Carbohydrates, or carbs, are the sugars, starches, and dietary fiber that occur in certain foods. The body breaks them down into glucose, which provides energy.

Carbohydrates are mainly found in plant foods. They also occur in dairy products in the form of a milk sugar called lactose. Foods high in carbohydrates include bread, pasta, beans, potatoes, rice, and cereals.

Carbohydrates play several roles in living organisms, including providing energy.

Byproducts of carbohydrates are involved in the immune system, the development of disease, blood clotting, and reproduction.

This article looks at types of carbohydrates, nutrition, and their effects on health. We also look at the relationship between carbohydrates and diabetes.

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Carbohydrates, also known as saccharides or carbs, provide energy for the body. Each gram of carbohydrates provides 4 calories.

The body breaks carbohydrates down into glucose, which is the primary energy source for the brain and muscles.

Carbohydrates are one of three macronutrients, which are nutrients that the body needs in larger amounts.

The other macronutrients are protein and fats. Proteins provide 4 calories per gram, and fats provide 9 calories per gram.

It’s generally recommended that people consume between 45-65% of their total calories in the form of carbohydrates per day. However, carbohydrate needs depend on many factors, including body size, activity levels, and blood sugar control.

The Food and Drug Administration (FDA) recommend that people get 275 g of carbohydrate each day in a 2,000-calorie diet. This includes dietary fiber, total sugars, and added sugars, which are listed on food labels.

Carbohydrates in foods occur in various forms, including the following:

  • Dietary fiber, a type of carbohydrate that the body cannot easily digest. It occurs naturally in fruits, vegetables, nuts, seeds, beans, and whole grains.
  • Total sugars, which include sugars that occur naturally in foods, such as dairy products, as well as added sugars, which are common in baked goods, sweets, and desserts. The body very easily digests and absorbs sugars.
  • Sugar alcohols, a type of carbohydrate that the body does not fully absorb. They have a sweet taste and fewer calories than sugar. Sugar alcohols are added to foods as reduced-calorie sweeteners, such as in chewing gum, baked goods, and sweets.

Dietary fiber helps promote regular bowel movements, lowers blood sugar and cholesterol, and may help reduce a person’s calorie intake. The FDA recommend that people get 28 grams (g) of dietary fiber per day in a 2,000-calorie diet.

Most people in the United States exceed the recommended daily limits for added sugar. This can increase a person’s risk of developing cardiovascular disease and dental cavities.

The Dietary Guidelines for Americans 2015–2020 recommend that people get less than 10% of their total daily calories from added sugars, which means less than 50 g of added sugars each day.

However, limiting added sugar as much as possible is best for overall health. The American Heart Association recommend that women limit added sugar to less than 6 teaspoons (25 g) per day and men limit their intake to less than 9 teaspoons (36 g) per day.

The chemical structures of carbohydrates contain carbon, hydrogen, and oxygen atoms. Two basic compounds make up carbohydrates: Aldehydes, which are double-bonded carbon and oxygen atoms, plus a hydrogen atom, and ketones, which are double-bonded carbon and oxygen atoms, plus two additional carbon atoms.

Carbohydrates can combine to form polymers, or chains, to create different types of carbohydrates. Carbohydrate can be monosaccharides, disaccharides, or polysaccharides.


Monosaccharides are single units of sugar. Examples include:

  • glucose, the body’s main source of energy
  • galactose, which is most readily available in milk and dairy products
  • fructose, which mostly occurs in fruits and vegetables


Disaccharides are two sugar molecules joined together. Examples include:

  • lactose, found in milk, which is made up of glucose and galactose
  • sucrose, or table sugar, which is made up of glucose and fructose


Polysaccharides are chains of many sugars. They can consist of hundreds or thousands of monosaccharides. Polysaccharides act as food stores for plants and animals. Examples include:

  • glycogen, which stores energy in the liver and muscles
  • starches, which are abundant in potatoes, rice, and wheat
  • cellulose, one of the main structural components of plants

Monosaccharides and disaccharides are simple carbohydrates, and polysaccharides are complex carbohydrates.

Simple carbohydrates are sugars. They consist of just one or two molecules. They provide a rapid source of energy, but the person soon feels hungry again. Examples include white bread, sugars, and candies.

Complex carbohydrates consist of long chains of sugar molecules. This includes whole grains and foods that contain fiber. Examples include fruits, vegetables, beans, and whole grain pasta.

Complex carbohydrates make a person feel full for longer and have more health benefits than simple carbohydrates, as they contain more vitamins, minerals, and fiber.

