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Food for Life - Carbohydrates for Energy

[Do Not Use]DK Publishing logo[Do Not Use]DK Publishing 2/07/2014 DKBooks
Photo: Soba noodles - Quick to prepare and made from buckwheat, soba noodles are high in fiber and very versatile. © Provided by DKBooks Soba noodles - Quick to prepare and made from buckwheat, soba noodles are high in fiber and very versatile.

Soba noodles - Quick to prepare and made from buckwheat, soba noodles are high in fiber and very versatile.

Carbohydrates for Energy

Carbohydrates form the foundation of a healthy diet, providing a readily available source of energy.

Carbohydrates are compounds composed of carbon, hydrogen, and oxygen and are generally classified as simple or complex, depending on their structure. Carbohydrates are obtained from grains, bread, and pasta, as well as from fruits, vegetables, legumes, and dairy products.

Variable complexity

All carbohydrates are composed of chains of sugar molecules. Those composed of just one or two sugar molecules are known as simple carbohydrates, and are divided into monosaccharides and disaccharides. Monosaccharides include glucose, which is present in the blood; fructose, which is found in fruits; and galactose, which is found in dairy products. Disaccharides include sucrose (table sugar) and lactose (the primary sugar present in milk).

Complex carbohydrates, also called polysaccharides, are composed of many simple-sugar molecules that are linked together. Examples of complex carbohydrates include starch, which gives potatoes and grains their hearty character; glycogen, which the body stores as a source of energy; and dietary fiber.

Why do we need them?

Carbohydrates provide energy for all the body’s activities. As they are digested, carbohydrates are broken down into simple sugars, such as glucose. Glucose supplies energy for most of the body’s activities and, in some cells and tissues such as red blood cells and the brain, it is the sole source of energy.

Carbohydrates are needed for building the nonessential amino acids that the body uses to create proteins . They also help in the processing of fat and in the building of cartilage, bone, and tissues of the nervous system.

Choosing carbohydrates

As the major source of energy, carbohydrates must form a large part of your diet, but you should choose the best types to optimize your health. This means eating a wide variety of different types of grains, fruits, and vegetables. As far as possible, try to eat whole grains and products made from unrefined grains in preference to refined varieties. In this way, you will benefit from the nutrients and fiber that are removed during the refining process .

Some researchers believe that the glycemic index (GI) provides a useful guide to the best carbohydrates, and that low-GI foods, which release sugar more slowly into the blood, are of particular benefit to people with diabetes and insulin resistance. However, we believe that while the concept of the glycemic index is interesting, it should not be relied on as the sole indicator of a carbohydrate’s healthfulness. Nutritional content and fiber are also important and these should be borne in mind when choosing carbohydrates.

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Insulin resistance

A reduced sensitivity in the tissues of the body to the action of the hormone insulin. As a result of this sensitivity, blood glucose does not enter those tissues to be used as a source of energy, so blood glucose levels remain abnormally high. The condition is found frequently in overweight and obese people.

Understanding the glycemic index

The glycemic index (GI) classifies foods according to how fast they release sugar (glucose) into the bloodstream. High-GI foods release glucose quickly, causing a rapid rise in blood-glucose levels, to which the body reacts with insulin, which turns on fat storage. Low-GI foods, in contrast, release glucose steadily over several hours, so less insulin is required. Diets based on low-GI foods are therefore recommended for those with diabetes and insulin resistance, as well as for people with cardiovascular disease and certain digestive disorders.

GI value

This figure depends on various factors, including the type of carbohydrate the food contains, how it has been processed, and the presence of fat and dietary fiber. In general, low-GI foods contain more fiber, are less processed, and do not contain as much glucose as high-GI foods. However, there is not a simple correlation between complex carbohydrates and low-GI values. For example, whole-grain oat cereal is a healthy carbohydrate, but it has a high-GI value, whereas fructose—the type of sugar found in fruits and frequently added to soft drinks in the form of corn syrup—has a low-GI value. However, this does not mean that products sweetened with corn syrup are healthy.

Glycemic loading

This is a concept that has been developed to deal with anomalies thrown up by the glycemic index, which cast doubt on its usefulness as a nutritional tool. For example, a well-known brand of chocolate fudge cake has a relatively low GI of 41, while a 100 percent whole-grain loaf has a GI of 62—though common sense tells us that the latter is healthier. To deal with such paradoxes, glycemic load is calculated by multiplying the GI value of a food by the amount of carbohydrate in one serving. This gives a figure that reflects both the time the food takes to be broken down into glucose and its carbohydrate content.


Our view is that while glycemic loading is a better indicator of glycemic response than glycemic index alone, this is still only part of the story. Other aspects of the nutritional value of foods must also be considered, including vitamin and mineral content, phytochemicals, fiber, and protein. In terms of health benefits, the evidence is clear that eating refined grain products increases the risk of a variety of diseases, while eating whole grains has beneficial health effects.

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