Metabolism in Starvation

 Metabolism in Starvation

Definition-Starvation is a severe deficiency in caloric energy intake, below the level needed to maintain an organism's life.

Introduction- It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, death. The term inanition refers to the symptoms and effects of starvation. Total starvation includes total lack of water, food and salts. The length of time, a person can survive, depends upon the fat stores. The longest period of survival never exceeds 9 to 10 weeks; Starvation induces a number of metabolic changes, some occurring within a few days. There is a progressive fall in B.M.R. body temperature, pulse rate and blood pressure. Ketosis develops and some retention of salt and water occurs. Metabolism of carbohydrate, fats and protein undergoes sever changes.

Causes- Starvation is an imbalance between energy intake and energy expenditure. The body expends more energy than it takes in. This imbalance can arise from one or more medical conditions or circumstantial situations, which can include:

1. Medical causes-

1. Anorexia nervosa
2. Bulimia nervosa
3. Eating disorder, not otherwise specified
4. Celiac disease
5. Coma
6. Major depressive disorder
7. Diabetes mellitus
8. Digestive disorders
9. Constant vomiting and Diarrhea

2. Non Medical causes-

1. Child, elder, or dependant abuse
2. Famine for any reason, such as  weather changes, political strife and war
3. Hunger striking
4. Excessive fasting
5. Poverty

Stages-

The symptoms of starvation show up in three stages. Phase one and two can show up in anyone that skips meals, reduces intake of foodor goes through a fasting period. Phase three is more severe, can be fatal, and results from long-term starvation.

Stage one-stage of carbohydrate depletion- Initially the body begins to maintain blood sugar levels by producing and breaking glycogen in the liver and also breaking down stored fat and protein. The liver can provide glycogen for the first few hours. After that, the body begins to break down fat and protein. Fatty acids are used by the body as an energy source for muscles, but lower the amount of glucose that gets to the brain. Another chemical that comes from fatty acids is glycerol. It can be used like glucose for energy, but eventually runs out.

Stage two-Stage of fat depletion-This phase two can last for up to weeks at a time. In this phase, the body mainly uses stored fat for energy. The breakdown occurs in the liver and turns fat into ketones. After fasting has gone on for one week, the brain will use these ketones and any leftover glucose. Using ketones lowers the need for glucose, and the body slows the breakdown of proteins.

Stage three- stage of breakdown of body proteins- By this point, the fat stores are gone and the body begins to turn to stored protein for energy. This means it needs to break down muscle tissues which are full of protein; the muscles break down very quickly. Protein is essential for our cells to work properly, and when it runs out, the cells can no longer function properly. The cause of death due to starvation is usually an infection, or the result of tissue breakdown. The body is unable to gain enough energy to fight off bacteria and viruses. The signs at the end stages include: hair color loss, skin flaking, swelling in the extremities, and a bloated belly. Even though they may feel hunger, people in the end-stage of starvation are usually unable to eat enough food.

Effects- The following effects are seen-

General condition- During the first two days there is a craving for food, particularly at meal times. But later on this craving subsides, weakness increases and a strong dislike to go for any physical or mental effort develops. At about this time the subject falls into a state of semi consciousness. The pulse rate and the body temperature remain almost normal till before death. The sleep increases and respiration becomes slower. Temperature falls before death. The amount of urine as well as its urea content falls. Stool is formed and may be passed during or at the close of the starvation period.

Body weight- The body weight is steadily lost. The daily loss in a person during the first ten days amounts to between 1-15% of the original body weight. At the onset of the fast changes are seen in the fat depots and subcutaneous tissue. The extracellular fluid in large quantity is also lost. Dissolution of the muscular tissue and protoplasmic structure occurs later. The muscle fibers are much reduced in size and many of the fibers are degenerated. Various tissues lose weight as under-

Tissue	Loss of weight
muscles	35%
brain	30%
heart	30%
Kidneys	20%
liver	55%
spleen	70%
Endocrines	2-6%

 

The organs and the tissues of the body are not affected alike. The more vital organs lose the least weight, whereas the less vital ones lose the most.

