just so we are all aware of ketosis from autolysis and muscle-sparing and what this really means.
Ketosis is basically the bodys switch from glucose as the main fuel-source to ketones in the absence of any external nourishment.
Due to the lack of any incoming energy, the body must turn to its own resources, a function called autolysis. Autolysis is the breaking down of fat-stores in the body in order to produce energy. The liver is in charge of converting these fats into a chemical called a ketone body, "the metabolic substances acetoacetic acid and beta-hydroxybutyric acid" and then distributing these bodies throughout the body via the blood stream. "When this fat utilization occurs, free fatty acids are released into the blood stream and are used by the liver for energy."
****The less one eats, (and in proportion to this) the more or less the body turns to these stored fats and creates these ketone bodies, the accumulation of which is referred to as ketosis.******
The Heart for example gets little energy from ketone bodies, as it uses mainly fatty acids.
The Brain receives its energy from ketone bodies when insufficient glucose is available (e.g., when fasting). In the event of low blood glucose, most other tissues have additional energy sources besides ketone bodies (such as fatty acids), but the brain does not. After the diet has been changed to lower blood glucose for 3 days, the brain gets 30% of its energy from ketone bodies. After about 40 days, this goes up to 70% (during the initial stages the brain does not burn ketones, since they are an important substrate for lipid synthesis in the brain). In time the brain reduces its glucose requirements from 120g to 40g per day.
Regarding muscle-sparing or conservation on a water-only fast or a severely restricted diet................
The shift from glucose to ketones as a fuel source generally begins on the second day of fasting and completed by the third.
In this interim period there is little to no glucose available and energy from fat-conversion is insufficient, but the body still needs fuel. So it accesses glucose from two sources. It firstly converts glycerol, available in the body's fat stores to glucose, but this is still insufficient. So it makes the rest that it needs from catabolizing, (breaking down), the amino acids in muscle tissue, using them in the liver for gluconeogenesis, or the making of glucose. Between 60 and 84 grams of protein are used on this second day of a water-only-fast, (2-3 ounces
of muscle tissue).
By the third day of fasting, ketone production is sufficient to provide nearly ALL the energy the body needs, and the body's protein begins to be strongly conserved. However, the body still needs a tiny amount of glucose for some functions, however, so a very small amount of protein, 18-24 grams, is still catabolized to supply it - from 1/2 to 1 ounce of muscle tissue per day.
Over a 30 day water-fast a person generally loses a maximum of 1-2 pounds
of muscle mass. This conservation of the body's protein is an evolutionary development that exists to protect muscle tissue and vital organs from damage during periods of insufficient food availability.