Carbohydrates: What are they and why do we need them?
Carbohydrates are one of the main types of nutrients that provide energy and structure to living things. They are found in many foods, especially plants, and can be classified into four major groups: monosaccharides, disaccharides, oligosaccharides, and polysaccharides.
Monosaccharides
Monosaccharides are the simplest and most basic form of carbohydrates. They consist of a single sugar unit with a general formula of C x (H 2 O) y , which means “watered carbon”. Some common examples of monosaccharides are glucose, fructose, and galactose, which all have the same molecular formula (C 6 H 12 O 6 ) but different structural arrangements. Monosaccharides are the building blocks of more complex carbohydrates and can be absorbed directly into the bloodstream.
Disaccharides
Disaccharides are formed when two monosaccharides are joined together by a chemical bond called a glycosidic linkage. The most common disaccharides are sucrose (table sugar), which is composed of glucose and fructose; lactose (milk sugar), which is composed of glucose and galactose; and maltose (malt sugar), which is composed of two glucose units. Disaccharides can be broken down into their constituent monosaccharides by enzymes in the digestive system.
Oligosaccharides
Oligosaccharides are short chains of three to ten monosaccharides linked together by glycosidic bonds. They are often found on the surface of cells and play important roles in cell recognition, communication, and immunity. Some oligosaccharides can also act as prebiotics, which are substances that stimulate the growth of beneficial bacteria in the gut.
Polysaccharides
Polysaccharides are long chains of hundreds or thousands of monosaccharides linked together by glycosidic bonds. They can be branched or unbranched, and can have different functions depending on their structure and properties. Some common examples of polysaccharides are starch, glycogen, cellulose, and chitin.
• Starch is the main storage form of glucose in plants. It is composed of two types of glucose polymers: amylose, which is linear and unbranched; and amylopectin, which is branched and has a tree-like structure. Starch can be digested by humans and other animals that have enzymes that can break down the glycosidic bonds.
• Glycogen is the main storage form of glucose in animals. It is similar to amylopectin in structure, but has more branches and is more compact. Glycogen is stored in the liver and muscles, and can be quickly mobilized to release glucose when needed.
• Cellulose is the most abundant organic compound on Earth and the main structural component of plant cell walls. It is composed of long, unbranched chains of glucose units linked by beta-glycosidic bonds, which give it high tensile strength and resistance to hydrolysis. Cellulose cannot be digested by humans and most animals, but some herbivores have symbiotic bacteria in their gut that can break down cellulose and release glucose.
• Chitin is a structural polysaccharide that forms the exoskeletons of insects, crustaceans, and fungi. It is composed of long chains of N-acetylglucosamine units linked by beta-glycosidic bonds. Chitin is similar to cellulose in structure and function, but has an additional nitrogen-containing group attached to each glucose unit.
Why do we need carbohydrates?
Carbohydrates are essential for life because they provide energy and structure to living organisms. Carbohydrates can be used as a source of fuel for cellular respiration, which is the process that converts glucose into ATP (adenosine triphosphate), the universal energy currency of cells. Carbohydrates can also be stored as glycogen or starch for later use when energy demand is high or food supply is low.
Carbohydrates also play important roles in maintaining the structure and function of cells and tissues. For example, cellulose and chitin provide mechanical support and protection to plants and animals; oligosaccharides mediate cell-cell interactions and immune responses; and polysaccharides such as hyaluronic acid and chondroitin sulfate form part of the extracellular matrix that surrounds cells.
How much carbohydrates do we need?
The amount of carbohydrates that we need depends on various factors such as age, activity level, health status, and personal preference. According to the Dietary Guidelines for Americans 2020-2025 , carbohydrates should provide 45% to 65% of total daily calories for adults. This means that for a person who consumes 2,000 calories per day, about 900 to 1,300 calories should come from carbohydrates.
However, not all carbohydrates are created equal. Some carbohydrates are more nutritious and beneficial than others. In general, it is recommended to choose complex carbohydrates that are rich in fiber, vitamins, minerals, antioxidants, and phytochemicals over simple carbohydrates that are high in added sugars or refined grains. Complex carbohydrates include whole grains, fruits, vegetables, legumes, nuts, seeds, and dairy products; while simple carbohydrates include candies, cakes, cookies, sodas, juices, white breads, pastas, rice, cereals etc.
Complex carbohydrates provide more sustained energy release than simple carbohydrates because they take longer to digest and absorb. They also help regulate blood sugar levels , lower cholesterol levels , prevent constipation , promote satiety , reduce inflammation , and support gut health . Simple carbohydrates , on the other hand , can cause spikes and crashes in blood sugar levels , increase triglyceride levels , contribute to weight gain , increase hunger , stimulate cravings , induce oxidative stress , and impair gut health .
Therefore , it is advisable to limit the intake of added sugars to less than 10% of total daily calories , as suggested by the Dietary Guidelines for Americans 2020-2025 . This means that for a person who consumes 2 ,000 calories per day , no more than 200 calories should come from added sugars . Added sugars include any sugars or sweeteners that are added to foods or beverages during processing or preparation , such as table sugar , honey , maple syrup , agave nectar , corn syrup , molasses etc .
Conclusion
Carbohydrates are vital nutrients that provide energy and structure to living things . They can be classified into four major groups : monosaccharides , disaccharides , oligosaccharides , and polysaccharides . Carbohydrates can have different functions depending on their structure and properties . Carbohydrates should provide 45% to 65% of total daily calories for adults , but it is important to choose complex carbohydrates over simple carbohydrates for optimal health benefits .