Category Archives: Nutrition and sport

Endurance sports and nutrition

What are endurance sports?

Endurance Sports
Fig. 1 – Endurance Sports

In the last years endurance sports, defined in the PASSCLAIM document of the European Commission as those lasting 30 min or more, are increasing in popularity and competitions as half marathons, marathons, even ultramarathons, half Ironmans, or Ironman competitions attract more and more people.
They are competitions which can last hours, or days in the more extreme case of ultramarathons.
Athletes at all levels should take care of training and nutrition to optimize performance and to avoid potential health threats.
In endurance sports the most likely contributors to fatigue are dehydration and carbohydrate depletion (especially liver and muscle glycogen).

Dehydration and endurance sports

Dehydration is due to sweat losses needed to dissipate the heat that is generated during exercise. To prevent the onset of fatigue from this cause, the nutritional target is to reduce sweat losses to less than 2–3% of body weight; it is equally important to avoid drinking in excess of sweating rate, especially low sodium drinks, to prevent hyponatraemia (low serum sodium levels).

Glycogen depletion and endurance sports

Muscle glycogen and blood glucose are the most important substrates from which muscle obtains the energy needed for contraction.
Fatigue during prolonged exercise is often associated with reduced blood glucose levels and muscle glycogen depletion; therefore, it is essential starting exercise/competition with high pre-exercise muscle and liver glycogen concentrations, the last one for the maintaining of normal blood glucose levels.

Other problems which reduce performance and can be an health threat of the athlete, especially in long-distance races, are gastrointestinal problems, hyperthermia and hyponatraemia.
Hyponatraemia has occasionally been reported, especially among slower competitors with very high intakes of low sodium drinks.
Gastrointestinal problems occur frequently, especially in long-distance races; both genetic predisposition and the intake of highly concentrated carbohydrate solutions, hyperosmotic drinks, as well as the intake of fibre, fat, and protein seem to be important in their occurrence.

References

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.

Anaerobic Conditions: Glycolysis to Lactate
Fig. 1 – Glycolysis to Lactate

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

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.. “Biochemical and physiological aspects of human nutrition” W.B. Saunders Company-An imprint of Elsevier Science, 2000

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 [Abstract]

Bergstrom J., Hultman E. A study of glycogen metabolism during exercise in man. Scand J Clin Invest 1967;19:218-28 [Abstract]

Bergstrom J., Hultman E. Muscle glycogen synthesis after exercise: an enhancing factor localized in muscle cells in man. Nature 1966;210:309-10 [Abstract]

Painelli V.S., Nicastro H., Lancha A. H.. Carbohydrate mouth rinse: does it improve endurance exercise performance? Nutrition Journal 2010;9:33 [Abstract]

Fares E.J., Kayser B. Carbohydrate mouth rinse effects on exercise capacity in pre- and postprandial States. J Nutr Metab 2011;385962. doi: 10.1155/2011/385962. Epub 2011 Jul 27 [Abstract]

Krogh A., Lindhard J. The relative value of fat and carbohydrate as sources of muscular energy. Biochem J 1920;14:290-363 [PDF]

Rollo I. Williams C. Effect of mouth-rinsing carbohydrate solutions on endurance performance. Sports Med. 2011;41(6):449-61 [Abstract]

Glycogen: definition, structure and functions

What is glycogen?

Glycogen Structure
Fig. 1 – Glycogen Structure

Glycogen is an homopolysaccharide formed by units of glucose. Chemically similar to amylopectin, and therefore sometimes referred to as animal starch, compared to the latter it is more compact, extensively branched and larger, reaching a molecular weight up to 108 Da corresponding to about 600000 glucose molecules.
As in the amylopectin, glucose units in the main chain and in the lateral chains are linked by α-(1→4) glycosidic bonds. Lateral chains are joined to the main chain by an α-(1→6) glycosidic bond; unlike amylopectin branches are more frequent, approximately every 10 glucose units (rather than every 25-30 as in amylopectin) and are formed by a smaller numbers of glucose units.
Glycogen is located in the cytosol of the cell in the form of hydrated granules of diameter between 1 to 4 µm and forms complexes with regulatory proteins and enzymes responsible for its synthesis and degradation.

