WIKIPEADIES Accessed 20 MAY 2010
Sports Nutrition – Carbohydrate – Carbs
Carbohydrate is arguably the most important source of energy for athletes. No matter what sport you play, carbs provide the energy that fuels muscle contractions. Once eaten, carbohydrates breakdown into smaller sugars (glucose, fructose and galactose) that get absorbed and used as energy. Any glucose not needed right away gets stored in the muscles and the liver in the form of glycogen. Once these glycogen stores are filled up, any extra gets stored as fat.
Glycogen is the source of energy most often used for exercise. It is needed for any short, intense bouts of exercise from sprinting to weight lifting because it is immediately accessible. Glycogen also supplies energy during the first few minutes of any sport. During long, slow duration exercise, fat can help fuel activity, but glycogen is still needed to help breakdown the fat into something the muscles can use.
Adequate carbohydrate intake also helps prevent protein from being used as energy. If the body doesn’t have enough carbohydrate, protein is broken down to make glucose for energy. Because the primary role of protein is as the building blocks for muscles, bone, skin, hair, and other tissues, relying on protein for energy (by failing to take in adequate carbohydrate) can limit your ability to build and maintain tissues. Additionally, this stresses the kidneys because they have to work harder to eliminate the by-products of this protein breakdown.
Carbohydrate has other specific functions in the body including fuelling the central nervous system (CNS) and brain.
One gram of carbohydrate provides four calories of energy. Athletes often talk about carbohydrate loading and carbohydrate depletion which refers to the amount of carbohydrate energy we can store in our muscles. This is generally around 2,000 carbohydrate calories, but we can change this number through depletion and loading. During depletion (from diet, exercise or a combination) we use up the stored carbohydrate.
If we don’t replenish these stores, we can run out of fuel for immediate exercise. Athletes often refer to this as “bonking” or “hitting the wall.” In the same way, eating large amounts of carbohydrates can increase these stores. This is often referred to as carbohydrate loading or carbo-loading. Our maximal carbohydrate storage is approximately 15 grams per kilogram of body weight [15 grams per 2.2 pounds]. So a 175-pound athlete could store up to 1200 grams of carbohydrate [4,800 calories]; enough energy to fuel high intensity exercise for quite some time.
How Carbohydrate Fuels Exercise
Carbohydrate stored as glycogen is an easily accessible source of energy for exercise. How long this energy supply lasts depends on the length and intensity of exercise and can range anywhere from 30 to 90 minutes or more. To avoid running out of energy during exercise, start with full glycogen stores, replenish them during exercise and refill them after exercise to be ready for the next workout.
Types of Carbohydrate
Carbohydrates are also divided into simple and complex forms. Simple sugars (carbs) are absorbed and converted to energy very quickly and provide a rapid source of energy. Fruit and energy drinks are a good source of simple carbohydrates.
Complex carbohydrates take a bit longer to be digested and absorbed into the body. They also take longer to breakdown and therefore provide energy at a slower rate than simple sugars. Examples of complex carbohydrates are breads, rice and pasta. Starch and fibber are also considered complex carbohydrates but fiber can not be digested or used for energy. Starch is probably the most important energy source in an athlete’s diet because it is broken down and stored as glycogen. Foods high in starch include whole grain breads, cereals, pasta, and grains.
The Position Statement from the Dieticians of Canada, the American Dietetic Association, and the American College of Sports Medicine, Canadian Journal of Dietetic Practice and Research in the Winter of 2000, 61(4):176-192.
Carbohydrates in Bananas
e you wondering about carb counts and health benefits of bananas? If you’re looking for a snack that’s healthy, fat-free and will fill you up, a banana is the perfect choice. It’s a little higher in carbs than some other fruits, but a large banana also has 2 grams of protein and 4 grams of fibre. Bananas are a good source of vitamin A, thiamine, riboflavin, niacin, vitamin B6, and folic acid, and are rich in potassium and other trace minerals.
