4 Carbohydrates in Grains, Fruits, and Vegetables

4.1 Overview

Carbohydrates are an important source of fuel for body cells. Carbohydrates are organized in molecules that are in single (monosaccharide), double (disaccharide), or multiple (polysaccharide) units. Glucose, fructose, and galactose are examples of monosaccharides; sucrose, lactose, and maltose are examples of disaccharides; and starch and fiber are examples of polysaccharides.^1,2,3

There are three primary carbohydrate groups: sugars, oligosaccharides, and polysaccharides. Examples of sugars include the monosaccharides glucose and fructose, the disaccharides sucrose and lactose, and the polyols sorbitol and mannitol. Examples of oligosaccharides include maltodextrin and raffinose. Examples of polysaccharides include starch and fiber.

Digestion of carbohydrates begins in the mouth with salivary amylase and continues in the small intestine with pancreatic amylase. For absorption to take place in the intestine, disaccharides and polysaccharides must be further reduced or broken down. This is accomplished by enzymes called disaccharidases. When necessary enzymes are missing, an intolerance results. Lactose intolerance is an example of one that is caused by an inability to produce lactase, an enzyme necessary for the digestion of milk sugar.

First introduced in the 1970s, the term dietary fiber describes carbohydrates derived from plant cell walls, including cellulose, hemicellulose, and nonstarch polysaccharides. Although widely used, the terms soluble and insoluble fiber are inexact. Soluble fiber includes both viscous (gel forming) and nonviscous. Fiber is further differentiated by whether it is fermentable, which rapidly forms gas in the gastrointestinal tract, or nonfermentable, which does not. Each contributes to health in a different way. One of the most important ways is to provide bulk that promotes a healthy tone in intestinal muscles. ^4,5,6,7,8

Objectives

• Describe the role of carbohydrates in a healthy diet and explore common food sources
• Discuss how we digest carbohydrates and utilize the products of digestion
• Identify dietary fiber as important to gastrointestinal health
• Describe the relationship between dietary carbohydrates and management of blood glucose levels

4.2 Carbohydrate Organization

Overview

Plants manufacture carbohydrates through photosynthesis. We can digest a plant storage form of carbohydrate called starch. Many of the foods that we enjoy are sources of dietary starch. We cannot digest cellulose, a fibrous form of carbohydrate that plants use for structural support. The only animal food that contains significant amounts of carbohydrates is milk.

The major food sources of carbohydrates are cereal crops such as rice, wheat, and maize; root crops such as potatoes and cassava; sugar crops such as sugar cane and sugar beets; pulses such as lentils and chickpeas; milk, which contains lactose; and most fruit and vegetables.

Carbohydrate makes an important contribution to daily caloric needs. In most parts of the world, carbohydrates represent at least 50 percent of all calories consumed, with grains providing half the total. In addition to providing energy, food containing carbohydrates supplies protein, vitamins, minerals, and phytochemicals. Found in inexpensive, easy-to-store foods such as rice, corn, beans, and wheat, carbohydrates are the backbone of many traditional eating patterns.

Key Concepts

• Carbohydrate organization and molecules
• Carbohydrate grouping
• Sweeteners

Carbohydrate Organization

Carbohydrates in food are organized as a monosaccharide, disaccharide, or polysaccharide. The smallest unit, monosaccharide, is a basic sugar from which other, more complex carbohydrate molecules are made. Dietary monosaccharides include glucose, galactose, and fructose.

Dietary disaccharides, or two-sugar carbohydrates, include sucrose, lactose, and trehalose. Oligosaccharides include maltodextrin, raffinose, stachyose, and fructooligosaccharide (FOS). The primary polysaccharides, or multiple-sugar carbohydrates, that you consume in your diet are starch and fiber. A nondietary polysaccharide found in the body is glycogen, which is a storage form found in animals.

Ingested carbohydrates are first acted upon by salivary amylase found in the mouth. This begins the digestion of large molecules into smaller units. In the small intestine, additional enzymes such as maltase, pancreatic amylase, and sucrase complete digestion, resulting in the release of glucose, fructose, and galactose. These single-unit molecules are then actively transported across the membranes of absorptive cells for eventual release into the bloodstream.

