the body. Amino acids cause a rise in both glucagon and GH (growth hormone). Amino acids also cause a rise in blood level of insulin.

Fat intake can slow down absorption of protein and carbohydrates immediately after eating, which may stall short-term energy needed for upcoming exertion. Fat intake also causes direct increase of fat storage from free fatty acids to stored triglycerides and adipose tissue.

Simple sugars, such as sucrose and glucose, are important for energy storage as glycogen in freshly exerted muscles when ingested within 45 minutes after exertion. Glucose alone causes a rise serum insulin, a fall in glucagon and a fall in serum GH (growth hormone).