The Complete Guide to Sports Nutrition (9th Edition)

PREFACE TO THE NINTH EDITION

It seems extraordinary that this book is now in its ninth edition. Since the first edition, it has undergone many revisions and updates as the science of sport and exercise nutrition has evolved over the years. When it was first published in 1993, sports nutrition was in its infancy and there was little reliable nutrition information available to athletes, coaches and nutrition practitioners. Since then, our knowledge of how nutrition influences sport and exercise performance has grown enormously, new guidelines have been developed and high-quality research continues to be published. There is now overwhelming evidence that diet significantly influences performance and recovery. Having advised hundreds of athletes over the past 30 years, I have seen first-hand how important diet is in supporting any training programme and helping athletes reach their goals.

The aim of this book has always been to translate the science of sport and exercise nutrition into practical information that athletes can understand and use. It provides evidence-based facts and recommendations in an easy-to-digest format, not opinions or anecdotes. All the information is backed with scientific studies, which are referenced in the text and listed at the back of the book. I am happy to report that, over the years, this book has remained a trusted reference and practical handbook for athletes, trainers, coaches, sports scientists, nutritionists and dietitians.

So, what’s new? This ninth edition includes brand new chapters on relative energy deficiency in sport (RED-S), gut health, immunity and recovery from injury. I have added research updates and findings from hundreds of sports nutrition studies around the world. Since the last edition, there has been a huge rise in interest in plant-based diets, with many athletes now reducing meat or switching to a vegan diet for health, ethical, environmental or performance reasons. As a result, research on the benefits of plant proteins has increased dramatically. The thinking around hydration, race fuelling and the management of gut problems has also evolved.

In recent years, research in sports nutrition has focused on new topics such as nutrition periodisation, ‘training low’, protein timing, low energy availability and optimisation of body composition. There has been a trend towards higher fat intakes and a move away from very low-fat diets once believed beneficial for athletes. However, the controversy surrounding low-carbohydrate diets is ongoing and new research is beginning to provide some interesting insights into the effects of strategic periods of carbohydrate restriction on training adaptations, body composition and performance.

Sports nutrition advice has changed considerably over recent years. For example, guidelines for carbohydrate and protein are now expressed in grams per kg body weight, instead of as a percentage of total energy, and tailored according to the fuel requirements and training goals of specific training sessions. There have been new recommendations on the optimal amount of protein to be consumed after training sessions as well as the timing and type of protein. New concepts such as metabolic efficiency and flexibility have evolved.

It is clear that when it comes to optimal performance, one size doesn’t fit all. Athletes should follow a personalised nutrition and hydration plan that takes account of the specific physiological demands of their event, their training and performance goals, practical considerations, food preferences and individual circumstances.

Scientists have also made progress in the quest for giving elite athletes the edge in long-duration competitions, with the development of sports drinks containing ‘multiple transportable carbohydrates’ that allow the body to absorb higher amounts of carbohydrate per hour. Other changes include the abolition of advice to drink ahead of thirst and a warning against overhydration during long events. There are no longer hard and fast guidelines on fluid intake and, in practice, athletes have to find a compromise between preventing hypohydration (see here) and ensuring they don’t overhydrate.

I have always taken a ‘food first’ approach when it comes to optimising nutrition for performance, despite the enormous array of expensive engineered supplements out there! Pills, powders and gels cannot replicate the complex matrix of nutrients and phytochemicals provided by natural food. What’s more, food tastes so much nicer and provides a lot more pleasure than any supplement. If it can improve recovery and performance then this has to be great news for every athlete.

I’ve watched with equal fascination and scepticism as more and more sports supplements appear on the market. Science continues to disprove the claims of most, which I continue to report in this book. However, there is sound evidence for the benefits of a small handful of supplements, which I have outlined in Chapter 7.

In this book, I have attempted to condense decades of sports nutrition research into practical guidelines and, ultimately, a step-by-step guide to developing a personalised nutrition plan. I hope you will find the information useful and that it will help you reach your sporting potential.

Anita Bean

1

An Overview of Sports Nutrition

There is universal scientific consensus that diet affects health, performance and recovery. A well-planned eating strategy will help support any training programme, whether you are training for fitness or for competition; promote efficient recovery between workouts; reduce the risk of illness or overtraining; and help you to achieve your potential in sport.

Of course, everyone has different nutritional needs and there is no single diet that suits all. Some athletes require more calories, protein or vitamins than others; and each sport has its unique nutritional demands. But it is possible to find broad scientific agreement as to what constitutes a healthy diet for sport generally. The following guidelines are based on the Joint Position Statement on Nutrition and Athletic Performance from the American College of Sports Medicine, Academy of Nutrition and Dietetics and Dietitians of Canada (Thomas et al., 2016), the International Olympic Committee Consensus Conference on Sports Nutrition (IOC, 2011) and the International Association of Athletics Federation (IAAF) Consensus Statement (Burke et al., 2019).

These organisations highlight the importance of nutrition strategies in optimising elite performance. They recognise the advances in sports nutrition research in recent years, including the need for nutrition periodisation, individualisation of nutrition plans to take into account the specificity and uniqueness of the event and performance goals, the new concepts of metabolic efficiency and flexibility, and energy availability (energy intake minus the energy cost of exercise); the importance of nutrient timing and optimising the intakes of protein after training to aid long-term maintenance or gain of muscle; greater intakes of carbohydrate (90 g/hr) for exercise over 3 hours; the importance of vitamin D for performance; and the need for a personalised hydration plan to prevent hypohydration as well as hyponatraemia. They recommend that the requirement for energy, carbohydrate and protein should be expressed using guidelines per kg body weight to take account of a range of body sizes.