Calorie, Carbohydrate and Fibre Counts for Bananas
1 small (6″ to 6-7/8″) banana:
Calories – 90, Fibre – 2.6 grams, Carbohydrates – 23.1 grams = 23100mg
1 medium (7″ to 7-7/8″) banana:
Calories – 105, Fibre – 3.1 grams, Carbohydrates – 27.0 grams
1 large (8″ to 8-7/8″) banana:
Calories – 121, Fibre – 4.0 grams, Carbohydrates – 31.1 grams
Counting the carbs of your food choices is one way to control blood sugar, and knowing the carb count for healthy foods like bananas can help you decide how to spend your daily allotment of carbs.
Another way to gauge the effect of bananas on blood sugar is the glycemic index. The glycemic index is a way of measuring how quickly a carbohydrate enters the bloodstream and how high it raises blood glucose levels.
The glycemic index is a scale from 1 to 100, with higher glycemic numbers indicating foods that raise blood sugar higher and faster than foods with lower glycemic numbers.
The glycemic index for bananas ranges from 42 to 51 depending on the ripeness of the banana. A perfectly ripe banana with completely yellow skin measures 51. An under-ripe banana that has a greenish-yellow skin has a glycemic index of 42. An over-ripe banana, with a yellow skin spotted with brown, has a GI of 48.
More information on carbohydrates and fruit…
Milligram, another metric unit of measure. Many vitamins and minerals are measured in milligrams, for example, 1,000 milligrams equal one gram.
1000m = 1g
Behavioural Signs of Eating Disorders
Eating Disorders anorexia Nervosa
The three most common eating disorders are anorexia nervosa (anorexia), bulimia nervosa (bulimia) and binge eating disorder. Though these eating disorders manifest themselves in different ways, they are each based on the underlying idea that the individuals who suffer from them can not separate their emotions from their eating habits, or in fact choose to use their eating habits to express their emotions, and this skews both the way and the amount that they eat.
Behavioural Signs of Anorexia
Anorexia is an eating disorder that manifests itself through an intense fear of gaining weight and body fat, and results in behaviours such as extreme dieting, outright fasting and excessive exercising to burn calories. Most anorexics do not recognise their behaviours as dangerous and may be so rigid in their regimes that they are unwilling to consider acting in a different way. Many anorexics engage in behaviours such as:
* Obsessively counting calories.
* Skipping meals.
* “Playing” with or pushing food around a plate rather than eating it.
* Hiding food (in a napkin, under a plate, etc.) to avoid eating it.
* Lying about having eaten in an attempt to avoid a meal or snack.
* Avoiding social events which require eating or involve food.
* Eating only a limited number or type of food.
* Exercising excessively, particularly after or “to make up for” eating.
* Dramatically losing weight.
* Showing excessive interest in weight, body image and fasting.
* Hiding behind loose or baggy clothing.
* Displaying low energy levels.
* Frequently falling ill.
* Sleeping excessively, including during the day.
* Showing low or no sex drive.
Behavioural Signs of Bulimia
Bulimia is an eating disorder that manifests itself through binge eating followed by purging behaviours such as vomiting or taking laxatives. Many bulimics engage in behaviours such as:
* Binging, or eating a great amount of food in one sitting.
* Purging, or attempting to get rid of eaten food by inducing vomiting or taking laxatives or diuretics.
* Hiding the reserved for binges including bread, pasta, sweets, desserts, crisps and ice cream.
* Lying about what has been eaten.
* Purging in secret.
* Hiding items such as laxatives or diuretics.
* Displaying concern for body weight, body shape and overall image.
* Frequently complaining of sore throats (brought on by repeated vomiting).
* Frequently complaining of dental problems (also brought on by repeated vomiting).
* Hiding behind loose or baggy clothing.
* Showing low or no sex drive.