Monosaccharides

The three monosaccharides found in the body are glucose, fructose, and galactose. Glucose is the principal source of energy for body cells. Circulating in the bloodstream, it is referred to as blood sugar. Glucose can be found in fruits and vegetables as well as in table sugar and foods made from grains. Glucose is the base unit for large polysaccharides such as starch that are made by plants.

Fructose is a monosaccharide found in fruits and honey. It is considered the sweetest of all the natural sugars. An example of a fructose source common to our food supply is high-fructose corn syrup (HFCS), a manufactured sweetener made from corn starch^.2 Due to its economical price and sweetness relative to sugar, this sweetener is widely used in the beverage and food-manufacturing industries. The third monosaccharide is galactose. Combined with glucose, it makes lactose, or milk sugar. Made only by animals, galactose is not in foods of plant origin. People who do not consume milk or dairy products do not encounter galactose.

Disaccharides

When two monosaccharides, or single-sugar carbohydrates, are joined, a disaccharide is formed. The most common disaccharides are sucrose (table sugar), lactose (milk sugar), and maltose (grain sugar). See Table 4.1. Sucrose is found in natural sweeteners, such as table sugar, honey, and maple sugar. It is formed when a unit of glucose is joined to a unit of fructose.

Lactose is formed when glucose is joined with galactose. It is found only in dairy products and is present in all types of fluid milk, including whole, reduced fat, low fat, and skim. Conversely, there is much less lactose in hard cheese such as cheddar. Lactose is the least sweet of the three disaccharides.

Maltose results when a unit of glucose is joined to a unit of glucose. Maltose is a source of energy for yeast during the fermentation process used in brewing beer and making bread. Maltose is less sweet than sucrose but adds a nice touch to a malted milkshake!

Polysaccharides

Many foods contain starch, a polysaccharide composed of repeating units of glucose. Amylose and amylopectin are examples of starch, a polysaccharide found in grains and some vegetables, such as beans. Modified starch is used in food manufacturing to improve the appearance and texture of food products. Resistant starch is a polysaccharide that is not well absorbed. An example of resistant starch is raw starch granules in a potato or an intact grain of wheat.

Additional carbohydrate examples include glycogen and fiber. Glycogen is a polysaccharide found in animal tissue, specifically the liver and muscles. It serves as a quick, if limited, energy source during exertion. Fiber is an indigestible carbohydrate found in many plant foods, including fruits, grains, and vegetables.

The polysaccharides group includes starch, modified starch, resistant starch, and fiber.

Polyols

Sugar alcohols, or polyols, have a chemical structure resembling both carbohydrates and alcohol. Even though polyols have an alcohol group, they don’t contain ethanol found in wine or beer. Sorbitol, mannitol, xylitol, maltitol, and isomalt are common polyols incorporated into manufactured foods to provide sweetness and texture.¹⁰

Your body is unable to completely digest and absorb polyols, and as a result, they contribute only one and a half to three calories per gram. In addition, the process by which they are converted to energy requires little insulin. Consequently, foods designed to provide sweetness without elevating blood glucose levels often contain polyols.

On a nutrition facts label (NFL), the figure for total carbohydrates includes polyols, even though they provide fewer calories per gram than other digestible carbohydrates. Products labeled as sugar-free or containing two or more polyols must list sugar alcohol on the label. Excess consumption (>20 grams/day) may cause diarrhea.

Sweeteners

The ingredients used to sweeten our foods are classified as either nutritive or caloric (providing significant calories) or nonnutritive (having few calories) sweeteners.⁵ Nutritive sweeteners contain carbohydrates and provide four calories per gram. Examples include table sugar, honey, and fructose.