Functions of glycogen

Glycogen, discovered in 1857 by French physiologist Claude Bernard, is the storage form of glucose, and therefore of energy, in animals in which it is present in the liver, muscle (skeletal and heart muscle) and in lower amounts in nearly all the other tissues and organs.
In humans it represents less than 1% of the body’s caloric stores (the other form of caloric reserve, much more abundant, is triacylglycerols stored in adipose tissue) and is essential for maintaining normal glycemia too.
It represents about 10% of liver weight and 1% of muscle weight; although it is present in a higher concentration in the liver, the total stores in muscle are much higher thanks to its greater mass (in a non-fasting 70 kg adult male there are about 100 g of glycogen in the liver and 250 g in the muscle).

  • Liver glycogen stores is a glucose reserve that hepatocyte releases when needed to maintain a normal blood sugar levels: if you consider glucose availability (in a non-fasting 70 kg adult male) there is about 10 grams or 40 kcal in body fluids while hepatic glycogen can supply, also after a fasting night, about 600 kcal.
  • In skeletal and cardiac muscle, glucose from glycogen stores remains within the cell and is used as an energy source for muscle work.
  • The brain contains a small amount of glycogen, primarily in astrocytes. It accumulates during sleep and is mobilized upon waking, therefore suggesting its functional role in the conscious brain. These glycogen reserves also provide a moderate degree of protection against hypoglycemia.
  • It has a specialized role in fetal lung type II pulmonary cells. At about 26 weeks of gestation these cells start to accumulate glycogen and then to synthesize pulmonary surfactant, using it as a major substrate for the synthesis of surfactant lipids, of which dipalmitoylphosphatidylcholine is the major component.
Glycogen: Dipalmitoylphosphatidylcholine
Fig. 1 – Dipalmitoylphosphatidylcholine

Glycogen and foods

It is absent from almost all foods because after an animal is killed it is rapidly broken down to glucose and then to lactic acid; it should be noted that the acidity consequently to lactic acid production gradually improves the texture and keeping qualities of the meat. The only dietary sources are oysters and other shellfish that are eaten virtually alive: they contain about 5% glycogen.

In humans, accumulation of glycogen is associated with weight gain due to water retention: for each gram of stored glycogen 3 grams of water are retained.

References

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

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.. “Biochemical and physiological aspects of human nutrition” W.B. Saunders Company-An imprint of Elsevier Science, 2000

Strategies to maximize muscle glycogen resynthesis after exercise

Strategies to maximize muscle glycogen resynthesis after exercise: contents in brief

Post-exercise muscle glycogen synthesis

An important energy source for working muscle is its glycogen store, whose level is correlated with the onset of fatigue.
The highly trained athlete not only has glycogen stores potentially higher but he is also able to synthesize it faster thanks to more efficient enzymes.
To synthesize glycogen it is necessary to ingest carbohydrates; but how many, which, when, and how often?

⇑ Back to the top ⇑

The two phases of muscle glycogen synthesis after exercise

In order to restore as quickly as possible muscle glycogen depots, it is useful to know that, as a result of training sessions that deplete muscle glycogen to values below 75% those at rest and not fasting, glycogen synthesis occurs in two phases.
To know and therefore take advantage of the biphasicity is important for those athletes who are engaged in more daily training sessions, or who otherwise have little time for recovery between a high intensity exercise and the subsequent one (less than 8 hours), in order to maximize glycogen synthesis and achieve the optimal performance during a second close exercise session.
The two phases are characterized by:

  • a different sensitivity to circulating insulin levels;
  • a different velocity.

⇑ Back to the top ⇑

Muscle glycogen synthesis after exercise: the first phase

Muscle Glycogen
Fig. 1 – Glycogen Structure

The first phase, immediately following the end of an activity and lasting 30-60 minutes, is insulin-independent, i.e. glucose uptake by muscle cell as glycogen synthesis are independent from hormone action.
This phase is characterized by an elevated rate of synthesis that however decreases rapidly if you do not take in carbohydrates: the maximum rate is in the first 30 minutes, then declines to about one fifth in 60 minutes, and to about one ninth in 120 minutes from the end of exercise.
How is it possible to take advantage of this first phase to replenish muscle glycogen stores as much as possible? By making sure that the greatest possible amount of glucose arrives to muscle in the phase immediately following to the end of exercise, best if done within the first 30 minutes.