The process leading to publication was extremely thorough and drew on the combined expertise of many of the world’s leading sports nutrition experts. Of course, these guidelines are only intended to give you an overview of the evidence linking nutrition and performance. Everyone is different and some people respond better or worse to various dietary strategies. So it is important to experiment and find out what works best for you. But, being based on high-quality research, these guidelines are a great place to start.

1. Energy

It is crucial that athletes meet their energy (calorie) needs during hard periods of training in order to achieve improvements in performance and maintain good health. Failure to consume sufficient energy can result in muscle loss, reduced performance, slow recovery, disruption of hormonal function (in females) and increased risk of fatigue, injury and illness. Researchers have recently identified the concept of energy availability (EA), defined as dietary intake minus exercise energy expenditure, or the amount of energy available to the body to perform all other functions after exercise training expenditure is subtracted. In healthy adults, a value of 45 kcal/kg fat-free mass (FFM)/day equates with energy balance and optimum health. It has been suggested that 30 kcal/kg FFM/day should be the lower threshold of energy availability in females. (Fat-free mass includes muscles, organs, fluid and bones.) A low EA may compromise athletic performance in the short and long term. It may occur when energy intake is too low, energy expenditure is too high or a combination of both. The term ‘relative energy deficiency in sport (RED-S)’ refers to the impaired physiological function, including metabolic rate, menstrual function, bone health, immunity, protein synthesis and cardiovascular health, caused by relative energy deficiency or low EA in male and female athletes. It more accurately describes the clinical syndrome previously known as the Female Athlete Triad.

Your daily calorie needs will depend on your genetic make-up, age, weight, body composition, your daily activity and your training programme. It is possible to estimate the number of calories you need daily from your body weight (BW) and your level of daily physical activity.

STEP 1: ESTIMATE YOUR RESTING METABOLIC RATE (RMR)

Your RMR is an estimate of how many calories you would burn if you were to do nothing but rest for 24 hours. It represents the minimum amount of energy needed to keep your body functioning, including breathing and keeping your heart beating. It can be estimated using the Mifflin-St Jeor equation, which utilises age, weight and height, and is considered more accurate than the more commonly used Harris-Benedict equation.

Men

(10 x weight (kg)) + (6.25 x height (cm)) – (5 x age (y)) + 5

Women

(10 x weight (kg)) + (6.25 x height (cm)) – (5 x age (y)) – 161

STEP 2: WORK OUT YOUR PHYSICAL ACTIVITY LEVEL (PAL)

This is the ratio of your overall daily energy expenditure to your RMR – a rough measure of your lifestyle activity.

• mostly inactive or sedentary (mainly sitting): 1.2

• fairly active (include walking and exercise 1–2 x week): 1.3

• moderately active (exercise 2–3 x weekly): 1.4

• active (exercise hard more than 3 x weekly): 1.5

• very active (exercise hard daily): 1.7

STEP 3: MULTIPLY YOUR RMR BY YOUR PAL TO WORK OUT YOUR TOTAL DAILY ENERGY EXPENDITURE

Daily calorie needs = RMR x PAL

This figure gives you a rough idea of your daily calorie requirement to maintain your weight. If you eat fewer calories, you will lose weight; if you eat more then you will gain weight.

Resting metabolic rate

The resting metabolic rate (RMR) is the amount of energy required to maintain the body’s normal metabolic activity, such as respiration, maintenance of body temperature and digestion. Specifically, it is the amount of energy required at rest with no additional activity. The energy consumed is sufficient only for the functioning of the vital organs. It is closely related to the basal metabolic rate (BMR), which can only be measured in an awake but totally rested and post-absorptive state, and in a neutrally temperate environment. It is quite restrictive and only used in clinical or laboratory settings. RMR accounts for 60–75% of the calories you burn daily. Generally, men have a higher RMR than women.

Physical activity includes all activities from doing the housework to walking and working out in the gym. The number of calories you burn in any activity depends on your weight, the type of activity and the duration of that activity.

2. Body composition

There is no single or ‘optimal’ body composition for a particular event or sport. Each individual athlete has an optimal fat range at which their performance improves yet their health does not suffer. However, this should not be achieved at the expense of continual low energy availability, otherwise performance and health are likely to be impaired. Instead, weight and body composition should be periodised in line with the training programme, accepting fluctuations throughout the year. Excessive weight gain should be avoided in the off-season and rapid weight loss strategies avoided in the competition season. The best time to lose weight is in the base training phase or well out from competition to minimise loss of performance. A modest energy deficit of 250–500 kcal/day to achieve a slow rate of weight loss (<1% per week) is recommended along with increasing protein intake to 1.8–2.7 g/kg BW/day to preserve muscle mass.

3. Carbohydrate

Carbohydrate is an important fuel for the brain and central nervous system as well as for muscular work. It is stored as glycogen in your liver and muscles. The size of the body’s carbohydrate stores is relatively limited. Approximately 100 g glycogen (equivalent to 400 kilocalories) may be stored in the liver, and up to 400 g glycogen (equivalent to 1600 kilocalories) in muscle cells. It is almost entirely depleted by the end of 90–120 minutes of moderate- to high-intensity exercise. The purpose of liver glycogen is to maintain blood sugar levels. When blood glucose dips, glycogen in the liver breaks down to release glucose into the bloodstream. The purpose of muscle glycogen is to fuel physical activity.