A whole food source of fructose is fruit. Including fruit in your daily fare adds dietary fiber, vitamins, minerals, and phytochemicals to your diet. Conversely, processed foods and soft drinks that contain HFCS, which is used to make foods more appetizing, are a significant source of added sugars. Polyols, or sugar alcohols, such as sorbitol, are nutritive sweeteners that are poorly absorbed and provide fewer than four calories per gram.

Nonnutritive sweeteners are (1) many times sweeter than sugar, (2) required in much smaller amounts, or (3) poorly digested. As a result, they provide fewer calories per serving. Examples of nonnutritive sweeteners include stevia, saccharin, aspartame, acesulfame-K, and sucralose.¹¹

Summary

Knowing more about carbohydrate organization helps us understand how different units function in our foods and provide energy for our bodies. Glucose is a monosaccharide or single-unit carbohydrate that circulates in our bloodstream. Sucrose is a disaccharide or two-unit carbohydrate that sweetens our foods. Starch is a polysaccharide or multiunit carbohydrate that provides energy, while fiber is a polysaccharide that gives our food bulk. Polyols are sugar alcohols that are used in manufacturing to provide a sweet taste while providing fewer calories per gram than sugar. Why? Polyols are poorly digested. Sweeteners are classified as nutritive or providing calories and nonnutritive or providing few or no calories.

4.3 Carbohydrate Digestion and Utilization

Overview

Digestion of carbohydrates begins in the mouth with salivary amylase and continues in the small intestine with pancreatic amylase. For absorption to take place in the intestine, disaccharides and polysaccharides must be further broken down by enzymes called disaccharidases. When enzymes are missing, an intolerance results. Lactose intolerance is an example of one that is caused by an inability to produce lactase, an enzyme necessary for the digestion of milk sugar.

When body supplies of glucose, a carbohydrate, are adequate, ingested protein is used for body maintenance, repair, and growth. When it is not, protein and stored fat serve as fuel for body metabolism. Recommendations for daily carbohydrate intake are based on the minimal amount needed to prevent ketosis, a condition characterized by the incomplete combustion of fats, resulting in elevated blood ketone levels, and they reflect the importance of carbohydrates for the brain.

Key Concepts

• Carbohydrate digestion
• Lactose intolerance and milk allergy
• Recommended daily intake

Carbohydrate Digestion

Digestion of carbohydrates is enhanced by food preparation techniques, such as cooking, that heat starches in the presence of moisture. For example, the starch in a potato is easier to digest when it is baked or boiled. Starch granules swell and burst, making starch more available for enzymatic action in the gastrointestinal tract.

When starch is in contact with the saliva in your mouth, salivary amylase begins the digestion process. As chewed foods enter the stomach, the acidic environment renders the salivary amylase inactive.

As churned foods, or chyme, moves to the upper small intestine, pancreatic amylase delivered via the common bile duct continues the breakdown of large polysaccharides. Subsequently, cells lining the intestine produce additional enzymes such as sucrase, maltase, and lactase that are designed for the digestion of disaccharides.

When key enzymes are not available or are present in insufficient amounts, the carbohydrates for which they are targeted are not digested. One example of this condition is lactose intolerance. After early childhood, most people experience a decrease in the production of lactase, an enzyme that breaks lactose into glucose and galactose. This deficiency is common and called lactose intolerance.

Lactose Intolerance

Simply drinking a glass of milk can initiate the symptoms of lactose intolerance. How? When lactose is consumed and not digested, a rich source of energy is propelled into the large intestine, where bacteria thrive. These bacteria rapidly multiply, producing gas and acid as waste products that cause abdominal cramps, gas, and diarrhea. In addition, an osmotic effect occurs where carbohydrate in the large intestine is more concentrated than that in surrounding tissues. As a result, water is drawn into the lumen to dilute the solution. This causes a bloated feeling.¹²

Digestion of lactose, or milk sugar, requires the presence of lactase, an enzyme. Lactase is produced by the cells of the small intestine and is used to digest or break down lactose into the monosaccharides glucose and galactose.

