Diet and Nutrition- Information regarding carbohydrates and their importance in your diet
Carbohydrates are compounds containing carbon, hydrogen and oxygen and are generally classified as sugars (simple), starches (complex) and fiber. The definition of sugar, as it would appear on a food label, is any mono- or disaccharide. A monosaccharide is a single sugar unit, many of which are connected to make starches (storage form of carbohydrates in plants) and glycogen (storage form of carbohydrates in humans). Monosaccharides include glucose (commonly referred to as blood sugar), fructose (fruit sugar) and galactose. Disaccharides (two sugar units) include sucrose (common sugar), lactose (milk sugar) and maltose. Carbohydrates are a chief source of energy for all body functions and muscular exertion. This leads to a rapid depletion of available and stored carbohydrates and creates a continual craving for this macronutrient. Carbohydrates also help to regulate the digestion and utilization of protein and fat.
Digestion, Absorption and Utilization
The principal carbohydrates present in food occur in the form of simple sugars, starches and cellulose. Simple sugars, such as those in honey and fruits, are very easily digested. Double sugars, such as table sugar, require some digestive action but are not nearly as complex as starches, such as those found in whole grain. Starches require prolonged enzymatic action in order to be broken down into simple sugars (i.e., glucose) for utilization. Cellulose, commonly found in the skins of fruits and vegetables, is largely indigestible by humans and contributes little energy value to the diet. It does, however, provide the bulk necessary for intestinal motility and aids elimination. The rate at which ingested carbohydrate raises blood sugar and its accompanying effect on insulin release is referred to as the glycemic index (GI). The GI for a food is determined when the particular food is consumed by itself and on an empty stomach. Mixed meals of protein, other carbohydrate and fat can alter the glycemic effect of single foods. Some fad diets place too much emphasis on the GI, stating that foods with a higher GI lead to fat storage, regardless of caloric intake. This leads to categorizing foods as “good” or “bad” based solely on their GI value. As stated earlier, weight gain or loss is related to total energy intake, not the source of the food eaten. However, foods lower on the glycemic index are good sources of complex carbohydrate as well as being high in fiber and overall nutritional value.
Fiber and Its Role in Health
One of the greatest contributions made by dietary complex carbohydrate is fiber. Higher intakes of dietary fiber are associated with lower incidence of heart disease and certain types of cancer.
Additional benefits of fiber in your diet include:
- Provides bulk in the diet, thus increasing the satiety value of foods.
- Some fibers also delay the emptying of the stomach, further increasing satiety.
- Prevents constipation and establishes regular bowel movements.
- Maintains good intestinal motility.
- Aids in the prevention of bacterial infections of the appendix (appendicitis).
- Helps to lower the risk of colon cancer.
- Helps to retain the health and tone of the digestive-tract muscles, therefore preventing diverticulosis, which causes the weakening of intestinal walls, then causing them to swell and distend.
- May reduce the risks of heart and artery disease by lowering blood cholesterol.
- Certain soluble fibers bind with cholesterol compounds and are excreted from the body in the feces, thereby lowering the body’s cholesterol content.
- Additionally, the substances produced by the bacteria’s digestion of soluble fiber may help inhibit the production of cholesterol and eliminate cholesterol from the blood.
- Regulates the body’s absorption of glucose (diabetics included) perhaps because fiber is believed to be capable of controlling the rate of digestion and assimilation of carbohydrates.
- High-fiber meals have been shown to exert regulatory effects on blood glucose levels for up to five hours after eating.
Pre-exercise
It is recommended that the diet of an athlete consist of a high-carbohydrate meal two to three hours prior to exercising for more than an hour. This will allow time for appropriate gastric emptying before exercise. This is especially helpful for morning workouts when glycogen stores are lowered by as much as 80 percent. If this is not feasible due to time constraints, a liquid meal such as a meal-replacement formula (MRF) may be used. One advantage to such formulas is their quick gastric emptying time. Some research suggests a carbohydrate intake of 1-4.5g/kg, between one and four hours prior to exercise respectively. In this study, the group whose diet included 4.5g/kg of carbohydrate four hours prior to exercise saw performance improved by 15 percent. To avoid gastrointestinal distress, smaller meals should be consumed closer to the exercise session.
