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Optimal Carbohydrate, Protein and Fat Consumption for Endurance
Carbohydrate Ingestion and Endurance Exercise Performance The energy requirements of the typical endurance athlete are enormous, and will far exceed the normal recommended dietary intake for healthy adults. Cyclists competing in the Tour de France consume around 6500 calories a day more than 2.5 x the normal recommended dietary intake without any significant increase in bodyweight, therefore, the 6500 calories are needed just to maintain bodyweight. In both endurance training, and competition, it is vital that enough calories are provided before during and after exercise. If too few calories are provided before, or during, exercise then performance will suffer as the reduced energy levels will lead to early fatigue. If too few calories are consumed immediately after exercise then the rate of recovery will be compromised and the athlete will suffer with reduced training and racing performance, and will put themselves at risk of overtraining. Therefore endurance athletes must strive to optimise nutrition by having an adequate intake of calories before, during, and after exercise. The primary energy sources during long distance events is the through the aerobic metabolism of fats and carbohydrates. At moderate exercise levels (60 70% of VO2max, 65 75% HR max), the major energy source is through the metabolism of fats (in the form of free fatty-acids) which provide over 50% of the energy requirements. However, as exercise intensity increases the proportion of energy supplied by fat decreases and the proportion of energy supplied by carbohydrate increases. As exercise intensity increases to around 85% VO2max (around the intensity of the lactate threshold) carbohydrates become an increasingly important energy source, supplying more than half the energy requirements. It is important to note that the total amount of energy supplied by fats doesnt change, rather it is the amount of energy provided by carbohydrate that actually increases as exercise intensity increases. Although, under all exercise levels, the metabolism of fats provides a significant amount of the total energy requirements, there is always an almost inexhaustible amount of fat for use in metabolism, in even the leanest athlete. This is easy to understand when you consider that just 1kg of fat will provide enough energy to run around 3 marathons. Therefore there is no benefit in increasing the intake of fat before or during exercise, in order to optimise performance. Rather, it is the type of fat in the diet that is important this will be discussed later in this section. Unlike the large amounts of energy stored in our body fat, we have relatively small stores of carbohydrate within our body. Following 60 minutes of intense aerobic exercise, muscle and liver glycogen (the bodys store of carbohydrate) can decrease by around 50%, and following 2 hours of exercise they may be almost fully depleted. Since, carbohydrates provide a large proportion of energy during moderate/intense physical activity, when carbohydrate stores are depleted the athlete will experience a significant increase in fatigue and performance will decrease significantly. Another, key point to remember is that, carbohydrates are involved in the complete metabolism of fats, and therefore when carbohydrate stores are drained the level of fat metabolism is also decreased. It is this point at which carbohydrate stores drop significantly, and metabolism is compromised, that is described as hitting the wall, by marathon runners. Therefore, it is important to keep our stores of carbohydrate topped up before, during, and after exercise, so as to optimise endurance performance. We will therefore begin our look at endurance nutrition by looking at the consumption of carbohydrate before, during and after exercise. Because carbohydrate stores are relatively small, compared with fat stores, endurance athletes must constantly consume large quantities of carbohydrates (4-5g of carbohydrate per pound of body weight per day) to maintain adequate stores. This means that a 150lb endurance athlete must consume around 600g of carbohydrate per day in order to maintain adequate carbohydrate stores. This is better taken as a number of small meals throughout the day (4-6 small meals), rather than 3 large meals. By consuming smaller meals you will ensure that more of the carbohydrate is used to replaced muscle and liver glycogen stores, and less is converted to, and stored as body fat. It is particularly important that athletes consume adequate amounts of carbohydrate over the few days building up to a race, and on the day of the race.
