The document discusses nitrogen balance, which is a measure of nitrogen intake versus nitrogen loss, with a positive balance indicating more intake than loss and thus protein synthesis, a negative balance indicating more loss than intake and thus malnutrition, and equilibrium indicating equal intake and loss. It provides details on sources of nitrogen loss from the body, factors that influence nitrogen requirements, and typical protein intake recommendations to achieve a balanced nitrogen state.

1. Nitrogen Balance
By
Jinal Tandel
Assistant Professor
IICP, CVMU

2. INTRODUCTION
• Proteins are the most abundant organic compounds and
constitute a major part of the body dry weight (10 – 12 kg in
adults).
• They perform a wide variety of static (structural) and
dynamic (enzyme, hormones, clotting factors, receptors
etc.) functions.

3. INTRODUCTION
• About half of the body protein (predominantly collagen) is
present in the supportive tissue (skeleton and connective)
while the other half is intracellular.
• Protein are nitrogen containing macro molecules consisting
of L-amino acids as the repeating units of the 20 amino
acids found in proteins, half can be synthesized by the body
(non-essential) while the rest have to be provided in the diet
(essential amino acids).

4. INTRODUCTION
• The proteins on degradation (proteolysis) release individual
amino acids.
• Amino acids are not just the structural components of
proteins.
• Each one of the 20 naturally occuring amino acids
undergoes its own metabolism and performs specific
functions.

5. INTRODUCTION
• Some of the amino acids also serve as precursors for the
synthesis of many biologically important compounds (e.g.
melanin, serotonin, creatine etc.).
• Certain amino acids may directly act as neurotransmitters
(e.g. glycine aspartate, glutamate).
• Protein metabolism is more appropriately learnt as
metabolism of amino acids.

6. NITROGEN BALANCE
• Nitrogen balance is the measure of nitrogen input with the
nitrogen output subtracted from it.
• Nitrogen Balance = Nitrogen intake - Nitrogen loss
• Blood urea nitrogen can be used in estimating nitrogen
balance, as can the urea concentration in urine.
• A positive value is often found during periods of growth,
tissue repair or pregnancy.

7. NITROGEN BALANCE
• This means that the intake of nitrogen into the body is
greater than the loss of nitrogen from the body, so there is
an increase in the total body pool of protein.
• A negative value can be associated with burns, fevers,
wasting diseases and other serious injuries and during
periods of fasting.
• This means that the amount of nitrogen excreted from the
body is greater than the amount of nitrogen ingested.

8. NITROGEN BALANCE
• A negative Nitrogen balance can be used as part of a clinical
evaluation of malnutrition.
• The term "nitrogen balance" refers to the amount of
nitrogen the body excretes, as opposed to the amount of
nitrogen the body takes in. All of the macronutrients like
protein, carbohydrate, and fat are made up of carbon,
hydrogen, and oxygen molecules.
• Protein alone also contains an additional nitrogen molecule.

9. NITROGEN BALANCE
• When the body digests protein, these nitrogen molecules are
generally released into the blood.
• Measuring bodily nitrogen levels can be the most accurate
way to determine whether the body is receiving adequate,
inadequate, or excess protein.
• There are three states of nitrogen balance: negative, positive
and equilibrium.
• If an individual has a negative nitrogen balance, that
person's nitrogen output is greater than his nitrogen input.

10. NITROGEN BALANCE
• Because protein is the only macronutrient containing a
nitrogen molecule, a negative balance can be a sign of
inadequate protein consumption and malnutrition.
• If an individual has a positive nitrogen balance, it means
that person is consuming more protein than his body needs.
• This is an ideal state for athletes and body builders, because
the extra protein will most likely contribute to muscle
growth.

11. NITROGEN BALANCE
• Excess protein can also help athletes and body builders
recover faster from workouts.
• If an individual's nitrogen balance has reached a state of
equilibrium, it means that person is excreting about the
same amount of nitrogen as he is taking in.
• This is generally a normal state of affairs for healthy adults
eating a balanced diet.

12. NITROGEN BALANCE
• Most people don't usually need to consume the high levels
of protein that body builders and athletes often need to grow
strong muscles.
• Nitrogen is usually excreted through the urine, so nitrogen
levels in the body are often measured using a urea nitrogen
test of urine.
• The results of the test are then typically compared to the
nitrogen content of the individual's diet.

13. NITROGEN BALANCE
• The person will generally be said to have a positive,
negative, or equal nitrogen balance, depending on the
difference between his urea nitrogen levels and the nitrogen
content of his diet.
• The human body usually needs more than just protein to
maintain appropriate nitrogen levels.
• Dietary protein should be of high quality, such as that
typically found in eggs and lean meats.

14. NITROGEN BALANCE
• The human body also generally needs an adequate supply of
fats and carbohydrates.
• These macronutrients are widely considered essential to
energy production.
• When dietary levels of fat and carbohydrate fall too low, the
body uses protein for energy, which may deplete the body's
nitrogen levels and inhibit the body's ability to renew
damaged cells.

15. NITROGEN BALANCE
• Nitrogen requirements include what is needed for both
tissue protein synthesis and the production of several
nitrogenous compounds involved in a range of functions
(hormones, neurotransmitters, immune competence and
peroxidative defenses).
• Under specific physiological and dietary conditions, the
dietary requirements for protein, amino acid and nitrogen
are determined by the nature of the metabolic demand that
must be satisfied.

16. NITROGEN BALANCE
• An evaluation of protein quality must therefore take into
account the different processes involved in amino acid and
nitrogen homeostasis.
• The achievement of nitrogen homeostasis involves a
complex series of changes in rates of whole body protein
turnover, amino acid oxidation, urea production and
nitrogen excretion during the fasting, fed, postprandial and
post absorptive periods of the day.

17. NITROGEN BALANCE
• Human nitrogen requirements are usually determined from
the nitrogen balance.
• The usual procedure is to regress nitrogen balance on intake
and to define the requirement as the intake level that would
produce a zero balance, i.e., equality of dietary N intake and
N losses (Fig. 1)

19. NITROGEN BALANCE
• Nitrogen losses occur in different ways.
• They mainly arise from urinary losses in the form of urea,
ammonia and creatinine but also in the form of fecal and
miscellaneous losses minimum nitrogen losses were
measured in subjects fed a protein-free diet for 1 week.

20. NITROGEN BALANCE
• Under these conditions, nitrogen losses were estimated at 36
mg/kg/d in urine, 12 mg/kg/d in feces and 8 mg/kg/d in
miscellaneous nitrogen losses (sweat, sebum,
desquamations, nails, hairs and saliva).
• Obligatory oxidative losses and indispensable ilea amino
acid losses have been reported to reach 162 and 18 mg/kg/d,
respectively.

21. NITROGEN BALANCE
• We determined total ileal nitrogen losses as reaching 9
mg/kg/d, i.e., 16% of ONL. Indispensable ileal amino acid
losses represent, ~10% of obligatory oxidative losses.
• From these estimations, ONL represent 54 mg/kg/d and
correspond to a protein requirement level of 0.34 g/kg/d.
• Because dietary protein utilization does not achieve 100%
efficiency, it has been suggested that an intake of 0.6 g/kg/d
of well-balanced protein will achieve a zero nitrogen
balance.

22. NITROGEN BALANCE
• The adequacy of this diet has been reported in studies
conducted over 2- or 3-mo periods. A safety coefficient is
added to this figure so that the final recommendation for
dietary protein is 0.75 g/kg/d. In children, the requirements
for growth must be integrated in addition to maintenance
requirements.

23. Reference
• Biochemistry by U.Satyanarayana and
U.Chakrapani. 3rd edition