Jamie Pope, Steven Nizielski, and Alison McCook NUTRITION for a Changing World FIRST EDITION Chapter 4 Carbohydrates Whole Grain Hype © 2016 by W. H. Freeman and Company & Scientific American

Chapter 4 Objectives Define “whole grain,” and explain what occurs when grain is refined Identify the primary functions of carbohydrates in food and in the body Describe the classifications of dietary carbohydrates and their chemical compositions Explain how carbohydrates are synthesized in plants and animals Identify the types and sources of fiber, and describe the health benefits of fiber Identify the sources of carbohydrates in foods, and describe the dietary recommendations for carbohydrate intake Outline the steps in carbohydrate digestion Describe the difference between nutritive and non-nutritive alternative sweeteners, and identify examples of each category

Whole Grains Are foods with whole grains good for you? Consumption of whole grains that are high in fiber reduces the risk of heart disease and diabetes What is a whole grain? To be called a whole grain, the grain does not have to be intact; its parts all just have to be there. So many processed foods are ground or separated during refining, with all the bits thrown back together afterward. This processing can lower the fiber, vitamin, mineral, and phytochemical content of the whole grain. A Harvard study in 2013 showed that the relation of fiber to carbohydrate provides the benefit to whole grains. The beneficial whole grains have a ratio lower than 10-to-1 of total carbohydrate to fiber.

What Is a Carbohydrate? Hydrated carbons Made of carbon, hydrogen, and oxygen One or more sugar molecules together Found in plant foods and milk Major fuel source for the body Provide 4 kcal of energy per gram Recommended intake is 45% to 65% of total daily calories

Simple Carbohydrates

Complex Carbohydrates Oligosaccharides: 3 to 9 linked sugars Polysaccharides: 10 linked sugars

Complex Carbohydrates Plants Photosynthesis Link glucose together Starch Fiber

Glycogen Stored glucose in the body Liver Muscle Broken down to provide glucose in the blood Muscle Broken down to provide energy to do work

Carbohydrate-Rich Foods Complex carbohydrates Grains Legumes Some vegetables Simple carbohydrates Fruits Many vegetables Milk

Sugars Added to Food Refined sugars added to processed foods Add flavor Increase energy density Decrease nutrient density Contribute to obesity Benefit of avoiding excess added sugars Reduce risk of dental caries Possible different names of sugars on ingredients lists are sugar, brown sugar, invert sugar, high fructose corn syrup (HFCS), corn syrup, malt syrup, maple syrup, concentrated fruit juice, honey, molasses, or dextrose.

Carbohydrate Intake Recommendations 2010 Dietary Guidelines for Americans Total: Consume at least half of all grains as whole grains. Increase whole grain intake by replacing refined grains with whole grains. Added Sugars: Reduce the intake of calories from added sugars Institute of Medicine Recommendations (DRIs) Total: RDA, 130 g/day; AMDR, 45% to 65% of total calories Fiber: AI, 14 g per 1,000 kcal/day Added Sugars: ≤25% of total calories consumed American Heart Association (2009) Added Sugars: Women, ≤100 kcal/day (25 g); Men, ≤150 kcal/day (38 g) World Health Organization (2003) Added Sugars: ≤10% of energy intake

Carbohydrate Digestion Enzymes digest to monosaccharides Amylase Sucrase Maltase Lactase

Carbohydrate Digestion Mouth Amylase Breaks starch into smaller links of glucose Small intestine Continue digestion of starch into maltose and glucose

Carbohydrate Digestion Small intestinal cells Maltase Hydrolyzes maltose to produce two glucose monosaccharides Sucrase Hydrolyzes sucrose to produce one glucose and one fructose monosaccharide Lactase Hydrolyzes lactose to produce one glucose and one galactose monosaccharide

Carbohydrate Absorption Monosaccharides are absorbed by small intestine then transported to the blood

Carbohydrate Use Energy for body Fructose and galactose Glucose Carried to the liver and converted to glucose Exported back into the blood as glucose Glucose Primary fuel for cells Stored as glycogen in liver and muscles Excess made into fat to store

Fiber Solubility Dietary fiber Functional fiber Soluble Form viscous gels Insoluble Increase fecal bulk Dietary fiber Functional fiber Total fiber = dietary fiber + functional fiber Soluble fibers can decrease gastric emptying and give a feeling of fullness. They can also bind bile in the intestine, helping decrease body cholesterol. Insoluble fiber is not fermented and persists in the colon, increasing fecal bulk, softening stools, and reducing constipation. Dietary fiber is undigested carbohydrates and lignin in intact plant foods. Functional fiber is nondigestible carbohydrates synthesized or extracted from plants or animals.

