Question

What is protein balance, and why is it important to understand this concept in health and recovery.

Answer 1

Proteins are essential nutrients for the human body. They are one of the building blocks of body tissue and can also serve as a fuel source. As a fuel, proteins provide as much energy density as carbohydrates: 4 kcal (17 kJ) per gram; in contrast, lipids provide 9 kcal (37 kJ) per gram. The most important aspect and defining characteristic of protein from a nutritional standpoint is its amino acid composition.Protein is a nutrient needed by the human body for growth and maintenance. Aside from water, proteins are the most abundant kind of molecules in the body. Protein can be found in all cells of the body and is the major structural component of all cells in the body, especially muscle. This also includes body organs, hair and skin. Proteins are also used in membranes, such as glycoproteins. When broken down into amino acids, they are used as precursors to nucleic acid, co-enzymes, hormones, immune response, cellular repair, and other molecules essential for life. Additionally, protein is needed to form blood cells

protein balance

Equilibrium between protein intake and anabolism, and protein catabolism and elimination of nitrogenous products.

The recommended daily intake of protein (0.8 g/kg per day) is based on long-term nitrogen balance studies and consists of three components:

• the average amount of high quality protein needed to maintain nitrogen balance (0.6 g/kg)
• safety factor to ascertain that 95% of the healthy population is covered (0.15 g/kg)
• allowance for the usual intake of proteins that are not entirely high quality protein (0.05 g/kg)

Nitrogen balance is measured by collection of nitrogen losses in urine, feces, skin and miscellaneous losses (sweat, secretions, etc) and subtracting these losses from measured nitrogen content of protein intake.At an intake of 1 g protein/kg per day, the nitrogen loss in urine will correspond to, approximately, 0.85 g/kg, the loss in feces will be equivalent to 0.1 g/kg per day and the loss from skin and miscellaneous sources will be equivalent to 0.03 g/kg per day.protein in foods of low digestibility will increase fecal nitrogen losses. Protein of low biological value will also increase urinary nitrogen loss. Digestibility and biological value are combined in the Net Protein Utilization (NPU), which is the fraction of protein retained in the body with an increase in intake of a specific dietary protein.

The amount of protein required to maintain nitrogen balance consists of two major components: essential amino acids (EAA) and essential nitrogen. the nitrogen requirement of the growing subject is largely determined by the EAA composition of the growing tissues, while in the adult depends on the needs for protein turnover of lean tissue, the synthesis of essential compounds such as hormones, as well as the increased requirements for wound healing or response to disease.in the diseased subject, synthetic reactions require yet another pattern of amino acids, e.g. proline for collagen synthesis, aromatic amino acids for synthesis of antibodies and acute phase proteins, and glutamine for rapidly dividing cells. In such conditions, amino acids that are not usually essential can become conditionally essential due to limited synthetic capacity, e.g. glutamine in the severely ill patient. Similarly, in patients with decreased liver function, cysteine may not be produced in sufficient quantities from methionine, and therefore the requirement for sulphur containing amino acids in these patients may not be covered by provision of methionine alone. In addition, after a period of weight loss, the adult subject may have a requirement for EAA resembling that of a growing child due to the needs for rebuilding of tissue.

loss of protein will severely affect the function of a number of organs including muscle, intestine, skin, immune cells, and liver. In the patient in intensive care, this loss can be increased to 1–2 g/kg per day when no protein is given. Immobilization by itself leads to wasting of muscle tissue.  long-term immobilization (with intact innervation), the loss of nitrogen from the body corresponds to only 0.05 g protein/kg per day and therefore the massive loss of nitrogen seen in patients in intensive care, and to lesser extents in other patient categories, is mainly due to the metabolic disturbances associated with disease processes.

Protein deficiency

Protein deficiency and malnutrition (PEM) can lead to variety of ailments including mental retardation and kwashiorkor.[53] Symptoms of kwashiorkor include apathy, diarrhea, inactivity, failure to grow, flaky skin, fatty liver, and edema of the belly and legs. This edema is explained by the action of lipoxygenase on arachidonic acid to form leukotrienes and the normal functioning of proteins in fluid balance and lipoprotein transport

Excess consumption

When amino acids are in excess of needs, the liver takes up the amino acids and deaminates them, a process converting the nitrogen from the amino acids into ammonia, further processed in the liver into urea via the urea cycle. Excretion of urea occurs via the kidneys. Other parts of the amino acid molecules can be converted into glucose and used for fuel.Excessive protein intake may increase calcium excretion in urine, occurring to compensate for the pH imbalance from oxidation of sulfur amino acids. This may lead to a higher risk of kidney stone formation from calcium in the renal circulatory system.