Glycogen: an efficient storage form of energy in anaerobic conditions

What is the net energy yield for the oxidation of a glucose unit from glycogen in anaerobic conditions?

In anaerobic conditions, the oxidation of a free glucose to lactate leads to the net production of two molecules of ATP.

Glucose from the action of glycogen phosphorylase: glucose-1-phosphate release (about 90% of the removed units)

Glycogen synthesis from free glucose costs two ATP units for each molecule; a glucose-1-phosphate is released by the action of glycogen phosphorylase, with recovering/saving of one of the two previous ATP molecules.
Therefore the oxidation of glucose to lactate starting from glucose-6-phosphate and not from free glucose yields three ATP molecules and not two (one ATP is expended in the activation stage instead of two, 4 ATP are produced in the third stage: three ATP gained).
The net rate between cost and yield is 1/3 (an energy conservation of about 66,7%).
The overall reaction is:

glycogen(n glucose residues) + 3 ADP + 3 Pi → glycogen(n-1 glucose residues) + 2 lactate + 3 ATP

If we combine glycogen synthesis, glycogen breakdown and finally glycolysis to lactate we obtain only one ATP molecule per stored glucose unit, that is the overall sum is:

glucose + ADP + Pi → 2 lactate + ATP

Glucose from the action of debranching enzyme: free glucose release (about 10% of the removed units)

The net yield in ATP between glycogen synthesis and breakdown is two ATP molecules expended because of free glucose is released.
In this case the oxidation of glucose starts from the not-prephosphorylated molecule and it yields two ATP molecules.
Therefore the net yield in ATP is zero.
Considering the oxidation of the glucose units from glycogen to lactate we have an energy conservation of:

1-(((1/3)*0,9)+((2/2)*0,1))=0,60

Conclusion

In anaerobic conditions, there is the conservation of about 60% of energy into the glycogen molecule, a good storage form of energy.

References

Arienti G. “Le basi molecolari della nutrizione”. Seconda edizione. Piccin, 2003

Berg J.M., Tymoczko J.L., and Stryer L. Biochemistry. 5th Edition. W. H. Freeman and Company, 2002

Cozzani I. and Dainese E. “Biochimica degli alimenti e della nutrizione”. Piccin Editore, 2006

Giampietro M. “L’alimentazione per l’esercizio fisico e lo sport”. Il Pensiero Scientifico Editore, 2005

Mahan LK, Escott-Stump S.: “Krause’s foods, nutrition, and diet therapy” 10th ed. 2000

Mariani Costantini A., Cannella C., Tomassi G. “Fondamenti di nutrizione umana”. 1th ed. Il Pensiero Scientifico Editore, 1999

Nelson D.L., M. M. Cox M.M. Lehninger. Principles of biochemistry. 4th Edition. W.H. Freeman and Company, 2004

Stipanuk M.H., Caudill M.A. Biochemical, physiological, and molecular aspects of human nutrition. 3rd Edition. Elsevier health sciences, 2013 [Google eBooks]

Income, education, adherence to a Mediterranean diet pattern and obesity prevalence

Income, education, Mediterranean diet and obesity

In a study published on British Medical Journal a research team has examined cross-sectional associations of income and education with an adherence to a Mediterranean dietary pattern and obesity prevalence on a sample of 13262 subjects (mean age 53±11, 50% men) out of 24 318 citizens (citizens of Molise, a region placed between Central and Southern Italy) randomly enrolled in the Moli-sani Project, a population based cohort study.
Household net income categories were considered as:

  • high (>40000 Euro/year);
  • medium–high (>25000 <40000 Euro/year);
  • low–medium (>10000<25000 Euro/year);
  • low (< 10000 Euro/year).

Education level was divided into three categories:

  • ≤8 (low) years of studies;
  • >8 and ≤13 (medium) years of studies;
  • >13 (high) years of studies.

Household higher income were significantly associated with greater adherence to a Mediterranean diet and to olive oil and vegetables dietary pattern, with odds of having the highest adherence to a Mediterranean diet clearly increased according to income levels (diet quality showed a continued improvement across the relatively small range of economic strata). Obesity prevalence was higher in the lowest-income group in comparison with the highest-income category.
Education was positively associated with adherence to Mediterranean diet and lower prevalence of obesity.

