Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
http://www.bupa.co.uk/health_information/html/healthy_living/lifestyle/exercise/diet_ex ercise/ Carbohydrate and the athlete Carbohydrates are made up of sugars and starch and they should be the major energy providers in your diet. Current recommendations aimed at the entire population state that carbohydrate should provide a minimum of 47 per cent of your total dietary energy (calories) with most of this coming from starchy carbohydrates.1Starch is a highly important nutrient in the diet and is the body's favourite "fuel". It is important because it provides most of our glucose, which is the only fuel the brain can use. In addition, starchy carbohydrates contain fibre and are very good at satisfying our appetites. Carbohydrate and the athlete A diet high in carbohydrates is particularly important for the athlete. We store very little glucose in the body so it is vital to have a regular intake of starch. This is because starch is converted to glycogen and stored in the liver and muscles. This glycogen is then used to meet muscles' energy needs by being converted back to glucose when the muscles exercise.If the muscles run out of glucose they can also burn body fat, but fat is not as efficient an energy source as glucose. Therefore high levels of glycogen will help you exercise at your optimum level. On the other hand, low levels will result in early fatigue and reduced exercise intensity. 2 Good Sources of starch Bread Cereals Porridge Oats Potatoes Beans Lentils Rice Pasta Noodles Sugars Sugar is available in many forms: Glucose - found naturally in fruit and vegetable juices Fructose - occurs naturally in fruit and vegetables and especially in honey Lactose and galactose - found in milk Sucrose - occurs naturally in sugar cane and sugar beet Maltose - available from fermented grain products. For more information on how certain foods affect blood sugar levels, see the section on glycaemic index. How much carbohydrate should you eat? Although the general recommendation for the population is that carbohydrates should supply a minimum of 47 per cent of dietary energy (calories), it is probably important for athletes to increase this. Many sports nutrition experts suggest a minimum of 60 per cent to 70 per cent.3 So how can you work how out many calories from carbohydrate you should actually be taking in on a daily basis? An easy method is as follows:- If your total calorie intake is, say, 3,000 calories/day then calories from carbohydrate 3,000 X 60 per cent = 1800 calories 1 gram of carbohydrate = 4 calories Therefore, 1,800 calories is equivalent to 450 grams of carbohydrate. Your total daily calorie intake from all sources should, of course, be linked to your body weight. In other words, you should be eating an amount that enables you to maintain your weight within its healthy range. To check whether your weight is within its healthy range, try our online body mass index . What about carbohydrate loading? In recent years there has been much discussion about the effectiveness of "loading up" with carbohydrates before endurance events. The aim of this is to increase muscle glycogen stores above normal levels so as to delay the onset of fatigue during an event. There does seem to be some merit in this approach4 and below is a suggested method for achieving carbohydrate loading over a seven-day period prior to an event. Day 1 Endurance training for one hour to deplete your muscle glycogen stores. Days 2, Taper off your training and eat a moderate carbohydrate 3&4 Days 5, 6&7 diet - 5 grams to 7 grams per kilogram of body weight. Taper off training further and rest. While doing this, have a high carbohydrate intake - 8 grams to 10 grams per kilogram of body Your might want to experiment with this approach during training. Carbohydrate intake while exercising Glucose, itself, is not stored in the body. Once the available glucose in the blood stream and cells' plasma is used up, the body then turns to its supply of glycogen. As mentioned earlier, your body has limited stores of glycogen in muscles and liver ready for conversion to glucose. So, it is likely that for longer exercise sessions - say, more than an hour - you are going to deplete your supplies of glycogen and, therefore, run low on glucose. Probably the best way to top up while actually exercising is with an isotonic sports drink (see section on Fluid intake) as this will provide glucose, fluid and also sodium. An intake of between 30 grams to 60 grams of carbohydrate an hour is recommended.5 This is about the maximum your muscles can take up from the bloodstream during exercise. Greater amounts have no further benefit. It is best to start taking in carbohydrate soon after the exercise session begins because of the delay in absorption. Carbohydrate intake after exercise How long does it take to restore glycogen levels after exercise? This depends on: How depleted your stores are after the exercise session Your fitness level The amount of carbohydrate you eat The extent of muscle damage It is best to replenish depleted stores of glycogen by taking in carbohydrate as soon as possible after your exercise session. During the first two hours, replenishment is most rapid and is approximately one and a half times the normal rat.6,7 During the following four hours, the rate slows down but remains higher than normal. Following this period, glycogen manufacture returns to the normal rate. Restoring your glycogen levels as quickly as possible is very important, particularly if you train every day or every other day. This will help you avoid fatigue and get the best out