Carbohydrates are the sugars, starches and fibers found in all plant foods and some dairy foods. The body converts carbohydrates into glucose, which is used in the bloodstream for immediate energy. Extra carbohydrates are either converted into a form of storage energy called glycogen or are converted into body fat. Fiber differs from the other two types of carbohydrates because it is not digested or absorbed by the body and therefore does not provide energy.
Most carbohydrates are divided into two classes:
Simple carbohydrates. These carbohydrates, which are sometimes called simple sugars, are made of one or two sugars and often taste sweet and are found in milk products, fruit, candy, soda and other sweets. Simple carbohydrates provide few essential nutrients and are high in calories.
Complex carbohydrates. Starches and fibers that are made of more than two sugars. They are found in whole grain breads and cereals, legumes and starchy vegetables that also provide vitamins, minerals and fiber.
In addition to providing the body with energy, carbohydrates offer numerous health benefits, including assistance in absorption of calcium, regulation of sugar circulating in the blood and a source of nutrients for “good” bacteria in the gastrointestinal tract that aid digestion.
However, consuming too many of some types of carbohydrates presents some health dangers. The sugars in carbohydrates are a leading cause of tooth decay. Excessive calorie intake, regardless of food type, also contributes to weight gain.
Experts from the Institute of Medicine (IOM) recommend that adults consume 45 to 65 percent of their daily calories from carbohydrates, with no more than 25 percent of total calories from added sugars. People trying to choose healthy carbohydrates are encouraged to look for whole grain products. Whole grain products can be identified by reading the ingredient list on food labels.
The U.S. Food and Drug Administration (FDA) allows food manufacturers to claim health benefits for those products with at least 51 percent whole grains by weight and less than 3 grams of fat per serving. A diet rich in whole grains, fruits and vegetables may help to reduce the risk of heart disease and certain cancers.
About carbohydrates
Carbohydrates are the sugars, starches and fibers found in all plant foods, including fruits, vegetables, legumes, beans and whole grains. They are also found in some dairy foods, such as milk. The body converts carbohydrates into a simple sugar called glucose for immediate energy. Carbohydrates not needed for immediate energy are converted into a substance called glycogen and stored in the body for reserve energy.
Carbohydrates provide the main source of energy to the body and are broken down during digestion into glucose. After glucose is absorbed into the bloodstream, a hormone called insulin moves it into the cells, where it is converted to energy. Fibers are not broken down and digested by the body, but they do provide numerous health benefits such as improved gastrointestinal function.
Carbohydrates also are the source of glycogen. This substance is stored primarily in the liver and muscles and can be broken down into glucose when the body does not receive enough carbohydrates from outside food sources. For example, glycogen stores may be called upon to provide energy during bursts of extra activity. The body can store about 400 grams of glycogen at any one time. When carbohydrate intake produces more glucose than the body can use and store, the excess glucose is turned into body fat.
The body gains energy by breaking down three major classes of foods. These groups, known as macronutrients, include fats, proteins and carbohydrates. All carbohydrates are made up of sugar molecules composed of various combinations of chains of carbon, hydrogen and oxygen molecules.
When a person consumes carbohydrates, the process of breaking down these substances begins in the mouth, with the help of amylase, an enzyme in saliva. The process continues in the stomach and then into the small intestine, where foods are broken down into simple sugars. nutrients are then absorbed and then moved by blood to the liver. In the liver, the substance undergoes the final conversion to glucose, which is then carried into the cells with the help of insulin (hormone secreted by the pancreas) to fuel body activities. Such activities include autonomic functions such as breathing, digestion and heartbeat, and forms of exertion such as running and lifting. In addition, glucose is the main fuel source for the brain.
To meet the body’s daily nutritional needs while minimizing risk for chronic diseases such as heart disease, the Institute of Medicine (IOM) dietary reference intakes report on macronutrients recommends that adults consume 45 to 65 percent of their daily calories from carbohydrates.
In addition, they recommend that no more than 25 percent of total daily calories should come from added sugars (those sugars added to foods during processing and manufacturing). This does not include those naturally occurring sugars, such as fructose in fruits or lactose in milk. Added sugars are often found in baked goods, desserts, sodas or candies. Most importantly, the IOM recommends that carbohydrate intake should come mainly from complex carbohydrates, which are also good sources of vitamins, minerals, phytochemicals and fiber. To meet these guidelines most Americans need to increase complex carbohydrate intake and lower fat intake.
Types and differences of carbohydrates
Most carbohydrates are divided into two classes: Simple carbohydrates and complex carbohydrates.
Simple carbohydrates are digested quickly and often taste sweet. They are found in milk products, fruit, candy, soda table sugar, honey and other sweets. Fruit and milk products are important sources of valuable nutrients, vitamins and minerals. Candy, soda and sweets provide few or no nutrients. Although these carbohydrates help provide fuel for energy, they are empty calories, with little or no nutritional value. An excess intake of calories can lead to undesired weight gain.
Simple carbohydrates are made up of either a single unit (monosaccharide) or two units (disaccharide) of sugar. There are three different types of monosaccharides:
Glucose. The most common form of sugar found in the bloodstream. In foods, it has a mildly sweet flavor.
Fructose. The sweetest of the sugars, it occurs naturally in fruits and honey. It is also found in high-fructose corn syrup (in soft drinks) and is a major source of sugar in the diet of Americans.
Galactose. Found in gums, sugar beets and the lactose of dairy products. It has very little sweet taste.
When two of these monosaccharides join together, they become disaccharides. The following are the three disaccharides found in foods:
Sucrose (glucose + fructose). Naturally occurs in sugar cane, sugar beets, honey and many fruits and vegetables. It is refined to make table sugar.
Lactose (glucose + galactose). Naturally occurs in milk and dairy products.
