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Introduction
A healthy balanced diet is essential for good health, whether you're an elite athlete or embarking on your first fitness programme. How can our diet help us to avoid fatigue and dehydration? Whatever your sport or exercise regime, you can optimise your training to reach your goals by 'eating for energy.' It doesn't matter what you are training for, the principles are the same. In this section we will explore which foods provide the energy fuel for exercise, and unravel the mystery as to why sports people put a greater emphasis on carbohydrates. Look into the important role of fluids. Delve into controversial issues, such as protein requirements, the purpose of vitamins and minerals in exercise, and the world of supplements and ergogenic aids. And, finally, discuss the issue of disordered eating - a growing trend amongst sports people.
Carbohydrates No matter what type of exercise you do, your body will always use some glucose for energy. The main source of glucose is the carbohydrate - sugars and starches - in your diet. The best way to keep your stores of glucose
stocked up is to eat a diet rich in carbohydrates, otherwise you
won't be able to train as hard or for as long and fatigue will quickly
set in. How much carbohydrate you need really depends on the amount
of training you do - the more glucose you use, the more you need
to eat to replenish your stores. All sugars and starches are carbohydrates. Basically, they can be divided into 3 groups: Monosaccharides glucose Glucose is found in most carbohydrate foods including sugars and starches. Most carbohydrates are eventually digested or converted into glucose for energy fuel. Fructose is found in fruits, vegetables and honey, and is converted into glucose by the liver. Galactose is found as part of lactose, the sugar found in milk. Disaccharides These are two molecules of sugar joined together. They are broken down into the monosaccharide sugars by digestion. The disaccharides are: Sucrose = glucose + fructose
Sucrose (table sugar) normally comes from sugar beet and cane, but can be found naturally in all fruits and vegetables. Lactose is found in milk and milk products. Maltose is formed when starch is broken down. Starches Starch is simply hundreds of molecules of glucose sugar joined together. When starch is digested, it is first broken down into maltose and then into glucose.
Just how much carbohydrate you need depends on the amount of exercise you do. You often hear how exercise requires a high carbohydrate diet - but what's high? Well, if you're physically active, then the optimal diet is one that contains 60-70% energy from carbohydrates. Maybe if you liked pie charts at school you could look at your meal and 'guesstimate' the proportion of foods containing carbohydrate - possible for one meal - but what about drinks and the rest of the day? The simpler way to calculate - no, wait, it's not that difficult - your daily carbohydrate needs is to first work out how much you require depending on the number of hours of exercise you do each week, and then multiply that by your weight in kilograms. Use the following list to work out how much carbohydrate - expressed in grams per day for every kilogram you weigh (g/d/kg) - your training programme needs:
For example, if you weighed 70
kg and exercised about an hour each day, your daily carbohydrate
requirement would be: 70 x 6 = 420g. Thanks to food labelling, the
majority of packaged foods will tell you how many grams of carbohydrate
per 100g - and often per portion - that food contains. You can use
our list below to discover roughly the amount of carbohydrate you
are getting from everyday foods and snacks:
If you are training frequently
then your daily carbohydrate needs will be high, and you will need
to eat frequent snacks and meals to achieve this. So don't forget
to look after your teeth by brushing twice a day with a fluoride
toothpaste, and make sure you visit the dentist regularly too. The next question we need to consider is - which type of carbohydrate? Seeing as most carbohydrates are broken down into glucose, one type is not necessarily any healthier than the next. When we're exercising, what is important is how quickly the carbohydrate is converted to glucose - and that's where the glycaemic index (GI) comes in. The GI of a food is a measure of that food's effect on blood glucose levels. It is worked out by comparing the rise in blood glucose after eating a food containing 50g of carbohydrate with the blood glucose rise after eating 50g of a reference food (glucose or white bread). The faster the rise in blood glucose, the higher the GI. Generally, foods are divided into three categories: Glucose Sucrose
Fractose Chocolate
Before, during and after exercise Try to eat high GI foods just before, during and immediately after exercise. Allow about 2 hours after a meal before exercising. Then 5-30 minutes prior to your work-out have a 50g carbohydrate snack. This will help maintain your glucose levels so that you can train more efficiently. It's probably best to avoid the more bulky (fibre-rich) carbohydrates, as these can cause abdominal discomfort. Experiment with different snacks to find which suit you best. If you exercise continuously for more than an hour, you will need to consume carbohydrates during your workout to avoid fatigue. One of the best ways to achieve this is by drinking sports drinks - not only do you get your carbohydrate but they also help keep you hydrated - see fluids. The best time to refuel and restock those vital glucose stores ready for the next workout is immediately after exercise! Try to eat a minimum of 50g of carbohydrates and preferably 1g carbohydrate per kg of body weight - 70g if you weigh 70kg - within the first 2 hours after exercise. Again, sports drinks are useful to replace fluid losses at the same time - all helping speed up that recovery process. In between exercise sessions - that's the majority of the time for most of us! - include a mixture of low to medium GI foods for your high carbohydrate diet. Watch out though - don't go overloading your bread, potatoes and pasta with lots of butter and cream - that would be a high fat diet! Also, go easy on more fatty carbohydrate snacks like cakes and biscuits - after all, aside from the health and fat issue, gram for gram, fat has twice as many calories as carbohydrate. This is something to consider if you need to watch your energy intake.
