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Nutrition and Sport Topic 37

Module 37.2

Nutrition for Endurance Sports

Anja Carlsohn

PhD, Nutritionist,

University of Education, Institute of Health Sciences,

Schwaebisch Gmuend, 73525, Germany

Learning Objectives

To demonstrate differences in physique, physiological demands, energy and nutrient

requirements in endurance athletes;

To apply recent recommendations for nutrient and fluid intake during habitual

endurance training periods as well as before, during and after endurance

competitions;

To critically argue pros and cons of using dietary supplements in endurance sports;

To be alert to potential clinical issues associated with nutrition in endurance sports

and to provide recommendations to reduce the risks.

Contents

1. The endurance athlete

1.1 Physique and physiological demands of endurance athletes

1.2 Energy requirements of endurance athletes in general training periods

1.3 Summary

2. Nutritional demands during general training periods

2.1 Recommendations for macronutrient intake

2.2 Fluids and electrolytes during the training process

2.3 Requirements of vitamins and minerals

2.4 Summary

3. Nutritional in specific situations: before, during and after endurance competitions

3.1 Nutritional competition preparation of the endurance athlete

3.2 Recommendations for food and fluid intake during endurance competitions

3.3 Nutrition for recovery from competition or exhausting training sessions

3.4 Summary

4. Dietary supplements used by endurance athletes

4.1 Supplements to support macronutrient intake

4.2 Vitamin, mineral and vitamin-mineral supplements

4.3 Ergogenic aids in endurance sports

4.4 Summary

5. Clinical issues concerning the nutrition of endurance athletes

5.1 Weight management, female athlete triad and eating disorders

5.2 Gastrointestinal distress

5.3 Hyponatraemia

5.4 Iron deficiency and iron deficiency anaemia

5.5 Summary

6. Summary

7. References


Key Messages

Energy requirements of endurance athletes may considerably vary depending on the

sports discipline, exercise period, sex and individual anthropometric characteristics.

During habitual training, endurance athletes should ingest at least 3-5 g of

carbohydrates per kg body mass per day, which may increase up to 8-12 g/kg/d

during intensive training periods;

The requirement for protein is increased in elite endurance athletes with 1.6 g/kg/d,

whereas moderate-intensity endurance athletes (up to 5 sessions of 45-60 min per

week) require 1.2 g/kg/d of protein. Recreational athletes exercising up to 5 times a

week for 30 min do not have protein requirements different from RDA (0.8-1.0

g/kg/d);

Fat intake should approximate 20-35 % of energy intake;

Optimized glycogen stores before competition, may improve endurance performance

by enabling maintenance of exercise intensity (=speed) to the end of a race.

Carbohydrate loading protocols include increased carbohydrate intake and tapered

exercise;

During long distance events, a carbohydrate intake of 30-90 g/h depending on

exercise duration may improve exercise performance. Using multiple transportable

carbohydrates (e.g. glucose-fructose mixture) significantly increases exogenous

carbohydrate oxidation;

To recover from exercise, rehydration and glycogen resynthesis should be

nutritionally supported. For each kilogram of body mass lost, 1.5 L of sodium-rich

fluids should be ingested. Glycogen resynthesis is elevated, when 1.2-1.5 g of

carbohydrates per hour are ingested during the first few hours post-exercise;

The efficacy, risks and benefits of using dietary supplements need to be carefully

assessed. Approximately 15% of dietary supplements worldwide were found to be

contaminated or laced with doping substances;

Health professionals and coaches should be aware of clinical issues such as the

female athlete triad, disordered eating, gastrointestinal complaints, hyponatraemia

and iron deficiency that may occur in endurance athletes.


1. The Endurance Athlete 1.1. Physique and Physiological Demands of Endurance Athletes

Endurance athletes may be involved in different sports such as running, cycling,

swimming, triathlon, canoe racing, skiing, skating, walking and others. Within these

sports, there are different disciplines. In conclusion, there are considerable differences in

the physiological and energy demands of endurance athletes. For example, running

1500 m (~3.5 - 4 min), 10.000 m (~26 - 30 min), marathons (~2.00 -2.25 hours),

ultra-marathons (> 6 hours), mountain runs (~45 min - >6 hours at altitudes of 1500-

4000 m above sea level) or steeplechase (~8-10 min) presents athletes with varying

training volumes (km per week), exercise intensities (highly aerobic vs. anaerobic

metabolism), different demands for high-intensity and long-lasting low-intensity training

or for accompanying (non-specific) exercise sessions such as technical training, strength

and power sessions or exercises in other sports.

