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Carbohydrates

 

There is probably no greater debate today than the one over the role of carbohydrates in our diets. Low-carb diets such as the Atkins diet have captured the public's attention to an extent that few other weight-loss plans have. As a result, more and more people have come to believe that carbohydrates are inherently bad. But that's not entirely the case. Starches and sugars are our major source of energy. Fiber, another form of carbohydrate, also has significant health benefits.

 

Almost all of the starches and sugars that humans burn for energy come from plants; the only major exception is lactose, the sugar in milk. In effect, each plant is a complex food factory that takes water from the soil, carbon dioxide from the air, and energy from the sun to make glucose, a simple sugar that is later converted into starch. As the plant develops and grows, it also makes various vitamins, minerals, and other phytochemicals, as well as some fat and protein. Consequently, we can get our carbohydrates and most of the other nutrients needed to sustain us from the thousands of different grains, seeds, fruits, and vegetables that can be grown.

 

Carbohydrates are classified according to their chemical structure and digestibility; they are divided into two groups: simple and complex. Simple carbohydrates, or sugars, can generally form crystals that dissolve in water and are easily digested. Naturally occurring sugars are found in a variety of fruits, some vegetables, and honey. Processed sugars include table sugar, brown sugar, and molasses.

 

Complex carbohydrates have a range of textures, flavors, colors, and molecular structures. Composed of complex chains of sugars, these carbohydrates are further classified as starches or fiber. Our digestive system can break down and metabolize most starches, which are found in an array of grains, vegetables, and some fruits. Our digestive system, however, lacks the enzymes that are needed to break down most fiber, including cellulose and other woody parts of the plant skeleton, and pectin and other gums that hold plant cells together. But dietary fiber is still important because it promotes smooth colon function and may help prevent some types of cancer, heart attacks, and other diseases.

 

Energy food

Our body metabolizes simple carbohydrates and starches into glucose, or blood sugar, the body's primary source of fuel. Carbohydrates are high-quality fuels because compared to proteins or fats little is required of the body to break them down in order to release their energy.

 

Glucose, the only form of carbohydrate that the body can use immediately, is essential for the functioning of the brain, nervous system, muscles, and various organs. At any given time, the blood can carry about an hour's supply of glucose. Any glucose that is not needed for immediate energy is converted into glycogen, a large molecule composed of a chain of glucose units, which is store in the liver and muscles; when necessary, the liver turns the glycogen back into glucose. the body can store enough glycogen to last for several hours o moderate activity.

 

Glycemic index (GI) researchers are learning that the rate at which carbohydrate-rich foods are digested and absorbed into the bloodstream also affects health. The rate at which a food causes blood sugar to rise can be measured and assigned a numerical value. This measure is referred to as the food's glycemic index. Foods with a low GI such as pumpernickel bread, rye bread, brown rice, bulgur, oatmeal, lentils, yams, apples, pears, and yogurt take longer to digest and cause a slower, more gradual rise in blood sugar. This means that energy is released more slowly, leading to more consistent energy levels. Low-GI foods are better for blood sugar control in diabetics and may help with weight loss. The carbohydrates in high-GI foods such as white bread, white rice, mashed potato, corn flakes, and watermelon are more quickly absorbed and so provide a quicker source of energy. for active people high-GI foods can be a source of quick energy to aid short-duration sports performance and recovery, while lower-GI foods are better for endurance.

 

When glucose reserves run low, the body turns first to protein and then to fat for conversion into glucose. Burning protein, however, robs the body of lean muscle tissue. In addition, if the body has to burn fat in the absence of carbohydrates, toxic by-products called ketones are released; these can lead to a potentially dangerous biochemical imbalance.

 

Complex carbohydrates

The human diet worldwide is based on complex carbohydrates. Populations that eat a higher-carbohydrate, low-fat diet generally enjoy good health. Vegetarian, Mediterranean, and Asian diets typically provide a high percentage of calories from complex carbohydrates in foods such as whole grains, lentils, beans, fruits, and vegetables. In North America, too much of the carbohydrate intake is in the form of simple sugars due to the high consumption of refined and processed foods. Another factor has been the proliferation of low-fat foods. Consumers often assume that these are also low-calorie foods. In many cases, fats have been replaced by carbohydrates with no great saving in calories. The many low-fat, high-carbohydrate foods available, including low-fat cookies, cakes, muffins, baked chips, and oversized bagels are all adding to expanding waistlines.

 

How much do you need ?

In 2002, a joint American-Canadian expert report provided a set of reference values for nutrient intakes for healthy Americans and Canadians. It suggests that adults get 45 to 65 percent of their caloric intake from carbohydrates. This translates to roughly 225 to 325 g of carbohydrates each day for a 2,000-calorie diet. Both children and adults should consume at least 130 g of carbohydrates a day. This is based on the minimum amount needed to produce enough glucose for the brain to function.. This amount is easily exceeded in the average North American diet. The problem is that the excess usually comes from refined carbohydrates.

 

Although refined carbohydrates, such as white flour and white rice, are just as good energy sources as whole-wheat flour and brown rice, processing removes many essential nutrients, including the B vitamins, iron, and other minerals, as well as dietary fiber. The best approach is to build a diet around whole or lightly processed grains, legumes, beans, and raw or slightly cooked vegetables and fruits.

 

Carb loading

Nutrition can have a significant impact on athletic performance and vice versa. Regular exercise increases the body's ability to utilize glucose efficiently and to store glycogen in muscle tissue. Thus, the fitter you are, the greater your ability to store the extra glycogen that is needed for endurance events, such as running a marathon or cross-country skiing. that's why carbohydrates are the preferred fuel for most sports.

 

Special concerns

Carbohydrates can be worked into almost any diet, but certain diseases may need adjustments. Diabetics must manage the total amount and type of carbs eaten at each meal and snack. Contrary to popular belief, sugar does not cause diabetes, nor do diabetics have to completely avoid sugar.

 

Those with heart disease need to emphasize high-fiber complex carbohydrates in their diet. Soluble fiber, found in oat bran and fruit pectin, helps lower cholesterol and plays an important role in preventing atherosclerosis, the buildup of fatty deposits in coronary arteries and other blood vessels.

 

Cancer patients are often advised to increase their carbohydrate intake and decrease fat intake, especially if they have cancers of the breast, colon, uterus, prostate, or skin. Evidence suggests certain fats may encourage tumor growth.

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