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As an athlete you expect the best from your body. You put in hours of training and preparation to get into peak condition to compete. But it’s a tough world, and there are many others putting in equal training efforts – so just how do you get the edge on the rest of the pack?

The answer is: through nutrition and diet.

Whether you are aiming to win an international championship, top your age group category or simply complete your first marathon, you must ensure you are optimally fuelling your body.

To back up all your hard work with the right nutrition you need to start with the basics. To compete you need to train; to train you need energy; to recover from training you need to replace the energy used in training. Where does that energy come from?

The answer is: from carbohydrates.

Our diet is composed of macronutrients (protein, fat and carbohydrates) and micronutrients (vitamins and minerals). Carbohydrate accounts for, on average, 50% of total energy intake, with fat supplying around 30% and protein the remaining 20%.

Carbohydrates exist in several formations, of which the most commonly consumed are monosaccharides (one sugar unit, also known as simple carbohydrates) and polysaccharides (many sugar units, or complex carbohydrates).

The type of carbohydrate consumed determines how quickly it becomes available to your body as an energy source, although most naturally-occurring foods contain a mixture of carbohydrate types, along with varying amounts of protein, fat and other nutrients. Good carbohydrate sources are often referred to as ‘carbohydrate-rich’. Not all carbohydrate sources are of equal value, and those that are also high in fat are not particularly useful to athletes. Different carbohydrate sources elicit different metabolic responses when eaten. If, for example, you are looking for a quick energy boost during or just before competition, it is best to consume a carbohydrate-rich food that enters your bloodstream quickly and is made rapidly available to your exercising muscles. Foods that work like this are said to have a high ‘glycaemic index’.

At rest, ingested carbohydrates travel via the bloodstream to your liver and skeletal muscle, where it is stored as glycogen. Skeletal muscle stores the bulk of glycogen in your body and acts as the main energy source during exercise. The amount of carbohydrate you can store varies and is greatly influenced by exercise, dietary carbohydrate intake and training status. The muscle carb stores of a man weighing 70kg may vary from as little as 300g to as much as 900g. By contrast, the liver can store only around 70g, with a range of 0-135g.

Liver glycogen reserves may be small, but they play a crucial role of delivering a constant supply of glucose to your brain, and muscles during exercise. Liver glycogen is broken down to glucose, which is the primary fuel source for the brain. If, during exercise, your liver fails to maintain blood glucose levels, you will experience the familiar light-headed feeling which is known technically as ‘hypoglycaemia’.

At rest, skeletal muscle stores are hardly taxed at all, but during exercise their stored glycogen is rapidly depleted, and if your tank isn’t full beforehand you will soon experience the unpleasant sensation of running on empty.

During prolonged low-intensity exercise, such as a long Sunday morning training run or bike ride, fat and carbohydrate oxidation provide the majority of energy required. As intensity increases, carbohydrates become the primary fuel source, as fats cannot be burned fast enough. If glycogen stores run empty, you must revert to fat oxidation, reducing the intensity at which you can exercise.

Many studies have shown that increasing the availability of glycogen to the muscles improves endurance exercise performance. And it may surprise you to know that muscle glycogen levels are also depleted by short repeated stints of high-intensity exercise, suggesting that middle distance runners and athletes whose sport involves repeated stints of running – such as football and tennis – would also benefit from high-carbohydrate diets. And that’s not the end of the story! During any form of prolonged or high-intensity exercise carbohydrate stores are taxed, and if the athlete is required to perform again the following day they must be refilled as fast as possible. To accomplish this, large amounts of rapidly-absorbed carbohydrates are needed soon after exercise and for the following 24 hours.

Considering the crucial role of carbohydrates during exercise, it should come as no surprise to learn that increasing the proportion of carbohydrates in your diet would help improve your performance. This theory first enjoyed popularity in the 1970s, when studies showed that dietary manipulation to increase pre-exercise muscle glycogen levels led to increased time to exhaustion. These early studies involved drastic emptying of muscle glycogen stores, then ‘loading’ them to higher levels, allowing glycogen ‘supercompensation’. There were unpleasant side effects to this carbohydrate loading method, though, and later studies have shown the same benefits can be reaped by simply tapering training and increasing your carbohydrate consumption to over 70% of total energy intake.

A high carbohydrate intake is essential for maintaining hard training and good performance. But stores are not infinite, and constantly need topping up. So how do you go about implementing an increased carbohydrate diet to enhance training capacity, improve competitive performance and speed recovery?

There are two separate aspects of nutrition to be addressed: the training diet, which is consumed on a daily basis for most of the year, and the competitive diet. The aims of the training diet are to ensure an adequate energy supply to enable you to carry out repeated hard-training sessions in order to improve fitness and perform in your sport. The aims of the competitive diet are split into three parts: pre-competition, during competition and post-competition.

During training, energy intake must be sufficient to meet the enhanced energy costs of exercise. When regular strenuous exercise is performed, at least 65% of total calorie intake should be from carbohydrates. Studies suggest that to meet the energy demands of a moderately intense training programme, 5-7g of carbohydrate per kg body mass per day is adequate. A more demanding training programme, eg that of an élite triathlete carrying out several training sessions per day at moderate-to-high intensities, would require 10-12g per kg.