Behavioural Signs of Binge Eating Disorder
Those suffering from binge eating disorder will consume large amounts of food at one sitting but will not purge or rid themselves of this food afterwards. Many binge eaters engage in behaviours such as:
* Ingesting an excessive amount of food, even if they are not hungry.
* Eating until they feel uncomfortable or sick.
* Hiding their eating habits due to shame or embarrassment.
* Hiding secret stashes of food for binges.
* “Grazing” for as long as food is available.
* Emotional eating, or eating when they feel stressed out or overwhelmed.
* Feeling out of control, ashamed and/or guilty both during and after a binge.
* Expressing disgust at their eating, weight, body or appearance.
Eating disorders are diagnosed using mental health criteria but most of the signs of eating disorders are behavioural. Anorexia, bulimia and binge eating disorder may all be recognised by the eating disorders in which sufferers engage and changing these behaviours is an important part of treatment.
The glycemic index (GI) measures carbohydrates according to how quickly they are absorbed and raise the glucose level of the blood. A low GI diet may help weight loss and may also help energy levels for endurance sports.
Food and drinks provide fuel for our body in the form of fat, protein, carbohydrates and alcohol. Carbohydrates are the body’s preferred fuel source. The glycemic index (GI) is a way to rate carbohydrates according to how quickly they are absorbed and raise the glucose level of the blood. It has replaced classifying carbohydrates as either ‘simple’ or ‘complex’.
Foods that contain carbohydrates include bread, breakfast cereals, rice, pasta, legumes, corn, potato, fruit, milk, yoghurt, sugar, biscuits, cakes and lollies.
Digesting and absorbing carbohydrates
The digestive system breaks down carbohydrate-containing foods into simple sugars, mainly glucose. For example, both rice and soft drink will be broken down to simple sugars in your digestive system. This simple sugar is then carried to each cell through the bloodstream.
The pancreas secretes a hormone called insulin, which helps the glucose to migrate from the blood into the cells. Once inside a cell, the glucose is ‘burned’ along with oxygen to produce energy. Our muscles, brain and nervous system all rely on glucose as their main fuel to make energy.
The body converts excess glucose from food into another form called glycogen. This is stored inside muscle tissue and the liver, ready to supplement blood sugar levels should they drop between meals or during physical activity.
The glycemic index
Carbohydrate-containing foods can be rated on a scale called the glycemic index (GI). This scale ranks carbohydrate-containing foods based on their effect on blood sugar levels over a period of time – usually two hours. The GI compares foods that have gram-for-gram the same amount of carbohydrate.
Carbohydrate-containing foods are compared with glucose (although sometimes white bread can be used as a reference food), which is given a GI score of 100. Carbohydrates that break down quickly during digestion have the highest glycemic indexes (GI more than 70). These high GI carbohydrates give a ‘quick hit’. The blood glucose response is fast and high.
Carbohydrates that break down slowly release glucose gradually into the bloodstream. They have low glycemic indexes (GI less than 55). The blood glucose response is slower and flatter.
Choosing between high and low GI foods
Which carbohydrate foods are best to eat? That depends on the situation. For example, the rate at which porridge and cornflakes are broken down to glucose is different. People with type 2 diabetes or impaired glucose tolerance have become resistant to the action of insulin or cannot produce insulin rapidly enough to match the release of glucose into the blood after eating carbohydrate-containing foods. This means their blood glucose levels may rise above the normal level.
Porridge is digested to simple sugars much more slowly than cornflakes so the body has a chance to respond with production of insulin and the rise in blood glucose levels is less. For this reason, porridge is a better choice of breakfast cereal than cornflakes for people with type 2 diabetes. It will also provide more sustained energy for other people as well.
How much you eat is also important
The amount of the carbohydrate-containing food you eat will also affect your blood glucose levels. For example, even though pasta has a low GI, it is not advisable for people with diabetes or impaired glucose tolerance to have a large serve. This is because the total amount of carbohydrate, and therefore the kilojoules, will be too high.