It should also be taken into consideration that elite competitive athletes may have other

nutritional demands compared to recreational athletes or persons involved in endurance

sports for health reasons. Recently, there seems to be a consensus that athletes

exercising less often than five times a week for 30-45 min do not have nutritional

requirements different from the sedentary population, as this relatively small amount of

exercise may be seen as normal physical activity (1, 2).

Typically, endurance athletes have a low body mass and normal to low body mass index

compared to sedentary people and athletes from other sports such as strength athletes

(3). Table 1 provides average anthropometric data of endurance athletes.

Table 1

Anthropometric characteristics of elite endurance athletes

Sport Height [m] Weight [kg] Body fat [%]

or sum of

skinfolds

Reference

1500 m run

(9 females)

1.65 ± 0.12 52.40 ± 6.96 51.4 ± 10. 8

(6 skinfolds)

(4)

Marathon (11

females)

1.58 ± 0.18 45.58 ± 6.82 44.4 ± 7. 7

(6 skinfolds)

(4)

1500 m run

(16 males)

1.78 ± 0.05 65.69 ± 3.94 36.9 ± 5. 1

(6 skinfolds)

(4)

Marathon

(17 males)

1.72 ± 0.04 59.85 ± 3.34 33.2 ± 5. 5

(6 skinfolds)

(4)

Rowing & canoeing

(9 females)

1.75 ± 0.07 69.3 ± 11.0 18.5 ± 4.0 (5)

Rowing & canoeing

(8 females)

1.93 ± 0.07 92.9 ± 10.0 12.7 ± 2.0 (5)

Triathletes

(10 females)

1.67 ± 0.07 56.4 ± 6.1 25.9 ± 9.4

(4 skinfolds)

(6)


1.2. Energy Requirements of Endurance Athletes in General Training

Periods

Energy requirements of endurance athletes may vary substantially between individuals

and between different training periods. The total energy expenditure (TEE) of endurance

athletes depends on their body mass, body composition, age, sex, their non-exercise

activity and the frequency, duration and intensity of exercise.

Total TEE of endurance athletes is typically 1.8 to 2.3-fold as high as the individual’s

resting energy expenditure (7), but may be higher (up to 4-fold) in professional

endurance athletes during short periods (8). Using the doubly labelled water technique

(DLW), Westerterp et al. observed a mean TEE of 3490±250 kcal/d in elite male Kenyan

runners during an intensive period of training (9). In ultra-endurance triathletes a mean

energy expenditure of 2630 ± 160 kcal/d was calculated from heart-rate monitoring

during competition (10). In elite female light-weight rowers, Hill et al. measured a mean

TEE of 3875 kcal/d using DLW during an intensive training period (11).

1.3. Summary

Endurance athletes represent a variety of sporting disciplines with different physiological

and metabolic demands. Therefore, only general nutritional recommendations are

available and should be provided in terms relative to body mass or energy expenditure to

account for the different physique of endurance athletes. As a rough estimation, energy

expenditure of endurance athletes is approximately twice as high as the resting energy

expenditure.

2. Nutritional Demands During General Training Periods 2.1. Recommendations for Macronutrient Intake

Meeting the energy demands of athletes is the major goal in endurance athletes.

Especially in females the energy intake is often observed to be considerably below the

estimated TEE. With low energy intake, even a high proportion of carbohydrates might be

insufficient to support adequate glycogen resynthesis during intensive training periods.

Vice versa, an athlete who consumes a moderate proportion of protein (~ 15 % of EI) in

a high energy diet may exceed the upper limit of intake for protein. Therefore,

recommendations for nutrients should be provided in absolute terms related to body

mass (i.e. g/kg/d) instead of proportions relative to energy intake.

Carbohydrate-rich foods (cereals, vegetables, legumes and products thereof) should be

the major source to account for elevated energy demands (2,7). During low-intensity

training periods (low-intensity or skill-based activities for less than 1 hour /day), a

carbohydrate intake of 3-5 g/kg/d seems to be appropriate to meet the demands of

endurance athletes (12).

In case of moderate training programmes (~ 1 h/d), 5-7 g/kg/d of carbohydrates are

recommended (12). For elite endurance athletes exercising 1-3 h/d or > 4 h with high-

to-moderate intensity a carbohydrate intake of 6-10 g/kg/d (8-12 g/kg/d, respectively) is

recommended to avoid glycogen depletion and negative effects on performance

outcomes or immune function (12). However, these recommendations need to be fine-

tuned considering the individual TEE, specific training needs and the individual’s feedback

from training performance (12).