Worldwide, approximately 65 percent of all adults experience some lactose intolerance. Interestingly, lactose intolerance is lowest among descendants of populations that relied on unfermented milk products as an important food source, and highest where these products were not historically used. People with Northern European ancestors represent a group that historically used milk, and as a result, only 5 percent of descendants are intolerant. Converse, 70-100 percent of people with East Asian ancestors where milk was not historically a major food source are intolerant.¹³

This does not preclude the consumption of milk and dairy products if consumed with other foods and in smaller portions. In addition, enzyme preparations are available that are taken prior to drinking milk. These preparations predigest the lactose, breaking it down into glucose and galactose, both of which are readily absorbed.

Milk Allergy

Lactose intolerance results when the cells of the small intestine no longer produce lactase, an enzyme that digests lactose. Lactose intolerance is a gastrointestinal disorder, and the associated symptoms are abdominal cramps and diarrhea.

A milk allergy is caused by an immune system reaction to a foreign substance or allergen.7 Proteins in milk from cattle can be allergens for some people who respond by manufacturing antibodies as the immune system attempts to neutralize the allergen.¹⁴

Casein and whey are two proteins in cow’s milk that trigger this response. Symptoms commonly associated with an allergic response are system wide (not limited to the gastrointestinal tract) and can range from a rash to a life-threatening constriction of the throat. Someone who is allergic to milk is advised to avoid all milk and milk products.

Protein-Sparing Effect

Carbohydrate is an important source of fuel for your body cells. The primary carbohydrate in the body is glucose, which is commonly referred to as blood sugar. When the body’s supply is adequate, protein is spared for building body tissues.

When adequate amounts are not present, in addition to utilizing fat stores, the liver shifts to deaminating, or dismantling, proteins to produce glucose. For this reason, it is important to eat an adequate amount of carbohydrates to maintain body efficiency, minimize utilization of protein for energy, and maximize complete oxidation of fat as a fuel.

Recommended Daily Intake

The Institute of Medicine (IOM) set the Recommended Dietary Allowance (RDA) for digestible carbohydrates based on the importance of carbohydrates as an energy source for the brain.8

The RDA for adult men and nonpregnant or lactating women is 130 grams/day; for pregnant women, 175 grams/day; and for lactating women, 210 grams/day. The acceptable macronutrient distribution range (AMDR) was set at 45-65 percent of total calories. See Table 4.2. To prevent ketosis, or a buildup of ketones in the blood accompanied by an increase in blood acidity, consume at least fifty to one hundred grams each day. Carbohydrate provides four calories per gram. Consumption of one hundred grams a day equates to four hundred calories, or 20 percent of a two-thousand-calorie diet.

Summary

Digestion of carbohydrates begins as soon as food is ingested. Enzymes such as amylase, sucrase, maltase, and lactase break down carbohydrate molecules into monosaccharides. Lactose intolerance is an example of a gastrointestinal disorder resulting from the lack of lactase, an enzyme needed for the digestion of lactose. A milk allergy is a response to one or more proteins in milk. By sparing its use as a fuel, adequate dietary carbohydrate supports the use of protein for body maintenance and repair. Recommended daily carbohydrate intakes are based on the prevention of ketosis.

4.4 Dietary Fiber

Overview

First introduced in the 1970s, the term dietary fiber describes carbohydrates derived from plant cell walls, including cellulose, hemicellulose, and nonstarch polysaccharides. Soluble fiber includes both viscous (gel forming) and nonviscous. Fiber is further differentiated by whether it is fermentable, which rapidly forms gas in the gastrointestinal tract, or nonfermentable, which does not. Each contributes to health in a different way. One of the most important is to provide bulk that promotes a healthy tone in intestinal muscles.

Key Concepts

• Soluble and insoluble fiber
• Fiber and gastrointestinal tract health
• Food sources

Soluble and Insoluble Dietary Fiber

Dietary fiber is made up of carbohydrates and lignin from plant foods that are not digested, including cellulose, hemicellulose, and nonstarch polysaccharides.9 Due to our inability to digest fiber, it is not considered to be a source of energy. Fiber in our foods provides bulk and texture, making our meals more interesting and satisfying.

