Carbohydrates

Purpose: The purpose of this guide is to provide both chemical and nutritional information about carbohydrates. 

What are carbohydrates?

When you think of carbohydrates, also referred to as carbs, you may think about rice, bread, potatoes, and pasta. This is true - all these foods are high in carbs. But what actually are carbs? 

Carbohydrates are made up of carbon, hydrogen, and oxygen atoms. Two or more of these atoms are paired together to form molecules. Molecules that include carbon in their structure are known as organic compounds.

Carbs are one of the three macronutrients (the other two being lipids and protein). Since the body cannot produce it in adequate amounts in order to sustain life without receiving it from the diet, carbohydrates are also considered an essential nutrient.

Overall, carbs are organic compounds consisting of carbon, hydrogen, and oxygen molecules in different arrangements that have a variety of forms and functions, including starches, sugars, glycogen, and cellulose.¹

What are the types of carbs?

Carbohydrates can be divided into categories. The three primary groups of carbs include monosaccharides, disaccharides, and polysaccharides.¹

Monosaccharides

Monosaccharides are monomers, or building blocks, of carbohydrates. Monosaccharides are considered a simple sugar and consist of 3-7 carbons. When grouping carbohydrates, the suffix -ose indicates that it is a monosaccharide, and the prefix tells the amount of carbons found in the monosaccharide. The following is a list of monosaccharides¹ ² : 

Trioses: 3 carbons

• Glyceraldehyde, dihydroxyacetone

Tetroses: 4 carbons

• Erythrose, threose, erythrulose

Pentoses: 5 carbons

• Ribose, arabinose, xylose, ribulose, xylulose

Hexoses

• Glucose, mannose, galactose, fructose, sorbose, tagatose

Common Monosaccharides 

Glucose/Dextrose: referred to as ‘blood sugar’. Found in some ripening fruits and vegetables, but hydrolysis of disaccharides and starch is the primary method of glucose within the diet.

Fructose: sugar found in fruit, found in honey and fruit naturally.² Derived from the disaccharide sucrose. 

Galactose: sugar found in milk, not often found in foods. Most galactose in the diet is derived from the disaccharide lactose. 

Deoxyribose: part of DNA

Ribose: part of nucleic acids RNA and DNA. Also within the structures of other nucleotides and adenosine triphosphate (ATP), used for energy within the cell.²

Disaccharides

When two monosaccharides link through dehydration synthesis reactions (water is removed during this reaction), a disaccharide is formed. Disaccharides are linked by acetal bonds (a.k.a. glycosidic bonds since they occur in carbs).¹ A disaccharide can be broken down into a monosaccharide through hydrolysis reactions (water is formed during this reaction). The following are types of disaccharides:

Sucrose: Glucose +Fructose, also known as table sugar found in several sources in the diet. ¹

Lactose: Glucose + Galactose, which is the sugar found in milk. ¹

Maltose: Glucose + Glucose, which is malt sugar. It is not significantly found in the diet alone but is a product of polysaccharide digestion.¹ 

Polysaccharides

When multiple monosaccharides (ranging from ten to hundreds) link together, they form polysaccharides. The alpha and beta positions of the linkages are designed to work with specific enzymes within the digestive system.¹ Polysaccharides are more complex chains and are referred to as complex carbs. The following are known polysaccharides:¹

Oligosaccharides: Polysaccharides that are made up of 3-10 monosaccharides. It includes stachyose, verbascose, and raffinose which ferments in the colon, producing gas.²

Glycogen: A branched-chain polymer that serves as a form of stored carbohydrates in animals.² In humans, glycogen is stored in the liver and muscle cells.

Starches: A  form of stored carbohydrates in plants and a major carb source in the diet. 

Starch comes in the form of amylose (straight-chain glucose polymer) and amylopectin (branched glucose polymer).² When broken down into smaller components, glucose is formed.²

Cellulose: Cell walls of plants that are indigestible for humans. It is considered a type of fiber that helps with gut motility and adds bulk to stool.²

What is the function of carbs in the body?

The main function of carbohydrates in the body is to provide energy, known as adenosine triphosphate, or ATP, when metabolized. Carbohydrates are limited in being a structural component of the body but are part of DNA and RNA in the form of monosaccharides deoxyribose and ribose.¹ Carbohydrates also aid in composing the glycocalyx which aids in cell recognition, bacteria resistance, and vascular functions.¹ Another example of a non-energy source of carbohydrates is the polysaccharide glycosaminoglycan which plays a role in body secretions and lubrication around joints and connective tissues.² 

What is the recommended amount of carbs?

The AMDR is reflective of dietary patterns of nutrients while the RDA focus is on meeting the requirement for daily functioning. The Acceptable Macronutrient Distribution Range (AMDR) of carbohydrates for individuals between 1-18+ is defined as 45-65% of daily calories.³ The AMDR is intended to set a caloric range for macronutrients that promote sufficient amounts of essential nutrients and lower chronic disease risk.³

The Recommended Dietary Allowances (RDA) for carbohydrates are 130 grams for children and adults between 1-70+ years old.³ The RDA is the sufficient amount of nutrients for 97-98% of healthy individuals. Carbohydrates provide 4 calories per gram whether simple or complex, and there are 15 grams of carbs in one serving. ³