Carbohydrates, or saccharides, are biomolecules. The four major classes of biomolecules are carbohydrates, proteins, nucleotides, and lipids. Carbohydrates are the most abundant of the four.
Also known as “carbs,” carbohydrates have several roles in living organisms, including energy transportation. They are also structural components of plants and insects.
Carbohydrate derivatives are involved in reproduction, the immune system, the development of disease, and blood clotting.
Fast facts on carbohydrates
“Saccharide” is another word for “carbohydrate.”
Foods high in carbohydrates include bread, pasta, beans, potatoes, rice, and cereals.
One gram of carbohydrate contains approximately 4 kilocalories
High glycemic index (GI) carbohydrates quickly enter the bloodstream as glucose
Switching to a low-GI diet improves the chance of a healthy weight and lifestyle
What are carbohydrates?
Sources of carbohydrate include whole grains, fruit, and vegetables.
Carbohydrates, also known as saccharides or carbs, are sugars or starches. They are a major food source and a key form of energy for most organisms.
They consist of carbon, hydrogen, and oxygen atoms.
Two basic compounds make up carbohydrates:
Aldehydes: These are double-bonded carbon and oxygen atoms, plus a hydrogen atom.
Ketones: These are double-bonded carbon and oxygen atoms, plus two additional carbon atoms.
Carbs can combine together to form polymers, or chains.
These polymers can function as:
long-term food storage molecules
protective membranes for organisms and cells
the main structural support for plants
Most organic matter on earth is made up of carbohydrates. They are involved in many aspects of life.
There are various types of carbohydrate. They include monosaccharides, disaccharides, and polysaccharides.
This is the smallest possible sugar unit. Examples include glucose, galactose, or fructose. Glucose is a major source of energy for a cell. “Blood sugar” means “glucose in the blood.”
In human nutrition, these include:
galactose, most readily available in milk and dairy products
fructose, mostly in vegetables and fruit
Disaccharides are two monosaccharide molecules bonded together, for example, lactose, maltose, and sucrose.
Bonding one glucose molecule with a galactose molecule produces lactose. Lactose is commonly found in milk.
Bonding one glucose molecule with a fructose molecule, produces a sucrose molecule.
Sucrose is found in table sugar. It is often results from photosynthesis, when sunlight absorbed by chlorophyll reacts with other compounds in plants.
Different polysaccharides act as food stores in plants and animals. They also play a structural role in the plant cell wall and the tough outer skeleton of insects.
Polysaccharides are a chain of two or more monosaccharides.
The chain may be:
branched, so that the molecule looks like a tree with branches and twigs
unbranched, where the molecule is a straight line
Polysaccharide molecule chains may consist of hundreds or thousands of monosaccharides.
Glycogen is a polysaccharide that humans and animals store in the liver and muscles.
Starches are glucose polymers that are made up of amylose and amylopectin. Rich sources include potatoes, rice, and wheat. Starches are not water soluble. Humans and animals digest them using amylase enzymes.
Cellulose is one of the main structural constituents of plants. Wood, paper, and cotton are mostly made of cellulose.
Simple and complex carbs
You may have heard about simple and complex carbohydrates.
Monosaccharides and disaccharides are simple carbohydrates, and polysaccharides are complex.
Simple carbohydrates are sugars. They consist of just one or two molecules.They provide a rapid source of energy, but the consumer soon feels hungry again. Examples include white bread, sugars, and candies.
Complex carbohydrates consist of long chains of sugar molecules. Wholegrains and foods that still have their fiber in are complex carbs. They tend to fill you up for longer, and they are considered more healthful, as they contain more vitamins, minerals, and fiber. Examples include fruits, vegetables, pulses, and wholemeal pasta.
Bread, pasta, beans, potatoes, bran, rice, and cereals are carbohydrate-rich foods. Most carbohydrate-rich foods have a high starch content. Carbohydrates are the most common source of energy for most organisms, including humans.
We could get all our energy from fats and proteins if we had to. One gram of carbohydrate contains approximately 4 kilocalories (kcal), the same amount as protein. One gram of fat contains around 9 kcal.
However, carbohydrates have other important functions:
the brain needs carbohydrates, specifically glucose, because neurons cannot burn fat
dietary fiber is made of polysaccharides that our bodies do not digest
The United States (U.S.) Dietary Guidelines 2015-2020 recommend obtaining 45 to 65 percent of energy needs from carbohydrates, and a maximum of 10 percent should come from simple carbohydrates, in other words, glucose and simple sugars.