Carbohydrate offers advantages over fat as a fuel since it provides more adenosine triphosphate (ATP) (see ‘What is ATP?’) per volume of oxygen and is therefore considered a more efficient fuel. There is significant evidence that performance of prolonged, sustained or intermittent high-intensity exercise is enhanced by strategies that maintain high carbohydrate availability (i.e. matching glycogen stores and blood glucose to the fuel demands of exercise).

When it is important to train hard or with high intensity, daily carbohydrate intakes should match the fuel needs of training and glycogen replenishment. General guidelines for carbohydrate intake to provide high carbohydrate availability are based on body weight (a proxy for the volume of muscle) and exercise load. These are shown in Table 1.1. The more active you are and the greater your muscle mass, the higher your carbohydrate needs.

While guidelines for carbohydrate intake have been provided in terms of percentage contribution to total dietary energy intake in the past, experts now recommend expressing carbohydrate requirements in terms of grams per kg body weight. Guidelines for daily intakes are 3–5 g to 5–7 g per kg of body weight (BW) per day for low- and moderate-intensity daily training lasting up to 1 hour respectively. Depending on the fuel cost of the training schedule, an endurance athlete may need to consume 8–12 g of carbohydrate per kg body weight each day (560–840 g per day for a 70 kg athlete) to ensure adequate glycogen stores.

Source: Burke et al., 2011.

To promote rapid post-exercise recovery, experts recommend consuming 1.0–1.2 g carbohydrate per kg BW per hour for the first 4 hours after exercise. If you plan to train again within 8 hours, it is important to begin refuelling as soon as possible after exercise. Moderate and high glycaemic index (GI) carbohydrates (see here) will promote faster recovery during this period. When carbohydrate intake is suboptimal for refuelling, adding protein to a meal/snack will enhance glycogen storage. However, for recovery periods of 24 hours or longer, the type and timing of carbohydrate intake is less critical, although you should choose nutrient-dense sources wherever possible.

It is recommended that the pre-exercise meal provides 1–4 g carbohydrate per kg body weight, depending on exercise intensity and duration, and that this should be consumed between 1 and 4 hours before exercise.

During exercise lasting less than 45 minutes, there is no performance advantage to be gained by consuming additional carbohydrates. For intense exercise lasting between 45 and 75 minutes, simply swilling (not swallowing) an energy drink in your mouth (‘mouth rinsing’) can improve performance. The carbohydrates stimulate oral sensors that act on the central nervous system (brain) to mask fatigue and reduce perceived exertion, thus allowing you to maintain exercise intensity for longer. But for exercise lasting longer than about 1 hour, consuming between 30 and 60 g carbohydrate helps maintain your blood glucose level, spare muscle glycogen stores, delay fatigue and increase your endurance. The amount depends on the intensity and duration of exercise, and is unrelated to body size.

The longer and the more intense your workout or event, the greater your carbohydrate needs. Previously, it was thought that the body could absorb only a maximum of 60 g carbohydrate per hour. However, recent research suggests that it may be higher – as much as 90 g, a level that would be appropriate during intense exercise lasting more than 3 hours. Studies have shown that consuming multiple transportable carbohydrates (e.g. glucose and fructose) increases the rate of carbohydrate uptake and oxidation during exercise compared with glucose alone. A 2:1 mixture of glucose + fructose is generally associated with minimal GI distress. Choose high-GI carbohydrates (e.g. sports drinks, energy gels and energy bars, bananas, fruit bars, cereal or breakfast bars), according to your personal preference and tolerance.

Source: Burke et al., 2011.

However, recent research has shown that training in a glycogen-depleted state can enhance the adaptive responses to exercise stimulus and increase exercise capacity. The concept of ‘training low but competing high’ as well as ‘carbohydrate periodisation’ (integrating short periods of ‘training low’ into the training programme) has become very popular among elite endurance athletes. Strategies include occasional fasted training, training following an overnight fast, and not replenishing carbohydrate stores after the first of two training sessions of the day. These have been shown to increase muscle adaptation to training by altering signalling and upregulating the metabolic response to exercise. However, it is important to undertake high-intensity training sessions with high carbohydrate stores. Whether implementing these strategies ultimately improves performance is unclear.

4. Protein

Amino acids from proteins form the building blocks for new tissues and the repair of body cells. They are also used for making enzymes, hormones and antibodies. Protein also provides a (small) fuel source for exercising muscles.

Athletes have higher protein requirements than non-active people. Extra protein is needed to compensate for the increased muscle breakdown that occurs during and after intense exercise, as well as to build new muscle cells. The Thomas et al. consensus statement recommends between 1.2 and 2.0 g protein/kg BW/day for athletes, which equates to 84–140 g daily for a 70 kg person, considerably more than for a sedentary person, who requires 0.75 g protein/kg BW daily. These recommendations encompass a range of training programmes and allow for adjustment according to individual needs, training goals and experience.

The timing as well as the amount of protein is crucial when it comes to promoting muscle repair and growth. It is best to distribute protein intake throughout the day rather than consuming it in just one or two meals. Experts recommend consuming 0.25 g protein/kg BW or 15–25 g protein with each main meal as well as immediately after exercise.

Several studies have found that eating carbohydrate and protein together immediately after exercise enhances recovery and promotes muscle building. The types of protein eaten after exercise is important – high-quality proteins, particularly fast-absorbed proteins that contain leucine (such as whey), are considered optimal for recovery. Leucine is both a substrate and a trigger for muscle protein synthesis (MPS). An intake of 2–3 g leucine has been shown to stimulate maximum MPS.

