9.2: Carbohydrate Overview and Structure

Carbohydrates are the perfect nutrient to meet your body’s nutritional needs. They nourish your brain and nervous system, provide energy to all of your cells (and within proper caloric limits), and help keep your body fit and lean. Specifically, digestible carbohydrates provide bulk in foods, vitamins, and minerals, while indigestible carbohydrates provide a good amount of fiber with a host of other health benefits. Like fruit, vegetables, and whole grains, the plants we eat synthesize the fast-releasing carbohydrate, glucose, from carbon dioxide in the air and water and by harnessing the sun’s energy. Plants convert the energy in sunlight to chemical energy in the molecule glucose. Plants use glucose to make other larger, more slow-releasing carbohydrates. When we eat plants, we harvest the energy of glucose to support life.

Carbohydrates are organic compounds containing a ratio of one carbon atom to two hydrogen atoms to one oxygen atom. Basically, they are hydrated carbons. The word “carbo” means carbon, and “hydrate” means water. Glucose is the more abundant carbohydrate in the human body.

Watch the video about carbohydrates and sugars

Carbohydrates: Two Very Different Types

There are two types of carbohydrates based on how quickly they break down in the body, either fast or slow:
Fast-releasing carbohydrates are sugars. Simple sugars break down very quickly, flooding your body with quick energy.

Slow-releasing carbohydrates are starches and fibers.
Starch molecules are found in abundance in grains, legumes, and root vegetables, such as potatoes. Eating raw foods containing starches provides very little energy as the digestive system has a hard time breaking them down. Cooking breaks down the crystal structure of starches, making them much easier to break down in the human body, providing energy.
Fiber provides something different from the body: humans lack the enzymes to break down fiber, but the bacteria in our gut biome can provide some assistance. These bacteria break down some of the fiber, but most of the fiber we consume functions to make us feel full (help us regulate our appetite) and help clean out the intestinal tract. Think of fiber as a broom that sweeps out the insides of your intestinal tract.

Functions of Carbohydrates

The four primary functions of carbohydrates in the body are:
1) To provide energy – The simplest carbohydrate, and the one most abundant in the body, is glucose. For all organisms, from bacteria to plants to animals, glucose is the preferred fuel source. The brain is completely dependent on glucose as its energy source (except during extreme starvation conditions). Many other more complex carbohydrates break down and become glucose in the body.
2) Store energy – Extra carbohydrates are stored in our liver and muscles, ready for the body to use if necessary; it’s like having a backup battery.
3) Build macromolecules – Although most absorbed glucose is used to make energy, some glucose is converted to ribose and deoxyribose, which are essential building blocks of important macromolecules, such as RNA, DNA, and ATP. Glucose is additionally utilized to make the molecule NADPH, which is important for protection against oxidative stress and is used in many other chemical reactions in the body. If all of the energy, glycogen-storing capacity, and building needs of the body are met, excess glucose can make fat.
4) Spare protein and fat for other uses – When the body needs glucose and doesn’t have any, the body will scavenge proteins (your muscles) and convert them into glucose. Adequate glucose in the body spares the breakdown of proteins from being used to make glucose needed by the body.

What Foods are Rich in Carbohydrates?

Carbohydrates are contained in all five food groups: grains, fruits, vegetables, meats, beans (only in some processed meats and beans), and dairy products. Fast-releasing carbohydrates are more prevalent in fruits, fruit juices, and dairy products, while slow-releasing carbohydrates are more plentiful in starchy vegetables, beans, and whole grains. Fast-releasing carbohydrates are also found in large amounts in processed foods, soft drinks, and sweets. On average, a serving of fruits, whole grains, or starches contains 15 grams of carbohydrates.
In choosing dietary sources of carbohydrates, the best ones are those that are nutrient-dense, meaning they contain more essential nutrients per calorie of energy. In general, nutrient-dense carbohydrates are minimally processed and include whole-grain bread and cereals, low-fat dairy products, fruits, vegetables, and beans. In contrast, empty-calorie carbohydrate foods are highly processed and often contain added sugars and fats. Soft drinks, cakes, cookies, and candy are examples of empty-calorie carbohydrates. When you choose nutrient-dense food, you give your body better nutrition and more opportunities to function optimally. We all want to live our best life, feel our best, chose our food wisely.