Carbohydrates are the body’s preferred source of energy. They are carbon, hydrogen and oxygen molecules arranged structurally in the form of rings. Carbohydrates provide energy for body function and activity by supplying immediate energy. This is accomplished by the transformation of carbohydrates into glucose, the main sugar in the blood, and the body’s basic fuel. Carbohydrates are stored in the liver, and in the muscle as glycogen. The body transforms glycogen in the liver into glucose, then releases glucose into the bloodstream when it’s required for energy.
CLASSIFICATION OF CARBOHYDRATES
Carbohydrates in the diet are classified as either monosaccharides or disaccharides (simple’s sugars), polysaccharides (complex sugars).
- Monosaccharides: Glucose and fructose are the principal monosaccharides found in food. Glucose is abundant in fruits, sweet corn, corn syrup and honey. Free fructose is found together with free glucose and sucrose in honey and fruits.
- Disaccharides: The most abundant disaccharides are sucrose (glucose-fructose), lactose (glucose + galactose), and maltose (glucose + glucose). Sucrose is ordinary “table sugar” and is abundant in molasses and maple syrup. Lactose is the principal sugar found in milk. Maltose is a product of enzyme digestion of polysaccharides. It is also found in significant quantities in beer and malt liquors. The term “sugar” refers to monosaccharides and disaccharides. “Added sugar” are those sugars and syrups added to foods during processing or preparation.
- Polysaccharides: Complex carbohydrates are polysaccharides (most often polymers of glucose), which don’t have a sweet taste. Starch is an example of complex carbohydrate that is found in abundance in plants. Common sources include wheat and other grains, potatoes, dried peas and beans, and vegetables.
Fiber: Dietary fiber is defined as the non-digestible carbohydrates and lignin (a complex polymer of phenylpropanoid sub-units) present in plants. Several different terms are used to describe this complex group of compounds. For example, functional fiber is the isolated, extracted or synthetic fiber that has proven health benefits. Total fiber is the sum of dietary fiber and functional fiber. Soluble fiber refers to fibers that form a viscous gel when mixed with a liquid. Insoluble fiber passes through the digestive tract largely intact. Dietary fiber provides little energy but has several beneficial effects. First, it adds bulk to the diet. Fiber can absorb ten to fifteen times its own weight in water, drawing fluid into the lumen of the intestine and increasing bowel mobility. Soluble fiber delays gastric emptying also results in reduced peaks of blood glucose following a meal. Second, consumption of soluble fiber has now been shown to lower LDL cholesterol levels by increasing fecal bile acid excretion and interfering with bile acid re-absorption. For example, diets rich in the soluble fiber oat bran (25 to 50g/day) are associated with a modest, but significant, reduction in risk for cardiovascular disease by lowering total LDL cholesterol levels. Also, fiber-rich diets decrease the risk of constipation, hemorrhoids, diverticulosis, and cancer colon. The recommended daily fiber intake is 25g/day for women and 38g/day for men.
DIETARY CARBOHYDRATE AND BLOOD GLUCOSE
Some carbohydrate-containing foods produce a rapid rise followed by a steep fall in blood glucose concentration, whereas others result in a gradual rise followed by a slow decline. The glycaemic index has been proposed to quantitate these differences in the time course of postprandial glucose concentrations. Glycemic index is defined as the area under the blood glucose curves seen after ingestion of a meal with carbohydrate-rich foods, compared with the area under the blood glucose curve observed after a meal consisting of the same amount of carbohydrate in the form of glucose or white bread. The clinical importance of glycaemic index is controversial. Food with low glycaemic index tends to create a sense of satiety over a longer period of time and may be helpful in limiting caloric intake. However, many experts feel that high nutrient fiber content, such as occurs in whole grains, fruits, and vegetables, is a better guide for selecting dietary carbohydrates.
REQUIREMENTS OF CARBOHYDRATES
Carbohydrates are not the essential nutrients because the carbon skeletons of amino acids can be converted into glucose. However, the absence of dietary carbohydrates leads to ketone body production and degradation of body protein whose constitute amino acids provide carbon skeletons for gluconeogenesis. The RDA for carbohydrate is set at 130g/day for adults and children, based on the amount of glucose used by carbohydrate-dependent tissues, such as the brain and erythrocytes. However, this level of intake is usually exceeded to meet energy needs. Adults should consume 45 to 65 percent of their total calories from carbohydrates. It is recommended that added sugar represent no more than 25 percent of the total energy because of concerns that sugar may displace nutrient-rich foods from the diet, potentially leading to deficiencies of certain micro-nutrients.
Contrary to popular belief, carbohydrates are not inherently fattening. They yield 4 kcal/g (the same as protein and less than half that of fat), and result in fat synthesis only when consumed in excess of the body’s energy needs.
COMPLEX CARBOHYDRATES MADE EASY
Avoid simple carbohydrates, these foods have a high glycaemic index. Simple carbohydrates enter the bloodstream quickly. Blood sugar rises causing large amounts of insulin to be released. This leads to storage of fat.
Complex carbohydrates work best for providing energy, and when trying to lose fat. Carbohydrates are filling and require more energy for digestion. Foods that have a low glycaemic index enter the bloodstream slowly.
FUEL YOUR WORKOUTS
Most athletes are weaker and out of energy towards the end of training. In order to grow fast and strong, you have to finish the exercise with fuel to spare.
In order to achieve this, an active athlete should have carbohydrates before, during and after activities.
BEFORE TRAINING: It is important to try to raise blood glucose levels as this has been shown to improve performance. This is best achieved by consuming an appropriate carbohydrate sports drink 2 to 3 hours before beginning. It is suggested that athletes start with 30 to 40 grams of carbs and over time build up to around 100 grams of carbs taken 2 to 3 hours pre-training.
DURING TRAINING: As carbohydrates (blood glucose and stored glycogen) are metabolized rapidly as a source of energy during physical exertion the minimum level of carb intake, to sustain energy and performance levels, you should be looking at consuming whilst on the go is 40 grams per hour. Research indicates that during intense physical exertion requirements for optimum performance may as high as 70 to 90 grams per hour. The best way to achieve this is to use a 5 to 10% carbohydrate rehydration drink (sports drink) or gel sachets followed by an appropriate amount of water. Using your typical sports drink this equates to around 750 ml to 1 liter per hour.
AFTER TRAINING: Fast acting simple carbs taken immediately after intense training can also help fuel performance quickly and effectively replenishing muscle and liver glycogen reserves that have been depleted during exercise. Scientific studies have confirmed that the level of glycogen stores before you start exercise is the most important fuel for your performance. To achieve results consume a liquid carbohydrate drink immediately after training, after this you should aim to eat carbohydrates in small meals throughout the day. i.e.: beans, sweet potatoes, pasta, oats, rice, whole wheat or brown bread, apples, and oranges.
BUYER BEWARE! A WIDE VARIETY OF SO CALLED “SPORTS DRINKS” ON THE MARKET ARE LOADED WITH SUCROSE (THIS IS DUE TO ITS GOOD TASTE AND COMMERCIAL COST EFFECTIVENESS). THIS HAS BEEN SHOWN IN MANY STUDIES TO BE A POOR CARBOHYDRATE CHOICE FOR PERFORMANCE.