Nitrogen balance studies in competitive endurance athletes suggest that athletes should

aim to ingest 1.2-1.4 g/kg/d of proteins (13, 14). Elite endurance athletes might require

up to 1.6 g/kg/d, whereas the protein requirement of recreational endurance athletes

(exercising 4-5x/week for 30 min) seems not to be higher than that of sedentary people

with 0.8-1.0 g/kg/d.


Regarding fat intake, endurance athletes should follow the recommendations for the

general population, i.e. 20-35 % of EI should be provided by fat. Here, the proportion of

energy from fatty acids is recommended to be 10 % saturated, 10 % monounsaturated

and 10 % polyunsaturated (7).

2.2. Fluids and Electrolytes in the Training Process

Sweat losses during exercise may considerably vary between endurance athletes and

depend on individual sweat rates, type, duration and intensity of exercise, sex, fitness

level and environmental factors such as heat or humidity (15). In the literature, typical

sweat rates of 1.49 L/h (range 0.75-2.23 L/h) for male half-marathon runners during

winter competitions and of 1.77 L/h (range 0.99-2.55 L/h) for cross-country running

during summer training are given (16, 17).

There is strong evidence that dehydration increases the physiologic strain and the

perceived effort to perform an exercise. A dehydration >2 % of body mass can adversely

affect exercise performance (15, 18). Thus, it is recommended to avoid dehydration >2

% of body mass by regular intake of fluids during exercise and to support adequate

hydration by regular meal consumption spread over the day (15, 18, 19). However, to

reduce the risk for exercise-induced hyponatremia overdrinking (i.e. weight gain during

exercise) should be avoided (15) (see chapter 5.3).

Sodium (~900 mg/L), potassium (~ 200 mg/L), calcium (~18 mg/L), zinc (~0.6 mg/L),

copper (~ 0,1 mg/L) and magnesium (~1,4 mg/L) are the major minerals found in

human sweat during exercise, with a huge intra-individual variety (20, 21). As there is

evidence that sodium loss may be linked to exercise-induced muscle cramps (21),

athletes prone to heavy sodium loss (“salty sweaters”) should consume sodium-

containing drinks during exercise lasting >90 min (18).

In case food intake is adequate, no additional electrolytes or minerals are required in the

sports drink during habitual training, except for “salty sweaters”, who might need

beverages containing 400-1000 mg/L of sodium (18, 19, 22).

2.3. Requirements of Vitamins and Minerals

There are no special micronutrient intake recommendations available for endurance

athletes. Recently, there is no evidence to assume that recommended daily allowances

(RDAs) for micronutrient intake do not cover the demands of athletes (7, 23). However,

there are some micronutrients that might be crucial, especially when the athlete’s diet is

restricted and/or losses are elevated.

For antioxidants such as vitamins C and E, an increased requirement due to exercise-

induced production of reactive oxygen species has been postulated (24, 25). However,

there is no prove for detrimental effects on health or performance in case of marginal

deficiencies (26, 27). In contrast, more recent studies suggest that supplementation of

athletes with vitamin C and/or E may adversely affect health and training adaptation for

both health-oriented and elite athletes (28, 29, 30, 31).

Prevalence of iron deficiency is high (~50 - 70 %) among athletes, especially among

females (32, 33, 34). Iron status may be adversely affected by endurance exercise (34,

35). Thus, an elevated requirement is anticipated, but no general recommendation

exists. There is strong evidence that iron deficiency anaemia reduces aerobic capacity

(36, 37), but the effect of iron deficiency without anaemia is still unclear (38). Another

exception where requirements might be in some cases higher than the RDAs for the

general population is sodium (see chapters 5.3 and 5.4)


2.4. Summary

Meeting the energy requirement is the major nutritional goal in endurance athletes.

Carbohydrate needs to avoid glycogen depletion vary from 3-5 g/kg/d during low-

intensity training periods, 5-7 g/kg/d in moderate training-periods to 8-12 g/kg/d in

periods of high-intensity high-volume training.

Both dehydration and sodium loss may be linked to exercise-induced muscle cramps.

Avoiding a dehydration >2 % of body mass by regular ingestion of sodium beverages

(400-1000 mg/L) and/or proper hydration before exercise are recommended.

Requirements for vitamins and minerals seem not to be higher than recommended daily

allowances for sedentary people, except for iron (esp. females) and sodium (esp. in salty

sweaters).

3. Nutrition in Specific Situations: Before, During and after Endurance Competitions Dietary concepts as well as single foods, fluids and/or sports supplements should not be

used at the day of competition for the first time. Individual preferences in taste and/or

palatability should be considered to avoid gastrointestinal discomfort and to achieve an

optimal voluntary intake of fluids and nutrients.