In a typical diet, carbohydrates are the main energy source for the body. The body uses them as fuel for the cells.

Many people have turned to low carb diets, such as the keto diet, for their potential health benefits and weight loss. However, some types of carbohydrates – including whole grains and dietary fiber – have substantial health benefits.

In fact, according to the Physicians Committee for Responsible Medicine, those who eat the most carbohydrates – especially from natural sources such as beans, whole grains, and vegetables — have a lower risk for obesity, type 2 diabetes, and heart disease.

Other types of carbohydrates, including simple carbohydrates such as white bread, have much lower nutritional value.

Added sugars are a type of carbohydrate that can have adverse health effects. Eating large amounts of foods that contain added sugars can contribute to obesity, type 2 diabetes, and cardiovascular disease.

When making dietary changes, it is important to aim for a healthful diet that contains the range of nutrients that the body needs.

Carbohydrates and obesity

Some argue that the global rise in obesity is linked to a high intake of carbs. However, a number of factors contribute to rising obesity rates, including:

  • lower physical activity levels
  • greater availability of ultraprocessed food or “junk food”
  • a lack of access to affordable fresh produce
  • oversized portions, which increase a person’s calorie intake
  • fewer hours of sleep
  • genetic factors
  • stress and emotional factors

What about diet foods?

Many manufacturers promote low carb diets to sell weight loss products, including nutritional bars and powders.

These products are not often healthful as many contain colorings, artificial sweeteners, emulsifiers, and other additives and are typically low in vitamins, minerals, and antioxidants, making them similar to junk food.

After a meal, the body breaks carbohydrates down into glucose, causing blood sugar levels to increase. This causes the pancreas to produce insulin, a hormone that allows the body’s cells to use this sugar for energy or storage.

Over time, repeated spikes in blood sugar levels can damage the cells that make insulin, wearing them out. Eventually, the body may stop producing insulin, or may not be able to use it properly. This is known as insulin resistance.

Eating carbohydrates or sugars alone does not cause diabetes. Carbohydrates are an important source of nutrients in most diets.

However, people are more likely to have insulin resistance and develop type 2 diabetes if they have overweight or obesity, which can be linked with a diet high in sugar.

Insulin resistance increases the risk of developing metabolic syndrome, which refers to a group of risk factors that raise the risk of heart disease, stroke, and other medical conditions.

If a person has elevated blood sugar levels, reducing their intake of added sugar and refined carbohydrates can help reduce their blood sugar levels, improve insulin resistance, and may help promote healthy weight loss if needed.

Reducing the risk

People can reduce their risk of insulin resistance by eating healthful carbohydrates, maintaining good sleeping habits, and exercising regularly.

Healthful carbohydrates include fruit, vegetables, legumes, whole grains, and some cereals. These foods contain essential vitamins, minerals, fiber, and key phytonutrients.

The Mediterranean diet has a moderate amount of carbohydrates from natural sources plus some animal or fish protein.

This diet has a lower impact on insulin requirements and subsequent health problems, compared with the standard American diet.

The glycemic index (GI) ranks how quickly a food raises blood sugar levels on a scale of 0 to 100.

Foods with a high GI cause rapid spikes in blood sugar. Foods with a low GI take longer for the body to digest, leading to more balanced blood sugar levels.

Eating lots of foods with a high GI may increase a person’s risk for type 2 diabetes and other health concerns, including heart disease and overweight.

A diet with plenty of low GI foods, together with exercise and regular sleep, can help a person maintain health and a moderate weight.

Low GI diet

One factor that increases the GI score of a food is the milling and grinding process, which often leaves no more than the starchy endosperm, or the inner part, of the seed or grain. This is mainly starch.

This process also eliminates other nutrients, such as minerals, vitamins, and dietary fibers.

To follow a low GI diet, a person can eat more unrefined foods, such as:

  • oats, barley, or bran
  • whole-grain bread
  • brown rice
  • plenty of fresh fruit and vegetables
  • fresh, whole fruit instead of juice
  • whole-grain pasta
  • salads and raw vegetables

Carbohydrates are an important source of energy for the body. Some types are more healthful than others. For instance, dietary fiber is a carbohydrate that protects heart and gut health, whereas added sugars can lead to an increased risk of type 2 diabetes, heart disease, and overweight.

Following a well-balanced diet that includes unprocessed carbohydrates, and getting enough sleep and physical activity, are more likely to lead to good health and a healthful body weight than focusing on or eliminating a particular nutrient.