Everything You Need to Know About Carbohydrates

White Rice

Verywell / Alexandra Shytsman

Carbohydrates are the primary source of energy for the body and include both simple sugars and larger complex carbohydrates. Your body can use carbohydrates right away or convert them into a storage form called glycogen. Excess carbohydrates can also be converted into fat.

Carbohydrate Chemistry

No matter how big they are, all carbohydrates are made of carbon, hydrogen, and oxygen with the general formula of Cx(H2O)y. For example, a simple sugar molecule like glucose is made up of six carbon atoms, 12 hydrogen atoms, and six oxygen atoms. It has the formula C6H12O6.

A large starch molecule can be made of many little sugar molecules connected to form a long chain. The small x and y in the general formula, Cx(H2O)y, can run into the hundreds.

Simple Sugars

Simple sugars are made up of one or two sugar units. Glucose is a common simple sugar that our bodies and brains use for energy every day. Glucose is called a monosaccharide, which means "single sugar." Other monosaccharides include fructose, galactose, and ribose.

Fructose is found in fruits and vegetables; galactose is found in milk; and ribose is best known as a part of ribonucleic acid, which is a part of the genetic material in our cells.

Rather than go deeper into the chemistry of simple sugars, it is important to know that the single sugars glucose, fructose, and galactose can form different combinations to become disaccharides, a term that means "two sugars." These sugars include:

  • Lactose (milk sugar) is made up of glucose and galactose molecules. People who are lactose intolerant can't digest this sugar properly.
  • Maltose (malt sugar) is produced during the malting of cereals such as barley.
  • Sucrose (table sugar) is composed of glucose and fructose molecules. That's the white powdery or granular substance we typically refer to as "sugar" when we are cooking or baking.

Simple sugars are water-soluble and easy for your body to digest into the individual glucose and fructose molecules. They're also quickly absorbed through the intestinal walls and into the bloodstream.

Complex Carbohydrates

Complex carbohydrates are long chains of single sugar units. For example, the complex carbohydrate we know as starch is made up of many glucose units. These complex carbohydrates can be in the form of long chains, or the chains can form branches. Complex carbohydrates include:

  • Cellulose is the structural component of plants. Cellulose helps plants keep their shape; so, in a way, it acts as a plant skeleton. Cellulose is one of the principal components of dietary fiber, along with lignin, chitin, pectin, beta-glucan, inulin, and oligosaccharides.
  • Glycogen is a form of glucose that the muscles and liver use for energy storage.
  • Starch is the energy storage form of carbohydrates found in plants, especially in the seeds and roots. Starch is made up of many glucose units linked together. Starchy food examples include rice, wheat, corn, and potatoes.

Dietary starch and cellulose are the complex carbohydrates that are essential for good health. Potatoes, dry beans, grains, rice, corn, squash, and peas contain significant amounts of starch.

Vegetables like broccoli, cauliflower, asparagus, lettuce, and other greens are not starchy. That's because the stems and leafy parts of plants don't contain much starch, but they do provide a great deal of cellulose. Since we can't digest cellulose, green and leafy vegetables contain fewer calories than the starchy vegetables.

Carbohydrate Metabolism

Your saliva contains a small amount of amylase which is an enzyme that begins to break down starch into smaller molecules while you are chewing.

Carbohydrate digestion continues in the small intestine with the help of pancreatic amylase. Amylase breaks carbohydrates down into monosaccharides that can be absorbed into the bloodstream. Once in the blood, the monosaccharides are either used for energy, or, with the assistance of insulin, are stored in the liver and muscles as glycogen, or converted into fat.

People with prediabetes, type 2 diabetes, or metabolic syndrome, may have insulin resistance which means that their cells are not sensitive to the insulin their body is making. Their pancreas may also be sluggish and unable to produce enough insulin to manage blood sugars. In this case, behavior modifications, such as dietary changes, exercise, and weight loss are indicated. If these interventions fail, they may need to take or medications, non-insulin injectables, or insulin.

Your body prefers to use glucose as the primary source of fuel for all your daily activity. Muscles need glucose to move, and organs need glucose to function. However, your body can make glucose from any extra dietary protein by a process called gluconeogenesis and it can also create energy from fat by a process called ketosis.