Conclusion

The study showed that a higher income and education are independently associated with a greater adherence to Mediterranean diet-like eating patterns and a lower prevalence of obesity.

References

Bonaccio M., Bonanni A.E., Di Castelnuovo A., De Lucia F.,Donati M.B.,de Gaetano G.,Iacoviello L., on behalf of the Moli-sani Project Investigators. Low income is associated with poor adherence to a Mediterranean diet and a higher prevalence of obesity: cross-sectional results from the Moli-sani study. BMJ Open 2012;2:e001685. doi:10.1136/bmjopen-2012-001685

Carbohydrate mouth rinse and endurance exercise performance

Carbohydrate mouth rinse and performance responses

The importance of carbohydrates as an energy source for exercise is well known: one of the first study to hypothesize and recognize their importance was the study of Krogh and Lindhardt at the beginning of the 20th century (1920); later, in the mid ‘60’s, Bergstrom and Hultman discovered the crucial role of muscle glycogen on endurance capacity.
Nowdays, the ergogenic effects of carbohydrate supplementation on endurance performance are well known; they are mediated by mechanisms such as:

  • a sparing effect on liver glycogen;
  • the maintenance of glycemia and rates of carbohydrate oxidation;
  • the stimulation of glycogen synthesis during low-intensity exercise ;
  • a possible stimulatory effect on the central nervous system.

However, their supplementation, immediately before and during exercise, has an improving effect also during exercise (running or cycling) of a shorter and more intense nature: >75% VO2max (maximal oxygen consumption) and ≤1 hour, during which euglycaemia is rarely challenged and adequate muscle glycogen store remains at the cessation of the exercise.

Hypothesis for carbohydrate mouth rinse

In the absence of a clear metabolic explanation it was speculated that ingesting carbohydrate solutions may have a ‘non-metabolic’ or ‘central effect’ on endurance performance. To explore this hypothesis many studies have investigated the performance responses of subjects when carbohydrate solutions (about 6% carbohydrate, often maltodextrins) are mouth rinsed during exercise, expectorating the solution before ingestion.
By functional magnetic resonance imaging and transcranial stimulation it was shown that carbohydrates in the mouth stimulate reward centers in the brain and increases corticomotor excitability, through oropharyngeal receptors which signal their presence to the brain.
Probably salivary amylase releases very few glucose units from maltodextrins which is probably what is needed in order to activate the purported carbohydrate receptors in the oropharynx (no glucose transporters in the oropharynx are known).
However, the performance response appears to be dependent upon the pre-exercise nutritional status of the subject: most part of the studies showing an improving effect on performance was conducted in a fasted states (3- to 15-h fasting).
Only one study has shown improvements of endurance capacity; in both fed and fasted states by carbohydrate mouth rinse, but in non-athletic subjects.

References

Beelen M., Berghuis J., Bonaparte B., Ballak S.B., Jeukendrup A.E., van Loon J. Carbohydrate mouth rinsing in the fed state: lack of enhancement of time-trial performance. Int J Sport Nutr Exerc Metab 2009;19(4):400-9. doi:10.1123/ijsnem.19.4.400

Bergstrom J., Hultman E. A study of glycogen metabolism during exercise in man. Scand J Clin Invest 1967;19:218-28. doi:10.3109/00365516709090629

Bergstrom J., Hultman E. Muscle glycogen synthesis after exercise: an enhancing factor localized in muscle cells in man. Nature 1966;210:309-10. doi:10.1038/210309a0

de Salles Painelli V.S., Nicastro H., Lancha A. H.. Carbohydrate mouth rinse: does it improve endurance exercise performance? Nutrition Journal 2010;9:33. doi:10.1186/1475-2891-9-33

Fares E.J., Kayser B. Carbohydrate mouth rinse effects on exercise capacity in pre- and postprandial States. J Nutr Metab 2011, Article ID 385962. doi:10.1155/2011/385962

Krogh A., Lindhard J. The relative value of fat and carbohydrate as sources of muscular energy. Biochem J 1920;14:290-363. doi:10.1042/bj0140290

Rollo I. Williams C. Effect of mouth-rinsing carbohydrate solutions on endurance performance. Sports Med. 2011;41(6):449-61. doi:10.2165/11588730-000000000-00000