Some athletes eat high-protein diets in the belief that extra protein leads to increased strength and muscle mass, but this isn’t true – it is stimulation of muscle tissue through exercise plus adequate – not extra – protein that leads to muscle growth. As protein is found in so many foods, most people – including athletes – eat a little more protein than they need. This isn’t harmful – the excess is broken down into urea (which is excreted) and fuel, which is either used for energy or stored as fat if your calorie intake exceeds your output.

5. Fat

Some fat is essential – it makes up part of the structure of all cell membranes, your brain tissue, nerve sheaths and bone marrow and it cushions your organs. Fat in food also provides essential fatty acids and the fat-soluble vitamins A, D and E, and is an important source of energy for exercise. The ACSM position statement currently makes no specific recommendation for fat intake. The focus should be on meeting carbohydrate and protein goals with fat making up the calorie balance. It is recommended that athletes’ fat intakes are consistent with public health guidelines for fat intake: less than 35% of daily energy intake. The exact amount depends on individual training and body composition goals. However, it is recommended that athletes should consume a minimum of 20% energy from fat, otherwise they risk deficient intakes of fat-soluble vitamins and essential fatty acids (Thomas et al., 2016).

The UK government recommends that the proportion of energy from saturated fatty acids be less than 10%, with the majority coming from unsaturated fatty acids. Omega-3s may be particularly beneficial for athletes, as they help increase the delivery of oxygen to muscles, improve endurance and may speed recovery and reduce inflammation and joint stiffness.

6. Hydration

You should ensure you are hydrated before starting training or competition by consuming 5–10 ml/kg body weight in the 2–4 hours prior to exercise, and aim to minimise hypohydration (see here) during exercise. Severe hypohydration can result in reduced endurance and strength, and heat-related illness. The IOC and American College of Sports Medicine advise matching your fluid intake to your fluid losses as closely as possible and limiting hypohydration to no more than 2–3% loss of body weight (e.g. a body weight loss of no more than 1.5 kg for a 75 kg person). Routinely weigh yourself before and after exercise, accounting for fluid consumed and urine lost, to estimate your sweat loss during exercise. A loss of 1 kg body weight equates to 1 litre of sweat lost.

Additionally, experts caution against overhydrating yourself before and during exercise, particularly in events lasting longer than 4 hours. Drinking too much water may dilute your blood so that your sodium levels fall. Although this is quite rare, it is potentially fatal. The American College of Sports Medicine advises drinking when you’re thirsty or drinking only to the point at which you’re maintaining your weight, not gaining weight.

Sports drinks containing sodium are advantageous when sweat losses are high (more than 1.2 litres/h) – for example, during intense exercise lasting more than 2 hours – because their sodium content will promote water retention and prevent hyponatraemia.

After exercise, both water and sodium need to be replaced to re-establish normal hydration. This can be achieved by normal eating and drinking practices if there is no urgent need for recovery. But for rapid recovery, or if you are severely hypohydrated, it is recommended you drink 25–50% more fluid than lost in sweat. You can replace fluid and sodium losses with rehydration drinks or water plus salty foods.

7. Vitamins and minerals

While intense exercise increases the requirement for several vitamins and minerals, there is no need for supplementation provided you are eating a balanced diet and consuming adequate energy to maintain body weight. The IOC, IAAF and ACSM believe most athletes are well able to meet their needs from food rather than supplements. There’s scant proof that vitamin and mineral supplements improve performance, although supplementation may be warranted in athletes eating a restricted diet or when food intake or choices are limited – for example, due to travel. However, athletes should be particularly aware of their needs for calcium, iron and vitamin D, as low intakes are relatively common among female athletes. The role of vitamin D in muscle structure and function, and the risk of deficiency, has been highlighted by the IOC and ASCM/AND/DC. Those who have low vitamin D intakes and get little exposure to the sun may need to take vitamin D supplements.

Similarly, there is insufficient evidence to recommend antioxidant supplementation for athletes. Caution against antioxidant supplements is currently advised during training, as oxidative stress may be beneficial to the muscles’ adaptation to exercise. The IOC also cautions against the indiscriminate use of supplements and warns of the risk of contamination with banned substances. Only a few have any performance benefit; these include creatine, caffeine, nitrate (as found in beetroot juice), beta-alanine and sodium bicarbonate, along with sports drinks, gels and bars and protein supplements. For the majority, there is little evidence to support their use as ergogenic aids (see ‘Definition of sports supplements and ergogenic aids’).

8. Competition nutrition

PRE-EVENT

Performance in endurance events lasting longer than 90 minutes may benefit from carbohydrate loading in the 36–48 hours prior to the event (10–12 g carbohydrate/kg BW/24 hours). During the 1–4 hours prior to a race, consume 1–4 g of carbohydrate per kg of body weight. Food choices should be high in carbohydrate and moderate in protein, while low in fat and fibre to reduce risk of gastrointestinal problems.

DURING THE EVENT

In events lasting less than 75 minutes, additional carbohydrate will not benefit performance but rinsing the mouth with an energy drink may reduce perception of fatigue via the central nervous system. In events lasting 1–2½ hours, consuming 30–60 g carbohydrate/h will help maintain blood glucose and liver glycogen, and increase endurance. In events lasting more than 2½ hours, it may be beneficial to increase carbohydrate intake to up to 90 g carbohydrate/h. This may be in the form of dual energy source drinks or gels, containing a mixture of glucose/maltodextrin and fructose to achieve faster carbohydrate absorption.

