Biology Stack Exchange is a question and answer site for biology researchers, academics, and students. Searching the internet, I have found lots of conflicting information from various fitness sites concerning when the human body burns fats, proteins and carbohydrates. My basic understanding was that the body will first utilize glucose and glycogen stores, followed by fats and finally proteins once the fat and glycogen stores become depleted. However many fitness websites claim that during high intensity physical activity, the body will prefer to burn protein over fat. Scientifically speaking, when does the body ordinarily burn the following food groups (proteins, fats and carbohydrates) and how does exercise influence this process?
If you are able to provide graphs or data to back up your answer this will be extra helpful because I am bored of all the speculation I see on other sites.
The system that regulates body energy store consumption is hugely complicated, but is mainly a cooperation between hormones released by the pancreas (insulin - lowers blood sugar and glucagon - raises blood sugar) and the liver (as the bodies main glycogen store and factory for various energy related tasks). Uptake of glucose from the periphery is reduced to preserve glucose for cells that can't easily use other fuels - e.g.


Unlike in the liver, glycogenolysis is not activated as there are no glucagon receptors in muscle tissue. High amounts of fatty acids are converted into Acetyl CoA to be used in respiration by the liver, but too much Acetyl-CoA is produced.
As the fast continues into a few days, adipose tissue adapts to producing large amounts of free fatty acids. This process can continue for a number of weeks, with the body eventually exhausting fatty acids in adipose tissue and being unable to produce ketone bodies in the liver, losing the inhibition of proteolysis causing a last ditch response of muscle breakdown for energy. Sprinting Glycogen stores are used, respiration is almost entirely anaerobic as blood vessels are constricted by the muscle activity and ventilation has not had time to increase. Middle distance running: aerobic metabolism takes over as the body adjusts to the higher oxygen demand. 2 Hours - A marathon requires roughly 700g of glycogen to complete, however the liver can only store around 500g.
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During the oral glucose tolerance test your blood glucose is tested two hours after drinking 75 grams of glucose.
When your blood sugar is too high or too low, Sometimes, no matter how hard you try to keep your blood sugar in the range your doctor has advised, it can be too high or too low. I also want to point out that proteins might be used for the first week of starvation but then fat takes over and only after all the fat has been consumed is protein utilisation started substantially. If glucose levels haven't been maintained by other means, hypoglycaemia results causing confusion, hallucinations and even coma and death. A starving subject would rely on fatty acids (directly and as ketones) and glucose derived from glycerol, lactate and amino acids.



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Comments

  1. 15.06.2016 at 11:18:24


    Based on estimated glomerular filtration rates that will.

    Author: zeri
  2. 15.06.2016 at 10:45:29


    Pancreas, the amount secreted into the diet.

    Author: orxan_yek