Nutritional Requirements for Distance Runners

Matthew Cole, Richard C. Blagrove, Meghan A. Brown, Jennie Carter and Justin D. Roberts

Highlights

• • Middle- and long-distance running events are largely fuelled by the oxidative metabolism of carbohydrate.
• • Carbohydrate intake should be 3-5 g kg body mass^-1-day^-1 for a runner undertaking low volumes (<1 hour) of moderate-intensity daily training, to 6—10 gkg body mass^_l-day^-1 for those engaged with high-volume (1-3 hours) running at a moderate-high intensity.
• • It is essential that a runner’s diet contains an adequate amount of fats (particularly polyunsaturated); however, evidence highlights that high fat-low carbohydrate diets may compromise performance during all but easy running sessions.
• • Protein intake should be —1.0-1.2 g kg body mass '-day^-1 for recreational endurance runners, —1.2-1.5 g-kg body mass ' day ¹ for competitive runners engaging in daily moderate-hard training (—60 min), and -1.6—2.0 g kg body mass^-1-day^-1 for elite endurance runners (particularly when undertaking intensive training).
• • Runners should aim to consume meals/snacks that contain a balance of nutrients and fluid (—5-7 mL-kg body mass^-1) every 3-4 hours throughout the day (5-6 ‘feeds’) to support metabolic regulation and meet caloric requirements.

Introduction

Achieving success in a distance running event is dependent upon the conversion of chemical energy' to mechanical energy to sustain a given speed. Middle-distance running events (800 m—3 km) require a high level of energy provision from both aerobic (energy' produced in the presence of oxy'gen) and anaerobic (energy produced without oxygen) sources and rely almost exclusively on carbohydrate to fuel higher-intensity performance. Long-distance running events (5 km—marathon) are heavily reliant on oxygen-dependent replenishment of energy', which requires an adequate delivery of oxy'gen and availability of carbohydrate and fat as metabolic fuels. Ultra-endurance events (>4 hours) have also increased in popularity over the last decade and present unique physiological challenges in terms of fatigue, hydration and energy demand (Tiller et al., 2019). Fatigue during marathon and ultra-distance running events can often be a consequence of muscle glycogen (carbohydrate) depletion, therefore ensuring that high pre-exercise muscle and liver glycogen concentrations are essential. A runner’s diet is of paramount importance for overall health and for provision of essential calories/nutrients to fuel training/racing and to support adaptive processes during recovery from training. Consequently, this chapter aims to provide evidence-based recommendations on appropriate nutrition practices for distance runners.

Energy Metabolism

To understand the nutritional requirements of various distance running events, it is important to first explain how metabolic energy systems resynthesise the high energy compound found in all muscle cells, adenosine triphosphate (ATP). The availability of ATP is critical for all skeletal muscle contractile activity, yet the intramuscular stores of ATP are sufficient to support only a few seconds of exercise (Hargreaves and Spriet, 2018). To maintain ATP levels within working muscles, three metabolic pathways are activated, two anaerobic pathways (substrate-level phosphorylation without oxygen) and an aerobic pathway (oxidative phosphorylation). Metabolism is a dynamic process with relative contribution of each energy' pathway during exercise dependent upon the duration and the intensity of activity; however, it is a common misconception that they switch on and off in a sequential or hierarchical order.

During very intense running, such as the first 100 m of a middle-distance race and sprint finishes, most ATP is resynthesised via the anaerobic energy pathways - the phosphocreatine system and anaerobic glycolytic system. The phosphocreatine system has a limited capacity (~10 sec) for ATP resynthesis, whereas anaerobic glycolytic capacity is approximately threefold higher (Hargreaves and Spriet, 2020). Sustained sprinting (30-60 sec) results in a high reliance on anaerobic glycolysis to maintain ATP levels, which is associated with accumulation of metabolic by-products - lactate and hydrogen ions. Blood lactate concentration reflects the activation of the anaerobic glycolytic system and therefore acts as a useful indicator of exercise intensity. However, there is still a widely held belief that lactic acid causes fatigue, which is incorrect (Brooks, 2001). Rather, it is the metabolites (magnesium ions, adenosine diphosphate, inorganic phosphates and hydrogen ions) and intra-cellular acidosis associated with the breakdown of ATP, phosphocreatine and glycogen during anaerobic metabolism that appear to cause rapid fatigue during high-intensity exercise (Allen et al., 2008). Nutritional strategies (e.g. bicarbonate, beta-alanine) that promote a more alkaline environment and metabolite buffering capacity may therefore provide an avenue for improving performance during middle-distance running events (see Chapter 11).

Distance running events lasting ~2 min and longer derive most of their energy from aerobic processes. Even the men’s 800 m event (world record 1:40.91) has a substantial (~60%) aerobic contribution (Duffield et al., 2005). Although oxidative phosphorylation is activated at the onset of exercise, it becomes the major ATP-generating pathway after ~60 sec of exercise. The rate at which oxygen consumption rises at the start of high-intensity exercise to meet the required energy demand via oxidative phosphorylation is known as ‘oxygen uptake kinetics’, and is an important determinant of endurance performance and highly trainable (Burnley and Jones, 2007). During high-intensity interval training sessions and middle-distance races, intramuscular stores of muscle glycogen and blood glucose (derived from liver glycogenolysis) provide the primary source of energy' (Hargreaves and Spriet, 2020).