Dietary fiber is typically classified as soluble or insoluble. This nomenclature, originated in early chemistry descriptions of nonstarch polysaccharides, was based on the ability of some types of fiber (soluble) to dissolve in water, while other types (insoluble) did not.

Soluble fiber includes both viscous (gel forming) and nonviscous. Fiber is further differentiated by whether it is fermentable or nonfermentable.11 Short-chain oligosaccharides are a type of soluble dietary fiber that is highly fermentable and rapidly forms gas in the GIT, causing bloating and flatulence. Conversely, long-chain soluble viscous fiber produces less gas and abdominal discomfort.

Fiber Provides Bulk and Supports Microflora

Even if you don’t distinguish between the different types of fiber, there are many benefits worth considering. Fibers provide bulk that exercises intestinal muscles and reduces the risk of constipation, diverticulosis, and hemorrhoids. The soft, moist texture of these fibers decreases pressure by promoting moderate muscle contractions that readily move materials along the lower gastrointestinal tract. Other fibers provide an energy source for bacteria residing in the large intestine, thereby maintaining a healthy microbial population that decreases the risk of disease.

Glucose and Lipid Absorption

Fiber slows glucose absorption from the small intestine, leading to a less severe rise in blood levels after a meal. Fiber also prolongs the time needed for the stomach to empty its contents into the small intestine. This delay contributes to a slow rise in postmeal blood glucose levels.

A diet well supplied with fibers also reduces the risk of cardiovascular disease. This is accomplished through direct and indirect mechanisms. Certain fibers directly reduce blood cholesterol by limiting the absorption of cholesterol and triglycerides. Others do so indirectly by increasing the loss of bile salts, which contain cholesterol.

The liver uses cholesterol to manufacture bile and must increase production when bile is lost during digestion. As the liver increases production, less cholesterol is available to circulate in the blood.

Fiber Recommendations

The National Academies of Science Engineering and Medicine recommends that men between the ages of eighteen to fifty years consume about thirty-eight grams of fiber per day, and women eighteen to fifty years, twenty-five grams. Most people living in the US do not meet recommendations and typically consume only about fifteen to sixteen grams per day. People assume that they have met their fiber needs by choosing foods labeled whole grain or those that are made from whole grain, which can leave them inadequate. While these foods contribute to daily fiber intake, vegetable and fruit sources are important too.

Finding Fiber in Foods

How do you find the fiber in your food? The number of grams of fiber per serving is found on the nutrition facts label under carbohydrate.¹⁵ Don’t worry about calories! As fiber is indigestible, it provides none. Selecting from a wide variety of foods ensures the consumption of all types of fiber. Include foods from grains, fruits, and vegetables, as each group contains a unique combination. Fiber intake should be increased gradually over a period of several weeks. Drink additional water to offset that  absorbed by fiber.

Examples of good fiber sources include the following: dried beans; dried peas and other legumes, such as baked beans, kidney beans, split peas, garbanzos, pinto beans, and black beans; bran cereals; green peas; dried fruit such as figs, apricots, and dates; raspberries, blackberries, and strawberries; sweet corn; rye, oats, buckwheat, and stone-ground cornmeal; bread, pasta, and muffins made with whole-grain flours; broccoli, green snap beans, and pole beans; and plums, pears, apples, raisins, prunes, nuts, and greens.

What about the term complex carbohydrates? First coined in the 1970s, this term is outdated and inexact. Confusion about the definition of complex carbohydrates is common. Sometimes it includes both starch and fiber, and other times only starch. Complex carbohydrates are used to describe foods high in starch, such as grains, as well as those low in starch, such as fruits and some vegetables. As a result, it is more useful to refer to carbohydrate components as belonging to one of three groups: sugars, oligosaccharides, or polysaccharides. Fiber is a nonstarch polysaccharide.