Maltose (glucose + glucose). Also known as malt sugar, it is the least common disaccharide in nature. It naturally occurs in barley.
All carbohydrates are chemical chains of hydrogen, oxygen and carbon. Complex carbohydrates also contain fibers that have large molecules not sensed by the sweet taste receptors on taste buds. They are found in whole grain breads and cereals, legumes and starchy vegetables that provide nutrition in the form of vitamins, minerals and fiber. Fiber in complex carbohydrates such as oatmeal protects starchy carbohydrates from digestive enzymes. This slowed absorption rate allows for improved digestive system function. Fiber can also help control blood cholesterol levels.
Complex carbohydrates are composed of at least three glucose units. In some cases, they may be composed of many monosaccharides strung together in compounds known as polysaccharides. The three polysaccharides that are crucial for nutrition are:
Glycogen. Storage form of energy in the body made up of glucose units. Limited amounts are found in meat, but it is not found at all in plants. Glycogen is known primarily as the stored form of glucose and is not a significant food source of carbohydrates. The primary storage sites for glycogen in the human body are the liver and the muscles.
Starches. Storage form of energy in plants made up of glucose units. Grains are the richest source of starch and provide the foundation of food energy for much of the world’s population. Starches are found in grains such as wheat and rice, root crops and tubers such as yams and potatoes, and legumes such as beans and peas.
Dietary fiber. Provide structure in stems, trunks, roots, leaves and skins of plants. They are made up of a variety of monosaccharides and other carbohydrate derivatives. Fibers are found in all plant-derived foods, including fruits, grains, legumes and vegetables.
Dietary fiber differs from starches because the bonds that hold together the sugar units in fiber cannot be broken down by digestive enzymes. Although some of the bacteria that live naturally in intestines can convert small amounts of the fiber into fatty acids, dietary fiber generally is not considered a source of energy.
Each type of carbohydrate contains four calories per gram. Gram for gram, simple and complex carbohydrates eventually add the same amount of glucose to the bloodstream. However, complex carbohydrates are broken down into glucose more slowly than simple carbohydrates. Complex carbohydrates provide important sources of essential nutrients for a healthy diet.
Some carbohydrates are considered to be neither simple nor complex. The starches and grains that are in the typical American diet are mostly highly refined grains, also called refined carbohydrates. This means that the fiber-rich outer layer or bran of the grain and the nutrient-rich inner part (also called the germ) are removed during the milling process, leaving only the endosperm, or middle part of the grain.
In contrast to refined grains, foods made with whole grains are digested and absorbed into the blood stream gradually, minimizing a quick rise in blood sugar. The protein, fat and fiber content of whole grain foods provide increased satiety (feeling full) and decrease feelings of hunger. Therefore, experts recommend eating a variety of whole grain foods instead of refined grains and simple sugars as part of a heart healthy diet.
For more about whole grains and refined grains, see Grains.
Health impact of carbohydrates
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.
Good sources of carbohydrates
Carbohydrates are an essential part of the human diet. They provide most of the energy for the body, as well as many vitamins and nutrients. They are found in abundance in many plant foods such as rice, pasta, beans, potatoes and many other grain products and vegetables.
When selecting grain products, people are urged to select whole grain foods such as whole-wheat bread, brown rice, whole-grain pasta, quinoa, whole oats and bulgur.
Many processed foods, such as ketchup, salad dressings, canned chili and frozen dinners
Certain foods contain few or no carbohydrates. They include proteins and fats such as:
Meat, poultry and fish
Eggs
Butter
Oils
Nuts such as almonds, seeds such as sunflower seeds and nut-like foods such as cashews and peanuts provide fats, carbohydrates and proteins in varying amounts.
Tips for choosing the right carbohydrates
People trying to choose healthy carbohydrates are encouraged to look for whole grain products. Whole grain products can be identified by reading the ingredient list on food labels. These ingredients are listed in descending order by weight. Even if a product claims that it is made with whole wheat, check the ingredient’s list to see where it appears on the list. If more than one grain product is listed, there is more of the first listed ingredient in the final product. Choose foods listing whole grain or whole wheat as the main ingredient, instead of products that are made with wheat flour, white flour or unbleached wheat flour.
Nutrition facts labels provide the amount of total carbohydrate, dietary fiber and sugars in one serving of a food product. Also, nutrient content claims provide additional information about the packaged product. It is important to become familiar with these nutrient content claims and what they mean. For example, foods that are labeled “sugar-free” may contain less than 0.5 grams of sugar per serving and are not necessarily sugar- or calorie-free. Products labeled as “reduced sugar” or “less sugar” must contain at least 25 percent less sugar per serving compared to a standard serving of the traditional food.
FDA health claims for carbohydrates
The U.S. Food and Drug Administration (FDA) allows food manufacturers to claim health benefits for products containing at least 51 percent whole grains by weight and less than three grams of fat per serving. The statement may say, “Diets rich in whole-grain foods and other plant foods and low in total fat, saturated fat and cholesterol may help to reduce the risk of heart disease and certain cancers.”
Questions for your doctor about carbohydrates
Preparing questions in advance can help patients have more meaningful discussions with health professionals regarding their conditions. Patients may wish to ask their doctor or registered dietitian the following questions about carbohydrates:
How can I tell if I have enough carbohydrates in my diet?
Where can I find help planning a diet that includes healthy carbohydrates?
Should I try to eat more complex carbohydrates rather than simple carbohydrates?
Which local stores sell whole-grain pastas, tortillas, etc.?
What are some cooking tips for increasing levels of healthy carbohydrates in meals?
How can I be sure that the wheat I’m purchasing is “whole grain” wheat?
What else should I look for on ingredients labels that can help me find healthy carbs?
What are the dangers of a diet low in carbohydrates?