Fiber

Fiber in the Body Insoluble fiber Soluble fiber Softens stool and decreases constipation Decreases hemorrhoids and diverticular disease Soluble fiber Slows stomach emptying Slows digestion and absorption Reduces the risk of coronary artery disease

Health Benefits of Fiber Soluble fiber may reduce the risk of cardiovascular disease. High-fiber foods promote satiety and may reduce the risk of obesity. High intakes of insoluble cereal fiber may reduce the risk of type 2 diabetes. Soluble fiber slows the increase in blood glucose following carbohydrate ingestion. High insoluble fiber intake softens stools and reduces the occurrence of constipation.

Lactose Intolerance Low lactase activity Lactose maldigestion Diarrhea Gas, cramps, abdominal pain Treatment Decrease dairy intake Lactase pills Calcium-rich foods Without lactase, the lactose doesn’t get broken down into glucose and galactose and absorbed, so the lactose passes through the intestine and draws water, causing loose stools or diarrhea. The lactose is metabolized by the bacteria forming gas and causing cramps and abdominal pain. Treatment is to decrease lactose intake or dairy products. Some people can tolerate small amounts as they have low levels of lactase. Some can tolerate yogurt or cheese because bacteria in the processing metabolize the lactose.

Sugar Alternatives Regulated Generally recognized as safe (GRAS) by the FDA

Nutritive Sweeteners Sugar alcohols are naturally occurring sugars in plants and berries that are poorly absorbed so they provide fewer calories. Overconsumption can cause diarrhea.

Non-Nutritive Sweeteners

Carbohydrates in the Diet Important source of energy Some choices are better than others Provide vitamins, minerals, fiber, and phytonutrients Best sources Minimally processed whole grains Vegetables Fruits Beans

Summary Carbohydrates, which are composed of carbon, hydrogen, and oxygen, contain 4 kcal/g and are found in plant foods and milk products In addition to serving as a primary energy source, carbohydrates are a source of fiber, act as added sweetness and flavor for food, and reduce the use of protein for energy The Institute of Medicine recommends that carbohydrate intake comprise 45% to 65% of total daily calorie intake Carbohydrates can be classified as simple (sugars) or complex (starch and fiber)

Summary (Cont’d) Simple carbohydrates include single sugar molecules, called monosaccharides (glucose, fructose, and galactose), or two-sugar units, called disaccharides (sucrose, lactose, and maltose) Monosaccharide glucose is the most abundant sugar circulating in the blood and serves as an essential energy source for the cells of the body Disaccharide sucrose (table sugar) is composed of glucose and fructose Lactose is the primary form of sugar found in milk; some individuals lack or have decreased levels of lactase, the enzyme needed to breakdown lactose, so they experience lactose intolerance

Summary (Cont’d) Complex carbohydrates are composed of linked monosaccharides that function as a stored form of energy “starch” or structural material “fiber,” depending upon how the sugars are linked Carbohydrate digestion is accomplished through the action of enzymes, and the carbohydrates are absorbed in the small intestine Fiber is indigestible by humans and has many health benefits Insoluble fiber aids in digestive health, and soluble fiber may lower risk of cardiovascular disease

Summary (Cont’d) Dietary fiber is the nondigestible fiber naturally found in plant foods; functional fiber is extracted or synthesized and added to foods during the manufacturing process; together they make up total fiber The DRI for fiber intake is 25 grams for woman and 38 grams for men Glycogen, a highly branched polysaccharide, is the storage form of glucose in humans and animals; stored primarily in the liver and muscles; liver glycogen can help maintain blood glucose The Dietary Guidelines for Americans recommend that we reduce intake of added sugars, which increase the risk of dental caries and provide empty calories Alternative sweeteners are regulated and considered “generally recognized as safe” (GRAS) by the FDA. Alternative sweeteners include nutritive sweeteners (sugar alcohols) and several non-nutritive sweeteners that are calorie-free and hundreds of times sweeter than sucrose.