Carb Requirements and Sources

The amount of carbohydrate you need will depend on a variety of factors, such as age, height, weight, and activity level to name a few. The Dietary Guidelines for Americans suggests that carbohydrates make up about 45-65% of you daily calories. 

One gram of carbohydrate contains 4 calories whether is it is sugar or starch. One slice of bread has about 12–15 grams of carbohydrates (although this will depend on how large the slice is and the ingredients that are used to make it). One typical chocolate bar may have about 50 grams of carbohydrates. A medium potato has about 37 grams of carbohydrates.

Although all carbohydrates have 4 calories per gram, some sources provide more beneficial micronutrients per calorie, thereby making them more health-promoting. Fruits, vegetables, legumes, nuts, seeds, and grains provide more nutrients than candy, sodas, and pastries. These foods are high in energy derived from carbohydrates but have little to no vitamins, minerals, phytochemicals, or fiber.

Healthy carbohydrate sources also have significant amounts of vitamins, minerals, phytochemicals, and fiber.

Depending on what percentage of calories you need to eat from carbohydrates, you can simply figure out how to calculate how many grams you need to eat per day. For example, if you are supposed to consume 50% of your calories from carbohydrates and you consume 2,000 calorie diet, then about 1,000 calories are allocated to carbohydrates. Each gram of carbohydrate has 4 calories so you can divide 1,000 by four to get 250 grams per day.

Of those 250 grams of daily carbohydrate, less than 10% should come from added table sugar and sweeteners. That's about 25 grams for a 2,000 calorie per day diet, equal to half a candy bar or less than one can of sugary soda.

Carb Counts for Common Foods

Once you know how many grams of carbs you need every day, you can select your foods based on their carb counts and fit them into your daily calorie and carb budget. To get an idea, review these approximate amounts from common foods.

  • Apple: One medium apple has 25g of carbs and 4.4g of fiber
  • Apple crisp: One serving has 28g of carbs and 4g of fiber
  • Asparagus: One cup has 3.7g of carbs and 1.8g of fiber
  • Blueberries: One cup has 21g of carbs and 3.6g of fiber
  • Bread: One slice contains 13.8g of carbs and 1.9g of fiber
  • Broccoli: One cup has 6g of carbs and 2.4g of fiber
  • Carrots: One cup has 6g of carbs and 1.5g of fiber
  • Cookie: One serving of Oreo cookies (3 cookies) has 25g of carbs and 1.2g of fiber
  • Dry beans like pinto beans: One cup has 45g of carbs and 15g of fiber
  • Grapefruit: One half medium fruit has 13g of carbs and 2g of fiber
  • Green beans: One cup has 7g of carbs and 2.7g of fiber
  • Lettuce: One small head has 9.6g of carbs and 2.9g of fiber
  • Low-fat milk: One 8-ounce glass has 12g of carbs and 0g of fiber
  • Marinara sauce: One half cup has 5g of carbs and 1g of fiber
  • Orange: One medium fruit has 15.4g of carbs and 3.1g of fiber
  • Orange juice: One 8-ounce cup has 25.8g of carbs and 0.5g of fiber
  • Pasta: One cup of cooked spaghetti has 43.2g of carbs and 2.5g of fiber
  • Potato: One medium potato with skin has 37g of carbs and 4g of fiber
  • Raisin bran cereal: One cup has 47.1g of carbs and 7g of fiber
  • Red wine: One 5-ounce glass has 3.8g of carbs and 0g of fiber
  • Snickers candy bar: Contains 35g of carbs and 1.3g of fiber
  • Strawberries: One half cup has 11.7g of carbs and 3g of fiber
  • Sweet corn: One medium ear has 19g of carbs and 2g of fiber
  • Tomato: One medium fruit has 3.5g of carbs and 1.1g of fiber

Nutrition facts labels on packaged foods also list the amount of carbohydrates per serving. It takes a little extra time and effort to look up the carbohydrate counts for all of the foods you eat, but with experience, you will begin to have a good idea of approximate calorie counts and carbohydrate counts.

13 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Shereen Lehman, MS
Shereen Lehman, MS, is a former writer for Verywell Fit and Reuters Health. She's a healthcare journalist who writes about healthy eating and offers evidence-based advice for regular people.