Nutrition Chapter 4

What is the cause of lactose intolerance, and what are the common symptoms?

A person has lactose intolerance when the body produces too little of the enzyme lactase needed to digest lactose (milk sugar). Undigested lactose remaining in the intestine draws liquid into the intestine from surrounding tissue and the bloodstream and intestinal bacteria use the undigested lactose for their own energy. These conditions cause irritating symptoms including nausea, pain, diarrhea, and excessive gas.

What are the names of the complex carbohydrates, and how do they differ from each other? What is their basic building block?

Another name for complex carbohydrates is polysaccharides, because the molecules are strands of many ("poly") repeating glucose molecules - their basic building block. The complex carbohydrates include glycogen, starch, and most fibers. Glycogen is the polysaccharide found in humans and animals. The structure of glycogen is highly branched. The body makes it from the glucose building blocks and stores small amounts of glycogen for the body's use. Starch is the digestible polysaccharide found in plants. Humans produce enzymes in their intestinal tract to break the bonds between glucose molecules so the glucose can be absorbed.Most fibers are also polysaccharides, but they differ from starch in one important way: humans do not make the enzymes to break the bonds, so the glucose in fiber cannot be absorbed. Review "Starch," "Glycogen," and "Fiber" as needed.

What factors besides increased intake of added sugars are contributing to rising rates of obesity and diabetes in developing countries?

As incomes rise, people tend to turn away from their traditional diets composed of whole foods because they can afford to eat more fats, animal proteins, fast foods, and highly processed foods. All of these contribute to higher calorie intakes, at the same time that populations are decreasing their physical activity.

What is the advantage of sugars consumed in fruits over the same sugars consumed in purified sweets?

Both fruit and refined sugar in sweets (sucrose and high fructose corn syrup - which is described later in the chapter) provide both fructose and glucose. However, the sugar in fruit is diluted with a high volume of water and is packaged with fiber, vitamins, minerals, and phytochemicals, so it is nutrient dense. Purified sweets provide "empty" calories.

What are the consequences of chronic high blood sugar (uncontrolled diabetes)?

Chronic high blood sugar can lead to many problems. Some cells convert excess glucose to toxic alcohols, causing cells to swell. In the eyes this causes vision problems. Other cells respond by abnormally attaching excess glucose to protein, interfering with the proteins' functions. Blood vessels and nerves are damaged in this way, causing loss of circulation and nerve function. Loss of blood flow damages the kidneys. The poor circulation also increases the likelihood of infections. Review "The Dangers of Diabetes" as needed.

What are the differences or similarities in symptoms for type 1 and type 2 diabetes?

Common symptoms are excessive thirst, urination, and hunger. A person may lose weight in spite of eating an appropriate amount or even excessive amount of food. Fatigue, infections, blurry vision, and poor wound healing are common in both types of diabetes. In type 1, the symptoms usually appear suddenly and dramatically. In type 2 the symptoms are more subtle and may develop gradually; often the individual blames the problems on obesity or old age. Review "Diabetes" as needed.

What is a disaccharide?

Disachharides are pairs of single sugars linked together. Examples include sucrose (glucose and fructose), maltose (glucose and glucose), and lactose (glucose and galactose).

How is fiber digested?

Fiber moves through the digestive system until it reaches the large intestine. The body does not produce an enzyme that can break down fiber, but living inside our colons are bacteria that can digest fiber. These bacteria break down fiber and as a byproduct gas is created and a small amount of energy is released and absorbed by the body. After the bacteria breaks down the fiber, what bulk remaining is passed through the colon and eliminated.

What are the benefits of fiber?

Foods that are high in fiber are good sources of vitamins, minerals, and phytochemicals, and they contribute little or no fat. Fiber specifically provides benefits such as promoting normal blood cholesterol levels, modulating blood glucose concentrations, maintaining healthy bowel function, and promoting a healthy body weight.

What are the essential functions of glucose?

Glucose is used for energy throughout the body, but it is the required energy source for the brain. Glucose is also required for metabolizing (using the energy from) fats.