In the presence of oxygen, pyruvate (converted from glucose) is transported to the mitochondria where it is used to produce acetyl co-enzyme-A, which forms the major entry point for metabolic fuels (fat and carbohydrate) into the Krebs cycle. The Krebs cycle degrades acetyl co-enzyme-A to carbon dioxide and hydrogen, plus resynthesises one molecule of ATP. The hydrogen atoms subsequently enter the electron transport chain that uses oxidative phosphorylation to yield 38 ATP molecules from glucose metabolism, or 129 ATP from a fatty acid. Despite the higher energy yield from a molecule of fat compared to carbohydrate, oxidation of carbohydrate is ~7% more efficient as it generates more ATP per volume of oxygen compared to fat, and the pathways that metabolise carbohydrate are far quicker (Spriet, 2014). This means carbohydrates are the preferred fuel when energy' is in high demand. An important adaptation to endurance training, however, is an increased reliance on fat as a fuel for exercise (Achten and Jeukendrup, 2004), which is important for sparing glycogen stores for later in an exercise bout or subsequent sessions.

Oxidative metabolism of carbohydrate and fat provides virtually all the ATP in skeletal muscle for long-distance running performance and continuous moderate-intensity training runs. At higher intensities of exercise (~80-100% maximal oxygen uptake (P0_2nm), i.e. 3 km to marathon pace in trained runners) carbohydrate oxidation dominates (Hargreaves and Spriet, 2020). Rates of fat oxidation are highest when the demand for energy is lower at ~60—65% of F0_2lmx (i.e. marathon pace in recreational runners, and ultra-distance running intensity). As exercise duration increases, oxidation of intramuscular glycogen and lipid stores decreases, corresponding with an increased reliance on muscle glucose and fatty acid uptake from the blood (van Loon et al., 2001). During prolonged running (> 90 min), liver glucose output can decrease to levels below muscle glucose uptake, resulting in hypoglycaemia (‘low blood sugar’). This risk of developing hypoglycaemia can be reduced by ensuring adequate pre-exercise liver glycogen levels and in-event carbohydrate ingestion (Coyle et al., 1983).

Energy Requirements

Consuming enough calories to meet daily energy' needs should be a priority for runners. The total daily energy requirement for runners depends upon a variety' of factors including age, sex, body mass (BM), body composition, basal metabolic rate, non-exercise physical activity levels and the nature (duration, mode, intensity') of exercise training. ‘Energy' balance’ refers to the ratio between energy intake (from foods, fluids and any supplements) and energy' expenditure, calculated as the sum of basal metabolic rate, the thermic effect of food, and the energy expended during non-exercise physical activity and exercise training. A longterm negative energy balance will result in weight loss, and a positive energy' balance will cause weight gain. Energy' needs can be estimated for active individuals using the Dietary Reference Intake method (Zello, 2006; Box 4.1). The definitions of physical activity' in these equations mean that for most recreational and competitive runners, exercise will be classified as ‘moderate-vigorous’ in nature. This method, and other equations, for estimation of daily energy' requirement provide only an approximation of average energy needs, so it should be used as a rough guide.

BOX 4.1 THE DIETARY REFERENCE INTAKE METHOD FOR ESTIMATING ENERGY REQUIREMENT FOR ADULTS (RODRIGUEZ ET AL, 2009). PA = PHYSICAL ACTIVITY

Adult Male

Energy requirement (kcal per day) = 622 - (9.53 x age in years) + {PA x ([15.91 x weight in kg] + [539.6 x height in m])}

Female Adult

Energy requirement (kcal per day) = 354 - (6.91 x age in years) + {PA x ([9.36 x weight in kg] + [726 x height in m])}

PA Level

• 1.0-1.39 Sedentary, typical daily living activities (e.g. household tasks, walking to bus)
• 1.4-1.59 Low active, typical daily living activities plus 30-60 min of daily moderate activity (e.g. walking at 5-7 km.fr¹)
• 1.6-1.89 Active, typical daily living activities plus 60 min of daily moderate activity
• 1.9-2.5 Very active, typical daily living activities plus 60 min of daily moderate

activity plus an additional 60 min of vigorous activity or 120 min of moderate activity.

Example

21-year-old male well-trained runner performing -60 min running per day (PA of 1.7) weighing 75 kg and 1.75 m in height:

Energy requirement = 622 - 200 + {1.7 x (1193 + 944)} = 4054 kcal per day*

* This requirement is relevant only to days where the PA level applies, e.g. on rest days (PA of 1.0-1.2) this value is likely to be -2600-3000 kcal per day.

‘Energy availability’ is defined as the energy derived from the diet minus exercise and physical activity energy expenditure expressed relative to fat free mass (FFM), providing the amount of energy ‘left over’ for normal physiological functions (Loucks et al., 2011). Current consensus is that optimal energy' availability for healthy physiological function in women is around 45 kcal-kg FFM^_1-day For women, 30 kcal-kg FFM '-day ¹ appears to represent the lowest threshold of energy availability before physiological systems are substantially perturbated (Mountjoy et al., 2018b). Emerging data also suggests males will also incur deleterious physiological effects during periods of low energy availability, but at a lower threshold of ~20-25 kcal-kg FFM 'day ¹ (Koehler et al., 2016; Fagerberg, 2017). High volumes of training often make it problematic for many endurance runners to meet their energy requirements, which can result in periods of low energy availability. Indeed, it has been estimated that 37% of female and 40% of male elite distance runners suffer from a syndrome known as ‘relative energy' deficiency in sport’ (RED-S; Heikura et al., 2017), which is associated with impairments in metabolic rate, menstrual function (for females), bone health, immunity and cardiovascular health (Mountjoy et al., 2014). Readers are referred to Chapter 18, which provides further detail on RED-S and how the syndrome can be avoided.

