This document discusses the physiology of fasting in the human body. It describes how during fasting, the body transitions through different stages as it depletes different fuel stores and metabolic pathways. Specifically, it discusses how fasting impacts various body systems including liver, adipose tissue, skeletal muscles, brain, kidneys, endocrine, cardiovascular, respiratory, sleep, and urinary systems. The key adaptations during fasting include increased fat breakdown and ketone body production by the liver to provide fuel, increased breakdown of glycogen and proteins initially, and increased hormones like growth hormone and glucagon that help mobilize fuels.

1. FASTING
PHYSIOLOGY
Sriloy Mohanty, B.N.Y.S

2. Contents…
 Introduction
 Biochemical cycles in fasting
 Stages of fasting and their physiology
 Physiology according to the systems
 Liver in fasting
 Adipose tissue in fasting
 Skeletal muscles in fasting
 Brain in fasting
 Kidney in fasting
 Endocrine system in fasting
 Cardiovascular system in fasting
 Respiratory system in fasting
 Sleep in fasting
 Urinary system in fasting

3. Introduction
Fasting is a complete voluntary
abstinence from taking any kind of
food for a definite period of time
During a fasting body lives in reserve.
(Dr.Herbert
M.Shelton)

4. What is fasting ???
 Abstinence from food
 For a limited period of time
 Only water
 Plasma levels of glucose, amino acid, TAG
falls
 Decline in Insulin secretion
 Increased glucagon secretion

5. Fuel store
Fuel storage in a normal adult of 70 kg male
 Fat:15.0kg =135,000kcal
 Protien:06.0kg =24,000kcal
 Glucose 0.2kg =800kcal
The fat storage is sufficient to meet energy
needs for about three month

6. Stages of fasting
 Stage 1:-gestrointestinal phage
 CHO depleated
 Stage 2:-
 Glycolysis
 Gluconeogenesis
 Fat oxidation
 Ketogenesis
 Stage 3:-
 Does not occurs in fasting

7. Enzymatic changes in fasting
The flow of intermediates through the
pathway of energy metabolism is
controlled by four mechanisms
 Availability of the substrate
 Allosstatic regulation of enzyme
 Covalent modification of enzymes
 Induction-repression of enzyme synthesis

8. Liver in fasting
 Carbohydrate metabolism
 1st glycogen degradation
 1st glucose is used till glucose level goes down
 Rapid mobilization of liver glycogenstores
 Then gluconeogenesis
 From muscle-glucogenic amino acid and lactate
 From adipose tissue-glycerol

9. Cont…
 Fat metabolism
 Increased fatty acid oxidation
 Obtained from TAG hydrolysis in adipose tissue
 It provides NADH and ATP required for gluconeogenesis
 Increased synthesis of ketone bodies
 When the concentration of acetyl CoA exceeds the
oxidative capacity
 Starts during 1-2 days of fasting
 Can be used by most of the tissue including brain

10. Adipose tissue in fasting
 Carbohydrate metabolism
 Fat metabolism
 Increased degradation of TAG
 Causeddue to increased catecholamines (nor-
epinephrine)
 Increased release of fatty acid
 Hydrolysis of stored TAG
 Bound to albumin
 Glycerol produced from TAG degradation is used as a
precursor for gluconeogenesis by liver
 Decreased uptake of fatty acid
 Lipoprotien lipase activity of adipose tissue is low

11. Resting skeletal system in
fasting
 Fuel source
i. Glucose
ii. Glycogen stores
iii. Fatty acid
 Carbohydrate metabolism
 Glucose to skeletal muscle by GLUT-4 protien
 Glucose metabolism is reduced because of
depressed circulating insulin

12. Cont…
 Lipid metabolism
 1st two weeks fatty acid from adipose tissue and
ketone bodies from liver
 3rd week ketone bodies level increases
 Protein metabolism
 1st few days-rapid break down of muscle protein
 Later the proteolysis decreases as brain start using
the ketone bodies as a fuel

13. Brain in fasting
 Day 1
 Glucose as a fuel
 (blood glucose maintained by hepatic
gluconeogenesis)
 2-3 week
 Increased plasma ketone bodies
 Replaces glucose as a primary fuel

14. Endocrine system in fasting
 Increased growth hormone levels
 Mobilizes the fats from adipose tissue
 Decreased thyroid hormones
 Decreased basal metabolic rate
 Decreased erythropoisis rate
 Decreased heart and respiratory rate
 Increased drowzyness

15. Cont…
 Decreased insulin
 Caused due to low blood sugar and Increased
glucagon levels
 Increased glucagon
 Increased glycolysis
 Increased gluconeogenesis
 Increased transport of amino acid
 Increased lypolytic and ketogenic action
 Increased free fatty acid in blood
 Increased ketogenesis

16. Cont…
 Increased aldosteron
Decreased sodium levels in body
Increased aldosteron
Increased retention of water and sodium
Increased ECF
Increased arterial blood pressure
Increased ANP, BNP, CNP
Excretion of water and sodium

17. Cont…
 Increased cortisol
 Increased adrenaline and nor-adrenaine
 Increased urination
 Increased brain activity
 Quick fatique
 Increased sweating
 Increased blood pressure(systolic)
 Increased general vasoconstriction
 Decreased blood coagulation
But in later stages all the functions alter,there is less
sweating, urination,etc.

18. Cardio-pulmonary system in
fastin
 Increased heart rate
 Increased contractibility
 Increased conductivity
 Increased secretion of
 Arterial natriuretic polypeptide
 Brain natriuretic polypeptide
 C-type natriuretic polypeptide
 Broncho dilatation
 Increased oxygenation

19. Blood
 Blood volume Increased
 RBC count remains same
 Blood becomes thin
 Decreased blood sugar, amino acid, TAG
 Decreased blood coagulation
 Decreased blood pressure
 General vasoconstriction
 Destruction of lymphocytes and basophils

20. GIT in fasting
 Increased secretion of GIT hormones
 Increased peristaltic movement
 Increased gherilin secretion
 Increased elimination

21. Sleep in fasting
 More sleep occures
 Drowzyness is Increased (Increased thyroid)

22. Urinary system in fasting
 Increased urine formation
 Increased ketouria (later stages)
 Increased sodium excretion
 Increased secretion of erythropoietin

23. Thank you…