AFTER THE EVENT

Replenish glycogen by consuming 1–1.2 g of carbohydrate/kg body weight in the first 4–6 hours after finishing. Consuming protein (in 15–25 g servings) in the recovery period also promotes glycogen recovery and enhances muscle protein resynthesis. Rehydrate with 25–50% more fluid than that lost in sweat.

The ‘Athlete’s Plate’

A balanced training diet is one that provides enough energy, carbohydrate, protein, fat, fibre, vitamins and minerals to support the physical demands of your training. These nutrients should come from a wide variety of foods. The key is consuming the right amounts and types of different foods that will fuel your workouts and events. To help you do this, I have created the Athlete’s Plate, which can be tailored to the day-to-day fuel demands of your training programme. It is based on the Public Health England’s EatWell Guide (Public Health England, 2016) and the Athlete’s Plate developed by the US Olympic Committee (USOC) dietitians and University of Colorado (UCCS). It gives you a simple guide to the types and proportions of foods you need to achieve a balanced training diet. Each food group supplies a similar profile of nutrients, thus giving you plenty of options and flexibility for planning your meals. It is a good idea to vary your meals as much as possible; the wider the variety of foods you eat, the more likely you are to meet your nutritional needs. The Athlete’s Plate can be adapted to meet the different fuel demands of your training on different days. Some days may be recovery or easy training days while others may comprise moderate or hard training.

The Athlete’s Plate divides foods into four main groups:

1.fruit and vegetables

2.protein-rich foods (including calcium-rich foods)

3.carbohydrate-rich foods

4.healthy fats

Fruit and vegetables – Aim to eat at least five portions a day. A portion is 80 g of any fresh or frozen fruit or vegetable, or 30 g of dried. For example, one small apple, banana or orange, about six strawberries, three broccoli florets or one carrot. Foods in this group are good sources of vitamin C, beta-carotene, folate and potassium, as well as fibre and phytonutrients. At each meal, aim to achieve a rainbow of colours – green, red, purple, yellow, white, and orange – varying them as much as possible. Each colour has its unique set of health-promoting phytonutrients, many of which act as antioxidants that help protect cells from damage and reduce inflammation after exercise.

Protein-rich foods – Include at least one serving of meat, poultry, fish, dairy (e.g. milk, cheese and yoghurt), eggs, beans, lentils, peas or soya products (e.g. soya milk alternative, tofu, tempeh and soya yoghurt alternative) in each meal. These foods should comprise roughly one-quarter of your plate. They also provide fibre, iron, zinc, and magnesium. Athletes need more protein than sedentary people so aim for at least 20 g protein per meal (see here).

Calcium-rich foods sub-group – Ensure that you include at least two portions of calcium-rich foods each day: dairy and calcium-fortified plant milk and yoghurt alternatives and calcium-set tofu. These also count towards your protein-rich foods.

Carbohydrate-rich foods – These include pasta, rice, oats, noodles, potatoes, sweet potatoes, bread and cereals. There is no minimum requirement for carbohydrate so adjust your portion size according to your activity level. The more active you are, the bigger the portions you must consume. Whole grains are preferred to refined grains because they contain the entire grain, which means they are richer in fibre, B vitamins and iron.

Healthy fats – These include nuts, seeds, avocados, and olive and rapeseed oil. Aim to include one food from this group in most of your meals. Nuts and seeds also provide protein, magnesium, fibre, iron and zinc.

EASY TRAINING OR RECOVERY DAYS

On recovery and easy training days, your fuel and carbohydrate needs will be relatively low. To ensure you get all the nutrients you need, aim for roughly one-half of your plate to be made up of fruit and vegetables, roughly one-quarter carbohydrate-rich foods, and roughly one-quarter protein-rich and calcium-rich foods. Include some healthy fats such as olive or rapeseed oil, nuts, seeds, nut butter or avocado in each meal.

MODERATE TRAINING DAYS

On moderate training days that comprise 1–2 hours’ moderate- or high-intensity endurance exercise your fuel and carbohydrate needs will be higher than on easy training days. Increase your intake of carbohydrate-rich foods. This will allow you to maintain muscle glycogen stores and support your training. Divide your plate into thirds and aim to have roughly one-third of your meal plate made up of carbohydrate-rich foods, roughly one-third protein-rich and calcium-rich foods and roughly one-third fruit and vegetables. Include some healthy fats such as olive or rapeseed oil, nuts, seeds, nut butter or avocado in each meal. You may add extra nutrient-rich snacks to meet your increased energy and nutritional needs.

HARD TRAINING DAYS

On hard training days that comprise more than 2 hours’ high-intensity endurance exercise, or two moderate- or high-intensity training sessions or events, your fuel and carbohydrate needs will be very high. Increase your intake of carbohydrate-rich foods. This will allow you to maintain muscle glycogen stores and support your training. Aim to have roughly one-half of your meal plate made up of carbohydrate-rich foods, roughly one-quarter protein-rich and calcium-rich foods and roughly one-quarter fruit and vegetables. Include some healthy fats such as olive or rapeseed oil, nuts, seeds, nut butter or avocado in each meal. You may add extra nutrient-rich snacks to meet your increased energy and nutritional needs.

RECOVERY/EASY TRAINING

Figure 1.1 The Athlete’s Plate for Easy Training or Recovery Days

MODERATE TRAINING

Figure 1.2 The Athlete’s Plate for Moderate Training Days

HARD TRAINING

Figure 1.3 The Athlete’s Plate for Hard Training Days

2

Energy for Exercise

When you exercise, your body must start producing energy much faster than it does when it is at rest. The muscles start to contract more strenuously, the heart beats faster to pump blood around the body more rapidly, and the lungs work harder. All these processes require extra energy. Where does it come from, and how can you make sure you have enough to last through a training session?