Macronutrients

Carbohydrate

Carbohydrate is the primary source of energy' for moderate and high-intensity exercise and therefore ensuring adequate dietary intake of carbohydrate is essential. Carbohydrate intake should vary according to the nature of the training (and competition) that is being undertaken at any given time. As a general guide, daily carbohydrate requirements for different ty'pes of training and event preparation are provided in Table 4.1. Based on these recommendations, an individual weighing 70 kg who runs on most days of the week in the form of continuous runs and interval training sessions (30-60 min in duration) should be consuming approximately 350 g of carbohydrate per day. Chapter 17 provides further detail on the importance, intake and timing of carbohydrate during recovery from training sessions, and Chapter 11 addresses pre-event carbohydrate loading for events lasting > 90 min.

Carbohydrates can be classified as simple (glucose, fructose, sucrose, lactose, maltose, e.g. sugar, honey, jams, energy' drinks/gels) and complex (starch, e.g. bread, pasta, wholegrains, potatoes, cereals). As foods from both carbohydrate types can generate similar post-prandial changes in insulin and blood sugar levels, a better classification is the glycaemic index (GI) scale (Donaldson et al., 2010). The GI value of a carbohydrate-rich food is measured on a scale from 0 to 100 that refers to how blood sugar levels rise in the hours post-consumption. Glucose, as a reference, has a score of 100, with values of > 70 considered high GI foods, 55-70 moderate GI foods, and < 55 low GI foods (Atkinson et al., 2008). Examples of high GI foods include potatoes, white bread/baguettes, bananas and cake products. Foods such as green vegetables, beans, wholemeal pasta, nuts, apricots, oranges and apples have a lower GI value. Low GI carbohydrate foods in the hours prior to exercise appears to provide a metabolic advantage over high GI foods due to a higher oxidation of fats in the early stages of exercise and more stable blood glucose levels (Donaldson et al., 2010). Immediately after

TABLE 4.1 Carbohydrate intake guidelines for distance runners during different training and event scenarios

Note: BM = body mass.

Source: Burke et al. (2011); Burke et al. (2017a); Thomas et al. (2016).

exercise, high GI carbohydrate foods appears to be more beneficial to maximise the rate of muscle glycogen resynthesis (Burke et al., 1993).

Fat

Fats are responsible for numerous physiological functions, so they are important for the maintenance of health and optimisation of performance in runners. Fats support important roles in cellular signalling and structural maintenance, nerve function, inflammatory processes, insulation and protection of vital organs, and energy provision. Moreover, it is important that an athlete’s diet contains the appropriate amount of essential fatty acids (fats that the body cannot make on its own) and fat-soluble vitamins (A, D, E and K). Although high fat intake and low density lipoprotein (LDL) cholesterol are associated with chronic diseases, fat should certainly not be viewed negatively and low intakes of dietary fat (< 20% of total energy') can negatively impact health and performance (Vitale and Getzin, 2019). Furthermore, cutting out certain food groups that are high in fat, e.g. dairy, can result in micronutrient deficiencies (Close and Morton, 2016). Fats have a higher energy density (9 kcal g^-1) compared to carbohydrate (4 kcal-g^M), therefore care should also be taken not to overconsume foods high in fat over prolonged periods.

Fats are typically classified as saturated and unsaturated; with unsaturated fat further sub-divided into monounsaturated and polyunsaturated fat. Essential fatty acids are considered polyunsaturated fats and are categorised as omega-3 and omega-6 fatty acids. Omega-3-rich foods include oily fish (e.g. salmon, tuna, mackerel), walnuts and flax seeds, and examples of dietary' sources of omega-6 fatty acids include vegetable oils, soybeans, eggs, nuts, avocado and meat/poultry/fish. Although the optimal ratio of omega-3/omega-6 fatty' acids is 1:1 to 4:1, it is apparent that typical Western diets are heavily deficient in omega-3 fatty acids (Patterson et al., 2012). Therefore, athletes are encouraged to increase weekly omega-3 fatty acid intake, e.g. three portions of oily fish per week (Close and Morton, 2016). Although reducing saturated fats from the diet (particularly processed meats) will likely improve health, they should be replaced with unsaturated fats rather than refined carbohy'drate (e.g. bread, pasta, potatoes, Astrup et al., 2011). Finally, hydrogenated fats (or ‘trans fat’), are artificially created fats typically used in manufactured food products and the fast food industry'. They provide no benefit to health and sports performance, and therefore runners should avoid foods that contain trans fats (Mozaffarian et al., 2006).

Protein

Proteins have many critical roles in the body' including as antibodies, enzymes and messengers, and to provide structure and support for cells. Proteins are composed of amino acids, with nine classified as ‘essential’ (must be consumed in the diet) and the remainder as ‘non-essential’ (the body can make its own if required). The current recommended daily allowance of protein for a sedentary non-athlete is 0.8 g-kg BM~'-day^_1; however, it appears those engaging in regular endurance exercise require more (Tarnopolsky, 2004). Protein requirements have been estimated at —1—1.2 g-kg BM '-day ⁴ for recreational endurance athletes (4—5 x ~30 min runs per week), 1.2-1.5 g-kg BM ‘-day¹ for competitive endurance athletes engaging in daily moderate-hard training (~60 min), and 1,6-2.0g-kg BM '-day¹ for elite endurance athletes and those performing frequent (> 3 times per week) strength training (Tarnopolsky 2004; Rodriguez et al., 2009; Kato et al., 2016). Regular intake of protein above these amounts does not provide further benefit to endurance athletes (Vitale and Getzin, 2019). Protein requirements for runners can be easily met through a ‘food-first’ approach. However, supplementary protein may be warranted when logistical challenges are faced, or when liquid meals may be preferred e.g. during acute recovery from training. If athletes choose to use nutritional supplements, they should preferably ensure it has been appropriately batch-tested under a recognised supplement quality assurance program (Maughan, 2013) as verified by an ‘Informed Sport’ logo (Smith et al., 2015).

