Carbohydrates are one of the four types of organic compounds, with the others being protein, lipids, and nucleic acids. Carbohydrates are molecules made of carbon (C), hydrogen (H), and oxygen (O), usually with the empirical formula Cm(H2O)n, where m and n are integers that may or may not be the same. Looking at the chemical formula, you see carbon and water, giving rise to the word “carbohydrate”. The body uses carbohydrates as a source of chemical energy and as a building block for structural components. Here are examples of carbohydrates and the foods that contain them.
Types of and Examples of Carbohydrates
A biochemist classifies carbohydrates according to how many linkages there are between sugar molecules. The basic building blocks are simple sugars, which combine to form more complex molecules, like glycogen, fiber, and starch.
The smallest carbohydrates are monosaccharides. Joining two sugar molecules together makes a disaccharide. Connecting three to nine sugar subunits (called “residues”) gives a polysaccharide. When more than nine residues bond together, you get an oligosaccharide.
| Class | Subgroup | Examples |
|---|---|---|
| Simple sugars (1-2 residues) | Monosaccharides Disaccharides Polyols | glucose, fructose sucrose, lactose, maltose mannitol, sorbitol |
| Oligosaccharides (3-9 residues) | Malto-oligosaccharides Other oligosaccharides | maltodextrin raffinose |
| Polysaccharides (>9 residues) | Starch Non-starch polysaccharides | amylopectin, modified starch cellulose, glycogen, pectin |
Carbohydrate Classes in Food
A food chemist typically classifies carbohydrates as either simple or complex. Here, a simple carbohydrate is a monosaccharide or disaccharide (a sugar), while a complex carbohydrate is an oligosaccharide or polysaccharide. The two types of carbohydrates serve different purposes in the body. Simple carbohydrates provide quick spikes of energy, while complex carbohydrates take longer to digest, aid in helping you feel full longer, and are the form the liver makes for storing sugar for later.
Another classification system is categorizing carbohydrates as sugars, starches, or fiber:
Sugars
Sugar in the diet often has a high glycemic index, meaning it gets digested quickly and raises blood sugar. However, not all sugars have this effect. For example, erythritol is a sugar alcohol that is sweeter than table sugar (sucrose), yet isn’t well-metabolized so it’s low in calories and doesn’t spike blood sugar.
Here are some examples of sugars and foods that contain them:
- Sugar (sucrose, found in most pastries, cakes, and cookies)
- Brown sugar (still sucrose)
- Corn syrup (mostly fructose)
- Honey (high in fructose and glucose)
- Glucose (found in syrups and dried fruits)
- Fructose (found in fruit juices, grapes, apples, watermelon, etc.)
- Lactose (milk)
Starches
While starch is a complex carbohydrate, most of the time it’s easily broken down into sugars. Here are examples of starchy foods:
- Grains (oats, wheat)
- Rice
- Bread
- Pasta
- Potatoes (and most other root vegetables)
- Pumpkin and squash
- Corn
- Peas (and most other legumes)
Fiber
Fibers tends not to contribute calories to the diet. Instead, it aids in digestion and helps you feel full longer. Here are examples of foods high in fiber:
- Whole-grain bread, cereal, pasta
- Oatmeal
- Fruits and vegetables with their skins
- Peanuts
- Tree nuts (almonds, walnuts, pecans)
- Seeds
- Leafy greens
Examples of Compounds That Are Not Carbohydrates
The other three classes of organic compounds are not carbohydrates: proteins, lipids, and nucleic acids. So, molecules that are not carbohydrates include amino acids, polypeptides, fatty acids, fats, oils, DNA, and RNA. As far as food is concerned, all cells contains all of the classes of compounds. But, some are much lower in carbohydrates than others. Foods that are either carbohydrate-free or else low in them include:
- Meat
- Eggs
- Fish
- Oil, whether from a plant or animal
- Fat, whether from a plant or animal
- Most cheeses
- Most nuts and seeds
Then, there are foods which contain carbohydrates, but not in a form humans digest and use. For example, wood consists mainly of the carbohydrate cellulose. But, if you eat it, your body doesn’t break down cellulose into sugars. Other types of carbohydrates that don’t get broken into sugars readily include fiber and non-nutritive sweeteners.
Pure elements and inorganic compounds also are not carbohydrates. So, carbon, zinc, water, and carbon dioxide are examples of chemicals that are not carbohydrates.
Good and Bad Carbs
Carbohydrates are not inherently good or bad. That being said, many people try to limit their intake of simple sugars and processed foods that contain starch with little to no fiber. But, simple sugars are not all bad. For example, fruits and vegetables contain sugars, yet are also rich in vitamins, minerals, and antioxidants.
References
- Fearon, W.F. (1949). Introduction to Biochemistry (2nd ed.). London: Heinemann. ISBN 9781483225395.
- Jenkins, D.J.; et al. (1986). “Simple and complex carbohydrates”. Nutrition Reviews. 44 (2): 44–9. doi:10.1111/j.1753-4887.1986.tb07585.x
- Maton, A.; et al. (1993). Human Biology and Health. Englewood Cliffs, New Jersey: Prentice Hall. ISBN 978-0-13-981176-0.
- Matthews, C.E.; Van Holde, K.E.; Ahern, K.G. (1999). Biochemistry (3rd ed.). Benjamin Cummings. ISBN 978-0-8053-3066-3
- Reynolds, A.; et al. (2019). “Carbohydrate quality and human health: a series of systematic reviews and meta-analyses”. Lancet. 393 (10170): 434–445. doi:10.1016/S0140-6736(18)31809-9