Fluids Heating up and colling down The main way we keep our bodies cool is by sweating.
Heat from the working muscles is transferred to the blood. The blood
flow to the skin is increased, and the heat is lost via evaporation
- sweating. Sweat comes from the water in your blood - so you need
to replace this vital fluid. Otherwise, you will become dehydrated
and suffer the consequences. Did you know? How much? The more you sweat, the more fluid you lose, and the more you need to drink to replace the fluid lost. Some people naturally sweat more than others. Plus the fitter you are, the more effectively you keep your body cool - so the more you sweat! Training harder and longer, and/or in hotter and more humid surroundings, will also make you sweat more. On average, we lose 1 litre of fluid for each hour we exercise. The easiest way to work out how much fluid you lose is to weigh yourself before and after exercise. Each kg of body weight loss is equivalent to a litre of fluid loss. However, you will lose further fluid as urine, so to compensate for this try to drink 1.5 litres of fluid for every kg of weight lost. Another way to check is by the colour of your urine - if it's pale and plentiful you're well-hydrated, but if it's dark and in short supply you'd better start drinking! A loss of just 2% in your body weight - that's 1.4kg or 1.4 litres if you weigh 70kg - will affect your ability to exercise. Plus, if you're competing, for every 1% drop in body weight there's a 5% drop in performance - that could mean the difference between coming first or last! If you keep exercising without replacing the fluid lost, you will become more and more dehydrated. You will no longer be able to keep your body cool, your body temperature will start to rise, you will begin to feel nauseous and lightheaded, and ultimately you will end up with fatigue or heat stroke. The only way to prevent this is to start off well-hydrated, and stay that way!
Before, during and after exercise The more you sweat, the more fluid you lose, the more you need to drink to replace the fluid lost. As always, prevention is better than cure - start your exercise session well-hydrated. Try to drink 300-500ml of fluid in the 15 minutes prior to your work-out. During exercise, aim to drink 150-250ml every 15 minutes to offset fluid losses - remember the more you sweat, the more you need to drink. The sooner you get into the habit of drinking during exercise the better. After exercise, how much fluid you need depends on how much you lost, but you'll probably need at least 500ml - use the guidelines above and either weigh yourself or check out your urine! Whatever you do - drink! Do not wait till you feel thirsty - this probably means you are already dehydrated. What's more, it is unlikely that you will drink too much water - not drinking enough is usually the problem! The only time it may cause a problem is if you're sweating very heavily for a prolonged period of time. In this situation, a sports drink containing sodium would be better than plain water, to prevent the occurrence of low blood sodium levels (hyponatraemia). Did you know... Which fluid? Which fluid you opt for depends on how hard and how long you exercise. You should find a flavour you like though - let's face it, if you don't like the taste you won't drink enough! If you're exercising at a low to moderate intensity for less than an hour then water is great. If you work-out continuously for more than an hour, then a sports drink would be a good idea. Not only will it help maintain better fluid levels, but the added carbohydrates will provide the vital glucose to help avoid fatigue. Most sports drinks are 5 - 8% carbohydrate - that's 5 - 8g of carbohydrate in every 100ml. This makes them 'isotonic' - a similar concentration to blood - and therefore quickly absorbed. In addition, sports drinks contain sodium to speed up fluid absorption and replace sweat losses. Finally, a word of warning about alcohol! Yes, alcohol in moderation is fine, but not just before exercise and not until you've properly rehydrated afterwards. Alcohol before exercise not only has a detrimental effect on co-ordination skills and exercise performance, but also increases the risk of injury. Furthermore, alcohol can cause dehydration - and we know we want to avoid that - as well as slowing down recovery from injury. All in all, not such a good idea in the exercise environment.