  • What to ingest?
    High glycemic index, but easy to digest and absorb, carbohydrates.
    Therefore, it is advisable to replace foods, even though of high glycemic index, that need some time for digestion and the subsequent absorption, with solutions/gel containing for example glucose and/or sucrose. These solutions ensure the maximal possible absorption rate and resupply of glucose to muscle because of they contain only glucose and are without fiber or anything else that could slow their digestion and the following absorption of the monosaccharide, that is, they are capable of producing high blood glucose levels in a relatively short time.
    It is also possible to play on temperature and concentration of the solution to accelerate the gastric transit.
    It should be further underlined that the use of these carbohydrate solutions is recommended only when the recovery time from a training/competition session causing significant depletion of muscle glycogen and the following one is short, less than 8 hours.
  • How many carbohydrates do you need?
    Many studies has been conducted to find the ideal amount of carbohydrates to ingest.
    If in post-exercise the athlete does not eat, glycogen synthesis rate is very low, while if he ingests adequate amounts of carbohydrates immediately after cessation of exercise, synthesis rate can reach a value over 20 times higher.
    From the analysis of scientific literature it seems reasonable to state that, as a result of training sessions that deplete muscle glycogen stores as seen above (<75% of those at rest and not fasting), the maximum synthesis rate is obtained by carbohydrate intake, with high glycemic index and high digestion and absorption rates, equal to about 1.2 g/kg of body weight/h for the next 4-5 hours from the end of exercise.
    In this way, the amount of glycogen produced is higher than 150% compared to the ingestion of 0.8 g/kg/h.
    Because further increases, up to 1.6 g/kg/h, do not lead to further rise in glycogen synthesis rate, the carbohydrate amount equal to 1.2 g/kg/h can be considered optimum to maximize the resynthesis rate of muscle glycogen stores during post-exercise.
  • And the frequency of carbohydrate ingestion?
    It was observed that if carbohydrates are ingested frequently, every 15-30 minutes, it seems there is a further stimulation of muscle glucose uptake as of muscle glycogen replenishment compared with ingestion at 2-hours intervals. Particularly, ingestions in the first post-exercise hours seem to optimize glycogen levels.

⇑ Back to the top ⇑

Muscle glycogen synthesis after exercise: the second phase

The second phase begins from the end of the first, lasts until the start of the last meal before the next exercise (hence, from several hours to days), and is insulin-dependent i.e. muscle glucose uptake and glycogen synthesis are sensitive to circulating hormone levels.
Moreover, you observe a significant reduction in muscle glycogen synthesis rate: with adequate carbohydrate intake the synthesis rate is at a value of about 10-30% lower than that observed during the first phase.
This phase can last for several hours, but tends to be shorter if:

In order to optimize the resynthesis rate of glycogen, experimental data indicate that meals with high glycemic index carbohydrates are more effective than those with low glycemic index carbohydrates; but if between a training/competition session and the subsequent one days and not hours spend, the evidences do not favor high glycemic index carbohydrates as compared to low glycemic index ones as long as an adequate amount is taken in.

⇑ Back to the top ⇑

Muscle glycogen synthesis rate and ingestion of carbohydrates and proteins

The combined ingestion of carbohydrates and proteins (or free insulinotropic amino acids) allows to obtain post-exercise glycogen synthesis rate that does not significantly differ from that obtained with larger amounts of carbohydrates alone. This could be an advantage for the athlete who may ingest smaller amount of carbohydrates, therefore reducing possible gastrointestinal complications commons during training/competition afterward to their great consumption.
From the analysis of scientific literature it seems reasonable to affirm that, after an exercise that depletes at least 75% of muscle glycogen stores, you can obtain a glycogen synthesis rate similar to that reached with 1.2 g/kg/h of carbohydrates alone (the maximum obtainable) with the coingestion of 0.8 g/kg/h of carbohydrates and 0.4 g/kg /h of proteins, maintaining the same frequency of ingestion, therefore every 15-30 minutes during the first 4-5 hours of post-exercise.

⇑ Back to the top ⇑

The two phases of muscle glycogen synthesis: molecular mechanisms

The biphasicity is consequence, in both phases, of an increase in:

  • glucose transport rate into cell;
  • the activity of glycogen synthase, the enzyme that catalyzes glycogen synthesis.