What factors have been popularly blamed for causing obesity and diabetes, but aren't guilty?

High carbohydrate intake alone, whether from starch, refined sugars, or high fructose corn syrup, does not cause obesity or diabetes. Body fatness, not carbohydrate intake, is most closely related to development of diabetes, and insulin resistance is usually a consequence of being overweight, not a cause.

What factors has research shown to cause obesity?

High carbohydrate intake alone, whether from starch, refined sugars, or high fructose corn syrup, does not cause obesity or diabetes. Body fatness, not carbohydrate intake, is most closely related to development of diabetes, and insulin resistance is usually a consequence of being overweight, not a cause. Review controversy 4 "Are Added Sugars 'Bad' for You?" as needed.

What are the differences or similarities in management for type 1 and type 2 diabetes?

In both types of diabetes, the goal is to maintain blood sugar in a normal range, avoiding the extreme high blood sugar levels that occur with diabetes. In type 1 diabetes blood sugar is controlled by injecting insulin (or using a small insulin pump) to match the patient's carbohydrate intake. People with type 1 diabetes may also experience extreme lows in blood sugar, so frequent self-monitoring of blood glucose is essential. In type 2 diabetes, several management approaches are important. One goal is to control body fatness through increased physical activity and a healthful food intake. Certain oral medications can help control blood sugar. (Some people with type 2 diabetes must eventually receive insulin injections.) Carbohydrate intake should be consistent from day to day. Review "Diabetes" as needed.

How does each of these affect the blood sugar level? Exercise, gastric juice, glucagon, insulin, and mucus.

Insulin lowers blood sugar by helping glucose enter cells where it is used for energy. Insulin prompts muscle and liver cells to store glucose as glycogen and it also prompts fat cell to turn the glucose into fatty acids to be stored as fat. Glucagon raises blood sugar by signaling the breakdown of glycogen. Exercise lowers blood sugar by helping glucose enter cells where it is used for energy. Gastric juice and mucus do not affect blood sugar levels.

How does the intake of refined carbohydrates/added sugars relate to body fatness?

It is easy to ingest unneeded calories by consuming foods and drinks sweetened with refined carbohydrates, whether this is from added sugars or high fructose corn syrup. Also, the calorie content of foods made with refined flour is usually higher than the whole grain products they replace. Review Controversy 4 "Are Added Sugars 'Bad' for You?" as needed.

What treatment approaches are recommended for lactose intolerance?

Lactose intolerance affects different people to varying degrees. Some people are fine drinking up to a cup of milk along with a meal because the other foods dilute the lactose and slow its progress through the digestive tract. People with more serious underproduction of lactase can buy milk already treated with lactase as well as over-the-counter enzyme pills or drops. Because milk is often avoided, a calcium deficiency can be a problem with this population, so other high-calcium choices should be added to the diet. Aged cheese contains almost no lactose so it can be a source of calcium, along with orange juice and soy milk that have been fortified with calcium.

What happens to monosaccharides after they are absorbed? What are the uses for glucose?

Monosaccharides are absorbed into the bloodstream and delivered to the liver. There fructose and galactose are converted to glucose which is delivered to body cells via the blood stream. Some glucose will be used for current energy needs, and some will be stored as glycogen. Glucose fragments can be combined to form fat or they can be used in combination with nitrogen to make some amino acids. (Notice that carbohydrate can be converted to fat, but fat cannot be converted to carbohydrate.) Review "Digestion and Absorption of Carbohydrate" as needed.

What is a monosaccharide?

Monosaccharides are single sugar units. Examples include glucose, fructose, and galactose

What kinds of foods are highest in fiber?

Plants are the sources of all dietary fiber. Meat does not contain fiber, although some meat alternates such as legumes are sources. Legumes and bran (found in whole grains) are particularly good sources of fiber. Some of the best sources of fiber include legumes, whole grains, vegetables, and fruits. Fruit juice, however, is not a source of fiber. Review figure 4-4, section "Why Do Nutrition Experts Recommend Fiber-Rich Foods?" and figure 4-5.

What is a polysaccharide?