The timing and type of protein that is consumed is equally as important as the absolute daily amount ingested. Athletes should avoid restricting their daily intake of protein foods to mealtimes and instead aim to consume protein ‘snacks’ throughout the day, particularly before and after exercise (Kerksick et ah, 2017). As explained in Chapter 17, protein intakes of 0.25- 0.30 g kg BIVT¹ (~20 g for a 70 kg individual), or 0.4 gkg BM ¹ for older adults, is likely to maximise muscle protein synthesis if consumed within the two-hour period after exercise (Moore, 2015). Similarly, dosages of 0.25-0.30 g kg BM'¹ (15-30 g for most runners) every 3-4 hours throughout the day (5-6 ‘feeds’) appears to optimise daily protein synthesis rates (Areta et ah, 2013; Jager et ah, 2017; Vitale and Getzin, 2019).

In addition to the quantity and timing of intake, the type of protein consumed is also important to consider. Whey protein (the water-soluble part of milk) is a high-quality, easily absorbed protein containing all nine essential amino acids. Crucially, protein sources that contain the essential amino acids known as the branched chain amino acids (leucine, isoleucine and valine) are particularly important, with leucine needed to ‘switch on’ muscle protein synthesis (Duan et ah, 2016). Foods high in milk-based protein result in higher muscle protein synthesis rates post-exercise compared to soya protein (Phillips et ah, 2009). Casein (found in milk, yogurt and cheese) is considered a slow-release protein and is therefore beneficial to consume prior to sleep to provide a sustained delivery of amino acids overnight (Res et ah, 2012). Animal-based foods (i.e. milk, eggs, cheese, red meat, fish, poultry) provide the most concentrated sources of essential amino acids. Whilst plant-based protein sources (e.g. soy products, tofu, pumpkin seeds, chia seeds, quinoa, lentils, chickpeas, nuts and other grains) contain lower amounts of essential amino acids, for the vegetarian and vegan runner it is possible to consume a diet complete in proteins by making structured and varied food choices (Jager et ah, 2017).

Micronutrients

Vitamins and minerals have many functions that are important for health and running performance, such as energy production, haemoglobin synthesis, maintenance of bone health, repair of damaged tissue, immune function and protection against oxidative damage (Rodriguez et ah, 2009). Vitamins and minerals are required only in small amounts; however, except for Vitamin D, they must be consumed through the diet. A list of the major vitamins and minerals important for runners, their physiological functions, recommended daily intake and food sources are shown in Table 4.2. Fat-soluble vitamins (vitamins A, D, E and K) are capable of being stored in the liver and fat cells for later use by other tissues. If dietary intake of these vitamins is low, the body will draw upon its stored reserves, however; if intakes are excessive and stores of these vitamins are saturated, this can cause adverse health issues. Water-soluble vitamins (B vitamins and vitamin C) cannot be stored; therefore, the body cannot draw upon any reserves if intake is low, and excessive consumption is mostly excreted.

Intake of Micronutrients

Inadequate micronutrient intake is known to compromise physical performance and can increase the risk of illness and infection (Lukaski, 2004; Sabetta et al., 2010). Dietary reference values provide the recommended intake of micronutrients for 97.5% of the population; however, regular exercise may increase the turnover and loss of these micronutrients, thus greater intakes of some vitamins and minerals may be required in runners (Woolf and Manore, 2006; Rodriguez et al., 2009). A balanced wholefood diet that contains at least five portions of a variety of fruit and vegetables (see Table 4.2) is usually enough to support the micronutrient requirements of most runners without the need for supplementation. It is also important to remember that increasing the total caloric intake to support the energy' demands of training will also increase the intake of micronutrients. Runners are at high risk of developing deficiencies if they: restrict their energy intake, have an unbalanced diet, dislike certain food groups or have allergies and lack sunlight exposure. Runners who fall into one or more of these categories may benefit from additional multivitamin/mineral supplementation (Close and Morton, 2016); however, advice should be sought from a qualified professional concerning the need for supplements. Although a sufficient intake of all vitamins and minerals is important for runners, this section will discuss the micronutrients that runners should pay most attention to.

The В Vitamins

The В vitamins have important roles in regulating energy’ metabolism, and folic acid and vitamin B₎₂ are required to produce new red blood cells. Consequently, a deficiency in the В vitamins can potentially hamper running performance, and low levels of folic acid and vitamin B₎₂can result in anaemia (lack of red blood cells; Lukaski, 2004). Research indicates that exercise may increase the requirements for vitamin B₂ and vitamin B₍₎; however, it is less clear whether there is an increased requirement for the other В vitamins (Woolf and Manore, 2006). Trained runners who consume a sufficient number of calories to support their exercise and lifestyle requirements tend not to be deficient in the В vitamins (Kaiserauer et al., 1989; Nieman et al., 1989; Habte et al., 2015; Nebl et al., 2019). To obtain adequate amounts of the В vitamins, foods such as wholegrains, fruits, vegetables, and lean meats should be consumed regularly (see Table 4.2).

