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Carbohydrates provide the main source of energy to the body and supplies four calories per gram. Fat provides more than twice as many calories (nine calories per gram) as carbohydrates, and protein and carbohydrates supply about an equal amount. However, carbohydrates are the body’s preferred source of energy, especially for fueling the brain. This is because carbohydrates are more easily digested and absorbed by the body for use as a source of energy. While fats and proteins can also be broken down and converted into energy, it is more efficient for the body to use carbohydrates.

Carbohydrates also protect the muscles by providing the body with a constant source of energy. If there is poor carbohydrate intake, the body will start to break down protein in muscle tissues to make the glucose it needs. People need to consume adequate levels of carbohydrates to prevent this. In addition, a lack of carbohydrate intake can cause the body to force fat to take an alternative metabolic pathway in which fat fragments combine to form ketone bodies. This can lead to a condition called ketosis that disrupts the body’s acid-base balance.

Fiber found in carbohydrates also produces numerous health benefits. Fiber contributes toward good digestive health, lowers cholesterol levels, and appears to play an important role in the prevention or management of chronic diseases.

Other benefits of carbohydrates include:

• Assistance in absorption of calcium
• Regulation of sugar circulating in the blood
• Source of nutrients for “good” bacteria in the gastrointestinal tract that aid digestion

Carbohydrates also can have negative effects in the body. Carbohydrates and sugars are the leading cause of tooth decay. The longer food remains on teeth, the more time bacteria in plaque have to produce acids that damage tooth enamel and promote tooth decay. Therefore, it is important to brush and floss after each meal, especially after eating carbohydrate-rich meals.

One recent study published in the American Journal of Clinical Nutrition found a link between eating diets ranking high in glycemic-index content and early age-related macular degeneration. In contrast, women who consumed foods with a lower glycemic index did not show signs of early macular degeneration.

Experts agree that excess calorie intake – regardless of whether the source is carbohydrate, fat or protein – will lead to weight gain. In addition, to promote weight loss, overweight people need to limit their calorie intake to be successful. Health guidelines recommend increasing regular physical activity and reducing the intake of extra calories from fats and sugars to prevent or reduce obesity.

There are many books recommending every extreme of carbohydrate intake for weight management or for peak performance. Some of the advocates of low-carbohydrate diets mislead consumers into thinking that a carbohydrate-rich diet causes insulin resistance or promotes weight gain. Carbohydrates do not promote or cause insulin resistance.  In addition, low carb diets are typically lacking in sufficient nutrients. Excess calories – whether from fat, protein or carbohydrates – can cause weight gain.

In recent years, many people have touted low-carb diets as a way to lose weight. One recent study published in the Journal of the American Medical Association found that premenopausal women who consumed diets very low in carbohydrates lost more weight over a one-year period than women who consumed diets higher in carbohydrates.

However, there is no conclusive evidence that low-carb diets cause greater weight loss. In fact, one recent Australian study found that diets high in carbohydrates that nonetheless rank low on the glycemic index (which measures how rapidly certain foods are converted to blood sugar) promote weight loss while also reducing both body fat stores and cardiovascular disease risk.

For now, the debate continues over whether low-carbohydrate or high-carbohydrate diets are more likely to cause weight loss.

Some experts have suggested that low-carb diets may pose certain health dangers. For example, many experts contend that low-carb diets increase the risk of heart disease because low-carb diets tend to encourage higher intake of animal products rich in unhealthy saturated fats and cholesterol.

While the debate over the heart risks of low-carb diets continues, a recent study by the Harvard School of Public Health found no significant link between eating a low-carb diet and increased risk of heart disease in women, even when these diets were high in saturated animal fats. In addition, the researchers reported evidence that a low-carb diet rich in vegetable sources of fat and protein may lower the risk of heart disease.