Before we can fully answer such questions, it is important to understand how the body produces energy, and what happens to it. This chapter looks at what takes place in the body when you exercise, where extra energy comes from, and how the fuel mixture used differs according to the intensity of exercise. It explains why fatigue occurs, how it might be delayed, and how you can get more out of training by changing your diet.

WHAT IS ENERGY?

Although we cannot actually see energy, we can see and feel its effects in terms of heat and physical work. But what exactly is it?

Energy is produced by the splitting of a chemical bond in a substance called adenosine triphosphate (ATP). This is often referred to as the body’s ‘energy currency’. It is produced in every cell of the body from the breakdown of carbohydrate, fat, protein and alcohol – four fuels that are transported and transformed by various biochemical processes into the same end product.

WHAT IS ATP?

ATP is a small molecule consisting of an adenosine ‘backbone’ with three phosphate groups attached (see Fig 2.1).

Energy is released when one of the phosphate groups splits off. When ATP loses one of its phosphate groups it becomes adenosine diphosphate, or ADP. Some energy is used to carry out work (such as muscle contractions), but most (around three-quarters) is given off as heat. This is why you feel warmer when you exercise. Once this has happened, ADP is converted back into ATP. A continual cycle takes place, in which ATP forms ADP and then becomes ATP again (see Fig 2.2).

Figure 2.1 ATP

THE INTER-CONVERSION OF ATP AND ADP

The body stores only very small amounts of ATP at any one time. There is just enough to keep up basic energy requirements while you are at rest – sufficient to keep the body ticking over. When you start exercising, energy demand suddenly increases, and ATP is used up within a few seconds. Therefore, more ATP must be produced in order to continue exercising. During intense exercise, muscle ATP production can increase 1000-fold.

HOW DOES THE BODY BURN ENERGY?

Total daily energy expenditure (TDEE) is comprised of four components: 1) resting metabolic rate (RMR, 2) the thermic effect of food (TEF), 3) exercise activity thermogenesis (EAT) and 4) non-exercise activity thermogenesis (NEAT) (see Fig 2.3). RMR is the energy burned at rest and makes up the largest component of TDEE, on average between 60 and 75%. TEF is the increase in energy expenditure above RMR that occurs after a meal and is the result of the digestion, absorption, metabolism and storage of food. It represents approximately 10% of TDEE, although the TEF for each macronutrient is different (see here). NEAT is the energy burned during all unplanned activity, and may include day-to-day activities such as walking, or involuntary movements such as fidgeting. It typically makes up 15% of TDEE. EAT is the energy burned during planned exercise and is the most variable component of TDEE, ranging from 5% in sedentary people up to 50% in athletes involved in heavy training. EAT and NEAT can both be controlled voluntarily and are therefore extremely important for maintenance of daily energy balance.

Figure 2.2 The relationship between ATP and ADP

Figure 2.3 The components of total daily energy expenditure (TDEE)

WHERE DOES ENERGY COME FROM?

There are four components in food and drink that are capable of providing energy (ATP):

1.carbohydrate

2.protein

3.fat

4.alcohol

When you eat a meal or have a drink, these components are broken down in the digestive system into their various constituents or building blocks. Then they are absorbed into the bloodstream. Carbohydrates are broken down into small, single sugar units, the monosaccharides: glucose (the most common unit), fructose and galactose. Fats are broken down into fatty acids, and proteins into amino acids. Alcohol is mostly absorbed directly into the blood.

The ultimate fate of all of these components is energy production, although carbohydrates, proteins and fats also have other important functions.

Carbohydrates and alcohol are used mainly for energy in the short term, while fats are used as a long-term energy store. Proteins can be used to produce energy either in ‘emergencies’ (for instance, when carbohydrates are in short supply) or when they have reached the end of their useful life. Sooner or later, all food and drink components are broken down to release energy. But the body is not very efficient at converting this energy into power. For example, during cycling, only 20% of the energy produced is converted into power. The rest becomes heat.

HOW IS ENERGY MEASURED?

Energy is measured in calories or joules. In scientific terms, 1 calorie is defined as the amount of heat required to increase the temperature of 1 gram (or 1 ml) of water by 1 degree centigrade (°C) (from 14.5 to 15.5 °C). The SI (International Unit System) unit for energy is the joule (J). One joule is defined as the work required to exert a force of 1 Newton for a distance of 1 metre.

As the calorie and the joule represent very small amounts of energy, kilocalories (kcal or Cal) and kilojoules (kJ) are more often used. As their names suggest, a kilocalorie is 1000 calories and a kilojoule 1000 joules. You have probably seen these units on food labels. When we mention calories in the everyday sense, we are really talking about Calories with a capital C, or kilocalories. So, food containing 100 kcal has enough energy potential to raise the temperature of 100 litres of water by 1°C.

To convert kilocalories into kilojoules, simply multiply by 4.2. For example:

• 1 kcal = 4.2 kJ

• 10 kcal = 42 kJ

To convert kilojoules into kilocalories, divide by 4.2. For example, if 100 g of food provides 400 kJ, and you wish to know how many kilocalories that is, divide 400 by 4.2 to find the equivalent number of kilocalories:

• 400 kJ ÷ 4.2 = 95 kcal

Metabolism

Metabolism is the sum of all the biochemical processes that occur in the body. There are two aspects: 1) anabolism is the formation of larger molecules; 2) catabolism is the breakdown of larger molecules into smaller molecules. Aerobic metabolism includes oxygen in the processes; anaerobic metabolism takes place without oxygen. A metabolite is a product of metabolism. That means that anything made in the body is a metabolite.