Vitamin D and Calcium

Vitamin D and calcium are particularly important for growth and repair of bone tissue and regulate nerve impulse transmission and muscle function. A deficiency in one or both of these micronutrients has been associated with low bone mineral density and stress fractures in runners (Nieves et al., 2010; Giffin et al., 2017). Calcium is obtained from the diet (e.g. dairy products, green leafy vegetables and nuts); however, vitamin D is mainly synthesised through sunlight. Runners who live in northern latitudes, spend long periods of time indoors, and train on treadmills or after sunset are therefore at risk of vitamin D deficiency (Close et al., 2013). Consequently, it is recommended that runners actively consume foods high in vitamin D (see Table 4.2) during the winter months, particularly if they are not able to train outdoors during daylight hours. Athletes showing symptoms of insufficiency (e.g. persistent fatigue, mood changes, bone pain, frequent illness), especially during winter months, should have their vitamin D status checked.

Antioxidants

During exercise (particularly of a high intensity), an increase in metabolism accelerates the production of free radicals (or reactive oxygen species). Reactive oxygen species are required for activating cellular signalling pathways that lead to important physiological adaptations; however, they also cause damage to lipids and proteins and contribute towards muscle damage and soreness (Schieber and Chandel, 2014). The main antioxidant micronutrients (vitamins C and E, beta carotene and selenium) and polyphenols mitigate the damaging effects of oxidative stress caused by the release of reactive oxygen species. There has been speculation that athletes require higher amounts of antioxidants in their diet; however, the evidence suggests that this may not the case (Gomez-Cabrera et al., 2008a). In fact, some evidence observed blunted exercise-induced increases in enzymatic antioxidants following supplementation of vitamin C and E, and attenuated training adaptations (Gomez-Cabrera et al., 2008b; Paulsen et al., 2014; Morrison et al., 2015). However, this may apply only to specific nutrients and/or be related to the timing of supplement ingestion (e.g. in close proximity to exercise). Other authors have indicated that fruit-derived polyphenols (>1000 mg-day^-1 for >3 days) may in fact support antioxidant and anti-inflammatory pathways which may have important implications for endurance or demanding high-intensity events (Bowtell and Kelly, 2019). Further research in this area is warranted, and at present runners should aim to consume a wholefood diet that provides a good variety of fruit and vegetables to meet antioxidant/polyphenol requirements.

Iron

Iron is required to produce oxygen-carrying proteins (haemoglobin and myoglobin) and enzymes involved in energy production. Due to the inflammation caused by running, the hormone hepcidin is upregulated in the hours following exercise, which compromises the absorption of dietary iron (Peeling et al., 2009). Furthermore, the rupture of blood vessels and gastrointestinal bleeding that occurs during running may also affect iron status (Deldicque and Francaux, 2015). For these reasons, iron requirements are ~70% higher for endurance runners compared to non-active individuals (Rodriguez et al., 2009).

Low iron status is common in runners, particularly women (Coates et al., 2017), which can impair muscle function, work capacity and lead to feelings of lethargy (Pasricha et al., 2010). The daily recommended intake of iron for pre-menopausal female runners (18 mg-day^-1 and 11-12 mg-day^-1 for hormonal contraceptive users) is higher than for male runners (8 mg-day^-1) to account for the regular losses of iron that occur through menstrual bleeding (Deldicque and Francaux, 2015; Pedlar et al., 2018). In adolescents experiencing a period of rapid growth and females who experience heavy menstrual bleeding, daily intake may need to be higher (Bruinvels et al., 2016). Vegetarian runners also struggle to obtain the recommended amount of iron per day due to the lower bioavailability of iron in plant-based foods compared to meat; therefore, iron requirements are 1.8 times higher in vegetarians compared to omnivores (Deldicque and Francaux, 2015). Long-distance runners, especially women, adolescents, vegetarians, and runners training at altitude, should be blood tested regularly to monitor iron status (Sim et al., 2019). Iron supplementation is currently not recommended for runners who have normal iron stores; however, those identified as being iron deficient (including non-anaemics) may benefit from taking an iron supplementation under the recommendation of a medical professional (Rubeor et al., 2018; Sim et al., 2019).

Other Minerals

There are 20 minerals that must be consumed in the diet; however, in addition to those discussed already, zinc and magnesium are most important for runners. Zinc is responsible for growth and repair of tissues, immune function and energy production; therefore, a deficiency affects thyroid hormones, metabolic rate and recover)'. Research indicates that athletes, particularly women, have low zinc levels, which suggests they have a higher requirement for zinc compared to those who are physically inactive (Chu et al., 2018). Magnesium plays several crucial roles associated with energy metabolism and regulates neuromuscular function. Endurance training may result in a degree of magnesium deficiency in some athletes (Casoni et al., 1990), highlighting that magnesium requirements for athletes are likely higher than non-active individuals (Bohl and Volpe, 2002; Zhang et al., 2017). Furthermore, high sweat rates without adequate intake of magnesium can cause a deficiency that impairs cardiovascular and neuromuscular function, leading to compromised endurance performance (Nielsen and Lukaski, 2006). However, whilst magnesium supplementation may support hormonal or metabolic demands of training (Golf et al., 1998), there is little evidence that magnesium supplementation directly benefits endurance performance (Terblanche et al., 1992; Zhang et al., 2017). Therefore, athletes who obtain enough magnesium in their diet likely do not require additional supplementation (Wang et al., 2017). If a runner is in energy balance and eats a diet that includes all food groups (see Table 4.2), there is little risk of not meeting the recommended daily intake of minerals. The difference between a safe and a toxic daily intake of minerals is smaller compared to vitamins, and therefore care should be taken when using supplements that minerals are not overconsumed, which can interfere with absorption of other micronutrients (Close and Morton, 2016).

Hydration

During everyday living, euhydration (normal levels of hydration) can be maintained quite easily via behavioural and biological controls (Belval et al., 2019). However, endurance exercise can result in fluid losses that can acutely impair performance (at ~2-3% of body mass) and requires restoration following exercise (Cheuvront et al., 2003). Recommendations for appropriate hydration strategies can be considered before, during and after exercise. In-event/ during exercise considerations are discussed in Chapter 11, and post-exercise guidelines to optimise re-hydration practices are provided in Chapter 17.