Summary

Provided by plant foods, dietary fiber is an important part of a healthy meal pattern. Soluble fiber dissolves in water, while insoluble fiber does not, thereby providing bulk. Viscous fiber forms gels that make you feel full and satisfied after a meal. Fiber provides intestinal muscles with a soft, moist substance that moves easily through the system and reduces the need for excess pressure. Fiber contributes to good health by moderating blood glucose rise after a meal, trapping and moving cholesterol-containing bile out of the body, and supporting a beneficial microflora. Most people don’t consume enough fiber, and eating more whole grains, fruits, and vegetables can improve fiber intake.

4.5 Carbohydrate and Blood Glucose

Overview

Insulin and glucagon regulate blood glucose levels. Insulin helps cells remove glucose from the bloodstream, thereby reducing levels. Glucagon mediates the release of glucose from body stores, such as glycogen, thereby increasing blood levels. Together these hormones maintain an optimal blood glucose level. When the body is unable to produce insulin or cells resist it, diabetes mellitus type 1 or 2 results.

The glycemic index (GI) describes a blood glucose response to a fifty-gram portion of a test food when compared to that of a standard food consumed by the same person. Foods with a high GI are digested and absorbed more quickly than those with a low GI. An understanding of GI helps you make good carbohydrate choices.

Key Concepts

• Hormones that closely regulate blood glucose levels
• Glycemic index, a tool for estimating response to eating carbohydrates
• Monitoring carbohydrate intake to manage diabetes mellitus

Blood Glucose Regulation

Blood glucose levels are maintained within a narrow range of 70 mg/dL to 110 mg/dL. Counterregulatory hormones, or hormones that work in opposition to each other, play a key role in maintaining these levels. Insulin is a hormone produced by the beta cells of the pancreas that promote the movement of glucose out of the bloodstream and into body cells. Glucagon is a counterregulatory hormone that is secreted when blood glucose levels are low, causing glucose to move back into the bloodstream.

Insulin

Blood insulin levels increase when blood glucose levels increase. This typically happens after consuming a meal containing carbohydrates. In response, the liver converts glucose to glycogen, the carbohydrate storage form. The liver also converts excess glucose into fat or triglycerides. Individuals who are concerned about their blood triglyceride levels should avoid excessive consumption of carbohydrates to limit triglyceride production by the liver. As glucose moves out of the bloodstream and into cells, blood levels of both glucose and insulin drop to the maintenance range.

Glucagon

Glucagon is a counterregulatory hormone that also affects blood glucose levels. It is released by the pancreas when you have not eaten in some time and your blood glucose levels start to fall. Glucagon prompts the liver to convert glycogen to glucose. To further increase blood glucose levels, the liver also manufactures glucose from amino acids and lactic acid. Released by the adrenal gland, epinephrine (adrenaline) also works to increase blood glucose levels.

Glycogen

A carbohydrate storage form found in your own body is glycogen. Glycogen is sometimes referred to as animal starch and is found in the liver and muscle tissue. It is a highly branched molecule composed of many glucose units. While the glycogen in muscle tissue provides a readily available source of glucose for muscles, only the liver can utilize its glycogen stores to release glucose into the bloodstream.

If you do not eat any carbohydrates, the glycogen reserves of the liver will be depleted in less than a day, at which point the body will resort to the breakdown of proteins to maintain adequate blood glucose levels.

Insulin protects the body from a blood glucose concentration that is too high by prompting the uptake of glucose by body cells, the synthesis of glycogen by the liver and muscle cells, and fat storage in adipose tissue and by stimulating protein synthesis. Glucagon protects the body from a concentration that is too low by signaling the liver to increase glucose production through the breakdown of glycogen, amino acids, and triglycerides.

Glycemic Index

The GI describes the blood glucose response to a fifty-gram portion of a test food when compared to that of a standard food, such as white bread, consumed by the same person. It is a difficult concept to generalize, as response varies from person to person. In addition, ingesting a single starch-containing food evokes a different blood glucose response than eating that same food in a meal containing fat and protein.

Other factors such as food crop variety influence carbohydrate content and, therefore, blood glucose response. For example, the type of potato grown in Australia is different than that grown in the US. The starch content of Australian and US potatoes is therefore different as well. Additionally, processing, storing, and cooking modify starch availability and subsequent glucose absorption.