Protein Are protein requirements increased by physical
activity? This seemingly simple question has been hotly debated
for years - and remains one of the most controversial issues in
sports nutrition. Protein and amino acids supplements Protein is essential for life, and is a major part of the body - found primarily in muscle. We need protein for the growth and repair of tissues. During digestion, proteins are broken down into smaller units called amino acids. There are 20 different amino acids, which can be combined to make many different proteins. Our bodies can make proteins from amino acids, but we are unable to produce nine of the acids - the essential ones - so these need to be supplied by our diet. Only some foods - the complete protein foods - contain all the essential amino acids. These are listed below: Milk and dairy products, As you can see from the list, animal sources contain all the essential amino acids, and by combining different plant proteins you can also make a complete protein food How Much? Our daily protein requirement is 0.75g per kg of body weight. So a person weighing 70kg would need 52.5g (70 x 0.75) of protein per day. If you are exercising more than an hour per day, then your daily requirement is slightly increased to 1.0 - 1.2 g of protein per kg of body weight - that's 70 - 84g if you weigh 70kg. Experts recommend a further increase for athletes: 1.2 - 1.4 g/kg/d for endurance athletes and 1.6 - 1.7 g/kg/d for strength athletes. However, they also state that there is no advantage - both in terms of performance or muscle size - to taking more than 2g of protein per kg/d, providing carbohydrate needs are met. Extra protein is not converted into muscle! In practice, providing you are eating enough food to meet your energy and carbohydrate requirements, then achieving these levels of protein intake is easy. If you're not convinced, then look at the list below to see the protein content of some common foods.
It is easy to meet your protein needs from food.
Despite the power of advertising, all a protein supplement will
do is contribute to your protein intake and the cost will burn a
large whole in your pocket! Plus there is no advantage to taking
expensive amino acid supplements. Vitamins Vitamins and minerals are of great interest
to the sports world, due to the belief that they will enhance health
and improve physical performance. Sure, an adequate supply of vitamins
and minerals is necessary for good health - but does exercise increase
our requirement? The simple answer - not really! Providing you are eating a healthy balanced diet that is not only adequate in energy, but also includes a wide variety of foods, you should have no problem getting all the vitamins and minerals you need. Furthermore, if you are exercising and not dieting, then you will need to eat more food to meet the increased energy demand. More food - providing it's a varied mixture - means you will also be getting more vitamins and minerals. Even athletes, providing their diet is adequate in terms of both quantity and quality, do not need extra vitamins and minerals. Supplementation Only if your diet does not provide enough vitamins and minerals and your body stores are low should you consider taking a low-dose multi-vitamin and mineral supplement. But it is not necessary to exceed requirements - more does not mean better and, in some instances, can be toxic. However, people who have restricted diets may be at risk. Supplements may be necessary where a diet is: Low in energy for weight loss. Nevertheless, it would still be better to adapt the diet to include more dietary sources of vitamins and minerals, rather than resort to taking a supplement. Supplements & Ergogenic Aids The use of nutritional supplements in sport is widespread. Ergogenic aids are substances that aim to enhance performance through effects on energy, alertness, or body composition. Energy Several nutritional ergogenic aids are effective at influencing energy. The most obvious examples are carbohydrate supplements - whether in the form of powders, gels or sports drinks. During prolonged exercise, carbohydrates provide extra energy fuel to help prevent fatigue. Sports drinks deliver water and fuel to the body fast - so help to avoid dehydration and fatigue. Several other ergogenic aids have been shown to be potentially beneficial for certain athletes. However, the long term effects are still unclear - so unless you're competing at the top level, they are probably not worth the cost, or indeed the risk! Creatine and bicarbonate supplements have been shown to be useful during high intensity work. Creatine supplementation can increase muscle creatine phosphate levels for use in the ATP-CP energy system. Alkaline salts, such as sodium bicarbonate (baking soda), can help to neutralise lactic acid and delay fatigue. Stimulants Caffeine is performance-enhancing due to being a central nervous system stimulant. However, if you are competing, a caffeine level in the urine above 12mg/l is not permitted. This level will be achieved by taking about 500mg caffeine - that's about 7 cups of coffee - in a short time. Caffeine is also a diuretic, so make sure you keep hydrated. Body Composition A variety of supplements - such as protein and amino acid supplements, carnitine, chromium and hydroxymethylbutyrate (HMB) - claim to enhance performance by affecting body composition, either by increasing muscle mass and/or reducing body fat. But these have generally been shown to be ineffective. Finally, bypass 'diet and fitness assessments' that are designed to find faults in your diet that can only be corrected by taking supplements. Supplements are simply a more efficient way of making a profit than encouraging you to eat a healthy balanced diet!