Carbohydrate Consumption Before Competition and Training In order to improve exercise performance, and to ensure that muscle and liver glycogen stores are adequately stocked, athletes should consume around 150-300g (pasta contains around 80g of carbohydrate per 100g) of carbohydrate around 3-4hours prior to competition or key training sessions. When consuming carbohydrates always ensure that you have an adequate intake of fluids as the storage of glycogen requires additional fluid storage. For every gram of glycogen stored there will be an additional 3 grams of water stored. It is important to note that consuming high-glycemic carbohydrate (fast releasing sugars such as glucose), in the hour, immediately before exercise, may have a negative effect on exercise performance. The reason for this is because the fast releasing sugars cause blood sugar levels to rise rapidly, within 5-10 minutes of consumption, which in turn cause an excessive release of insulin. In this case, the rapid rise in insulin levels has two negative effects that may adversely affect performance: 1) the excessive rise in insulin overcompensates for the amount of sugar in the blood and causes a state of low blood sugar (hypoglycaemia); 2) high insulin levels inhibit the mobilization and utilization of fat as an energy source, and therefore carbohydrate (or glycogen) metabolism must increase to compensate. Both of these factors lead to an increased rate of carbohydrate metabolism and thus increases the rate of glycogen depletion. Because fat metabolism is decreased and carbohydrate metabolism increased, as soon as you then start your race, or training session, carbohydrate metabolism will then have to further increase and therefore the rate of glycogen depletion will be even greater, resulting in an earlier point of glycogen depletion. This can easily be avoided by consuming your last energy drink around 60-90 minutes before exercise. When preparing for a long distance race of 2hours+ duration, like a marathon, you should increase your carbohydrate intake, by around 100-200g per day, over the last 3-4 days before the race, and decrease training volume (by 25-50%) over the last week prior to the race. This will ensure that you have full glycogen stores going into the race. For races of less than around 30-90 minutes duration, glycogen stores should be adequate as long as you maintain normal dietary intakes of carbohydrate (4-5g per pound of body weight per day for an endurance athlete), and just reduce training volume by 25-50% over the last week before the race. Before long duration, or intense, training sessions you would be wise to consume 300-400ml of fluid containing around 25-30g of glucose in the last 5 minutes before exercise.
Carbohydrate Consumption During Competition and Training The consumption of carbohydrate (either liquid or solids) during exercise enhances exercise performance during high-intensity and long-duration aerobic exercise. The consumption of carbohydrates during exercise around 60 80% VO2max (80% VO2max is approximately marathon intensity for well trained athletes) can delay the point of fatigue by around 15-30minutes. The ingested carbohydrate (which should be in the form of glucose for best effects during exercise) raises blood sugar levels which can then be used to fuel the muscles and thus sparing the valuable muscle glycogen and aiding exercise performance. Another consideration is that either competing in a long distance race or doing a long duration training session, places a large amount of stress on the immune system. This increases your chances of succumbing to illness, particularly upper respiratory tract infections. In fact, following a long endurance event like the marathon you are up to 6 times more likely to get ill. The negative effects of endurance training on immune health are mainly due to a lowering of blood sugar levels. When blood sugar levels are low, the brain responds by increasing the levels of two key hormones (cortisol and epinephrine). While these two hormones help to elevate blood sugar levels they both have negative effects on the immune system. Cortisol, in particular has a very negative effect on immune health by lowering the numbers of lymphocytes very important white blood cells that fight invading pathogens. The rise in both of these key hormones, and therefore the negative effects on the immune system, can be prevented, or reduced, by keeping blood sugar levels elevated throughout training, or racing. An additional problem, is that during long duration training, you cause large amounts of damage to your muscles the membranes of the muscles become damaged, muscle cells become damaged and break down, and protein structures within the muscles are broken down and used as energy. Again this problem is exacerbated by low levels of blood sugar. When blood sugar levels drop, cortisol levels in the blood rise. One of the negative effects of cortisol is an increased rate of muscle breakdown. The cortisol is actually encouraging your muscles to breakdown protein, and use it as an energy source in order to preserve blood sugar levels and muscle glycogen stores. This problem can be avoided, or reduced, by keeping blood sugar levels elevated throughout training, or racing. Endurance athletes competing in events of around 2hours duration would be wise to take an energy drink containing 5-8% carbohydrate (ideally around 40g of carbohydrate in a 500ml drink) to the start line and to start to ingest this immediately on starting the race. Consume this over the first half hour of the race and then continue to drink around 500ml every half hour of energy drink from the drink stations. This will help to maintain blood sugar levels and delay the point of fatigue. In order to delay fatigue, maintain immune function, and reduce muscle breakdown during your long continuous aerobic training you should consume around 150-300ml of fluid with around 5-8% carbohydrate (7.5-15g) every 15 minutes. This will help to maintain hydration levels, blood sugar levels, and delay the point of fatigue.
