| Taken from The Fasting Path by Stephen Harrod Buhner p73 One of the major physical changes that occurs during fasting, ketosis takes place only when the intake of carbohydrates (the source of most of the body's glucose) falls far enough to force the body to use fast stores for fuel. Normally, as soon as carbohdrates are consumed and detected by the body, the pancreas secretes and releases insulin. This is used to help process the glucose that the body gains from carbohydrates. Ketosis can occur only when insulin levels fall nearly to zero, and they will only do so if no carbohydrates or sugars are being ingested. Insulin in the blood inhibits the release of fatty acids from adipose tissue. THis is an evolutionary conservation tactic-in periods of abundant food, the tendency for the body to increase fast stores is maximized. These fast stores are saved until they are needed during periods of low food availability. So when carbohydrate intake falls nearly to zero for longer than 24 hours, the liver's production of a chemical called glucagon rises. THis activates an enzyme in adipose tissue called lipase, which starts the process of lipolysis, or the conversion of fats to usable ketones. Glucagon's ketogenic and lipolytic actions are inactivated by even tiny amounts of insulin; this is why during fasting,in order to maximize ketosis, no carbohydrate intake should occur. As a fast progresses and as ketone concentration in the blood remains higher than glucose, the body begins to prefer ketones or fatty acids to glucose as a source of energy.
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