Polysaccharides are chains of multiple single sugar units. Examples include starch, fiber, and glycogen.

Describe the process of starch digestion and absorption: Where are enzymes produced (consider the mouth, stomach, pancreas, and small intestine)? What are the starch digestion products in each place?

Starch digestion begins in the mouth, where an enzyme in saliva starts to digest starch, breaking the starch into smaller polysaccharides. Carbohydrate digestion stops in the acidic stomach environment. In the small intestine enzymes supplied by the pancreas digest the starch to disaccharides. Then enzymes on the surface of the intestine cells (i.e. on the villi) break down the disaccharides to monosaccharides which are absorbed. Review "Digestion and Absorption of Carbohydrate" as needed.

What are major food sources of sucrose? Of starch?

Sucrose, or table sugar, is refined from the juice of sugar cane or sugar beets. Sucrose is an ingredient in many cookies, snack foods, and desserts. Review "Disaccharides." Starch is found in the edible seeds of corn, wheat (milled into flour), other grains, and in starchy vegetables.

What are the 3 simple sugars important in nutrition? What are the 3 disaccharides, their component monosaccharides, and their common names (if they have one)?

The 3 simple sugars are glucose (sometimes called dextrose), fructose (fruit sugar), and galactose. The 3 disaccharides are sucrose (also called table sugar, made up glucose and fructose), lactose (milk sugar, made up of glucose and galactose), and maltose (made up of 2 glucose molecules).

What parts of a grain kernel are present in whole-grain flour? What parts are present in refined flour?

The endosperm, germ, and bran are all included in whole-grain flour. Refined flour uses only the endosperm. Review " Whole Grains" and Table 4-4 as needed.

How does indigestible, unabsorbed fiber reduce cholesterol in the blood?

The main mechanism seems to be that some fibers in foods combine with cholesterol-containing bile in the intestine, which is excreted in the feces. The liver then withdraws cholesterol from blood to make bile used in fat digestion.

How similar are high fructose corn syrup (HFCS) and sucrose?

They have similar percent compositions of glucose and fructose and similar effects on blood sugar. HFCS has some advantages in food processing, which is why it is so widely used.

What nutrients are added to refined flour when it is enriched?

Thiamin, riboflavin, niacin, folate (all B-vitamins) and iron (a mineral) are added to refined flour. Review "Enrichment of Refined Grains" as needed.

What are the differences or similarities in causes for type 1 and type 2 diabetes?

Type 1 diabetes occurs when the pancreas stops producing insulin, often as a result of an autoimmune attack on the insulin-producing cells in the pancreas. Type 2 diabetes occurs when the body's cells become resistant to insulin. This resistance occurs most often in people who are sedentary and overweight, but especially if the fat is accumulated around the waist. Genetics plays a role in both type 1 and type 2 diabetes. Review "Diabetes" as needed.

Which of the following helps PREVENT type 2 diabetes?

Weight control, exercise, and a healthy lifestyle

What is the difference between breads labeled as wheat, whole-grain (or multi-grain), and 100% whole-wheat (or 100% whole grain)?

Wheat simply means the flour has been made from wheat kernels, but most often this term is used with refined wheat flour. Whole-grain and multi-grain bread means that some of these flours have been used in making the bread. Only when the label indicates 100% whole wheat (or grain) does the consumer know that all of the flour used is whole grain. Review "A consumer's Guide to...Finding Whole Grain Foods" as needed.

What happens when dietary carbohydrate intake is very low? What are ketones, and what is their role in the body?

When dietary carbohydrate intake is very low, the body reverts to its back-up plan: If glucose is not available for metabolizing fat, fat fragments combine and form ketones. The brain can use ketones as a fuel source, but there is a serious disadvantage to this back-up plan: a high level of ketones in the blood ("ketosis") changes the acid-base balance in the body, which alters many body processes. Review "Splitting Glucose for Energy" as needed.

What nutrients are higher in whole grain flour than in enriched flour?

Whole grain flours are higher in magnesium, zinc, vitamin B6, vitamin E, chromium, and fiber.