The glycemic load (GL) is a concept that builds on GI as it takes into account both the GI of the food and the amount of carbohydrate in a portion. GL is based on the idea that a high GI food consumed in small quantities would give the same effect on blood glucose levels as larger quantities of a low GI food. GL is easily calculated by multiplying the GI by the number of grams of carbohydrate in a serving of food.
GI and weight loss
A low GI diet is commonly promoted as an effective way to help lose weight by controlling blood sugars and appetite. When high and low GI diets are compared head-to-head, however, the scientific evidence to date, has shown that there is no additional benefit for weight loss of a low GI diet over a similar diet of nutrient composition that is high GI.
While GI can be a useful guide in planning a diet, it should not be the only consideration. Both the serving size of foods and the nutritional quality of the diet are just as important things to consider.
GI and exercise
Eating low GI foods two hours before endurance events, such as long distance running, may improve exercise capacity. It is thought that the meal will have left your stomach before you start the event but remains in your small intestine releasing energy for a few hours afterwards. On the other hand, high GI foods are recommended during the first 24 hours of recovery after an event to rapidly replenish muscle fuel stores (glycogen).
High GI foods are influenced by low GI foods
Generally, eating low GI foods and high GI foods at the same time has the effect of ‘averaging’ the GI. This is important, as most foods are eaten as part of a meal and this affects the GI value of foods. For example, eating cornflakes (a higher GI food) with milk (a lower GI food) will reduce the effect on blood sugar levels.
If a person with diabetes experiences a ‘hypo’, where the blood glucose levels fall below the normal range of 3.5–8mmol/L, they need to eat carbohydrate-containing foods (preferably those with a high GI) to restore their blood sugar levels to normal quickly. For example, eating five jellybeans will help to raise blood glucose levels quickly.
GI scale examples
Some examples of the GI rating of various carbohydrates include:
* Low GI (less than 55) – soy products, beans, fruit, milk, pasta, grainy bread, porridge and lentils.
* Medium GI (55 to 70) – sugar, orange juice, basmati rice and wholemeal bread.
* High GI (greater than 70) – potatoes, white bread and long-grain rice.
Factors that affect the GI of a food
Factors such as the size, texture, viscosity (internal friction or ‘thickness’) and ripeness of a food affect its GI. For instance, an unripe banana may have a GI of 30 while a ripe banana has a GI of 51. Both ripe and unripe bananas have a low GI.
Fat, protein, soluble fibre, fructose (a carbohydrate found in fruit) and lactose (the carbohydrate in milk) also generally lower a food’s glycemic response. Fat and acid foods (like vinegar, lemon juice or acidic fruit) slow the rate at which the stomach empties and so slow the rate of digestion, resulting in a lower GI. Other factors present in food, such as phytates in wholegrain breads and cereals, may also delay a food’s absorption and thus lower the GI.
Cooking and processing can also affect the GI – food that is broken down into fine or smaller particles will be more easily absorbed and so has a higher GI. Foods that have been cooked and allowed to cool, potatoes for example, can have a lower GI when eaten cold than when cooked.
GI symbol on packaged foods
A food packaging symbol for comparing the effect of different foods on blood sugar was launched in Australia in July 2002. The GI symbol, G – Glycemic index tested, indicates the GI rating of packaged food products in supermarkets. It ranks food products based on the speed at which they break down from carbohydrate to sugar in the bloodstream.
The GI symbol only appears on food products that meet certain nutrient criteria for that food category. High and intermediate GI soft drinks, cordials, syrups, confectionery and sugars are excluded. Jams, honey and other carbohydrate-containing spreads are not necessarily excluded.
Using the GI as a guide to healthy eating
The GI can be used as a guide to healthy eating, as long as you are aware of the limitations. For example, the GI of some fruits, vegetables and cereals can be higher than foods that are considered to be treats, such as biscuits and cakes. This does not mean we should replace fruit, vegetables and cereals with treats, because the former are rich in important nutrients and antioxidants and the latter are not. GI can be a useful concept in making good food substitution choices, such as having oats instead of cornflakes or eating grainy bread instead of white bread.