Beginning exercise/competition in a euhydrated state is usually easy to achieve if sufficient beverages and meals have been consumed in the hours leading up to the session/event (Sawka et al., 2007). However, if an athlete is in a hot environment they are not fully acclimatised to, they exercise shortly after waking, and/or they have experienced substantial fluid deficits in the previous 8 hours, then an active pre-hydration strategy may need to be used (Sawka et al., 2007). Regularly monitoring hydration status in the hours leading up to a session/event is the best way to determine whether additional fluid is required (Close and Morton, 2016). Within

(Continued)

Note: BM = body mass; НС = hormonal contraceptive. * Multiply by 1.8 for vegetarians.

a field-based setting, a urine osmolality of <700 mOsmol kg BM ¹ and a urine colour that is pale yellow provide an indication of euhydration prior to exercise (Sawka et al., 2007). Validated urine colour charts can be found online; for example, www.usada.org/athletes/ substances/nutrition/fluids-and-hydration/. Runners should aim to slowly drink ~5-7 mLkg BM ¹ (~400-500 ml for a 70 kg individual) at least 4 hours prior to exercise. If the runner does not urinate or urine is dark, a further 3-5 mL kg BM^-1 (~250-300 ml for a 70 kg individual) of fluid should be slowly consumed ~2 hours before the event (Maughan et al., 1996; Shirreffs and Maughan, 1998). Beverages containing a small amount of sodium (460-1150 mg-L ¹ or 20-50 mEq-L ') or consumed with a snack containing salt will help fluids to be absorbed (Ray et al., 1998). Attempting to drink more fluid than the aforementioned recommendation does not provide a performance advantage, increases the likelihood of having to urinate during the exercise/event, and in extreme cases risks hyponatraemia (see Chapter 11; Sawka et al., 2007).

The Distance Runners' Diet

The previous sections have provided evidence-based guidelines on appropriate intake of energy', macro- and micronutrients for a runner. Despite consensus in these areas, decisions on what foods to eat, how much and appropriate timings of consumption remain highly individual and depend upon numerous factors including: age, sex, food preferences, food availability, allergies/intolerances, lifestyle, budget, racing and training goals, time of year, training volume and intensity, training modalities, training environment, etc. Intense running sessions can also suppress appetite, and many runners prefer not to exercise within several hours of eating (Kerksick et al., 2018). Therefore, each runner requires a unique and constantly changing nutrition plan that is suited to their own needs (Heikura et al., 2018a). Boxes 4.2 and 4.3 provide two case studies of runners with different nutritional requirements and how their diets might look.

When using a high-carbohydrate availability diet, the percentage of energy contributed from carbohydrate, fat and protein consumed as a proportion of total energy' intake in a runners diet should be roughly 45-55%, 25-35%, 10-15% respectively (Kerksick et al., 2018). Higher percentages of energy' derived from carbohydrate (60-70%) have been recommended to support high volumes of training or in the days leading up to a marathon/ultra-distance event (Coyle, 1991). Presenting macronutrient intake targets as percentages can cause confusion due to the differences in the calorie density within macronutrients, which may lead to athletes consuming more or less of each macronutrient than intended (Burke et al., 2011). Furthermore, a runner’s diet could comprise an appropriate proportion of carbohydrate (e.g. 50%), but total energy intake may only be 2000 kcal day^-1, which would be insufficient to support energy' demands (Rodriguez et al., 2009). It is therefore more appropriate to calculate macronutrient requirements in absolute terms (gkg BM ’-day⁴), as indicated throughout this chapter.

As carbohydrate is the main fuel used during high intensities of exercise (> 80% of K0_2llMX), there is a need to ensure adequate muscle glycogen stores prior to hard (i.e. ‘tempo’, intervals, fartlek) running sessions. It takes approximately 4 hours for carbohydrate to be digested and absorbed into the muscles and liver as glycogen; therefore, wherever possible, pre-session meals should be consumed 4-5 hours prior to runs (Kerksick et al., 2017). Ingesting a light carbohydrate and protein snack ~1 hour prior to intense exercise may also be beneficial (Cade et al., 1991) and provides an option for those who train early in the morning. It is recommended that carbohydrate, protein and fluid intake is spread over the day, evenly spaced (every 3-4 hours) across 5-6 meals or snacks (Kerksick et al., 2018).

Low Carbohydrate-High Fat Diets

High-carbohydrate diets have been researched and recommended for endurance athletes for decades (e.g. Hyman, 1970; Brewer et al., 1988). However, there has been a growing interest in the use of low carbohydrate-high fat (or ‘ketogenic’) diets over the last 5-10 years (Burke, 2015). A ketogenic diet typically involves consuming < 5% of total energy intake from carbohydrate (<50 g-day^-1), 15-20% protein and 75-80% fat (Burke, 2020). High-fat diets (ketogenic and non-ketogenic) have been proposed to improve endurance performance by increasing fatty acid availability and decreasing glycogen utilisation (Volek et al., 2015). Studies have observed similar endurance capacity with high-carbohydrate and high-fat approaches when the exercise intensity remains low (60-70% of P0_2lMX) (Phinney et al., 1983; Shaw et al., 2019). However, this intensity of exercise is far lower than most runners use during competitive events at all distances up to the marathon. Indeed, at higher intensities of exercise, performance and exercise economy appears to be impaired by following a high-fat diet (Havemann et al., 2006; Burke et al., 2017b) due to an decreased activation of glycogenolysis and the pyruvate dehydrogenase enzyme (Stellingwerff et al., 2006). Although high-intensity training and event performance may be compromised by following a ketogenic diet, there may be beneficial adaptations to fat metabolism by undertaking some training with low glycogen (Hulston et al., 2010). Therefore, an alternative approach is to manipulate dietary fat and carbohydrate within training phases and prior to competitions to take advantage of the potential benefits associated with both types of dietary approach (Burke et al., 2018).