However, the molecular mechanisms underlying these changes are different.
In the first phase, the increase in glucose transport rate, independent from insulin presence, is mediated by the translocation, induced by the contraction, of glucose transporters, called GLUT4, on the cytoplasmatic membrane of the muscle cell.
In addition, the low glycogen levels also stimulate glucose transport as it is believed that a large portion of transporter-containing vesicles are bound to glycogen, and therefore they may become available when its levels are depleted.
Finally, the low muscle glycogen levels stimulate glycogen synthase activity too: it has been demonstrated that these levels are a regulator of enzyme activity far more potent than insulin.
In the second phase, the increase in muscle glycogen synthesis is due to insulin action on glucose transporters and on glycogen synthase activity of muscle cell. This sensibility to the action of circulating insulin, that can persist up to 48 hours, depending on carbohydrate intake and the amount of resynthesized muscle glycogen, has attracted much attention: it is in fact possible, through appropriate nutritional intervention, to increase the secretion in order to improve glycogen synthesis itself, but also protein anabolism, reducing at the same time the protein-breakdown rate.

⇑ Back to the top ⇑

Glycogen synthesis rate and insulin

The coingestion of carbohydrates and proteins (or free amino acids) increases postprandial insulin secretion compared to carbohydrates alone (in some studies there was an increase in hormone secretion 2-3 times higher compared to carbohydrates alone).
It was speculated that, thanks to the higher circulating insulin concentrations, further increases in post-exercise glycogen synthesis rate could be obtained compared to those observed with carbohydrates alone, but in reality it does not seem so. In fact, if carbohydrate intake is increased to 1.2 g/kg/h plus 0.4 g/kg/h of proteins no further increases in glycogen synthesis rate are observed if compared to those obtained with the ingestion of carbohydrates alone in the same amount (1,2 g/kg/h, that, as mentioned above, like the coingestion of 0,8 g/kg/h of carbohydrates and 0,4 g/kg/h of proteins, allows to attain the maximum achievable rate in post-exercise) or in isoenergetic quantities, that is, 1.6 g/kg (proteins and carbohydrates contain the same calorie/g)

⇑ Back to the top ⇑

Insulin and preferential carbohydrate storage

The greater circulating insulin levels reached with the coingestion of carbohydrates and proteins (or free amino acids) might stimulate the accumulation of ingested carbohydrates in tissues most sensitive to its action, such as liver and previously worked muscle, thus resulting in a more efficient storage, for the purposes of sport activity, of the same carbohydrates.

⇑ Back to the top ⇑

References

Beelen M., Burke L.M., Gibala M.J., van Loon J.C. Nutritional strategies to promote postexercise recovery. Int J Sport Nutr Exerc Metab 2010:20(6);515-32 doi:10.1123/ijsnem.20.6.515

Berardi J.M., Noreen E.E., Lemon P.W.R. Recovery from a cycling time trial is enhanced with carbohydrate-protein supplementation vs. isoenergetic carbohydrate supplementation. J Intern Soc Sports Nutrition 2008;5:24 doi:10.1186/1550-2783-5-24

Betts J., Williams C., Duffy K., Gunner F. The influence of carbohydrate and protein ingestion during recovery from prolonged exercise on subsequent endurance performance. J Sports Sciences 2007;25(13):1449-60 doi:10.1080/02640410701213459

Howarth K.R., Moreau N.A., Phillips S.M., and Gibala M.J. Coingestion of protein with carbohydrate during recovery from endurance exercise stimulates skeletal muscle protein synthesis in humans. J Appl Physiol 2009:106;1394–1402 doi:10.1152/japplphysiol.90333.2008

Jentjens R., Jeukendrup A. E. Determinants of post-exercise glycogen synthesis during short-term recovery. Sports Medicine 2003:33(2);117-144 doi:10.2165/00007256-200333020-00004

Millard-Stafford M., Childers W.L., Conger S.A., Kampfer A.J., Rahnert J.A. Recovery nutrition: timing and composition after endurance exercise. Curr Sports Med Rep 2008;7(4):193-201 doi:10.1249/JSR.0b013e31817fc0fd

Price T.B., Rothman D.L., Taylor R., Avison M.J., Shulman G.I., Shulman R.G. Human muscle glycogen resynthesis after exercise: insulin-dependent and –independent phases. J App Physiol 1994:76(1);104–111 doi:10.1152/jappl.1994.76.1.104

van Loon L.J.C., Saris W.H.M., Kruijshoop M., Wagenmakers A.J.M. Maximizing postexercise muscle glycogen synthesis: carbohydrate supplementation and the application of amino acid or protein hydrolysate mixtures. Am J Clin Nutr 2000;72: 106-111 doi:10.1093/ajcn/72.1.106

Skeletal muscle glycogen stores and sports

Functions of skeletal muscle glycogen

Muscle glycogen represents a source of glucose, therefore energy, that can be used by muscle during physical activity: it is an energy store where needed!
Furthermore a close relationship exists between the onset of fatigue and depletion of its muscle stores.