It is not always possible or necessary to choose all low GI foods. There is room in a healthy diet for moderate to high GI foods and many of these foods can provide important sources of nutrients. If you mix a low GI food with a high GI food, you will get an intermediate GI for that meal.
Tips for healthy eating
Some practical suggestions include:
* Use a breakfast cereal based on oats, barley or bran.
* Use grainy breads or breads with soy.
* Enjoy all types of fruit and vegetables.
* Eat plenty of salad vegetables with vinaigrette dressing.
* Eat a variety of carbohydrate-containing foods. If the main sources of carbohydrates in your diet are bread and potatoes then try lentils, legumes, pasta, basmati rice and pita breads.
* Focus more on the serving size of foods, rather than its GI rating alone.
Expert medical supervision
If you have a medical condition, such as diabetes, it is important to seek the advice of your doctor or specialist before making any changes to your diet.
Where to get help
* Your doctor
* An accredited practising dietician, contact the Dieticians Association of Australia
* Nutrition Australia
Things to remember
* The glycemic index (GI) rates carbohydrates according to how quickly they raise the glucose level of the blood.
* The glycaemic load (GL) rates carbohydrates according to the glycaemic index and the amount of carbohydrate in the food.
* A low GI rating of a food does not mean you can eat a larger serve of that food – the total amount of carbohydrate and kilojoules consumed are still important.
* Choose a diet containing plenty of fruits, vegetables and legumes but with smaller helpings of potatoes and less highly refined grain products and concentrated sugar.
Nutrition and Hydration for Performance
* Standard amino acids
o Aspartic acid (aspartate)
o Glutamic acid (glutamate)
o Isoleucine (branched chain amino acid)
o Leucine (branched chain amino acid)
o Valine (branched chain amino acid)
* Butyric acid
* Caprioc acid
* Caprylic acid
* Capric acid
* Lauric acid
* Myristic acid
* Pentadecanoic acid
* Palmitic acid
* Heptadec acid
* Stearic acid
* Arachidic acid
* Behenate acid
* Tetracos acid
* Compound acid
* Oleic acid
* Erucic acid
* Nervonic acid
* Linoleic acid
* Linolenic acid
* eicosapentaenoic acid (EPA) – an essential fatty acid
* DHA (docosahexaenoic acid) – an essential fatty acid
Essential fatty acids
* eicosapentaenoic acid (EPA)
* DHA (docosahexaenoic acid)
* Omega 3 fatty acids
* Omega 6 fatty acids
* Trans fatty acids
Substances that provide energy
* Carbohydrates are compounds made up of sugars. Carbohydrates are classified by their number of sugar units: monosaccharides (such as glucose and fructose), disaccharides (such as sucrose and lactose), oligosaccharides, and polysaccharides (such as starch, glycogen, and cellulose).
* Proteins are organic compounds that consist of the amino acids joined by peptide bonds. The body cannot manufacture some of the amino acids (termed essential amino acids); the diet must supply these. In nutrition, proteins are broken down through digestion by proteases back into free amino acids.
* Fats consist of a glycerin molecule with three fatty acids attached. Fatty acids are unbranched hydrocarbon chains, connected by single bonds alone (saturated fatty acids) or by both double and single bonds (unsaturated fatty acids). Fats are needed to keep cell membranes functioning properly, to insulate body organs against shock, to keep body temperature stable, and to maintain healthy skin and hair. The body does not manufacture certain fatty acids (termed essential fatty acids) and the diet must supply these.
Fat has an energy content of 9 kcal/g (~37.7 kJ/g); proteins and carbohydrates 4 kcal/g (~16.7 kJ/g). Ethanol (grain alcohol) has an energy content of 7 kcal/g (~29.3 kJ/g).