The body’s rate of energy expenditure is called the metabolic rate. Your basal metabolic rate (BMR) is the number of calories expended to maintain essential processes such as breathing and organ function during sleep. However, most methods measure the resting metabolic rate (RMR), which is the number of calories burned over 24 hours while lying down but not sleeping.

WHY DO DIFFERENT FOODS PROVIDE DIFFERENT AMOUNTS OF ENERGY?

Foods are made of different amounts of carbohydrates, fats, proteins and alcohol. Each of these nutrients provides a certain quantity of energy when it is broken down in the body. For instance, 1 g of carbohydrate or protein releases about 4 kcal of energy, while 1 g of fat releases 9 kcal, and 1 g of alcohol releases 7 kcal.

THE ENERGY VALUE OF DIFFERENT FOOD COMPONENTS

1 g of each of the following provides:

• carbohydrate: 4 kcal (17 kj)

• fat: 9 kcal (38 kj)

• protein: 4 kcal (17 kj)

• alcohol: 7 kcal (29 kj)

Fat is the most concentrated form of energy, providing the body with more than twice as much energy as carbohydrate or protein, and also more than alcohol. However, it is not necessarily the ‘best’ form of energy for exercise.

All foods contain a mixture of nutrients, and the energy value of a particular food depends on the amount of carbohydrate, fat and protein it contains. For example, one slice of wholemeal bread provides roughly the same amount of energy as one pat (7 g) of butter. However, their composition is very different. In bread, most energy (75%) comes from carbohydrate, while in butter, virtually all (99.7%) comes from fat.

HOW DOES MY BODY STORE CARBOHYDRATE?

Carbohydrate is stored as glycogen in the muscles and liver, along with about three times its own weight of water. Altogether there is about three times more glycogen stored in the muscles than in the liver. Glycogen is a large molecule, similar to starch, made up of many glucose units joined together. However, the body can store only a relatively small amount of glycogen – there is no endless supply! Like the petrol tank in a car, the body can hold only a certain amount.

The total store of glycogen in the average body amounts to about 500 g, with approximately 400 g in the muscles and 100 g in the liver. This store is equivalent to about 2000 kcal – enough to last 1 day if you were to eat nothing and do no activity. This is why a low-carbohydrate diet tends to make people lose quite a lot of weight in the first few days. The weight loss is almost entirely due to loss of glycogen and water.

Glycogen stores can be almost entirely depleted by the end of 90–120 minutes of moderate- or high-intensity exercise and at this point you would experience extreme fatigue. Endurance athletes have higher muscle glycogen concentrations compared with sedentary people. Increasing your muscle mass will also increase your storage capacity for glycogen.

The purpose of liver glycogen is to maintain blood glucose levels both at rest and during prolonged exercise.

Small amounts of glucose are present in the blood (approximately 4 g, which is equivalent to 16 kcal) and the concentration is kept within a very narrow range (between 4 and 5.5 mmol/litre, or 70–100 mg/100 ml), both at rest and during exercise. This allows normal body functions to continue. When blood glucose levels rise, the pancreas releases insulin, which causes glucose to move from the blood into the liver and muscle cells. If glucose is not needed for energy immediately it is stored in the form of glycogen, a process known as glycogenesis. Conversely, when blood glucose levels fall, the pancreas releases glucagon, which tells the liver and muscles to break down glycogen and release it back into the bloodstream as glucose, a process known as glycogenolysis.

Once glycogen stores are full, surplus glucose may be converted to fat in a process known as de novo lipogenesis (DNL). However, this process is inefficient and only stores a small amount of fat when you are in positive energy balance (Acheson et al., 1988). Rather than being converted to fat, excessive carbohydrate intake usually leads to fat storage from fat. This is due to oxidative priority: carbohydrate is preferentially oxidised at the expense of fat oxidation (Cronise et al., 2017). Thus, an excessive carbohydrate intake slows or displaces fat oxidation, resulting in fat storage mainly from dietary fat.

HOW DOES MY BODY STORE FAT?

Fat is stored as adipose (fat) tissue in almost every region of the body. A small amount of fat, about 300–400 g, is stored in muscles – this is called intramuscular fat – but the majority is stored around the organs and beneath the skin. The amount stored in different parts of the body depends on genetic make-up and individual hormone balance. The average 70 kg person stores 10–15 kg fat. Interestingly, people who store fat mostly around their abdomen (the classic potbelly shape) have a higher risk of heart disease than those who store fat mostly around their hips and thighs (the classic pear shape).

Unfortunately, there is little you can do to change the way that your body distributes fat. But you can definitely change the amount of fat that is stored, as you will see in Chapter 9.

You will probably find that your basic shape is similar to that of one or both of your parents. Males usually take after their father, and females after their mother. Female hormones tend to favour fat storage around the hips and thighs, while male hormones encourage fat storage around the middle. This is why, in general, women are ‘pear shaped’ and men are ‘apple shaped’.

Source: Cahill, 1976.

HOW DOES MY BODY STORE PROTEIN?

Protein is not stored in the same way as carbohydrate and fat. It forms muscle and organ tissue, so it is mainly used as a building material rather than an energy store. However, proteins can be broken down to release energy if need be, so muscles and organs represent a large source of potential energy.