3.1. Nutritional Competition Preparation of the Endurance Athlete

Depletion of glycogen stores in liver and muscle are a major cause of fatigue during

endurance exercise (39). Therefore, glycogen status should be optimized before

competition. Increased carbohydrate intake and tapered exercise or rest are a

prerequisite for glycogen storage (40, 41, 42).

Glycogen synthesis is known to follow a biphasic manner, with an initial rapid phase

(insulin-independent, fast rate of glycogen-synthesis during the first 4-24 hours after

exercise) followed by a slow phase (insulin-dependent, slow rate of glycogen synthesis,

up to several days following exercise) (43, 44). Depleted glycogen stores support an

effective glycogen resynthesis (43, 44). Normally, 24 hours of rest accompanied by a

carbohydrate intake of 7-10 g/kg/d are adequate to normalize glycogen stores (45, 46).

There are different carbohydrate loading protocols available to maximize glycogen stores

before events lasting >90 min. The original carboloading protocol, also known as “Saltin

diet” was established in the 1970ies and included a 3-4 days depleting phase (glycogen

depleting exercise combined with low carbohydrate intake) and a 3-4 days loading phase

with tapered exercise and high carbohydrate ingestion (47, 48).Sherman et al. observed

that glycogen supercompensation also occurs within 3-4 days without depleting phase,

when 3-4 days of exercise rest are combined with a high carbohydrate intake (49). More

recently, Bussau et al. observed that one day of rest is sufficient to maximize glycogen

stores, when the carbohydrate intake is ~10 g/kg/d (50).

All these carbohydrate loading protocols are still used by athletes, as all protocols have

advantages and disadvantages. Short carboloading protocols that require exercise rest

may not be suitable for all athletes, especially for those who need a ‘fine tuning’ of

training or an activity stimulus in the days before competition. Others might be afraid of

gaining weight due to excessive carbohydrate consumption over several days, so the

shorter protocol (50) might be more appropriate for those athletes. The original

carboloading protocol by Karlsson and Saltin requires hard training in the week before

competition at already depleted glycogen stores. The decreased training performance due

to low glycogen availability shortly before a competition and the potentially adverse

effects on the immune function (51) are regarded the major disadvantages of this early

protocol.

Recently, a carbohydrate intake of 10-12 g/kg/d for 36-48 hours before competitions

lasting >90 min is recommended (12). Carbohydrate-rich foods and fluids low in fiber


and fat spread over several meals and snacks may be helpful to achieve the

carbohydrate intake goals. Performance benefits from carbohydrate loading (i.e.

maintaining the speed at the end of the race) seem to persist even when carbohydrates

are consumed during the competition (52, 53).

For the pre-exercise meal some general aspects should be followed: the meal should

provide sufficient fluids to ensure euhydration before starting the exercise, it should be

low in fat and fibre to reduce gastrointestinal complaints and improve gastric emptying

and should be familiar to the athlete (7). Pre-exercise meals that are ingested 3-4 hours

before competition may have a carbohydrate content of 200-300 g. Depending on the

individual needs and palatability, 1-4 g of carbohydrate per kg body mass 1-4 hours

before exercise are recommended (12). Carbohydrate-rich pre-exercise meals that have

a low glycemic index promote the availability of sustained carbohydrates during exercise

and should therefore be preferred (54).

3.2. Recommendations for Food and Fluid Intake during Endurance Competitions

During endurance events, carbohydrates, fluids and sodium should be ingested

depending on the exercise duration, intensity and environmental conditions.

In the 2009 Joint Position statement of the American College of Sports Medicine, the

American Dietetic Association and the Dietitians of Canada, evidence for performance

benefits is provided (55-56), when endurance athletes consume 0.7 g/kg/h

carbohydrates (~30-60 g/h) during exercise (7). This recommendation takes into

account that the oxidation rate from exogenous glucose is ~ 1 g/min, even at high rates

of intake (57).

However, more recent studies have shown that the carbohydrate oxidation rate may be

increased up to 1.75 g/min, when multiple transportable carbohydrates using different

intestinal transporters are ingested (56). Recently, a mixture of glucose (using sodium-

dependent glucose transporter-1 [SGLT-1]) and fructose (using glucose transporter 5

[Glut5]) is recommended for ingestion during distance events (56).

