The document summarizes metabolism during fed and fasted states. During feeding, carbohydrates, fats, and proteins from food are absorbed and stored or used for energy in the liver, adipose tissue, muscle, and brain. The liver converts nutrients to glycogen, triglycerides, or sends to other tissues. In fasting, glycogen stores are used for glucose followed by gluconeogenesis and lipolysis while ketone bodies and fatty acids provide energy and preserve proteins.
2. STARVE FEED CYCLE
• Use of metabolic fuel for storage and energy production
• During absorptive stage – Storage
• During post absorptive stage/starvation – Used as fuel
Food intake
CO2 + H2O + Urea
Storage
Metabolism
Absorptive stage
Post absorptive stage
4. FED STATE CARBOHYDRATE METABOLISM: LIVER
Glucose from GUT
Uptake to liver via GLUT - 2
Phosphorylation by glucokinase
Glucose – 6 – phosphate formation
Glycogen synthesis
PPP pathway
NADPH generation
Facilitates FA synthesis
Activation of PDH complex
Acetyl CoA
*
5. FED STATE LIPID METABOLISM: LIVER
Chylomicron remnants
Glycerol
Pyruvate
Fatty acids
* Glycolysis
Glycerol
Acetyl CoA
TAG
VLDLTo adipose tissue
6. FED STATE PROTEIN METABOLISM: LIVER
Amino acids from GUT
Acetyl CoA
TCA cycle Pyruvate
Protein synthesis
To replenish the proteins,
that have been used during
postabsorptive state
BCAAs are
transferred
to muscle
7. FED STATE CARBOHYDRATE METABOLISM: ADIPOSE
Glucose from GUT
Influx of Glucose to adipocytes via GLUT-4
Phosphorylation by glucokinase
Glucose – 6 – phosphate formation
Activation of
PDH complex
PPP pathway
NADPH
generation
Acetyl CoA Facilitates FA synthesis
Glycerol
8. FED STATE LIPID METABOLISM: ADIPOSE
Chlylomicrons
(From GUT)
VLDL
(From Liver)
Lipoprotein lipase
Fatty acid Acetyl CoA
TAG
Chylomicron remnants
Stored in Adipocytes
9. FED STATE CARBOHYDRATE METABOLISM: MUSCLE
Glucose from GUT
Uptake to muscle via GLUT - 4
Phosphorylation by hexokinase
Glucose – 6 – phosphate formation
Glycogen synthesisActivation of PDH complex
Acetyl CoA TCA cycle and energy generation
10. FED STATE PROTEIN METABOLISM: MUSCLE
Amino acids from GUT
BCAAs are
transferred
to muscle
Transfer to muscle for
protein synthesis
Energy
production
and protein
synthesis
11. FED STATE METABOLISM: BRAIN
Glucose from GUT
Uptake to brain via GLUT - 1
Glucose – 6 - phosphate
Pyruvate
Acetyl CoA
TCA cycle
14. Stages of fasting
Stage Duration Sources of glucose
Early
From 10-12 hours
after meals, upto 2
days
Hepatic
glycogenolysis,
gluconeogenesis
Intermediate 2 days to 24 days
Gluconeogenesis,
fatty acid oxidation
and ketone bodies
Advanced Beyond 24 days
FA oxidation and
ketone bodies
15. Starve-feed switch
• Blood insulin : glucagon ratio is the switch
• In fed state the ratio is 0.5
• After overnight fasting, the ratio is 0.15
• High ratio promotes glycogenesis, glycolysis
• Low ratio promotes glycogenolysis, neoglucogenesis
19. PROLONGED STARVATION - LIPOLYSIS
Starvation
Acetyl CoA
Carboxylase
HSL
Malonyl CoA
CPT-1
Fatty acyl CoA
Acetyl CoA
Pyruvate
Oxaloacetate Neoglucogenesis
TAG Glycerol
20. PROLONGED STARVATION – KETOGENESIS
Acetyl CoA
Ketone bodies
Oxaloacetate for TCA ATP generation from FA
24. METABOLISM IN ADIPOCYTE DURING FASTING
TAG
Fatty acids Glycerol
To tissue as
energy source
To liver for
gluconeogenesis
Acetyl CoA Energy production
25. Adipose tissue and muscle cannot utilize glucose formed
from neoglucogenesis during fasting. Why?
26. METABOLISM IN MUSCLE DURING FASTING
Fatty acids
Ketone bodies
Acetyl CoA
Acetyl CoA
TCA cycleAmino acids
Gluconeogenic precur.
27. Insulin : Glucagon, Epinephrine
Adenylate cyclase
cAMP
Active protein kinase
Enzyme phosphorylation
Glycolysis
Lipogenesis
Chol. synthesis
Protein synthesis
Gluconeogenesis
Fatty acid oxidation
28. Work ATP use
ATP AMP
Active AMP kinase
Enzyme phosphorylation
Glycogenolysis
FA oxidation
Glycolysis
Lipogenesis
Cholesterol synthesis
Protein synthesis
Notas del editor
Fed state – NO gluconeogenesis, as acetyl CoA is being used for FA synthesis
FA synthesis from acetyl CoA is promoted by increased citrate from TCA cycle, and increase formation of malonyl CoA, which ultimately inhibit CPT-1 of FA oxidation
Glycerol kinase is present in liver
Transaminases for BCAA is present only in muscles
Blood glucose level in fed state is 100-110 mg%
Blood glucose after overnight fasting is 70 mg%
Main purposes of lipolysis:
Provides ATP for body function
Provides glucose for vital need of body
NADH from oxidation of FA pushes acetyl CoA to ketogenesis
Liver lacks thiophorase, that’s why cant use ketone bodies
Because no insulin
Initially FA and ketone bodies, after 3 weeks, only FA oxidation, which produces Acetyl CoA, which inhibits PDH and spares pyruvate for gluconeogenesis
Muscle cannot sense glucagon level. Only sense fall of insulin and sustained glucocorticoids