Metabolism- During starvation, the body has to depend upon its own tissue materials. Of the three food stuffs-glycogen, fat and protein the liver glycogen store is first mobilized. The protein, mobilized from stored protein in the tissue, is transformed into glucose (Gluconeogenesis).

This initial stage will last for not more than two days. In the next stage 80%-90% of energy requirements are met from fats and the remainder (10-20%) from the proteins. Since adipose tissue represents the largest amount of stored food, the second stage will last for the longest period over two weeks.

In the third stage, when the fat-store is almost exhausted, energy requirements are derived from the breakdown of the body proteins. The cell substance will break up with a consequent dislocation of cell metabolism and cell life. This state of affairs, it continued, it will lead to death. The third stage lasts for less than one week

The determination of total RQ and of non-protein R.Q will indicate the extent to which these three molecules are burning at the three stages. The R.Q. is highest at the first stage and diminishes later on.

Metabolic Changes- A brief description of the different metabolic changes is given below-

Carbohydrate metabolism- Carbohydrate store becomes almost depleted in the first two days. The blood sugar is maintained at a steady level even up to the end. This steady level is believed to be due to Gluconeogenesis in the liver.

Fat metabolism- Fat which remains in adipose tissue (element variable) is used first. It goes into the liver where it is completely oxidized and an increased amount of acetyl coenzyme A is produced, resulting formation of ketone bodies whereas due to absence of carbohydrates, fat oxidation usually remains incomplete producing ketosis and acidosis. Thus alkali reserve diminished and various ill-effects of ketosis are produced. Ketones from the liver pass into the blood and ketone bodies appear in the urine. The acidosis is compensated by bicarbonate of blood, increased pulmonary ventilation and increased elimination of CO₂, from the alveoli, creased ammonia formation in the kidney and excretion of ammo salts in the urine.

Protein metabolism- Tissue protein is broken down and amino acids formed after hydrolysis constitute the amino acid pool. The amino acids from this pool are utilized for the maintenance of the structural and functional efficiency of the vital organs. The amino acids also undergo deamination in the liver and the non-nitrogenous part helps in the maintenance of the blood sugar level. The amount of nitrogen excretion during the first few days is directly proportional to the amount of protein intake before starvation. The average daily excretion in the first week is about 10 gm. During the second and third weeks the values are very low. But just before death when proteins are rapidly breaking down the urinary nitrogen rises (premortal rise).

The end products of endogenous protein metabolism, i.e. Creatinine, creatine, neutral sulphur compounds and uric acid are the main nitrogenous products. Creatine excretion gradually falls as the weight of muscles diminishes. On the fifth day of starvation a man excretes 11.4 gm of nitrogen and the energy output is about 2,000 calories. 6-25 gm of protein when broken down eliminates 1 gm of nitrogen. The urinary nitrogen indicates 6.25x11.4=71-5 gm of protein catabolism. Thus the energy liberated at that amount of protein catabolism is 71.5x4.1 Cal=300 calories. The rest of the calories are derived from 190 gm of fat.

Mineral metabolism- Phosphorus and sulphur excretion in urine at first rises and then falls. The excretion of calcium is elevated and that of chloride, sodium, potassium and magnesium is reduced during starvation. Changes in blood and urine during starvation

Blood changes-

(1) Acidosis with diminished alkali reserve.

(2) Low blood sugar,

(3) Increased blood fats.

(4) Presence of ketone bodies.

(5) Raised potassium (Showing breakdown of tissue cells).

Urine changes-

(1) Volume becomes less.

(2) Nitrogen content steadily falls.

(3) Presence of abnormal constituents like creatine, ketones, etc

(4) Ammonia excretion increases as also the ammonia coefficient.

(5) Rise of acidity.

(6) Fall of potassium that causes chlorine retention (Index of breakdown of tissues).