Diagram of the interactions of main metabolic pathways

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 1: Average Fuel Storage in a "Normal" 65 kg Man*
Tissue Total amount of fuel Estimated duration of fuel reserve hours (days)
  g kJ Starvation walking running (long distance)
 Liver glycogen 90 1500

3.6

(0.15)

1.2

(0.05)

0.31

(0.013)

 Extracellular glucose 20 320

0.72

(0.03)

0.24

(0.01)

0.07

(0.003)

 Adipose fat 9,000 337,000

816

(34)

259

(10.8)

67

(2.79)

 Protein 8,800 150,000

288

(15)

115

(4.8)

31

(1.3)

Muscle glycogen 350 6,000

1.44

(0.6)

4.8

(0.20)

1.2

(0.05)

* Assuming 12% of body weight is fat for normal men (normal women are about 26%)

Data from E. A. Newsholme & A. R. Leach (1983) Biochemistry for the Medical Sciences, John Wiley, NY. p 337.

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 2: Tissue Fuel Usage in Fed and Fasting States in Humans

 Tissue

Fed 

Fasting
 used released used released
Liver Glucose (stored as glycogen), Amino acids, Fatty acids Fats, Glucose Amino acids, Lactate, Fatty acids, Glycerol Glucose, Ketone bodies
 Kidney  Glucose   Amino acids, Lactate, Fatty acids, Glycerol   Glucose
 Intestine  Glucose, Aspartate & Glutamate, Asparagine & Glutamine Fatty acids, Amino acids other than asx & glx, Carbohydrates     
 Adipose  Glucose     Fatty acids, glycerol 
 Muscle  Glucose (some stored as glycogen), Branched chain amino acids  Lactate, Alanine & Glutamine  Fatty acids, Ketone bodies, Branched chain amino acids  Amino acids other than branched chain, Lactate
 Brain  Glucose  -  Glucose & Ketone bodies  -

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 3: Concentrations of Major Fuels During Starvation in Man
Substance 

Serum or plasma concentration (mM) 

 Days

Fed 1 2 3 4 5 6 7  28-42
Glucose 5.5 4.7 4.1 3.8 3.6 3.6 3.5 3.5  3.6
 Fatty acids 0.30 0.42 0.82 1.04 1.15 1.27 1.18 1.88  1.44
 Ketone bodies 0.01 0.03 0.55 2.15 2.89 3.64 3.98 5.34  7.32
Insulin* >40 15.2 9.2 8.0 7.7 8.6 7.7 8.3  6

 *Insulin concentration is expressed in mU/mL

Data from E. A. Newsholme & A. R. Leach (1983) Biochemistry for the Medical Sciences, John Wiley, NY. pp 338 & 539.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Redrawn from R.W. McGilvery (1979) Biochemistry: A Functional Approach. W. B. Saunders Company, Philadelphia: p 704

Plot of human fuel usage vs. exercise intensity as % maximum oxygen use

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fuel Utilization in Prolonged Exercise

 

Fuel O2 utilization

 

Fuel Concentrations in Blood (mM)

  Blood-delivered Fuels
Exercise Time (min) Muscle Glycogen Glucose Fatty Acid Glucose Lactate Fatty Acid Glycerol
0       4.5 1.1 0.66 0.04
40 36% 27% 37% 4.6 1.3 0.78 0.19
90 22% 41% 37%        
180 14% 36% 50% 3.5 1.4 1.57 0.39
240 8% 30% 62% 3.1 1.8 1.83 0.48
Data from E. A. Newsholme & A. R. Leach (1983) Biochemistry for the Medical Sciences, John Wiley, NY. pp 370-372.

 

 

 

Last modified 7 May 2010