Maximum carbohydrate oxidation rate form exogenous sources may be achieved by

ingesting glucose and fructose (ratio 2:1) at amounts of 1.8 g/min, i.e. ~70 g/h of

glucose and 35 g/h of fructose during exercise (56). The administration form of the

multiple transportable carbohydrate mixture does not influence the oxidation rate, thus

athletes may combine beverages, carbohydrate bars or gels during long-distance events

(58, 59). Co-ingestion of proteins during endurance exercise seems not to have beneficial

effects on muscle protein synthesis rate (60). To achieve an optimal balance between the

requirements for carbohydrate absorption and fluid delivery, carbohydrate concentration

should range between 5-10 %, with the lower concentration when fluid delivery is more

important than carbohydrate absorption (i.e. in hot and humid environments) (15).

For endurance competitions of shorter duration, the finding that carbohydrate mouth

rinsing improves exercise performance in endurance events lasting 30-75 min may be of

interest. Although the potential mechanisms are not fully understood, there seems to be

a receptor-mediated effect of carbohydrate mouth rinsing on the brain that reduces

fatigue and leads to performance benefits besides the metabolic advantages (61- 63).

However, it seems that carbohydrate ingestion during relatively short (<30 min) high-

intensity exercises does not improve exercise performance (64).

Fig. 1 summarizes recent recommendations for carbohydrate intake during exercise.


Fig. 1 Carbohydrate intake recommendations for highly-trained, competitive endurance

athletes during exercise (modified from (65)).

3.3 Nutrition for Recovery from Competition or Exhausting Training Sessions

Adequate nutrition may support post-exercise recovery, especially rehydration and

glycogen resynthesis following endurance events with a certain degree of dehydration

and glycogen depletion.

Shirreffs et al. (1997) analysed the effect on fluid restoration of differently concentrated

sodium solutions in amounts equivalent to 50 %, 100 %, 150 % and 200 % of exercise-

induced body mass loss (66). They found that high-sodium solutions (~60 mmol/L or

~1330 mg/L) at amounts of 150 % of body mass loss are most effective in restoration of

fluid losses. Thus, expert panels recommend to ingest 1.5 L of a sodium-containing fluid

for each kg of body mass lost during exercise to support rapid recovery from dehydration

(15). Voluntary drinking after exhausting exercise may be supported by adding palatable

flavour and carbohydrates (19).

Immediate consumption of carbohydrates following glycogen-depleting exercise can

enhance glycogen resynthesis rates (43, 64). A carbohydrate ingestion of 1.2 -1.5 g/h

per kg body mass during the first few hours following exercise was shown to significantly

increase glycogen restoration (43, 68). Although carbohydrates with high glycemic index

(GI) have been supposed to promote glycogen resynthesis (54), more recent studies

failed to show a performance enhancing effect when a high GI recovery diet was

consumed compared to a low GI diet (67). This might be explained by the sufficient

carbohydrate intake during the first few hours after exercise, where glycogen resynthesis

is insulin-independent (see chapter 3.1).

Adding proteins to recovery beverages might be helpful (69-70), although no additional

increase in glycogen resynthesis rate was observed when carbohydrate intake exceeds

1.2 g/kg/h (71). In case a high carbohydrate intake cannot be achieved, a reduced

carbohydrate ingestion (~0.8 g/kg/h) is as effective as 1.0-1.2 g/kg/h carbohydrate,

when ~0.2-0.4 g/kg/h of protein is co-ingested (43, 68).

Exercise duration

30-75 min

1-2 hours

2-3 hours

> 2.5 hours

Carbohydrate intake recommendations during exercise

Mouth rinsing or small amounts of single or multiple transportable carbohydrates

30 g/h of single or multiple transportable carbohydrates.

60 g/h of single or multiple transportable carbohydrates.

90 g/h of multiple transportable carbohydrates (i.e. glucose-fructose mixture with glucose:fructose relation of 2:1)


As fat is known to delay carbohydrate absorption due to delayed gastric emptying (72)

post-exercise meals and snacks should be low in fat.

To achieve these nutritional targets, athletes may consume beverages or non-liquid foods

that are rich in carbohydrates, spread over smaller dosages every 15-20 min. A

combination of carbohydrate containing fluids and foods might be a prudent choice to

support muscle glycogen recovery.

3.4. Summary

Supporting rehydration and glycogen resynthesis are the major nutritional goals during

recovery from exercise. Rehydration is most effective when a fluid volume equivalent to

150 % of sweat loss is ingested (i.e. 1.5 L for each kg of body mass lost). Recovery

beverages should be high in sodium to support fluid retention in the body. For the first 2-

4 hours post-exercise, ingestion of carbohydrates at amounts of 1.2-1.5 g/kg/h spread

into smaller dosages (fluids or low-fat snacks) every 15-20 min is recommended. In case

such a high carbohydrate intake cannot be achieved, adding ~ 0.4 g/h of protein (e.g.

milk-based recovery beverage) may support glycogen resynthesis.