During Exercise
For exercise lasting more than one hour, carbohydrate feedings during exercise can help supply glucose to working muscles whose glycogen stores are dwindling. This technique also maintains blood-glucose levels, increasing time to exhaustion by 20-60 minutes. It is recommended that endurance athletes consume between 30 and 60 grams of carbohydrate every hour to accomplish this. Popular sports beverages (such as Gatorade, Powerade and All- Sport) are perfect for this goal and have the added benefit of replacing fluid losses, also benefiting performance. The replacement of carbohydrate and water has individual benefits that together are additive.
One study showed that performance during one hour of intense cycling was improved by 12 percent with the consumption of 1330 ml (~53 oz.) of water containing 79g of carbohydrates. The National Academy of Sports Medicine (NASM) concurs that following the American College of Sports Medicine guidelines of consuming 600-1200 ml (20-40 oz.) of fluid per hour containing between four and eight percent carbohydrate will contribute to better performance for the endurance athlete.
After Exercise
Repeated days of strenuous exercise take their toll on the athlete’s glycogen stores. A high carbohydrate diet helps to replenish glycogen stores; however, the timing of carbohydrate ingestion can also be important to maximizing recovery. Consuming 1.5 g/kg/wt of carbohydrate within 30 minutes of completing exercise is recommended to maximize glycogen replenishment. Delaying carbohydrate intake by even two hours can decrease total muscle glycogen synthesis by 66 percent. The post-workout environment may hasten glycogen repletion due to increased blood flow to the muscles and an increased sensitivity of the cells to the effects of insulin. Additional meals of 1.5 g/kg of carbohydrate every two hours are recommended to completely restore muscle glycogen.
For Altering Body Composition
Carbohydrates should generally make up the highest percentage of macronutrient calories in a diet when one is attempting fat loss or muscle gain. Carbohydrates provide variety, valuable nutrients and volume to the diet. The satiating value of complex carbohydrate is especially important when one is in a caloric deficit for the goal of fat loss. For most moderately active adults, a diet with a carbohydrate intake of between 50 and 60 percent is recommended. This will provide sufficient food volume and the fuel necessary for energy and productive workouts. Despite the popularity of low-carbohydrate diets and the perpetuation of erroneous claims regarding type or time of carbohydrate intake, there is no need for one to reduce carbohydrate percentage to lose fat (see Carbohydrate and Weight Gain section). Weight loss or gain is related to total caloric intake, not the macronutrient profile of the diet. The weight lost on a low-carbohydrate diet can be attributed to two factors: low caloric intake and loss of fat-free mass (FFM). When one begins dropping carbohydrate-rich foods from their diet, it is inevitable that caloric intake is reduced. Added to the caloric reduction are dwindling glycogen stores. For every gram of glucose taken out of glycogen, it brings with it 2.7 g of water. This loss of muscle glycogen (including water) can be quite significant in the first week of a low-carbohydrate diet, and adds to the pounds lost on the scale. This is how low carbohydrate fad diets can promise dramatic weight loss in such a short period of time. Long term success in weight loss is associated with a realistic eating style, not one that severely limits or omits one of the macronutrients.
QUICK REFERENCE
- Each gram of carbohydrate yields four calories.
- Good complex carbohydrates bring in nutrition that fat and protein cannot.
- Carbohydrates are the perfect and preferred form of energy.
- Carbohydrates constantly need to be replaced, causing a craving that must be satisfied.
- Carbohydrates maintain satiety by keeping glycogen stores full and adding bulk to the diet.
- Parts of the central nervous system rely exclusively on carbohydrate.
- Carbohydrates help maintain proper cellular fluid balance, maximizing cellular efficiency.
- Carbohydrates are needed in order to efficiently burn and utilize fat and protein.
- Consistent intake of low-glycemic carbohydrates helps maintain proper blood-sugar levels.
- Carbohydrates spare protein for building muscle.
- Daily diet should include 25 grams of fiber.
- Carbohydrate intake typically should be between 50 and 70 percent of total caloric intake according to preference, performance and satiety.
- Fruits, whole grains and vegetables are all excellent sources of fiber.
- Carbohydrate recommendations would be estimated after protein and fat requirements are met.