Nature Has Designed the Human System with the Capacity to Fast

The human body has been designed to fast safely. Certain biochemical changes
take place when no food is taken that enable the body to fuel itself by burning
up its fat reserves and conserving its vital tissues. As this book illustrates, the
design of the human system is so masterful that it has built into it the blueprint
to change its fuel consumption to fast safely.

The innate intelligence of the body is remarkable, as represented by the
biochemical changes that occur in the fasting state. Glucose is a simple sugar
that supplies the necessary fuel our body needs. Normally, if we don't eat for a
day or two, we start to utilize muscle tissue to make the glucose needed by the
body, since glucose can be manufactured .from amino acids stored in our
muscles. If we continue to fast, however, the body senses what is occurring
and attempts to conserve its lean muscle mass by a few different mechanisms.

Fats are broken down to fatty acids that can then be utilized by the muscles,
heart, and liver for energy. The brain, however, is the major utilizer of energy
when the body is at rest. The brain cannot be fueled from fatty acids; it
requires glucose to fuel its operations.

A special adaptation occurs in the fasting state whereby the brain can fuel
itself with ketones instead of glucose. By the third day of a total fast, the liver
starts generating a large quantity of ketones from the body's fat stores. As the
level of ketones rises in the bloodstream, the brain and other organs begin to
use these ketones as their major fuel, thus greatly diminishing the utilization of
glucose by the body. This significantly limits muscle wasting. These keto acids
are utilized for fuel primarily by the brain, muscle tissue, and the heart.

This production of ketones, called ketosis, develops within 48 hours in
females and 72 hours in males, and muscle wasting at this time decreases to
very low levels. This is known as protein sparing.

Thus, the human organism responds to the fasting state by attempting to
maximally conserve its muscle and lean body tissue. With severely restrictive
diets, like juice fasts, the body does lose weight, but the brain and other
organs do not subsist mainly on ketones. Therefore, proportionately to weight
lost, juice fasts and severely restrictive diets cause us to lose more lean body
tissue and less fatty tissue than do total fasts