Glycogen as energy source

Carbohydrates and fatty acids represent the main energy source for muscle during exercise and their relative contribution varies depending on:

  • the intensity and duration of exercise;
  • the level of training.

If for fatty acids there are no problems regarding body stores so it is not for carbohydrates whose stores, present in glycogen form principally in the liver and the muscle, are modest, less than 5% of total body energy stores: in a non-fasting 70 kg adult male there are about 250 g of glycogen in the muscle and 100 g in the liver, for a total energy of about 1400 kcal. In athletes the amount could be higher, for example in the best marathoners, again considering an adult male as above, you can reach up to 475 g in total, muscle plus liver, which corresponds to about 1900 kcal.
In spite of this, glycogen contribution to the total energy needed to sustain muscular workload rises with the increase of exercise intensity, whereas we reduce that in the form of fatty acids.
Furthermore, in the absence of replenishment with exogenous carbohydrates, performance is determined by the endogenous stores of liver and skeletal muscle glycogen, of which relative consumption is different: an increase of intensity increases that of the second (muscle) while remain more or less constant in that of the first (liver).

Skeletal muscle glycogen and intese exercises

In fact, skeletal muscle glycogen represents the most important energy reserve for prolonged moderate-high intensity exercise, an importance that increase in the case of high-intensity interval exercise (common in training session undertaken by swimmers runners, rowers or in team-sport players) or in resistance exercise, therefore both endurance and resistance exercises. If for example we consider the marathon about 80% of utilized energy derives from carbohydrate oxidation, for the most part skeletal muscle glycogen.
Finally, the replenishment rate of glycogen stores in post-exercise is one of the most important factors in establishing necessary recovery time.

Muscle glycogen and fatigue

Fatigue and low glycogen levels are closely correlate but it is not clear which mechanisms are at the basis of this relationship; one hypothesis is that there exists a minimum glycogen concentration that is “protected” and is resistant to being used during exercise, perhaps to ensure an energy reserve in case of extreme necessity.
Because of the closely relationship between skeletal muscle glycogen depletion and fatigue, its replenish rate in the post-exercise is one of the most important factors in determining necessary recovery time.

References

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

Beelen M., Burke L.M., Gibala M.J., van Loon J.C. Nutritional strategies to promote postexercise recovery. Int J Sport Nutr Exerc Metab 2010:20(6);515-32 doi:10.1123/ijsnem.20.6.515

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.. “Biochemical and physiological aspects of human nutrition” W.B. Saunders Company-An imprint of Elsevier Science, 2000

Daily protein requirements for athletes

Daily protein requirements and sports

Proteins Requirements
Fig. 1 – Food High in Proteins

It is now accepted by athletes, coaches and athletic trainers that proper diet is one of the cornerstones for achieving better athletic performance. Despite this widely spread assumption, many, even at the highest levels, still believe that an high protein intake is fundamental in the athlete’s diet. This opinion is not new and is deeply rooted in the imaginary of many people almost as if, eating meat, even of big and strong animals, we were able to gain their strength and vitality too.
The function of proteins as energy-supplier for working muscle was hypothesized for the first time by von Liebig in ‘800 and it is because of his studies if, even today, animal proteins, and therefore meats, are often believed having great importance in the energy balance in the athlete’s diet, despite nearly two centuries in which biochemistry and sports medicine have made enormous progress.
Really, by the end of ‘800 von Pettenkofer and Voit and, at the beginning of ‘900, Christensen and Hansen retrenched their importance for energy purposes, also for the muscle engaged  in sport performance, instead bringing out the prominent role played by carbohydrates and lipids.
Of course we shouldn’t think that proteins are not useful for the athlete or sedentary people. The question we need to answer is how many proteins a competitive athlete, engaged in intense and daily workouts, often two daily sessions (for 3-6 hours), 7/7, for more than 10 months a year, needs per day. We can immediately say that, compared to the general population, and with the exception of some sports, (see below) the recommended amount of protein is greater.

