CHAPTER 7 LESSON: 1 Carbohydrate Introduction

Fiber Intake of the U.S. Population

current intake, which averages around 18 grams per day for men and 15 grams per day for women (WWEAI, NHANES 2009-2010). In the United States, it is recommended that women consume a daily intake of 25 grams of fiber, whereas men should consume 38 grams.

Figure: Overview of Carbohydrate Form and Structure summarizes all the different sugar unit forms along with key characteristics of each.

Carbohydrates follow a sequential classification system derived from the number of sugar units contained within the structure or chain. Although humans may ingest a variety of different carbohydrates (e.g., starches and sugars), the digestive process breaks them down into their individual building blocks (called monosaccharides), which represent the only absorbable form of carbohydrates to the body.

Amylopectin

A branched-chain and digestible form of starch containing glucose molecules.

Functional Fiber

A compound derived from isolated indigestible fiber to potentially provide some of the health-promoting benefits of natural fiber.

Diverticulosis

A condition that occurs when pockets of collected stool called diverticula form in the walls of the digestive tract, forcing the inner layer of the intestinal wall to push through its outer lining.

Insoluble fiber offer several benefits that include the following

Digestive health—It adds bulk and draws water into the GI tract. It improves regularity in the large intestine to avoid constipation and other bowel-related health problems (e.g., hemorrhoids). Reduces risk of cancer—It improves movement through the large intestine. It reduces the risk of colon cancer and other large intestinal diseases (e.g., diverticulosis). Weight loss—By delaying gastric emptying (from stomach), it promotes an overall feeling of fullness, reducing caloric intake.

Table: Good Food Sources of Fiber

provides a brief list of good food sources of fiber that individuals can consider for increasing overall fiber intake (USDA, 2014).

Carbohydrate Structure

scientific classifications: monosaccharides or single sugar units, disaccharides or paired sugar units, and polysaccharides, which represent longer sugar unit chains. It is the monosaccharides and disaccharides that are collectively known as simple sugars to many. A smaller subgroup, called oligosaccharides, also exists, containing 3 to 10 sugar units. Polysaccharides and oligosaccharides are known as complex carbohydrates.

(Figure: Polysaccharide Structures of Amylose, Amylopectin, and Fiber).

Polysaccharide chains are arranged as straight-chain structures called amylose, branched-chain structures called amylopectin, and as a block structure called fiber (Figure: Polysaccharide Structures of Amylose, Amylopectin, and Fiber). Both amylose and amylopectin are digestible and make up approximately 20% and 80% of the digestible starches found in vegetables, grains, pasta, rice, and beans, respectively (Smith et al., 2018). Because enzymes digest from open ends of a structure, amylopectin will digest to the absorbable monosaccharide form of glucose faster than amylose.

Match the form of fiber to its correct definition.

Soluble - A type of dietary fiber that dissolves in water to form a gel; associated with heart health benefits and glucose control. Insoluble - A type of dietary fiber that does not dissolve in water; associated with promoting bowel regularity.

Match the carbohydrate foods to their correct type.

Starches - Grains, Veg, Rice, Barley Sugar - Milk, Fruit, Candy

Figure: Structure of Disaccharides; Sucrose, Maltose, and Lactose

Sucrose is comprised of one glucose molecule joined with one fructose molecule. Examples include cane sugar, brown sugar, and date sugar. Sucrose contributes as a primary sugar in most fruits. Lactose is comprised of one glucose molecule joined with one galactose molecule. It is only found in dairy products. Maltose is comprised of two glucose molecules. Examples include corn syrup, brown rice syrup, and molasses.

Glycogenolysis

The process of breaking down the glycogen molecule into its individual glucose units for entry into the energy pathways.

Glycogenesis

The process of forming glycogen from glucose.

Glycogen

The storage molecule of carbohydrate found in animals and located in muscle and liver cells.

Table: Oligosaccharides

These partially-digestible polymers are found in legumes (e.g., peas, lentils, or beans) and plant sources; contain glucose, fructose, and/or galactose; and are touted for health-promoting benefits (Bernadot, 2012). Oligosaccharides are largely resistant to digestion because the human digestive tract lacks the necessary enzymes that can chemically break down many of these structures. This allows them to pass to the large intestine where intestinal bacteria act on them. They essentially serve as food for our large intestinal bacteria and are also referred to as prebiotics. This category includes fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS), and inulin, extracted from chicory root

Match the disaccharide to its correct structure.

lactose - glucose + galatose Maltose - glucose +glucose Sucrose - glucose + fructose

Carbohydrates are found in three distinct locations within the body.