The best way to use the GI is to rank foods.¹⁶ Generally speaking, low GI foods are digested more slowly than high GI foods. Consequently, low GI foods raise postmeal blood glucose levels only slightly, whereas, high GI generate a sharp increase in glucose levels. A low GI diet is associated with a reduced risk of chronic disease, including diabetes and elevated blood cholesterol. Low GI foods contain more fiber, thus benefiting the health of the large intestine.

Low GI foods include kidney beans, lentils, chickpeas, pearled barley, lightly refined grains (e.g., whole-grain or whole wheat bread, rice, or pasta), unsweetened yogurt, and peanuts.

High GI foods include instant mashed potatoes, instant rice, sweetened cereals, table sugar, white bagel, jellybeans, pancakes, and dates.

Diabetes Mellitus

Diabetes is characterized by elevated blood glucose levels and alterations in the metabolism of carbohydrates, fat, and protein. There are two types of diabetes—type 1 and type 2—as well as a prediabetes condition.¹⁷ Individuals with diabetes monitor their consumption of carbohydrate foods to balance what they eat with medication or insulin injections. The CDC reported that 10.5 percent of the US population has diabetes, with 21.4 percent of those with diabetes undiagnosed or unaware of their condition.^18,19

For those counting carbohydrates, a serving contains fifteen grams. Careful attention is given to how much carbohydrates are consumed at one time and throughout the day. Successful management of diabetes requires an understanding of which foods contain carbohydrates, the degree to which each elevates blood glucose levels, and how to use medications and insulin to maintain blood glucose levels within the normal range.

Type 1

Individuals with type 1 diabetes represent only about 5-10 percent of all people living in the US with diabetes. Type 1 is characterized by hyperglycemia (elevated blood glucose levels), polydipsia (excess thirst), polyuria (excess urination), glycosuria (glucose in the urine), dehydration, increased appetite, and weight loss.

Type 1 diabetes involves a genetic predisposition and a triggering event, such as a traumatic injury or illness. An autoimmune attack on the insulin-producing cells of the pancreas is triggered. Eventually, insulin-producing cells are destroyed and can no longer supply the body with insulin.

The onset of type 1 diabetes usually occurs before forty and most commonly around fourteen years of age. The onset of symptoms is sudden, and an external source of insulin is required to correct blood glucose levels and prevent severe complications and possible death.

Type 2

Type 2 diabetes involves a genetic tendency, the increased resistance to the action of insulin by body cells, and pancreatic cell defects. It is characterized by abnormal insulin secretion by the pancreas coupled with cellular resistance to insulin. As body cells become more and more resistant to insulin, the pancreas adapts by producing ever-increasing amounts. The pancreatic cells eventually become exhausted, and insulin production drops.

Obesity is thought to cause insulin resistance; however, people of normal weight also can exhibit these symptoms. This condition may persist for some time before diagnosis.

Individuals with either type of diabetes are at increased risk of heart and vascular disease. Achieving a desirable body weight, getting exercise, maintaining blood glucose levels within the normal range, and eating low to moderate amounts of fats all contribute to lowering the risk.

Carbohydrate and Health

Carbohydrates are an important part of a healthy diet.19 They are found in a wide variety of plant foods that give our diet taste and texture. Selecting whole foods from different groups ensures adequate consumption of the vitamins, minerals, phytochemicals, and fibers that are associated with carbohydrate foods. Include cereals, pulses, root crops, fruits, vegetables, and milk in a well-balanced diet.

Summary

The amount of glucose circulating in the bloodstream is closely regulated by two hormones, insulin and glucagon, that work in opposition to each other. A blood glucose level that falls below the desirable range of 70-110 mg/dL stimulates the pancreatic release of glucagon, which increases the production of glucose in the liver. Levels above the desirable range stimulate the release of insulin, which removes glucose from the bloodstream by facilitating cellular uptake. A glycemic index is a tool for ranking blood glucose response to carbohydrates in foods, but it is inexact. Use it to categorize foods based on the likelihood of impacting blood glucose levels.