Metabolic fate of proteins at rest and during exercise

In a healthy adult subject engaged in a non-competitive physical activity, the daily protein requirements is about 0.85 g/kg desirable body weight, as shown by WHO.
Proteins turnover in healthy adults, about 3-4 g/kg body weight/day (or 210-280 g for a 70 kg adult), is slower for the muscle than the other tissues and decreasing with age, and is related to the amount of amino acids in the diet and protein catabolism.
At rest the anabolic process, especially of synthesis, uses about 75% amino acids while the remaining 25% undergoes oxidative process, that will lead to CO2 and urea release (for the removal of ammonia).
During physical activity, as result of the decreased availability of sugars, i.e. muscle glycogen and blood glucose used for energy purposes, as well as the intervention of cortisol, the percentage of amino acids destinated to anabolic processes is reduced while it increases that of amino acids diverted to catabolic processes, that is, it occurs an increase in the destruction of tissue proteins.
At the end of physical activity, for about two hours, anabolic processes remain low whereupon it occurs their sharp increase that brings them to values ​​higher than basal ones, so, training induces an increase in protein synthesis even in the absence of an increase in proteins intake.

What determines the daily protein requirements?

There are many factors to be taken into account in the calculation of the daily protein requirements.

  • The age of the subject (if, for example, he/she is in the age of development).
  • Gender: female athletes may require higher levels as their energy intake is lower.
  • An adequate carbohydrate intake reduces their consumption.
    During physical activity, glucogenic amino acids may be used as energy source directly in the muscle, after their conversion to glucose in the liver through gluconeogenesis.
    An adequate carbohydrate intake before and during prolonged exercise lowers the use of body proteins.
  • The amount of carbohydrates stored in muscles and liver (glycogen) (see above).
  • The energy intake of the diet.
    A reduced energy intake increases protein requirements; conversely, the higher energy intake, the lower the amount of protein required to achieve nitrogen balance; usually there is a nitrogen retention of 1-2 mg per kcal introduced.
    If the athlete is engaged in very hard competition/workouts, or if he requires an increase in muscle masses (e.g. strength sports) nitrogen balance must be positive; a negative balance indicates a loss of muscle mass.
    The nitrogen balance is calculated as difference between the nitrogen taken with proteins (equal to: g. proteins/6.25) and the lost one (equal to: urinary urea in 24 hours, in g., x0.56]; in formula:

Nb (nitrogen balance) = (g. protein/6.25) – [urinary urea in 24 hours, in g., x0.56)]

  • The type of competition/workouts that the athlete is doing, either resistance or endurance, as well as the duration and intensity of the exercise itself.
    Resistance training leads to an increase in protein turnover in muscle, stimulating protein synthesis to a greater extent than protein degradation; both processes are influenced by the recovery between a training and the next one as well as by the degree of training (more training less loss).
    In the resistance and endurance performances the optimal protein requirements in younger people as for those who train less time are estimated at 1.3 to 1.5 g protein/kg body weight, while in adult athletes who train more time is slightly lower, about 1-1.2 g/Kg of body weight.
    Why?
    In subjects engaged in a hard physical activity, proteins are used not only for plastic purposes, which are incremented, but also for energy purposes being able to satisfy in some cases up to 10-15% of the total energy demand.
    Indeed, intense aerobic performances, longer than 60 minutes, obtain about 3-5% of the consumed energy by the oxidation of protein substrates; if we add to this the proteins required for the repair of damaged tissue protein structures, it results a daily protein demand about 1.2 to 1.4 g/kg body weight.
    If the effort is intense and longer than 90 minutes (as it may occur in road cycling, running, swimming, or cross-country skiing), also in relation to the amount of available glycogen in muscle and liver (see above), the amount of proteins used for energy purposes can get to satisfy, in the latter stages of a prolonged endurance exercise, 15% of the energy needs of the athlete.
  • The physical condition.
  • When needed, the desired weight.
    Athletes attempting to lose weight or maintain a low weight may need more proteins.

From the above, protein requirements don’t exceed 1.5 g/kg body weight, also for an adult athlete engaged in intense and protracted workouts, while if you consider the amount of protein used for energy purposes, you do not go over 15% of the daily energy needs.
So, it’s clear that diets which supply higher amounts (sometimes much higher) of proteins aren’t of any use, stimulate the loss of calcium in bones and overload of work liver and kidney. Moreover, excess proteins don’t accumulate but are used to fat synthesis.

How to meet the increased protein requirements of athletes

Protein Requirements
Fig. 2 – Road Cycling

A diet that provides 12 to 15% of its calories from protein will be quite sufficient to satisfy the needs of almost all of the athletes, also those engaged in exhausting workouts.
In fact, with the exception of some sports whose energy expenditure is low, close to that of sedentary subject (for example: shooting, or artistic and rhythmic gymnastics), athletes need a high amount of calories and, for some sports such as road cycling, swimming or cross-country skiing, it may be double/triple than that of a sedentary subject.
The increase in food intake is accompanied by a parallel increase in protein intake, because only a few foods such as honey, maltodextrin, fructose, sugar and vegetable oils are protein-free, or nearly protein-free.