A small amount of glucose located in the blood is needed for distribution to all parts of the body (e.g., brain and central nervous system, which both prefer glucose as a fuel). Blood glucose stores are small, ranging between 3 to 5 grams in a small adult, to about 10 to 15 grams in a very-large male. The average adult stores around 2,000 to 2,500 kcal, whereas an endurance athlete can expand their storage capacity to over 3,000 kcal. It is estimated that an average adult will burn about 100 kcal/mile; therefore, the amount of glycogen stores in the body would cover about 20 miles. A moderate amount of glycogen is stored in the liver, which is needed to preserve blood sugar. Liver cells store approximately 50 grams per kilogram (22.7g/lb.) of tissue, and, considering how the liver weighs approximately 1.5 to 2.5 kg, this totals about 75 to 125 grams (300 to 500 kcal) Lastly, large quantities of glycogen are stored in muscle tissue, which serve to fuel muscular work. Normal carbohydrate storage in muscle cells is approximately 15 grams per kilogram (6.8 g/lb.) of muscle tissue. Considering how muscle comprises approximately 30% of a woman's mass and close to 40% of a man's mass, this averages somewhere between 250 and 600 grams (1,000 to 2,400 kcal) in muscle tissue.

Amylose

A straight-chain and digestible form of starch containing glucose molecules.

Soluble Fiber (Water soluble)

A type of dietary fiber that dissolves in water to form a gel, associated with heart health benefits and glucose control. Examples of soluble fiber include pectins, gums, and mucilages that originate from the inside of the plant cell. They are called soluble because they either dissolve or swell when placed in water and most can be digested by the bacteria living within the large intestine. Therefore, they are also sometimes called fermentable. Soluble fibers are found in oat bran, oatmeal, beans, fruits (e.g., apples or pears) and vegetables (e.g., artichoke, leeks, or sweet potatoes), as well as in many commercial products like salad dressings, jams, and jellies

Insoluble Fiber (Water insoluble)

A type of dietary fiber that does not dissolve in water, associated with promoting bowel regularity. They form the structural parts of plants and include compounds like cellulose, hemicellulose, and lignin, and are often found in the outermost portion of grains, vegetables, fruits, and seeds (e.g., whole-grain wheat, celery, brown rice, quinoa, apple peels, or broccoli). They are called insoluble or non-fermentable because they do not dissolve in water and are not easily digested by intestinal bacteria

Added Sugars (Disaccharides)

Added sugars are those not naturally occurring in food groups and include syrups and other caloric sweeteners found in candy (sweets) and sweetened beverages (soda). Added sugars are sugars that are added to foods or food products, not sugars that are naturally contained in the food.

Fiber

Although fiber represents most of the indigestible portions of plant food, it is not a single compound. It is a group of compounds that share similar characteristics and are generally classified as either soluble or insoluble.

Locations of Carbohydrates in the Body

Blood glucose stores are small, ranging between 3 to 5 grams in a small adult, to about 10 to 15 grams in a very-large male. The average adult stores around 2,000 to 2,500 kcal, whereas an endurance athlete can expand their storage capacity to over 3,000 kcal. It is estimated that an average adult will burn about 100 kcal/mile; therefore, the amount of glycogen stores in the body would cover about 20 miles. Liver cells store approximately 50 grams per kilogram (22.7g/lb.) of tissue, and, considering how the liver weighs approximately 1.5 to 2.5 kg, this totals about 75 to 125 grams (300 to 500 kcal). Normal carbohydrate storage in muscle cells is approximately 15 grams per kilogram (6.8 g/lb.) of muscle tissue. Considering how muscle comprises approximately 30% of a woman's mass and close to 40% of a man's mass, this averages somewhere between 250 and 600 grams (1,000 to 2,400 kcal) in muscle tissue.

Table: Carbohydrates

Carbohydrates are often referred to as sugars and starches, or as simple and complex carbohydrates. Examples of starches include grains, corn, rice, barley, vegetables, beans, and wheat, whereas examples of sugars include sweets (candy), sugar (cane sugar), fruit, and milk (Table: Carbohydrates). Except for lactose (milk sugar) and glycogen (the storage form of carbohydrates in the body), all carbohydrates are plant-derived. Food for Thought Carbohydrates contain the elements carbon, hydrogen, and oxygen. Hydrogen and oxygen form water (H2O), hence the term hydrate, which then combines with the carbon atoms (or, if viewed differently, the water molecule hydrates the carbon).