of your training.8 Key points For the athlete, carbohydrates should provide 60 per cent to 70 per cent of total dietary energy (calories). Most of this coming from starch Simple sugar is not a good source of energy as it can upset the body's metabolism Starchy carbohydrates are the body's favourite fuel Glucose is the only fuel the brain can use and is the favourite for muscles Glucose is not stored in the body Glycogen, which is stored in the liver and muscles, is converted to glucose to provide energy for physical activity Carbohydrate loading can help performance in endurance events Depleted muscle glycogen stores should be replaced as soon as possible after exercise, ideally within two hours. Glycaemic index and the athlete You can significantly improve your performance by eating the right mix of complex and simple carbohydrates. Getting the right balance will give you an energy boost just when you need it and it is not as hard to achieve as it might sound. All you have to know is a food's glycaemic index. What is the glycaemic index (GI)? Glycaemic index (GI) is a numerical system that tells you how fast a particular food triggers a rise in your blood sugar levels. A food with a high GI will cause a fast rise in blood sugar while a food with a low GI will bring about a slower rise. Why is this important? From a health point of view, sharp increases in blood sugar are thought to be undesirable because of the effect this has on insulin levels. Diets high in simple carbohydrates and low in starch have been shown to significantly increase the risk of developing diabetes, high blood fat levels, high blood pressure and heart disease.1,2,3,4 Why is this important for the athlete? For the athlete, knowing the GI of different foods is important for reasons other than just health. Getting the balance between complex and simple carbohydrates right can significantly influence performance. Many experts recommend a low glycaemic index meal one to two hours before an exercise session.5 It is thought that the slower, more consistent, release of energy will improve performance by delaying fatigue. It has also been found that low GI meals produce higher blood sugar and fatty acid levels during the latter stages of exercise.6,7 For endurance sports, this is very advantageous. During exercise, when blood sugar levels need to be maintained, one way to achieve this is to drink an isotonic sports drink. This will provide glucose, which is quickly absorbed, fluid and also sodium. After exercise, however, when muscles' stores of sugar (glycogen) need to be quickly restored, a high GI food is a good choice. This is because the simple sugars contained in a high GI food are rapidly absorbed into the blood stream. In turn, this rapid absorption stimulates insulin release and that results in increased uptake by the muscle cells of glucose and their manufacture of glycogen. So, knowing the GI of various foods can clearly help you plan your diet in a way that will help to optimise your performance. How is glycaemic index for a food worked out? The glycaemic index of any particular food is worked out by comparing it with a "reference food" for which a GI has already been established. In other words, the effect of the food being tested on blood sugar levels is monitored at set intervals over a two-hour period and the results compared with the reference food. Glucose is the reference food normally used or, occasionally, white bread. It is possible that you may see the same food with two different glycaemic index figures. If glucose has been used as the reference food, the GI figure is lower than if white bread has been used. The reason for the difference is that pure glucose is absorbed into the blood stream much more quickly than the complex carbohydrates in white bread. However, both figures mean the same. So, for example, baked potato has a GI of 85 (when glucose is used as the reference food) which means that its effect on blood sugar levels is 85 per cent that of glucose. Therefore, baked potato have less of an effect on blood sugar levels. The GI of glucose has been set at 100 and nearly all foods will fall below this figure. If white bread was used as the "reference food" the figure for the GI of baked potato would be 128. This is because baked potato has a greater effect on blood sugar levels than white bread. White bread, when used as the reference food, is given the notional GI figure of 100 and quite a number of foods will have a higher GI figure than this. Click here to view the GI of a range of foods Which component in food increases blood sugar? It is the carbohydrate in food which influences blood sugar levels. Carbohydrate is made up of various simple carbohydrates and starch (see section on carbohydrate). Starch is referred to as a complex carbohydrate because it is a large molecule made up of many different sugar units all joined together. While simple carbohydrates are small molecules made up of just one or two sugar units. Because of their small size and simple construction, simple carbohydrates are easily absorbed into the blood stream. The result is a rapid rise in blood sugar levels. In contrast, complex carbohydrates (such as starch) need to be broken down into their individual sugar units before they can be absorbed. For this reason, they take some time to be absorbed into the blood stream. The result is a much slower rise in blood sugar levels. What about meals and glycaemic index? We often eat meals made up of various foods, rather than just one food on its own, so how can you work out the GI of the meal? Various factors such as the fat, protein and fibre content of meals together with cooking methods can influence the GI of the entire meal as these will influence how quickly absorption takes place from the gut into the blood stream. The following method for working out the GI of a whole meal has been suggested. 