If you are training at the lower end of the intensity scale, putting in around 6-8 sessions a week, it is still important to maintain a high carbohydrate intake, although not as high as for two sessions a day. Simply adjust the total daily intake to around 5g/kg body mass/day. Carbohydrates should still make up the same percentage of your overall energy intake, but it is important to keep fat intake low to ensure you can eat enough carbohydrates without pushing your overall total calorie intake high enough to cause weight gain.

Achieving a high carbohydrate intake is difficult unless you are able to choose from a range of carbohydrates. Some carbohydrate-rich sources are also high in fat, and should be eaten only occasionally or sparingly. Most naturally-occurring carbohydrates are low in fat, and there are often low-fat alternatives available for convenient processed foods.

Complex carbohydrates such as rice, pasta and potatoes can form a main meal base. When you are striving to achieve a high daily carbohydrate intake, it is often necessary to supplement your main meals with convenient carbohydrate-rich snacks or fluids consisting predominantly of simple sugars. These are less bulky, contain less indigestible fibre and have lower water content than complex carbohydrates. As mentioned, you should consume the high-fat carbs only in limited amounts. Remember that since all milk has the same carbohydrate content, differing only in fat content, semi-skim and skim milk is more suited to an athlete’s need.

When carbohydrates are accounting for a large proportion of the training diet, it is important to ensure that your needs for other macro- and micronutrients are met. It is common for athletes to focus on achieving a high-carbohydrate diet at the expense of the nutritional quality of their diet as a whole, and this can lead to other problems associated with a poor diet, such as anaemia. It is possible to meet all the nutritional demands of your body with some carefully planned food combinations, involving nutritious high-carbohydrate foods.

After a hard training session, whether it was an interval session involving short intense bursts of exercise that rapidly depleted your glycogen stores, or a prolonged endurance session, your goal is to get those muscles resynthesising glycogen again as soon as possible for fast recovery. There is an abundance of evidence showing that by rapidly replenishing muscle glycogen stores you can reduce the time needed to recover before the next hard training session and enhance subsequent performance.

By ingesting carbohydrate-rich foods immediately after exercise, when muscles are most receptive, you will put yourself in a good position to recover as fast as possible. During the first two hours post-exercise, muscle resynthesis rates are maximal and you should take advantage of this by eating as soon as you can.

Recovery from lower-intensity sessions does not require as high a carbohydrate intake as hard or prolonged sessions, but make it a habit to eat a high-carbohydrate snack or meal straight after training. Post-exercise is not the time to restrict your calorie intake. A high-carbohydrate feeding now will mean you are ready for the next session sooner. And it is the repeated hard training – not starving yourself – that will help you lose pounds.

The optimal rate of carbohydrate ingestion post-exercise appears to be at least 50g every two hours, for at least 20 hours, to provide approximately 500-600g carbohydrate in total. Larger amounts of carbohydrate do not appear to produce any further benefits.

Foods with a high glycaemic index increase the rate of glycogen synthesis following exercise. Remember, the higher the glycaemic index, the more rapidly the food is absorbed and is therefore available to your muscles. By avoiding low-glycaemic-index foods in favour of those with a moderate-to-high index, you will be more successful in promoting muscle glycogen synthesis.

Providing you select foods that are rapidly absorbed, it does not matter whether the carbohydrate is in solid or liquid form; neither does it matter whether you consume small frequent meals over 24 hours or a few large meals, as long as you replace the glycogen.

Fluid replacement is also vital after hard exercise, and by taking in some of the carbohydrate in liquid form, you will achieve the dual benefit of replacing lost fluids. Appetite is often suppressed after hard exercise, so it is important to choose food or drinks that stimulate your taste buds. If liquids are preferred, there are many sports drinks that supply around 6g carbohydrate per 100ml, such as PowerAde and Gatorade. Ordinary soft drinks such as Ribena and Oasis are also good sources of carbohydrates.

It may not be practical to consume 50g of carbohydrate every two hours, in which case you could go for 100g per 4 hours or 150g per 6 hours, to allow for such activities as sleep, travel and work. If solid foods are preferred, compact high-energy sources are best, such as muffins, energy bars, sweets and bananas. The wide range of low-fat biscuits, cakes and snacks marketed for promoting weight loss include very good sources of concentrated carbohydrates; for example, McVities Go Ahead! crispy slices provide 10g of carbohydrate per slice (that’s 70% carbohydrate), while a 500ml bottle of Lucozade Sport and two NutriGrain bars will provide you with enough carbohydrate to keep you going until you can sit down to a proper meal.

The competition diet differs from the training diet in that it is tailored towards a specific event and is consumed with the aim of maximising your performance in that event. In the short term it may not be nutritionally sound, as you will be aiming to squeeze in as many carbs as you can at the expense of other nutrients.

How you prepare for a competition depends on the challenge the race poses in terms of taxing your fuel resources. A race of over 90 minutes of moderate-to-high intensity will certainly require glycogen supplies to be maximally topped up beforehand, and studies have shown that increasing glycogen stores will improve performance of even short intense exercise periods. If the race is less than an hour, and you have maintained a high-carbohydrate training diet, a final high-carb meal the evening before, as described below, should be sufficient.

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