BOX 4.2 CASE STUDY 1

Shelly is a 16-year-old female middle-distance runner who competed for her county last summer. She currently runs four times per week (two interval training sessions at her Athletics Club; one 45 min and one 60 min run both at moderate intensity) plus performs two 30 min strength and conditioning sessions each week. She attends college every day and has a busy social life. She is vegetarian but her parents are unsure whether she is eating a sufficiently healthy diet. Her body mass is relatively stable at 52 kg and her BMI is 20 kg m². She has regular menstrual cycles and has not had any injuries in the last year.

Suggested weekday diet plan:

Breakfast (7:30 am)

Bran flakes (70 g) + semi-skimmed milk (200 ml) + tap water (250 ml)

Energy: 325 kcal, Carbohydrate: 56 g, Protein: 14 g, Fat: 5 g

Mid-Morning Snack (Whilst at College) (10:00 am)

Almonds (20 g) + Creek-style yoghurt (150 g) + tap water (250 ml)

Energy: 318 kcal, Carbohydrate: 8 g, Protein: 13 g, Fat: 26 g

Lunch (13:00 pm)

Red and white quinoa (210 g) + salad tomatoes (85 g) + cucumber (30 g) + 2 Tsp hummus (-20 g) + baby spinach (80 g) + tap water (300 ml) + dried apricots (50 g) Energy: 410 kcal, Carbohydrate: 63 g, Protein: 7 7 g, Fat: 10 g

Pre-Training Snack (16:00 pm)

Medium banana (-100 g) + tap water (300 ml)

Energy: 84 kcal, Carbohydrate: 20 g, Protein: I g, Fat: 0 g

17:00-18:00 pm Training

Post-Training Snack (18:30 pm)

Chocolate milk (300 ml) + 4 fig rolls (-84 g)

Energy: 521 kcal, Carbohydrate: 87 g, Protein: 14 g, Fat: 13 g

Dinner (19:30 pm)

Egg noodles (180 g) + tofu (45 g) + broccoli (45 g) + carrots (45 g) + edamame beans (45 g) + sesame seeds (15 g) all fried in 1 Tsp sesame oil (-4 g) + tap water (500 ml) Energy: 625 kcal, Carbohydrate: 69 g, Protein: 31 g, Fat: 25 g

Total Daily Breakdown of Key Nutrients

Energy: 2,283 kcal

Carbohydrate: 303 g (5.8 g kg"¹, 53% energy intake), Protein: 90 g (1.7 g kg"¹, 16% of energy intake), Fat: 79 g (1.5 g kg"¹, 31 % of energy intake)

Calcium: 1420 mg, Iron: 30 mg, Zinc: 13 mg, Vitamin B₁₂: 4 pg, Vitamin C: 96 mg

BOX 4.3 CASE STUDY 2

Jim is a 54-year-old male recreational long-distance runner who has run six marathons since he turned 50 years old. He is currently training for a major city marathon in 2 months and aims to break 5 hours. He runs most days and has built his long run back up to 20 miles on a Sunday morning. Jim and his wife have two teenage children who play sport most evenings. His full-time job is based in an office, but he often goes out for the day with his family at weekends. He suffers from mild Achilles tendonitis, which some days prevents him from running. Jim feels he is quite lazy with what he currently eats and often binges on junk food after runs and in the evening. He is 180 cm tall and his current body mass is 75 kg (BMI of 23.1 kg m²).

Suggested Sunday diet plan:

Breakfast (7:30 am)

• 70 g oats made with 200 ml semi-skimmed milk topped with 160 g strawberries & 2 tsp pumpkin seeds 300 ml beetroot juice
• 1 slice wholegrain toast + 1 tsp butter + 300 ml water Energy: 730 kcal, Carbohydrate: 105 g, Protein: 25 g, Fat: 24 g
• 9:30-11:30 am - two-hour training run

Post-Training Snack (11:30 am)

Wholemeal bagel (100 g) + 1 tbsp crunchy peanut butter + 1 banana + 500 ml water Energy: 468 kcal, Carbohydrate: 77 g, Protein: 18 g, Fat: 9 g

Lunch (13:00 pm)

Grilled chicken breast mini fillet (50 g cooked in 1 tsp rapeseed oil) + 300 g boiled basmati rice + 80 g boiled broccoli + 90 g boiled carrots + 500 ml water Energy: 516 kcal, Carbohydrate: 87 g, Protein: 27 g, Fat: 7 g

Mid-Afternoon Snack (16:00 pm)

Ciabatta (90 g) filled with 1 thick slice of beef (20 g) + 40 g spinach + 1 tsp light mayonnaise + 300 ml water

Energy: 291 kcal, Carbohydrate: 44 g, Protein: 15 g, Fat: 6 g

Dinner (18:30 pm)

Grilled salmon fillet chunks (80 g cooked in 1 tsp rapeseed oil) + 300 g new potatoes with rosemary + 80 g boiled green beans + 85 g cannellini beans + 500 ml water Energy: 534 kcal, Carbohydrate: 59 g, Protein: 31 g, Fat: 19 g

Evening Snacks (21:00 pm)

90 g natural yoghurt + 140 g frozen mixed berries + 1 tbsp honey + 50 g granola + 30 g raisins