Carbohydrate Consumption After Competition and Training Following, endurance training, your muscles will likely have reduced stores of muscle glycogen. It is important for optimum recovery that you restock these glycogen stores as quickly as possible. Ideally, you should look to restock carbohydrate levels within a two hour period of completing exercise after two hours the rate of carbohydrate replenishing slows down and if you do not consume enough carbohydrate within the 2 hour window your glycogen stores will not be fully replenished. Another consideration, is that consuming carbohydrate immediately after exercise inhibits the breakdown of muscle tissue and actually encourages the building of new protein. This is particularly important when you consider that following endurance training, many of your muscle proteins, and muscle cells will be damaged, or torn apart, and will need to be rebuilt in order for complete recovery to occur. If additional carbohydrate is not consumed then further proteins may be broken down to use for energy to fuel the rebuilding process. Following endurance training cortisol levels will be raised as we know cortisol encourages the breakdown of muscle tissue so by consuming carbohydrate immediately after exercise, as well as during exercise, you will prevent further rises in cortisol and will reduce muscle breakdown and encourage muscle protein re-synthesis. One of the reasons why carbohydrate ingestion, immediately after exercise, enhances the building of new muscle tissue, is down to the way the carbohydrate increases insulin levels. Insulin is an anabolic hormone that is it encourages the building of new muscle tissue and therefore increased insulin levels will have a very positive impact on protein building within the muscle tissue. So, by consuming sufficient quantities of carbohydrate, immediately after training or racing, and again after 60-90minutes, and a further amount every 2-3hours until you have consumed around 500g of carbohydrate, you will not only replenish muscle glycogen stores but will also push your muscles towards building muscle rather than breaking it down. Following intense, or prolonged, endurance training or racing you should consume any energy drink, or energy bar, containing around 50-75g of fast releasing carbohydrate immediately upon completion of the exercise. Aim to consume 1g of carbohydrate for every kg of bodyweight so if you weigh 60kg you would consume 60g of carbohydrate immediately on completion of training or racing. It is better to consume fast releasing sugars at this time, as they are more readily digested, and enter the blood stream more quickly, and therefore speed up glycogen re-synthesis rates. After 60-90 minutes, consume another 50-75g of carbohydrate. Continue to consume around 50-75g of carbohydrate every 2hours until you have consumed around 500g. Glycogen levels are only replaced at a rate of about 5-7% every hour, so it may take 15-20hours for glycogen levels to return to normal. To further enhance recovery consider taking 2-3g of BCAAs (Branch Chain Amino Acids) or 2-5g of Glutamine with your initial recovery drink. These will further enhance protein re-synthesis and reduce muscle breakdown, thereby aiding recovery. The speed at which different sugars enters the blood stream is measured by the Glycemic Index (GI). Sugars that are fast releasing (enter the blood stream quickly) have a high GI, whereas foods that enter the blood stream more slowly have a low GI.
Glycemic Index of Common Foods
Protein Intake and Endurance Exercise Performance The recommended daily amount of protein is 0.8g per kg of body weight. However, endurance athletes, like strength athletes require around twice this amount 1.5g of protein per kg of bodyweight. Therefore a 60kg endurance athlete would require approximately 90g of protein per day. It is likely that most endurance athletes, because of their small body size would consume this amount of protein in their normal diet. Vegetarians may benefit from the consumption of additional protein in the form of Whey or Soya protein. Endurance athletes should be careful not to consume excessive amounts of protein (i.e. above 2g of protein per kg of bodyweight). Very high protein diets have been associated with a possible increased risk of kidney disease or may exacerbate an existing kidney problem. An excessive consumption of protein may result in an increase in the amount of protein being stored as fat. This would lead to an increase in the amount of Urea (a waste product that must be removed by the kidneys). This leads to an increase in the amount of urea being excreted in the urine. An increased amount of urine production and excretion may decrease the level of hydration and increase your risk of de-hydration. Obviously it is not desirable for an endurance athlete to be in a dehydrated state. Ideally an endurance athlete should consume around 15-20% of their total calories in the form of protein.
Fat Intake and Endurance Exercise Performance Endurance athletes should consume around 20-25% of calories through the consumption of fats. It is likely that most endurance athletes consume around this amount of fat and there is certainly no need to consume additional fats within the diet. Be careful to consume healthy fats. Use unprocessed vegetable oils such as Virgin Olive Oil, cold pressed sunflower oils, and use Olive oil spreads instead of margarines. Be careful not to consume more than 30g of saturated fats in your foods, it is far healthier to consume mono-unsaturated and poly-unsaturated fats which both have positive effects on health. Consider consuming 2-3 portions of oily fish per week, such as mackerel or herring, as these contain the important essential fatty acids omega-3 which are vital for heart health, good circulation, mobility of joints, and have a positive effect on fat metabolism by increasing the rate of fat metabolism and reducing the storage of fat in adipose tissue. It is worth considering taking fish oil capsules (containing high concentrations of the important Omega-3 fatty acids EPA and DHA) to ensure you are getting an adequate supply of these important substances go for 2-3 capsules of fish oils per day. Other positive effects of omega-3 fatty acids are: 1) improved delivery of oxygen to the working muscles; 2) Improved aerobic metabolism; and 3) increased release of the Human Growth Hormone (Somatotropin) which may help to improve recovery and reduce bodyfat levels. |
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