4. Dietary Supplements Used by Endurance Athletes

As for the general population, using supplements increases the athlete’s risk to exceed

the tolerable upper level of intake for the given nutrient(s). In addition, supplements

may be contaminated or faked with doping substances, with a worldwide prevalence of

~15 % of supplements containing WADA (World anti-doping association) banned

substances without declaration (73). Despite the risks and contraindications of dietary

and ergogenic supplements used by athletes (73-75), there might be a few supplements

that may be useful for some endurance athletes in certain conditions.

In general, athletes use supplements to support recovery from exercise, to improve

health and performance, to prevent or treat illness and because they believe not to have

a balanced diet. Most often, vitamins, minerals and protein supplements are used (74).

Considering the risks of consuming undeclared WADA banned substances and/or

exceeding tolerable levels of intake, a thorough risk-benefit assessment must be

conducted before using dietary supplements.

4.1. Supplements to Support Macronutrient Intake

In training periods where a high carbohydrate intake is required (chapters 3.1 to 3.3)

athletes might have difficulties to achieve the nutritional goals (76). Here, concentrated

carbohydrate sources (i.e. carbohydrate-rich beverages, gels or bars) can help to

increase carbohydrate intake. Although carbohydrate-rich supplements may not have a

performance benefit compared to meals, athletes might regard them more convenient

(i.e. no effort to prepare a meal, palatable, convenient storage).

For athletes with restricted availability of foods and/or elevated energy demands,

carbohydrate, protein or liquid meal supplements may be helpful during short periods to

achieve the macronutrient and energy requirements.

4.2. Vitamin, Mineral and Vitamin-mineral Supplements

As detailed in chapter 2.3, there is recently no additional micronutrient requirement for

endurance athletes quantified that generally justifies vitamin and/or mineral supplement

use by athletes. In situations where requirements cannot be met by food intake (i.e.

athletes during travelling, in periods of restricted food intake, during training camps with

limited availability of fresh and balanced food or athletes with food intolerances etc.)

vitamin and/or mineral supplements can be considered as a short-term alternative that

should be discussed with a health-professional (i.e. physician, nutritionist) (74).


4.3. Ergogenic Aids in Endurance Sports

There are only few dietary supplements that may have ergogenic effects to endurance

athletes, which includes caffeine, buffering substances (i.e. sodium bicarbonate, or

sodium citrate) and creatine.

For caffeine (which was removed from the WADA prohibited list in 2004), a stimulating

effect on fatty acid utilization resulting in a glycogen sparing effect was anticipated (77).

However, more recent data suggest that the primary performance enhancing effect of

caffeine is caused by a reduction of perceived ratings of fatigue and/or to central nervous

system stimulation (78-79). The magnitude of performance benefits increases with

increased duration of the exercise task (79). These performance benefits may be

achieved with relatively small doses of caffeine (1-3 mg/kg body mass) before or during

exercise (80-81). Side effects of caffeine intake (i.e. insomnia, headache, gastrointestinal

complaints or increased urinary flow) should be outweighed before using caffeine as an

ergogenic aid (74).

Buffering agents are used by endurance athletes involved in medium-term (1-60 min),

high-intensity exercise. Ingestion of 0.3-0.5 g/kg sodium bicarbonate or sodium citrate

was shown to have a moderate performance benefit in different endurance sports, with a

positive association between level of acidosis achieved during exercise and beneficial

effects of the buffering agent (82). Side effects (gastrointestinal complaints such as

diarrhoea, cramping) should be considered (7).

Creatine was found to enhance glycogen synthesis and may therefore be helpful in

situations where a fast recovery of glycogen stores is required (83). However, there is no

evidence that creatine supplementation results in performance enhancement in

endurance athletes. In contrast, side-effects such as weight gain may be a contra-

indication for endurance athletes in weight-bearing sports.

4.4. Summary

There is no evidence that endurance athletes have higher macro- or micronutrient

demands that essentially require dietary supplements. Dietary supplements (vitamins,

minerals or macronutrients) may however be a short-term option to achieve dietary

goals in periods where food intake is limited. There is little evidence for ergogenic effects

of supplements in endurance sports, except for caffeine and buffering agents. In the

recent Consensus Statement, the International Olympic Committee (IOC) clearly reveals

that supplements may not compensate for poor food choices and inadequate diets (22).

5. Clinical Issues Concerning the Nutrition of Endurance Athletes

5.1 Weight Management, Female Athlete Triad and Eating Disorders

In both male and female endurance athletes energy intake levels below estimated energy

expenditure has been reported (9, 84-85). Reducing body mass and body fat is often

seen as an competitive advantage by athletes (3, 86).