8 Calculate the total carbohydrate content of the meal, then work out the contribution each individual food makes to the total carbohydrate content. For example, the GI of an average breakfast is calculated below: Food Carbohydrate (g) % of total carbohydrate Orange Juice (150 ml) GI Contribution to meal GI 12.5 26% 46 26% X 46 = 12 Weetabix (30g) 21 43% 69 43% X 69 = 30 Milk (150 ml) 7 15% 27 15% X 27 = 4 1 slice of toast 13 27% 70 27% X 70 = 19 Total 48 100% Meal GI = 65 Key points a high GI food has a more dramatic effect on blood sugar levels than a low GI food rapid rises in blood sugar levels are undesirable and are linked to various health problems (particularly diabetes) low GI foods/meals should be eaten one to two hours before exercise during exercise blood sugar levels can be maintained with isotonic sports drinks a high GI food is a good choice immediately after an exercise session Calories and the athlete How many calories do we need each day? The Department of Health recommends that men should take in around 2,550 kcalories per day and women around 1,940 kcalories per day.1 These are averages and some people will need more and some people will need less - it depends on how active you are. Really, the best rule of thumb is that your calorie intake should be just enough to maintain a healthy body weight (see Weight management for the athlete), no matter how active or inactive your life is. Why do we gain or lose weight? The only thing that influences whether we gain, lose or maintain weight is the number of calories we take in compared with the number of calories our bodies use up. This is just as true for the athlete as it is for everyone else. Calories taken in Calories used up 3,000 kcalories 2,500 kcalories Gain weight 3,000 kcalories 3,500 kcalories Lose weight 3,000 kcalories 3,000 kcalories Stable weight How are the calories used? Even when we aren't exercising, we require energy just to maintain our bodies and their vital functions. Without energy our bodies would cease to function. The table below shows the energy usage of a sedentary person with a low level of physical activity: % Energy Function Used Basal Metabolic Rate (BMR) - energy used to fuel essential activities such as 65% breathing, organ and cellular function during rest or while asleep Thermogenesis - energy used to digest and metabolise food and maintain body 10% temperatures Physical activity - energy used for movement, for example walking, running, lifting and 25% pulling Energy balance Not only is it important to make sure that you are eating just enough calories to keep your weight healthy, but it is also important to make sure that you get the energy from the right sources. The foods and drinks we take in supply energy from four main sources. Food source Calories per gram Fats 9 kcalories per gram Carbohydrates 4 kcalories per gram Protein 4 kcalories per gram Alcohol (for some people) 7 kcalories per gram For the body to work at its peak you should try to have the right foods and drinks. For your diet and calorie intake to be balanced you should aim for: Food source Contribution to daily calorie intake Fats No more than 33 percent Carbohydrates At least 47 percent Protein Roughly 15 percent Alcohol No more than 5 percent For people who do not drink alcohol the percentage calorie intake from carbohydrate should be increased.1 And for athletes, experts recommend that you should increase your energy contribution from carbohydrates to roughly 60 percent and decrease your intake of fat by the corresponding amount. 2 Key points aim to keep your body weight within its healthy range weight loss, gain or maintenance depends on the number of calories taken in compared with the number of calories used up calorie intake should not come from just one energy source but from a range of sources and foods the balance between carbohydrates, fats, protein and alcohol taken in is important in helping the body to work at its peak. | health information | health living | lifestyle | exercise Vitamins and minerals and the athlete For a long time it was believed that the body only needed proteins, fats, carbohydrates and a number of minerals to stay fit and healthy. But then it was discovered that these dietary components were not enough - tiny amounts of other materials were essential to keep the body functioning. These vital ingredients were named vitamins. Vitamins - what are they? Vitamins are organic compounds that help regulate fat, carbohydrate and protein metabolism in the body. They cannot be made by the body and have to be provided by the food we eat - fortunately we only need tiny amounts of these vitamins. Vitamins are not an energy source, but they play a vital role in releasing the energy stored in the other foods we eat. In addition, our enzyme, nervous, hormonal and immune systems are dependent on vitamins for regulation and control. Because of this vitamins are essential for good health, wellbeing and growth. Vitamins are divided into two types: water-soluble and fat-soluble. Water-soluble: These vitamins cannot be stored in the body and need to be replaced regularly through our diet. Fat-soluble: These vitamins are stored in the body and include vitamins A, D, E and K. Although these vitamins can be stored, they should still be part of a healthy diet Minerals - what are they? Minerals are inorganic elements that have many roles in the