Smoothie (100 g frozen pineapple, 1 orange, 200 ml semi-skimmed milk, 7г avocado) Energy: 832 kcal, Carbohydrate: 122 g, Protein: 22 g, Fat: 28 g

Energy: 3,371 kcal

Carbohydrate: 494 g (6.6 g kg"¹, 59% of energy intake), Protein: 138 g (1.8 g kg "¹, 16% of energy intake), Fat: 93 g (1.2 g kg"¹, 25% of energy intake)

Calcium: 1316 mg, Iron: 20 mg, Zinc: 10 mg, Vitamin B12: 7 qg, Vitamin C: 335 mg

Periodised Nutrition

Periodised nutrition refers to “the planned, purposeful, and strategic use of specific nutritional interventions to enhance the adaptations targeted by individual exercise sessions or periodic training plans, or to obtain other effects that will enhance performance in the longer term” (Jeukendrup, 2017). In other words, periodised nutrition is the manipulation of an athlete’s diet to best support training prescription and enhance adaptive processes (Stellingwerff et al., 2019). A detailed discussion of the various strategies and approaches to manipulating nutrient availability over the course of a competitive season and training/event week is beyond the scope of this chapter. Readers are referred to several excellent reviews (Jeukendrup, 2017; Burke et al., 2018; Stellingwerff et al., 2019) and case studies (Stellingwerff, 2012; Heikura et al., 2018a) that address this topical area of nutrition. Although all nutrients can be strategically periodised around a runner’s training, environment and event/ competition schedule, manipulation of the fuels that provide energy for exercise have naturally been the focus of most research in this area. Beyond the recommendations presented in Table 4.1 around high carbohydrate intake before training (‘train high’), during competition and post-exercise, several acute interventions that involve reducing carbohydrate availability prior to exercise (‘train low’) have been investigated (Burke et al., 2018). A brief summary of the main strategies associated with manipulation of carbohydrate availability is provided in Table 4.3.

For long-distance runners preparing for events from the half-marathon to the ultramarathon, preservation of liver and muscle glycogen stores should be considered part of the training adaptation process. Steady pace training sessions in a fasted or semi-depleted (lowered glycogen) state (the classic ‘train low-compete high’ approach) during the preparatory and building phases of training may support cellular and enzymatic adaptations associated with increased fat oxidation (Baar and McGee, 2008; Burke et al., 2018). These augmented adaptations may have important benefits for longer duration pace maintenance (as exercise in tensity'/race pace is typically lower in longer-duration events), particularly following acute glycogen replenishment. However, such practices require careful monitoring to avoid diet- related fatigue and/or immunosuppression.

The approaches described in Table 4.3 can be deliberately used over the course of a training week and mesocycle to ensure high-quality training and boost adaptation. Intuitively, runs above lactate threshold (i.e. ‘tempo’, intervals and fartlek) performed at a hard-severe intensity are heavily dependent upon carbohydrate, therefore a ‘train high’ approach would be best, whereas the ‘train low’ strategy is more suitable for runs where the intensity is below lactate threshold (i.e. medium- to long-duration recovery runs). For example, a high-intensity interval training session would be performed after consuming a carbohydrate-rich meal 4-5 hours prior (‘train high’), but a long moderate-intensity run

64 Matthew Cole et al.

TABLE 4.3 Common acute strategies associated with manipulation of carbohydrate availability to maximise training/event performance and augment training adaptation

Source: Jeukendrup (2017); Burke el al. (2018); Impey cl al. (2018); Stellingwerff, Morton and Burke (2019). Note: BM = body mass.

performed the following day could be completed with reduced carbohydrate availability (‘train low’). The low glycogen state in the second session could have been achieved via a combination of‘sleep low’, ‘recover low’ and a low daily carbohydrate intake (Stellingwerff et al., 2019).

Summary

Meeting the energy demands of training and event participation should be a major nutritional goal for all distance runners. All but the lowest intensities (60-65% F0_2mjx) of aerobic exercise rely on carbohydrate as the primary fuel for maintaining ATP levels in skeletal muscle. Therefore, consumption of carbohydrate-rich meals and snacks that total 3-5 g-kg BM ¹ each day for runners undertaking low volume (< 1 hour per day') training and 6-10 g-kg BM ' day^-1 for those logging high volume (1-3 hours per day) of running, should prevent glycogen depletion. Runners should not attempt to remove fat from their diets; however, consumption of foods containing omega-3 fatty acids may need to be increased, and products containing ‘trans fats’ should be reduced. Low carbohydrate—high fat (ketogenic) diets are inadequate for supporting the fuelling needs of most runners; however, acute periods of low carbohydrate availability' during moderate intensity runs (‘train low’) and recovery periods (‘recover low’) appears to have short-term utility and can augment training adaptation. Protein intake should be ~1.0—1.2 g-kg BM ¹ -day ¹ for recreational endurance runners, 1.2-1.5 g-kg BM '-day¹ for competitive runners engaging in daily moderate-hard training (~60 min), and 1.6-2.0 g-kg BM '-day¹ for elite endurance runners. Runners should aim to consume 5-6 meals/snacks evenly spaced throughout the day (every 3-4 hours) that contain a balance of nutrients and fluid to ensure a state of euhydration (~5-7 mL kg '). In the 2 hours after exercise, carbohydrate consumed at a rate of 1.2 g-hour'¹ and a protein intake of0.25-0.30 g-kg BM ¹ should adequately support recovery and adaptation processes. Runners should ensure they consume at least five portions of fruits and vegetables every' day to ensure daily recommended intakes of vitamins and minerals are met.

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