However, the purpose to reduce body mass for a competitive advantage may result in

dieting and/or in disordered eating or eating disorders. Rosendahl et al. reported a

prevalence of eating disorders in 10 % of endurance athletes (87). In Norway, an

increase of the prevalence of eating disorders among elite athletes from 20 % in 1990 to

28 % in 2002 was observed (86). For athletes, there are different risk factors identified:

predisposing factors (family background, individual factors), precipitating factors (e.g. a

comment on body shape) and perpetuating factors such as initial performance benefits

(88).

Body mass and body composition of elite endurance athletes may vary from those

observed in the general population with lower body mass, body mass index and body fat

content as a result of high exercise-induced energy expenditure (see chapter 1.1).

However, long-term restricted eating or low energy availability may have adverse effects


Female

athlete triad

Disordered eating /Eating disorder orinadequate food intake, low energy availibility

Amenorrheaor

Subclinical disruptions ofmenstrual cycles

Osteoporosisor

osteopenia, failure to achievepeak bone mass

on both health and performance (88). This includes cardiovascular, endocrine,

reproductive, gastrointestinal and renal disturbances and the central nervous system

(88).

Dieting athletes may slip into disordered eating and severe eating disorders, which in

turn may lead to abnormal menstrual cycles and impaired bone remodelling leading to

premature osteopenia or osteoporosis (86). The term “female athlete triad” denotes the

occurrence of all three symptoms (disordered eating, amenorrhea and osteoporosis, or

subclinical presentations thereof, Fig. 2) (88-89).

The prevalence of the female athlete triad varies between 4-27 % in elite athletes,

depending on whether all three or only two out of three criteria needed to be met for

diagnosis (90). Long-term health consequences (impairment of reproductive function,

premature osteoporosis) may not be excluded.

Fig. 2 Components of the female athlete triad (modified from (89)).

Similar health problems may occur in male endurance athletes with restricted diets.

Rector et al. analysed body fat and bone mineral density in recreational male cyclists and

63% of them were diagnosed with osteopenia (91). To reduce the risk of detrimental

effects on health and performance, athletes should follow a diet and training regime that

ensures an energy availability of 30-45 kcal/kg fat-free mass per day. Here, energy

availability denotes the remaining energy from dietary intake for the body after

subtracting exercise-related energy expenditure (92) (Fig. 3).

Fig. 3 Energy availability to maintain health and performance in athletes

energy intake

Energy spent forexercise

energy availabilty

(without exercise)

Should not fall below30-45 kcal/kg FFM/d


5.2. Gastrointestinal Distress (“Runner’s Diarrhoea”)

There is a high prevalence (30-50 %) of gastrointestinal (GI) complaints during long-

distance events reported by runners, triathletes and other endurance athletes (93). The

complaints include stomach or intestinal cramping, vomiting, diarrhoea or nausea (94).

Dehydration, delayed gastric emptying, redistribution of the blood-flow and movements

of the gut during exercise are regarded the main causes for GI complaints during

endurance exercise (94).

To reduce GI distress athletes should be encouraged to consume well-tolerated foods and

fluids low in fat and fibre sufficiently before the onset of exercise. During exercise,

approximately 0.5 L/hour of a beverage containing carbohydrates and sodium is

recommended. To avoid additional delay in gastric emptying, hyperosmolar solutions

should be avoided (94). Carbohydrate concentration in sports beverages should not

exceed 6% (95).

5.3. Hyponatraemia

Exercise-induced hyponatremia (EIH) was reported in marathons and other (ultra-)

endurance events and is characterized by a plasma-sodium level below 135 mmol/l (96 -

99). Incidence of hyponatremia in ultra-endurance events ranges from 0.3% to 27 %

(100).

EIH is a life-threatening condition with symptoms that may be taken for symptoms of

hypoglycaemia, heat stroke, exercise exhaustion or exercise-associated collapse when

laboratory assessment is not available (100). Known causes for EIH include overdrinking

(i.e. drinking in excess of fluid losses via sweat or urinary losses), overexpression of

arginine vasopressin during exercise and inadequate exchange during osmotic and non-

osmotic sodium stores in the body (101). A hot and humid environment, events lasting

>4 hours, female sex, slower finishing times and the use of nonsteroidal anti-

inflammatory drugs are considered additional risk factors for EIH (100).