body's functioning. Apart from their more well-known roles in the formation of strong bones and teeth, they also help to control the nervous system, fluid balance in tissues, muscle contractions, some hormonal functions and enzyme secretion. Minerals are as essential as vitamins and, just like most vitamins, they cannot be made in the body. All our bodies' mineral needs have to be supplied from our diets. Where do we get our vitamins and minerals from and what role does each play? Vitamins Function Food sources Vitamin A Necessary for vision in dim light, Fish liver oils (for example cod (found in two forms: for healthy skin and surface or halibut liver oil), liver, carrots, retinol and beta carotene) tissues, especially those which fortified margarine, cheese and excrete mucus (for example the dark green leafy vegetables intestines, lungs and vagina). In addition, it prevents infections and is necessary for the immune system Vitamin D For the growth and maintenance Oily fish, eggs, milk, fortified (found in two main forms: of bones and teeth through breakfast cereals and fortified cholecalciferol and regulation of absorption and margarine. Also created in the ergocalciferol) metabolism of calcium body by action of sunlight on the skin Vitamin E Protection of cell membranes Vegetable oils, eggs, whole (found as a group of compounds and fats from oxidative damage; grains, green vegetables and called tocopherols) protection of vitamin A, immune nuts system and nervous system Vitamin K Is necessary for normal blood Dark green leafy vegetables, (covers a number of clotting and energy metabolism liver, meat, potatoes and compounds, including cereals phylloquinone) Vitamin B1 For energy metabolism, Bread, potatoes, milk, meat (thiamin) especially from carbohydrates (especially pork), offal, whole grain cereals and fortified breakfast cereals Vitamin B2 Essential for the utilisation of Milk, meat (particularly liver) and (riboflavin) energy from foods, especially eggs fats and proteins Niacin (also known as vitamin Necessary for energy Meat, potatoes, bread and PP) metabolism fortified breakfast cereals Pantothenic Acid (also known Energy metabolism and Yeast, liver, whole grains, as vitamin B5) production of neurotransmitters greens and nuts. In fact it is for the nervous system found in virtually all foods Vitamin B6 Necessary for protein Potatoes, vegetables, meat, (found as a group of metabolism, particularly of milk and fish compounds, including haemoglobin (nicotinic acid) pyridoxine) Vitamin B12 For the production of blood (red (found as a group of cells), nervous system, Liver, milk, fish and eggs compounds, including synthesis of DNA cyanocobalamin and hydroxocobalamin) Folic Acid (also known as Necessary for the production of vitamin Bc or M) blood (red cells), nervous Offal and raw green vegetables system, synthesis of DNA Biotin (also known as vitamin H) For protein and fat metabolism Liver and kidneys, whole grains and nuts Vitamin C Necessary for the maintenance Fresh fruit, especially citrus (found as a group of of connective tissues (including fruits and vegetables compounds, including ascorbic tendons, ligaments and (particularly potatoes) acid) cartilage). In addition, it helps wound healing, production of hormones, the immune system and protects vitamins A and E Minerals Function Food sources Sodium Helps regulate body fluids and Salt, bread and cereal products, is involved in energy release, bacon, ham, shellfish, smoked functioning of nerves and fish, soy sauce and foods that muscle contraction. Increases have been preserved by using blood pressure salt Is used in the body's fluid Potatoes, vegetables, greens, balance and is involved in pork, dairy products, fruit membrane functions, muscle (especially bananas) and juices Potassium function and reduces blood pressure Calcium Magnesium For bones and teeth, blood Milk, cheese, bread and flour, clotting, hormone secretion, green leafy vegetables and muscle and nerve function small oily fish with bones Involved in muscle tone and Milk, bread, potatoes and activates enzymes vegetables Iron Necessary for the manufacture Red meats, liver, flour and of haemoglobin in blood (red cereal products, potatoes and cells) oxygen transport and vegetables transfer to tissues, activates enzymes Zinc For growth, bone metabolism, Meat, liver, seafood (especially activation of enzymes, release oysters) milk, bread and cereals of vitamin A from liver, immune system, taste and insulin storage Copper Essential for enzyme function, Oysters, mussels, whelks, liver, especially blood formation, bone brewer's yeast, whole grains, metabolism, immune system, nuts and cocoa nerve function and energy metabolism Manganese Necessary for enzyme Wholemeal bread, wheat germ, activation and cell structure nuts, avocados, peas and tea (works with calcium and iron) Molybdenum Involved in enzyme functions Liver, kidney, wheat germ, lentils, sunflower seeds, eggs and beans Selenium Has an enzyme function Nuts (especially brazils), seeds, protecting cell membranes and bread, fish and meat (especially fats from oxidative damage pork) (works with vitamin E) Chromium Enhances the action of insulin Egg yolk, liver, cheese, on glucose uptake by cells wholemeal products, molasses and brewer's yeast Iodine Phosphorus A necessary component of Oily fish, seaweed, meat, milk thyroid hormones and iodised table salt Accommodates energy stores, Dairy products, eggs, meat, fish, bones, membrane function and soya beans, soya products, growth pulses and wheat bran Am I getting enough? Most experts now agree that a balanced diet should provide you with all the