Anatomy of a GRAIN

Hairs of brush Bran Endosperm Germ In their natural growing state, whole grains consist of the entire seed, known as a kernel. The kernel consists of three parts: the bran, germ, and endosperm. The bran is the outermost layer of the kernel and is designed to protect the kernel from the environment. It contains B vitamins, antioxidants, and fiber. The germ is the embryo of the kernel and contains B vitamins, minerals, some protein, and healthy fats. The endosperm is the largest portion of the kernel. It contains starchy carbohydrates, some protein, and small amounts of vitamins and minerals. During most refining processes, the bran and germ are removed from the kernel. As such, much of the fiber and nutrients are lost. Examples of this process including removing the outer layer of a whole-grain kernel to convert brown rice to white rice.

Figure: Breakdown of Carbohydrates

However, our digestive process breaks down our digestible complex carbohydrates to their building blocks: the monosaccharides that are then absorbed into the body (Figure: Breakdown of Carbohydrates). Once absorbed, carbohydrates can be used immediately as a source of fuel or can be stored as glycogen in specific cells. In fact, the largest storage depots for carbohydrates (glycogen) are the muscle and liver cells.

Table: Soluble and Insoluble Fibers

If a food is listed as a good source of fiber, it may contain insoluble fiber, soluble fiber, or both. See Table: Soluble and Insoluble Fibers for examples of soluble and insoluble fiber foods sources and potential health benefits.

Figure: The Molecular Structure of Glycogen

It is a large molecule with a pinwheel orientation centered around a protein core (glycogenin), and it can range from 100 to over 30,000 glucose units (Figure: The Molecular Structure of Glycogen ). It is important to note that there is no fructose in glycogen; only glucose molecules are used to form glycogen. It has a highly branched structure, which allows enzymes to rapidly break the molecule apart as needed during glycogenolysis. The formation of glycogen (glycogenesis) occurs under action of glycogen synthase, an enzyme that is most active immediately after meals and after exercise.

Match the carbohydrate classification to the correct definition.

Oligosaccharides - 3 -10 sugar units Monosaccharides - single sugar unit Disaccharides - Paired sugar units Polysaccharides - Longer than 10 sugar units

Figure: Molecular Structure of Monosaccharides; Glucose, Galactose, and Fructose

They are each composed of carbon, hydrogen, and oxygen Subsequently, they are called hydrocarbons and they have the same molecular structure of C6H12O6. Although assembled with the same number of elements, the orientation of these elements within the molecule renders them uniquely different. Notice the difference in the molecular structure of fructose in comparison to glucose and galactose, which are both similar. This difference helps explain why fructose and glucose are absorbed and function differently in the body. While glucose and fructose are found in many food sources, galactose is only present in dairy products, forming part of the milk-sugar lactose.

Polysaccharides

They define glucose chains longer than 10 units in length, but they can be as large as several thousand glucose units in length. Polysaccharides are also complex carbohydrates and comprise starches, fibers and glycogen.

Disaccharides (added sugars)

They define pairs of sugar units. The 3 nutritionally important ones to humans are sucrose, maltose, and lactose. ex: sugar, corn syrup, lactose

Oligosaccharides

They define sugar units ranging from 3 to 10 units in length and are largely indigestible to humans.

Monosaccharides

They define the single sugar units of glucose (sometimes also referred to as dextrin or dextrose), fructose, and galactose and represent the absorbable forms of nutritionally important carbohydrates for the body.

Soluble fiber offer several benefits that include the following

Weight loss—It can delay gastric emptying (from the stomach) and it promotes an overall feeling of fullness, thereby potentially reducing caloric intake. Reducing risk for cardiovascular disease—It can bind to cholesterol particles. It can prevent its absorption and help remove this compound from the body. Bowel movement and intestinal health—It attracts water and it promotes bulk to the stool, which can safeguard against constipation. Diabetes protection—This carbohydrate is not absorbed. It can, therefore, reduce potential blood sugar spikes. Improved absorption of foods—It slows the movement of food through the small intestine. It can enhance nutrient absorption.