To prevent EIH, athletes should be advised to follow a moderate hydration regime (~500

ml per exercise hour or less) instead of following old recommendations to drink as much

as tolerable (15, 95). Consuming carbohydrate-electrolyte solutions is recommended

during long-distance events (95). Athletes should avoid gaining weight during exercise

(i.e. avoid overdrinking) (15).

5.4. Iron Deficiency and Iron Deficiency Anaemia

Iron deficiency is the most prevalent nutrient deficiency worldwide. In the literature,

results are controversial whether or not athletes have a higher prevalence of iron

deficiency (102-104) or, in contrast, a better iron status (105 - 106).

Risk factors for iron depletion in endurance athletes include poor iron intake, poor iron

availability (due to high carbohydrate intake), foot strike haemolysis, increased iron loss,

altered intestinal absorption, vegetarian diets, altitude training and female sex (7, 28).

Iron requirements in endurance athletes (esp. runners) may be increased by

approximately 70 % (107).

It is non-controversial that iron deficiency anaemia adversely affects endurance

performance (108 - 109). However, the effect of iron deficiency without anaemia on

exercise performance remains equivocal, at least at early stages of iron depletion (98,

110-111). Athletes at risk should be individually counselled how to increase dietary iron

intake and iron availability from food. Iron supplementation must be supervised by a

health professional. Recently, a regular screening for iron deficiency in endurance

athletes accompanied by a supervised iron supplementation to correct for iron depletion

is recommended (7, 83, 112).


5.5. Summary

Prevalence of restricted or disordered eating and eating disorders is high among

endurance athletes, especially among females. The female athlete triad is a symptom

complex consisting of restricted or eating disorders, amenorrhea and osteoporosis and

subclinical presentations thereof. Energy availability (i.e. energy intake – energy spent

for exercise) should not fall below 30-45 kcal/kg FFM/d.

Gastrointestinal complaints are often reported by endurance athletes, esp. in runners. To

reduce gastrointestinal stress, sufficient gaps between food intake and exercise, intake of

well-tolerated foods and fluids and a moderate fluid intake during exercise (~0.5 L /h) is

recommended.

Exercise-induced hyponatremia is a life-threatening condition reported in endurance

events lasting >4 hours. Athletes should be encouraged to temper their fluid

consumption not allowing for weight gain during exercise and to consume sodium

beverages such as commercial carbohydrate-electrolyte drinks.

Iron deficiency and iron deficiency anaemia are common nutrient deficiencies among

athletes, especially females. Athletes at risk should be counselled to increase iron intake

and/or to reduce inhibitors of iron absorption and need to be regularly screened for

depleted iron stores and anaemia.

6. Summary (overall)

Endurance athletes represent a variety of sporting disciplines with different physiological

and metabolic demands. Meeting the energy requirement is the major nutritional goal in

endurance athletes. General carbohydrate needs to avoid glycogen depletion vary from

3-5 g/kg/d during low-intensity training periods, 5-7 g/kg/d in moderate training-periods

to 8-12 g/kg/d in periods of high-intensity high-volume training.

Exercise-induced hyponatremia is a life-threatening condition reported in endurance

events lasting >4 hours. Athletes should be encouraged to temper their fluid

consumption not allowing for weight gain during exercise and to consume sodium

beverages such as commercial carbohydrate-electrolyte drinks.

Both dehydration and sodium loss may be linked to exercise-induced muscle cramps.

Avoiding a dehydration >2 % of body mass by regular ingestion of sodium beverages

(400-1000 mg/L) and/or proper hydration before exercise are recommended.

Supporting rehydration and glycogen resynthesis are the major nutritional goals during

recovery from exercise. Rehydration is most effective when a sodium containing fluid

volume equivalent to 150 % of sweat loss is ingested (i.e. 1.5 L for each kg of body mass

lost). For the first 2-4 hours post-exercise, ingestion of carbohydrates at amounts of 1.2-

1.5 g/kg/h spread into smaller dosages every 15-20 min is recommended.

Requirements for vitamins and minerals seem not to be higher than recommended daily

allowances for sedentary people, except for iron (esp. females) and sodium (esp. in salty

sweaters). Dietary supplements may be contaminated with banned substances and may

not compensate for poor food choices and inadequate diets.

Prevalence of restricted or disordered eating and eating disorders is high among

endurance athletes, especially among females. Energy availability (i.e. energy intake –

energy spent for exercise) should not fall below 30-45 kcal/kg FFM/d to avoid health

consequences such as symptoms of the female athlete triad.


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Nutrition and Sport Topic 37lllnutrition.com/mod_lll/TOPIC37/m372.pdf · Nutrition and Sport Topic 37 Module 37.2 Nutrition for Endurance Sports Anja Carlsohn PhD, Nutritionist, University