Calculation of protein requirements of athletes

If you consider an energy demand of 3500 kcal/die, with a protein intake equal to 15% of total daily calories, you have:

3500 x 0.15 = 525 Kcal

As 1 gram of protein contains 4 calories, you obtain:

525/4 = 131 g of proteins

Dividing the number found by the highest protein requirements seen above (1.5 g/kg body weight/day), you obtain:

131/1.5 = 87 kg

that is, the energy needs of a 87 kg athlete engaged in intense workouts are satisfied.
Repeating the same calculations for a caloric intake of 5000 , you obtain  187 g of protein; dividing it by 1.5 the result is 125 kg, that is, the energy needs of a 125 kg athlete are satisfied.
These protein intakes can be met by a Mediterranean-type diet, without protein or amino acids supplements.

References

Giampietro M. L’alimentazione per l’esercizio fisico e lo sport. Il Pensiero Scientifico Editore. Prima edizione 2005

Protein and amino acid requirements in human nutrition. Report of a joint FAO/WHO/UNU expert consultation. 2002 (WHO technical report series ; no. 935) [PDF]

Nutrition for athletes: strategies for training and competition

Nutrition for athletes: science and myths

Nutrition for Athletes
Fig. 1 – Fruit and Vegetables

The right diet is one of the basic foundations for achieving the best athletic performance.
Unfortunately, there aren’t special diets or “magic” foods.
Athletes, as the rest of the population, should follow a Mediterranean-type diet, so providing an adequate intake of energy, of mineral salts, vitamins, antioxidants, fiber and water, keeping at the same time  good  balance  of caloric intake by wisely splitting it during the day.
Finally, they should avoid as much as possible industrial foods or fast foods.

Nutrition for athletes and the distribution of meals and calories

Still more than sedentary man, because of his greater caloric intake, athlete will have to consume more meals during the day to avoid concentrating an excessive amount of calories (and food) in one meal.
In this way, he will:

  • avoid reaching lunch-time and especially dinner-time with an excessive hunger;
  • digest foods more easily, not engaging the digestive system with too much abundant meals.
  • avoid any increases in blood chemistry parameters associated with an increased risk of cardiovascular disease, such as hypertriglyceridemia and hypercholesterolemia.

Of course, in nutrition for athletes, the distribution of the meals will have to consider also training and competition times. The best distribution might be: breakfast, lunch and dinner plus two snacks, one in the morning and the other in the afternoon.

Breakfast

Nutrition for Athletes
Fig. 2 – Glass of Milk

It is of one of most important and often underestimated meals of the day, that should never be skipped.
Typical breakfast foods are milk and/or yogurt, fruit juice (better if freshly squeezed seasonal fruit; when you buy a packaged fruit juice, select it without added sugar/sweeteners and with a caloric content of about 45 kcal/100 g), freshly made tea,bread, dry cookies without cream (however moderately), corn flakes without addition of syrup, honey, fresh/dry fruit, chocolate, and jam/honey (the last three in moderation).
Breakfast will be consumed considering the time when physical activity, and still more the competition, is made.
In nutrition for athletes, as for sedentary population,the breakfast should represent about 15% of the daily caloric intake, to pass to 20% without mid-morning snack.

Lunch

It should represent the meal in which the major part of complex carbohydrates is taken up that is pasta, rice, barley, cous-cous, oats, millet, etc (better if “al dente” with a light seasoning), based on personal preferences.
To limit glycemic increase it is advisable to eat, after a dish rich in carbohydrates, vegetables, fresh or cooked (in the latter when possible, better if steamed), but avoiding potatoes, cooked carrots and onions (foods with an high glycemic index). Bread, if present, should be eaten moderately.
At the end of the lunch a fruit can be eaten as well (if it doesn’t cause feelings of bloating when eaten at the end of the meal; in the case, fruit may be eaten during snacks) and/or a dessert without cream.
Seasonal fruit and vegetable will ensure an adequate intake of mineral salts, vitamins, fiber and water.
It is advisable having lunch at least two-three hours before the start of training sessions/competition, in order to allow a complete digestion, normalization of postprandial glycemic peaks and of insulin response before starting workout.
In nutrition for athletes, the lunch should represent 25-30% of the daily caloric intake.