Disordered eating Some people, both male and female (and in particular
athletes), don't consider training and exercise sufficient to achieve
an idealised body shape and/or level of thinness. Consequently,
to meet their weight goals, Disordered eating is a very serious problem. In the UK, there are at least 60,000 people diagnosed with an eating disorder. However, in reality the number of people affected is more likely to be nearer 1.1 million - that's about 2% of the total population. This severe underestimation of the problem illustrates just how much those affected by eating disorders are reluctant to admit they have a problem, and are unwilling to seek help, Even when they do, others are often slow to realise the extent of the problem. Anyone can develop an eating disorder regardless of age, sex, race or background. Women are ten times more likely to be affected by eating disorders than men, and it's more common in 15-25 year olds. In addition, there is now a worrying and growing trend of eating disorders amongst sports people, to the extent that the term disordered eating has been coined. Disordered eating implies not a definitive end-point, but a spectrum of abnormal behaviour - ranging from slightly restricting the diet, to occasional bingeing and vomiting, to the extreme clinical categories of anorexia nervosa and bulimia nervosa. Disordered eating is extremely common within the sports world, particularly amongst women. Surveys have suggested that 16% to 72% of female athletes are affected, with the incidence being greater in those sports where a low body weight - aesthetic, endurance and weight class sports - is preferential. So why athletes? Well, the personal attributes that make someone excel as an athlete - being goal-orientated, driven, compulsive and a perfectionist - are also the characteristics that make someone more vulnerable to developing an eating disorder. Some athletes, driven to achieve that idealised body weight and shape, adopt disordered eating patterns. The most common practices include: Eating small portions. Furthermore, training provides another means by which to lose body fat and weight. The health consequences of disordered eating, if left unnoticed, can be dire. These unhealthy dietary practices, which result in not meeting the energy demand of training, lead to low energy levels. This, in turn, impairs sports performance, increases risk of fatigue and injury, and ultimately leads to menstrual dysfunction.
Disordered eating involving acute weight loss and marked weight fluctuations (4.5kg loss and regain) has been associated with amenorrhoea (absence of periods). A variety of menstrual disorders, including oligomenorrhoea (irregular cycles) and amenorrhoea (absent cycles), are recognised as occurring more frequently in female athletes - again, particularly in sports where leanness is emphasised. Genetic, reproductive, and environmental factors - body composition, diet, training, performance level, sport and stress - all affect menstrual function. However, explaining menstrual irregularities is complex and not completely understood. What is understood is the seriousness of the problem. Menstrual dysfunction that results in oestrogen deficiency can have a detrimental effect on bones, to the extent that the risk of developing osteoporosis is increased. Osteoporosis Osteoporosis is a devastating bone disease, where the bones become so weak that they break under minimal trauma - such as falling over, or in extreme cases, just by coughing or being hugged. We lay down bone mineral while we're young until we reach what is known as 'peak bone mass' - the maximum amount of mineral in our bones - at around 30 years old. The sex hormones, oestrogen in particular, are important in the formation and maintenance of bone mineral. Therefore, any factor that contributes to menstrual dysfunction can have a direct or indirect influence on bone mineral status. Consequently, when menstrual irregularities occur, regardless of the cause, the individual is at risk of compromised bone health. Several factors have been associated with a reduced bone mineral density: Menstrual dysfunction. Hence, athletes with eating disorders and menstrual dysfunction are at increased risk of having sub-optimal bone density. Furthermore, not only is there a higher incidence of stress fractures found in athletes with menstrual dysfunction, but all too often the bone loss in affected individuals is irreversible. Any amenorrhoea that persists for longer than 6 months without being treated will result in irreversible bone loss. In addition, these young athletes are losing bone mineral at a time when they should be laying it down - and with only a limited time left until they are in their 30s, it is unlikely that they will be able to achieve an optimal peak bone mass. The result? Compromised bone health for life. Prevention The female athlete triad refers to the three interrelated conditions: disordered eating, amenorrhoea and osteoporosis. Every portion of the triad increases the chance of morbidity and mortality, but the dangers of the three together are synergistic. Early detection of females at risk from the triad and appropriate intervention is of the utmost importance. Lifestyle changes are difficult for everyone, and particularly complicated for individuals with disordered eating patterns. Furthermore, it is important to eliminate the notion that one can restructure one's own body to resemble somebody else's body shape or some idealised image. Females who exercise must be made aware that amenorrhoea is not a normal consequence of training, but is a clear sign that health is being compromised. Prevention is the only long-term solution. The way forward is to eat a healthy balanced diet that is sufficient in energy and contains a wide variety of foods, for both optimum physical performance and long-term health.
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