References

1. Dietary Reference Intakes Tables and Applications. National Academies of Science Engineering Medicine. Health and Medicine Division. http://nationalacademies.org/hmd/Activities/Nutrition/SummaryDRIs/DRI-Tables.aspx. Updated October 2019. Accessed January 16, 2021.
2. Trowell H. Dietary fibre, ischaemic heart disease and diabetes mellitus. Proc Nutr Sci. 1973;32(3):151-157. doi:10.1079/pns19730033.
3. Codex Alimentarius Commission. World Health Organization. Food and Agriculture Organization of the United Nations. http://www.fao.org/tempref/codex/Meetings/CCNFSDU/ccnfsdu26/nf2603ae.pdf. Published July 2004. Accessed January 16, 2021.
4. El-Saihy M, Ystaf SO, Mazzawi T, Gundersen D. Dietary fiber in irritable bowel syndrome. Intern J Molec Medic. 2017;40(3):670. doi:10.3892/ijmm.2017.3072.
5. Dietary Fiber: Essential for a Healthy Diet. Mayo Clinic. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/fiber/art-20043983. Published November 2018. Accessed January 16, 2021.
6. Dietary Reference Intakes: Macronutrients. National Academies of Science Engineering Medicine. Health and Medicine Division. http://www.nationalacademies.org/hmd/~/media/Files/Activity%20Files/Nutrition/DRI-Tables/8_Macronutrient%20Summary.pdf. Accessed January 16, 2021.
7. Quagliani D, Felt-Gundersen P. Closing American’s fiber intake gap. Am J Lifestyle Med. 2017;11(1):80-85. doi:10.1177/1559827615588079.
8. Dietary Fiber: What It Is. US Food and Drug Administration. https://www.accessdata.fda.gov/scripts/interactivenutritionfactslabel/factsheets/dietary_fiber.pdf. Accessed January 16, 2021.
9. Total Carbohydrate: What It Is. US Food and Drug Administration. https://www.accessdata.fda.gov/scripts/InteractiveNutritionFactsLabel/factsheets/Total_Carbohydrate.pdf. Accessed January 16, 2021.
10. Sugar Alcohol Fact Sheet. International Food Information Council Foundation. https://staging.foodinsight.org/sugar-alcohols-fact-sheet/. Published October 2009. Accessed January 16, 2021.
11. Nutritive and Nonnutritive Sweetener. National Agricultural Library. US Department of Agriculture. https://www.nal.usda.gov/fnic/nutritive-and-nonnutritive-sweetener-resources. Accessed January 16, 2021.
12. Lactose Intolerance. US National Library of Medicine. https://ghr.nlm.nih.gov/condition/lactose-intolerance#statistics. Published February 2020. Accessed January 16, 2021.
13. Milk Allergy. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/milk-allergy/symptoms-causes/syc-20375101. Published June 2018. Accessed January 16, 2021.
14. Slavin J, Carlson J. Carbohydrates. Adv Nutr. 2014;5(6):760-761.
15. Glycemic Index for 60+ Foods: Measuring Carbohydrate Effects Can Help Glucose Management. Harvard Health Publishing. Harvard Medical School. https://www.health.harvard.edu/diseases-and-conditions/glycemic-index-and-glycemic-load-for-100-foods. Updated January 2020. Accessed January 16, 2021.
16. Diabetes. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/diabetes/diagnosis-treatment/drc-20371451. Published August 2018. Accessed January 16, 2021.
17. National Diabetes Statistics Report, 2020. Centers for Disease Control and Prevention. https://www.cdc.gov/diabetes/data/statistics/statistics-report.html. Reviewed February 2020. Accessed January 16, 2021.
18. O’Callaghan A, van Sinderen D. Bifidobacteria and their role as member of the human gut microbiota. Front Microbiol. 2016;7:925. doi:10.3389/fmicb.2016.00925.