WHICH FUELS ARE MOST IMPORTANT FOR EXERCISE?

Carbohydrates, fats and proteins are all capable of providing energy for exercise; they can all be transported to, and broken down in, muscle cells. Alcohol, however, cannot be used directly by muscles for energy during exercise, no matter how strenuously they may be working. Only the liver has the specific enzymes needed to break down alcohol. You cannot break down alcohol faster by exercising harder, either – the liver carries out its job at a fixed speed. Do not think you can work off a few drinks by going for a jog, or by drinking a cup of black coffee!

Proteins do not make a substantial contribution to the fuel mixture. It is only when carbohydrate availability is low, such as during very prolonged or very intense bouts of exercise, that proteins play a more important role in giving the body energy.

The production of ATP during most forms of exercise comes mainly from broken-down carbohydrates and fats.

Table 2.1 illustrates the potential energy available from the different types of fuel that are stored in the body.

WHEN IS PROTEIN USED FOR ENERGY?

Protein is not usually a major source of energy, but it may play a more important role during the latter stages of very strenuous or prolonged exercise as glycogen stores become depleted. For example, during the last stages of a marathon or a long-distance cycle race, when glycogen stores are exhausted, protein in muscles (and organs) may be broken down to make up to 15% of the body’s fuel mixture.

During a period of semi-starvation, or if a person follows a low-carbohydrate diet, glycogen would be in short supply, so more proteins would be broken down to provide the body with fuel. Up to half of the weight lost by someone following a low-calorie or low-carbohydrate diet comes from protein (muscle) loss. Some people think that if they deplete their glycogen stores by following a low-carbohydrate diet, they will force their body to break down more fat and lose weight. This is not the case: you risk losing muscle as well as fat, and there are many other disadvantages, too. These are discussed in Chapter 3.

How is energy produced?

The body has three main energy systems it can use for different types of physical activity. These are called:

1.the ATP–PC (phosphagen) system

2.the anaerobic glycolytic, or lactic acid, system

3.the aerobic system – comprising the glycolytic (carbohydrate) and lipolytic (fat) systems

At rest, muscle cells contain only a very small amount of ATP, enough to maintain basic energy needs and allow you to exercise at maximal intensity for about 1 second. To continue exercising, ATP must be regenerated from one of the three energy systems, each of which has a very different biochemical pathway and rate at which it produces ATP.

Figure 2.4 PC splits to release energy to regenerate ATP rapidly

HOW DOES THE ATP–PC SYSTEM WORK?

This system uses ATP and phosphocreatine (PC) that is stored within the muscle cells to generate energy for maximal bursts of strength and speed that last for up to 6 seconds. The ATP–PC system would be used, for example, during a 20 m sprint, a near-maximal lift in the gym, or a single jump. Phosphocreatine is a high-energy compound formed when the protein, creatine, is linked to a phosphate molecule (see here). The PC system can be thought of as a back-up to ATP. The job of PC is to regenerate ATP rapidly (see Fig. 2.4). PC breaks down into creatine and phosphate, and the free phosphate bond transfers to a molecule of ADP forming a new ATP molecule. The ATP–PC system can release energy very quickly, but, unfortunately, it is in very limited supply and can provide only 3–4 kcal. After this, the amount of energy produced by the ATP–PC system falls dramatically, and ATP must be produced from other fuels, such as glycogen or fat. When this happens, other systems take over.

What is creatine?

Creatine is a compound that’s made naturally in our bodies to supply energy. It is mainly produced in the liver from the amino acids glycine, arginine and methionine. From the liver, it is transported in the blood to the muscle cells where it is combined with phosphate to make phosphocreatine (PC).

The muscle cells turn over about 2–3 g of creatine a day. Once PC is broken down into ATP (energy), it can be recycled into PC or converted into another substance called creatinine, which is then removed via the kidneys in the urine.

Creatine can be obtained in the diet from fish (tuna, salmon, cod), beef and pork (approx. 3–5 g creatine/kg uncooked fish or meat). That means vegetarians have no dietary sources. However, to have a performance-boosting effect, creatine has to be taken in large doses. This is higher than you could reasonably expect to get from food. You would need to eat at least 2 kg of raw steak a day to load your muscles with creatine.

The average-sized person stores about 120 g creatine, almost all in skeletal muscles (higher levels in fast-twitch muscle fibres, see here). Of this amount, 60–70% is stored as PC, 30–40% as free creatine.

Figure 2.5 Anaerobic energy system

HOW DOES THE ANAEROBIC GLYCOLYTIC SYSTEM WORK?

This system is activated as soon as you begin high-intensity activity. It dominates in events lasting up to 90 seconds, such as a weight training set in the gym or a 400–800 m sprint. In order to meet sudden, large demands for energy, glucose bypasses the energy producing pathways that would normally use oxygen, and follows a different route that does not use oxygen. This saves a good deal of time. After 30 seconds of high-intensity exercise this system contributes up to 60% of your energy output; after 2 minutes its contribution falls to only 35%.

The anaerobic glycolytic system uses carbohydrate in the form of muscle glycogen or glucose as fuel. Glycogen is broken down to glucose, which rapidly breaks down in the absence of oxygen to form ATP and pyruvate, which is then converted into lactate (see Fig. 2.5). Each glucose molecule produces only two ATP molecules under anaerobic conditions, making it a very inefficient system. The body’s glycogen stores dwindle quickly, proving that the benefits of a fast delivery service come at a price. The gradual build-up of lactate and the associated hydrogen ions causes the pH in the cell to fall (i.e. an increase in