Dinner

In this meal, it is advisable to give priority to proteins rather than carbohydrates, hence fish, white or red meat (the last one lean and less frequently) or legumes (rich in slow absorption carbohydrates, fiber and mineral salts) will be present, with seasonal vegetables, fresh or cooked, (recommended is also a vegetable soup, that will help in restoring liquids), moderate bread, and fruit (if it doesn’t cause feelings of bloating when eaten at the end of the meal, as seen for lunch).
It is advisable to eat legumes at dinner to avoid bothersome bloating during training.
In nutrition for athletes, the dinner should represent 25-30% of the daily caloric intake.

Snacks

In nutrition for athletes, to ensure adequate distribution of calories, often much higher than in the sedentary man and avoid an excessive accumulation at major meals, at least two snacks must be present, one at mid-morning and the other at mid-afternoon. Assume preferably fruit (moderately also dry fruit, advisable walnuts and almonds), yogurt/milk, dry cookies or a sandwich with lean sliced salami (e.g. lean raw ham or cured raw beef), cottage cheese (soft fresh cheese) or simply with extra-virgin olive oil and tomato or other vegetables (always choose seasonal vegetables).
The snack should represent 10-15% of the daily caloric intake.

Nutrition for athletes and caloric intake

In nutrition for athletes, caloric intake must be matched to energy consumption that, in turn, depends on:

  • sex;
  • age;
  • growing phase;
  • physical structure;
  • level of physical activity (training plane, competition, recovery);
  • even possible pathological states.

Athlete’s diet must consider energy consumption due to workload sustained during training sessions.
In fact, if there are sports (as swimming, running, rowing or cross-country skiing) whose training sessions cause an increase of energy requirement in excess of 50% compared to needs referred to a moderately active lifestyle, in other sports (as artistic or rhythmic gymnastics, shooting etc.) the consumption related to the activity may be modest.
So, the only difference in nourishment between a sedentary or moderately active man and an athlete engaged in sports causing a large increase of energy requirement will be of quantitative type: the greater is the energy expenditure linked to physical activity, the greater will be the caloric intake.

References

Giampietro M. L’alimentazione per l’esercizio fisico e lo sport. Il Pensiero Scientifico Editore. Prima edizione 2005

Jeukendrup A.E. Nutrition for endurance sports: marathon, triathlon, and road cycling. J Sport Sci 2011:29;sup1, S91-S99 [Abstract]

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

Shils M.E., Olson J.A., Shike M., Ross A.C.: “Modern nutrition in health and disease” 9th ed. 1999

Nutrition and sport: what to eat?

The major part of the calories (55-60%) must derive from carbohydrates (complex ones 80%, simple ones 20%), essential fuels for the muscle both during rapid and intense efforts than in endurance performances, present in daily feeding in great amounts in pasta, rice, spelt, barley, cous-cous, potatoes, bread, legumes (many of them rich in proteins as well), rusks, biscuits, corn flakes, sweet fruit, even dry sweet fruit, etc.
Lipids (fats and oils), important energy source for sports in which aerobic metabolism is greatly involved as those of long duration, should bring 25-30% of daily calories. The main lipid source, in a Mediterranean diet, is extra-virgin olive oil (the foundation of Mediterranean diet); the remaining part will came from those present foods (the so-called “hidden fat”) as in meat and meat products, milk and cheeses, eggs, oily dry fruits, oilseed etc. and, between seasoning fats, butter (better avoid margarine, often rich in industrial trans fatty acids, a real poison). As previously mentioned it is advisable to avoid fast food and industrial products (in particular bakery products such as cookies, snacks, cakes, croissants, pastries, French fries, fried chicken etc.) because lipids present in these foods, unless clearly specified in the package, are never extra-virgin olive oil but mostly palm or coconut oil and often partially hydrogenated vegetable oils as well.
The daily lipid intake must not be less than 20% of daily calories because it could occur an insufficient intake of essential fatty acids and fat-soluble vitamins; moreover, considering athletes with very high energetic demands, their deficiency would cause too much abundant meals (lipids 9 Kcal/g, carbohydrates 4 Kcal/g, so more than double) and not very desirable (fats increase palatability of foods).
The remaining calories (12-15%) come from proteins, both of animal origin (meat, fish, egg, milk and dairy products), 2/3 of the total, and vegetal origin (legumes and cereals), the remaining 1/3.

References