FASTING
Feasting on a holiday dinner floods your body with excess energy that is stored for future use. On the other hand, fasting and starvation deprive you of energy, so your body must employ an opposing strategy – the mobilization of fuel.  Whether starvation occurs in a child during a famine, a young woman with anorexia nervosa, a patient with AIDS wasting syndrome, or a person intentionally fasting, the body responds in the same way.
 Some people deprive themselves of food for a purpose – to lose weight, to stage a political protest, to participate in a religious fast, or to “cleanse” their bodies. The cleansing motivation is ironic, since fasting actually unleashes potentially damaging toxins to circulate throughout the body.  Over time, fat stores accumulate environmental toxins, such as DDT, PCBs, and benzene.  In the case of PCBs, despite the fact that Congress banned their use decades ago, more than 9 out of 10 Americans still have traces in their body fat.  When bound in adipose tissue, toxins are relatively harmless.  But fasting breaks down adipose tissue and releases these toxins, giving them a second chance to damage cells.  While the liver – the body’s detoxification center – and the intestines remove a small portion of these liberated toxins, the balance remain in circulation, where they can wreak havoc.

Survival Priorities and Potential Energy Sources
Starvation confronts your body with several dilemmas.  Where it is going to get energy to fuel survival needs? What should it burn first – fat, protein, or carbohydrate? Can it conserve its energy reserves? Which tissues should it sacrifice to ensure survival?
 Your body’s first priority is to preserve glucose-dependent tissue: red blood cells, brain cells, and the rest of the central nervous system.  Your brain will not tolerate even a short interruption in the supply of adequate energy.  Once your body depletes its carbohydrate reserves, it begins sacrificing readily available circulating amino acids to make glucose and ATP (ATP is your body’s energy).
 Your body’s second priority is to maintain muscle mass.  In the face of danger, we rely upon our ability for “fight or flight.” This survival mechanism requires a large muscle mass so we can move quickly and effectively. Your body grudgingly uses muscle protein for energy and breaks it down rapidly only in the final stages of starvation.
 Although your body stores most of its energy reserve in body fat, triglycerides (another word for fat) are a poor source of glucose.  Your body can make a small amount of glucose form he glycerol backbone, but it cannot make any glucose from fatty acids. This means your body’s primary energy stores – fat – are incompatible with your body’s paramount energy priority - glucose for you brain. To meet this metabolic challenge, your body’s antistarvation strategies include a glucose-sparing mechanism. Your body shifts to fatty acids and ketone bodies to fuel its needs. In time, even your brain adapts as most, but not all, it cells come to rely on ketone bodies for fuel.

The Prolonged Fast: In the Beginning
What happens during the fasting state? Let’s take a metabolic look at Fasting Frank, a political activist determined to make a dramatic statement. Frank begins fasting at sundown, planning to drink nothing but water and to consume no other foods.
 The first few hours are no different form you nightly fast between dinner and breakfast. As blood glucose drops to fasting baseline levels, the liver breaks down glycogen to glucose.  Gluconeogenesis becomes highly active and begins churning out glucose form circulating amino acids.  The liver pours glucose into the bloodstream to supply other organs and altruistically shifts to fatty acids for its own energy needs.  Muscle cells also start burning fatty acids.  After about 12 hours, the battle to maintain a constant supply of blood glucose exhausts nearly all carbohydrate stores.
 During the next few days, fat and protein are the primary fuels.  To preserve structural proteins, especially muscle mass, Frank’s body first turns to easily metabolized amino acids. It uses some to produce ATP and others to make glucose.  Glucogenic amino acids, especially alanine, furnish about 90 % of the brain’s glucose supply.  As Frank’s body breaks down triglycerides for fuel, the glycerol portion supplies the remaining 10 %.  After a couple of days, productions of ketone bodies ramp up, augmenting the fuel supply.
 
The Early Weeks
As starvation continues, Frank’s body initiates everal energy-conservation strategies.  It ratchest down its energy use by lowering body temperature, pulse rate, blood pressure, and resting metabolism.   He becomes lethargic, reducing the amount of energy expended in activity.   Frank may begin to have detectable signs of mild vitamin deficiencies as his body depletes its small reserves of vitamin C and most B vitamins.
 If Frank’s body continued to rapidly break down protein, he would survive less than three weeks.  To avoid such a quick demise, protein breakdown slows drastically and gluconeogenesis drops by two-thirds or more.  To pick up the slack, his body doubles the rate of fat breakdown to supply fatty acids for fuel and glycerol for glucose. Ketone bodies pour into the bloodstream.  Ketone bodies are an important glucose-sparing energy source for the brain and red blood cells. After about 10 of fasting, ketone bodies meet most of the nervous system’s energy needs. Yet some brain cells can use only glucose.  To maintain a small, but essential, supply of blood glucose, protein breakdown crawls along, supplying small amounts of amino acids for gluconeogenesis.

Several Weeks of Fasting
The average person has bout three weeks of fat stores, and the rate of fat depletion is fairly constant.  As the later stages of starvation exhaust the final fat stores, the body turns again to protein, its sole remaining fuel source.  You can see some of the effects of accelerated protein breakdown in starving children suffering from kwashiorkor.  The loss of blood proteins leads to the swollen limbs and bulging stomachs that typify this type of protein-energy malnutrition.

The End is Near
In the final stage of protein depletion, the body deteriorates rapidly. You can see the sever muscle atrophy and emaciation in photos of Holocaust victims. Their bodies sacrificed muscle tissue in attempts to preserve brain tissue.  Even organ tissues were not spared.  The final stage of starvation attacks the liver and intestines, greatly depleting them.  It moderately depletes the heart and kidneys and even mounts a small attack on the nervous system.  Amazingly, staving people can cling to life until they lose about half their body proteins, after which death generally occurs.
 How long can a person survive total starvation? Several years ago, some Irish prisoners starved themselves to death –the average time was 60 days.  Most people survive total starvation for one to three months.

Starvation survival factors include:
? Starting % body fat.  Ample fat tissue prolongs survival.
? Age. Middle-aged people survive longer than children and the elderly.
? Gender. Women fare better due to a higher proportion of body fat.
? Energy expenditure levels. Increased activity leads to earlier death.

Some vocabulary you might need to read this.
Glucose – A common monosaccharide that is a componet of disaccharides (sucrose, lactose, and maltose) and various complex carbohydrates. Glucose is the only form of energy your brain and central nervous system uses to function.

Glucogenic – A term describing an amino acid whose carbon skeltion can be used in gluconeogenesis to form glucose.

Gluconeogenesis – Synthesis of glucose within the body from noncarboyhydrate precursors such as amino acids, lactic acid, and glycerol. Fatty acids cannot be converted to glucose.

Glycerol – The backbone of mono-, di-, and triglycerides.

Ketone bodies – Molecules formed from fat when cells do not have nough available carbohydrate to break down fat completely. Sometimes improperly called ketones.

Ketones – Organic compounds that contain a chemical group consisting of a carbon and oxygen double bond bound to two hydrocarbons. Pyruvate and fructose are examples of ketones.

Triglycerides – Fats composed of three fatty acid chains linked to a glycerol molecule.

RESOURCES:
Insel, Paul and Turner, R. Elaine. Discovering Nutrition. Jones and Bartlett Publishers, 2003.

NOTE:
This is a description of what occurs to your body during fasting and starvation. In martial arts books and other materials it is not generally suggested to do a pure water-fast for more than 7 days.

Article submitted by Allison Warren