“Food builds big bridges. If you can eat with someone, you can learn from them, and, when you learn from someone, you can make big changes. We changed the courses of America in this restaurant over bowls of gumbo. We can talk to each other and relate to each other when we eat together.“

– Chef Leah Chase

Carbohydrates: Energy From Plants

Carbohydrates are often associated with having a negative impact on health and/or not being necessary at all, when, in fact, the opposite is true. Carbohydrates are essential and, therefore, should constitute most of an individual’s daily caloric intake. Animals, including humans, are perpetually linked to plants as all carbohydrates come from plants.

Recall that plants convert the energy in sunlight to chemical energy in the form of glucose, the main carbohydrate for almost all living organisms. When we eat plants, we harvest the energy of glucose to support life’s processes.

Carbohydrates are a group of organic compounds containing a ratio of one carbon atom to two hydrogen atoms to one oxygen atom. Carbohydrates are a group of 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. Synonymous with the term carbohydrate is the Greek word “saccharide,” which means sugar.

Simple Carbohydrates (Sugars)

Monosaccharides

For all organisms, from bacteria to plants to animals, glucose is the preferred fuel source and the human body’s most abundant carbohydrate. The brain depends on glucose as its energy source (except during extreme starvation). The chemical formula for glucose is C₆H₁₂O_6, which contains six carbon, twelve hydrogen, and six oxygen atoms. The monosaccharide galactose differs from glucose only in that a hydroxyl (−OH) group faces in a different direction on the fourth carbon (Figure 4.2 “Structures of the Three Most Common Monosaccharides: Glucose, Galactose, and Fructose”). This minor structural alteration causes galactose to be less stable than glucose. As a result, the liver rapidly converts it to glucose. Most absorbed galactose is utilized for energy production in cells after converting to glucose. (Galactose is one of two simple sugars bound together to make up the sugar in milk. It is later freed during the digestion process.)
Fructose also has the same chemical formula as glucose but differs in its chemical structure. The fructose ring contains four carbons, while the glucose ring contains five. Fructose, in contrast to glucose, is not an energy source for other cells in the body. Mostly found in fruits, honey, and sugarcane, fructose is one of the most common monosaccharides in nature.

Pentoses are less common monosaccharides that have only five carbons and not six. The pentoses are abundant in the nucleic acids RNA and DNA, and also as components of fiber.
Lastly, there are sugar alcohols, which are industrially synthesized derivatives of monosaccharides. Some examples of sugar alcohols are sorbitol, xylitol, and glycerol. (Xylitol is similar in sweetness to table sugar). Sugar alcohols are often used instead of table sugar to sweeten foods as they are incompletely digested and absorbed, and therefore less caloric. The bacteria in your mouth opposes them, hence sugar alcohols do not cause tooth decay. Interestingly, the sensation of “coolness” that occurs when chewing gum containing sugar alcohols comes from dissolving in the mouth, a chemical reaction that requires heat from the inside.

Disaccharides

Disaccharides are pairs of two monosaccharides linked together, all containing one glucose molecule. Disaccharides include sucrose, lactose, and maltose. Sucrose (table sugar) comprises one glucose molecule and one fructose molecule linked via a covalent bond. Sucrose is also found in many fruits and vegetables, and at high concentrations in sugar beets and sugarcane, which are used to make table sugar. Lactose is commonly known as milk sugar, is composed of one glucose unit and one galactose unit. Lactose is prevalent in dairy products such as milk, yogurt, and cheese. Maltose consists of two glucose molecules covalently bonded together. It is a common breakdown product of plant starches and is rarely found in foods as a disaccharide.

Complex Carbohydrates

Complex carbohydrates are polysaccharides, long chains of the monosaccharide glucose, that may be branched or unbranched. There are two main groups of polysaccharides: starches and fibers.

Starches

Starch is found in abundance in grains, legumes, and root vegetables, such as potatoes. Amylose, a plant starch, is a linear chain containing hundreds of glucose units. Amylopectin, another plant starch, is a branched chain containing thousands of glucose units. Starch molecules form crystals and are the energy-storing molecules of plants. Amylose and amylopectin are contained together in foods, but the smaller one, amylose, is less abundant. Eating raw foods containing starches provides very little energy as the digestive system has a hard time breaking them. Cooking breaks down the crystal structure of starches, making them much easier to break down in the human body. The starches that remain intact throughout digestion are called resistant starches. Bacteria in the gut can break some of these down and may benefit gastrointestinal health. Isolated and modified starches are used widely in the food industry and during cooking as food thickeners.

Humans and animals store glucose in the form of the very large molecule, glycogen. It is predominantly found in liver and muscle tissue in animals.

Dietary Fibers

Dietary fibers are polysaccharides that are highly branched and cross-linked. Some dietary fibers are pectin, gums, cellulose, hemicellulose, and lignin. Lignin, however, is not composed of carbohydrate units. Humans do not produce the enzymes to break down dietary fiber; however, bacteria in the large intestine (colon) do.

Dietary fiber is very beneficial to our health. The Dietary Guidelines Advisory Committee recommend that a healthy dietary pattern is one that is nutrient dense and higher in fiber.^[1]

Dietary fiber is categorized as either water-soluble or insoluble. Some examples of soluble fibers are inulin, pectin, and guar gum, and they are found in peas, beans, oats, barley, and rye. Cellulose and lignin are insoluble fibers; a few dietary sources are whole-grain foods, flax, cauliflower, and avocados. Cellulose is the most abundant fiber in plants, making up the cell walls and providing structure. Soluble fibers are more easily accessible to bacterial enzymes in the large intestine so that they can be broken down to a greater extent than insoluble fibers. Still, even some breakdown of cellulose and other insoluble fibers occurs.

The last class of fiber is functional fiber. Functional fibers have been added to foods and shown to provide health benefits to humans. Functional fibers may be extracted from plants and purified or synthetically made. An example of a functional fiber is psyllium-seed husk. Scientific studies show that consuming psyllium-seed husk reduces blood cholesterol levels, and the FDA has approved this health claim. Total dietary fiber intake is the sum of dietary fiber and functional fiber consumed.