vitamins and minerals you need. This is provided you eat a variety of foods from each of the food groups (see section on balanced diet) and, of course, in sufficient quantity. By quantity, we mean enough food for you to maintain a healthy body weight. To check that your body weight is in the correct range for your height, why not try our online body mass index (BMI) calculator. Clearly, different people have different requirements and, because of this, helpful guidelines have been established by the Department of Health.1 These are called Dietary Reference Values or DRVs. For any particular nutrient (where the scientific information is available) there are three values. LRNI (Lower Reference Nutrient Intake). This is for a small number of people who have low needs and represents about 3 per cent of the population. Most people will need more than this. EAR (Estimated Average Requirement). Is the amount of a nutrient needed by an average person. So many people will need more and many will need less. RNI (Reference Nutrient Intake). The amount of a nutrient that should cater for the needs of 97 per cent of the population. It is more than most people require and only very few people (3 per cent) will need more. This is also known as the Recommended Daily Amount or RDA. It is this value you will see on the sides of cereal packets. It is important to remember that DRVs are aimed at populations of people, not individuals. As such they are guidelines and not targets for you to aim for. Athletes - do they have different requirements? Generally speaking, like the rest of us, athletes should get all the vitamins and minerals from their diet. Because athletes use up more energy than inactive people, they probably eat more too, and so any increased requirement for vitamins or minerals should be met by their increased food intake (providing the diet is balanced). However, some studies2,3,4 have shown that many athletes don't have adequate vitamin and mineral intakes. This may be because they restrict calorie intake in order to manage weight. Other reasons for inadequate vitamin and mineral intake include irregular training routines that making meal planning difficult and following a dietary "fad" that is not providing a balanced diet. Will vitamin and mineral supplements enhance athletic performance? A lot of work has been carried out to try to establish whether vitamin and mineral supplements improve athletic performance. So far, there is little evidence that any improvement occurs in athletes who are well nourished. The only improvements observed have been in people whose diets were previously deficient in one nutrient or another, adding supplements just brought them up to their optimum level. In summary, if you are not deficient in any vitamins or minerals, then supplementing your diet will not bring about any improvement in performance. Nevertheless, if you do have some sort of deficiency, then correcting this may well be of benefit. Choosing a supplement Most people will probably not be aware of any minor vitamin and mineral deficiencies as the symptoms may be slight, while gross deficiencies are very uncommon in this country. Nevertheless, you may want to take a supplement as an "insurance policy", based on the principle that, at the very least, it will not harm you and may possibly be of benefit. If you do decide to take a supplement then it is best to choose a well formulated multi-vitamin and mineral supplement that contains all the main vitamins and minerals. What about specific vitamins or mineral supplements? It is best not to use supplements that contain just one or two specific vitamins or minerals. This is because vitamins and minerals work in harmony and an excessive amount of just one can impair the absorption or effectiveness of others. Correct balance is important. Furthermore, some vitamins, particularly the fat-soluble vitamins, can be harmful in excess quantities as they tend to build up in the body and cause problems. With water-soluble vitamins, amounts over and above the body's requirements are simply lost from the body in urine and do not provide any additional benefit - so you will be wasting your money! You will notice on the packaging of supplements that for each particular vitamin or mineral it may list the "% of RDA". RDA simply means the Recommended Daily Amount so, for example, if say for Vitamin C it says "100% RDA", this means that it contains 100 per cent of your daily allowance. The RDA is similar to the RNI in Dietary Reference Values. You will probably notice that many supplements exceed the RDA, however, this is not necessarily harmful as the safety margins are very high and well-formulated supplements are well within the acceptable range. RDAs were formulated to cater for the vast majority of a population (nearly 100 per cent). This means that many people will require less. However, RDAs were also set at a level where it was known that there were no adverse effects. Key points Most vitamins and all minerals cannot be made by the body, so need to come from your diet A balanced diet should provide you with all vitamins and minerals you need If you are well nourished already, supplements will not improve performance If you are slightly deficient in some nutrients, a supplement may benefit performance Gross vitamin deficiencies are rare in this country The fat-soluble vitamins, A D E and K, may cause side-effects if taken in very high quantities When choosing a supplement choose a well-balanced multi-vitamin and mineral supplement Supplements containing a single vitamin or mineral are best avoided because it is difficult to get the balance right