Chapter 4: Carbohydrates, Sugars, Starches and Fiber

© 2010 Pearson Education, Inc.

Chapter 4: Carbohydrates, Sugars, Starches and Fiber


What Are Carbohydrates?

Produced by plants during photosynthesis After eating plant foods, humans convert the carbohydrates

into glucose Glucose

• Most abundant carbohydrate

• Preferred source of energy for the blood, brain, and nervous system

Carbohydrate-rich plant foods make up the foundation of diets all over the world


Classification of Carbohydrates

Simple carbohydrates

• Monosaccharide

• Disaccharide

• Perceived as sweeter than complex carbohydrates

- Mixes with saliva and reacts with taste buds Oligosaccharides Complex carbohydrates

• Polysaccharides


Monosaccharides

Three nutritionally important monosaccharides

• Glucose

• Fructose

• Galactose


Monosaccharides

Glucose

• Blood glucose and blood sugar in the body

• Most abundant monosaccharide in the body

- Is the preferred and main source of energy for the brain and red blood cells

• Part of every disaccharide

• Only monosaccharide in starches


Monosaccharides

Fructose

• Sweetest of natural sugars

• Found abundantly in fruits

• Part of high-fructose corn syrup Galactose

• Commonly occurs as part of dissaccharide lactose

Figure 4.2

The Structural Differences between Glucose, Galactose, and Fructose


Disaccharides

Three Disaccharides

• Sucrose

- Most common

• Lactose

• Maltose

- Least common

- Formed from digestion of starches

Figure 4.3

Monosaccharides Link to Form Disaccharides


Polysaccharides

Starch• Plants store glucose in chains of starch

- Amylose- Straight chain- More resistant to digestion- Resistant starch

May improve health of digestive tract May improve glucose tolerance May stimulate growth of beneficial intestinal

bacteria- Amylopectin

- Branched chains- Easier to digest


Polysaccharides

Fiber

• Nondigestible polysaccharides

• Provides no energy

• Classification

- Soluble

- Pectins, beta-glucan, some gums, mucilage

- Easily fermented by intestinal bacteria

• Carbon dioxide, methane, some fatty acids

- Insoluble

- Cellulose, lignin, some hemicelluloses

- Not easily fermented


Fiber Health Benefits

Soluble fibers

• Slow gastric emptying and may delay absorption of some nutrients

- Helps reduce serum cholesterol

- Improve appetite control

- Normalize blood glucose levels

• May help protect against colon cancer Insoluble fibers

• Relieves constipation Most plant foods contain both soluble and insoluble fibers


Polysaccharides

Glycogen

• Storage form of glucose in animals

• Long, branched chains of glucose

• Stored in liver and muscle

• Liver glycogen response to blood glucose (BG) levels

BG glycogen breakdown BG

• Muscle glycogen can be broken down for energy for the muscle

Figure 4.4

The Comparison of Starch and Glycogen Molecules


Oligosaccharides

Similar in length to simple carbohydrates Similar in makeup to polysaccharides Humans lack the enzymes necessary to digest them Intestinal microflora digest and ferment them

• Cause bloating, discomfort, and flatulence Food sources

• Legumes, beans, cabbage, brussels sprouts, broccoli

Figure 4.7

The Structure of an Oligosaccharide


Quick Review

Complex carbohydrates

• Polysaccharides: starch, fiber, glycogen

• Fiber

- Soluble – fermented by intestinal bacteria; moves slowly

- Insoluble – moves quickly through and reduces constipation

- Functional – added to foods Oligosaccharides

• Contain three to ten units

• Part of cellulose in cell walls


Carbohydrate Digestion and Absorption

Disaccharides and starches are digested to monosaccharides Monosaccharides are easily absorbed Fiber passes through the GI tract undigested

Figure 4.8a

Figure 4.8b

Figure 4.8c

Figure 4.8d


Absorption of Carbohydrates

Once digested to monosaccharides • Absorbed through the intestinal cell mucosa• Transported to the liver via the portal vein• Metabolic needs direct fate of the monosaccharides

- Galactose and fructose• Used by the liver for energy• Converted to glucose

- Glucose• Used for energy• Converted to glycogen through glycogenesis• Converted to glycerol and fatty acids for storage in

addipocytes

Figure 4.9

Glucose Is Stored in the Liver and Muscle Cells as Glycogen


Quick Review

Digestion of carbohydrates begins in the mouth Most carbohydrate digestion takes place in the small

intestine Carbohydrates are broken down to monosaccharides for

absorption Monosaccharides are converted to glucose in the liver and

• Used as energy

• Stored as glycogen in the liver and muscle cells

• Stored as glycerol and fatty acids in the adipocytes Fiber travels to the colon undigested and most is eliminated

from the body


Lactose Intolerance

Deficiency of lactase, the enzyme that digest lactose

• Maldigestion – inability to digest lactose due to low levels of the enzyme

• Intolerance

- Maldigestion resulting in nausea, cramps, bloating, flatulence, and diarrhea


Functions of Carbohydrate

Provide energy

• 4 kilocalories per gram Maintain blood glucose

• Carbohydrate intake

• Glycogenolysis > 4 hours after a meal Spare protein

• Prevents the need for glyconogenesis Prevents ketosis


How to Maintain Blood Glucose Levels

Goal for blood glucose is 70–100 mg/dl Insulin – lowers blood glucose levels

• Needed for glucose to enter the cell from the blood stream- Exception: liver, kidney, and brain cells

• Helps convert glucose to glycogen through glycogenesis• Helps convert glucose to fatty acids through lipogenesis• Inhibits lipolysis

Glucagon – increases blood glucose levels• Stimulates the release of glucose into the blood• Stimulates glycogenolysis• Stimulates gluconeogensis

Figure 4.10

Insulin and Glucagon Regulate Glucose Metabolism


How to Maintain Blood Glucose Levels

Epinephrine and norepinephrine – increases blood glucose

• Stimulate glycogenolysis and gluconeogenesis Cortisol – increases blood glucose

• Stimulates gluconeogensis

• Reduces uptake of glucose by the muscle cells Growth hormone – increases blood glucose

• Stimulates fat breakdown for energy

• Reduces uptake of glucose by the muscles

• Increase glucose production in the liver


Quick Review

Glucose is the body’s preferred source of energy

• Especially the brain and red blood cells Adequate carbohydrate intake

• Maintains blood glucose levels

• Spares protein

• Prevents ketosis Blood glucose levels are maintained by two hormones

• Insulin which lowers blood glucose levels

• Glucagon which raises blood glucose levels Epinephrine, norepinephrine, corisol, and growth hormone

raise blood glucose levels.


Glycemic Index

Classifies the effects of carbohydrate-containing foods on blood glucose

May be helpful for diabetics Glycemic index (GI) refers to the measured upward rise,

peaks, and falls of blood glucose following consumption of high-carbohydrate food

• Ranks foods according blood glucose


Glycemic Load

Glycemic load (GL) – adjust GI by taking into account the amount of carbohydrate consumed in a typical serving of food

Factors affecting GI

• Ripeness of fruit

• Cooking

• Processing

• Size of food pieces

• Amount of fiber

• Combinations of food eaten


Glycemic Index and Glycemic Load

Usefulness of GI and GL for disease prevention and weight management is controversial

Is helpful in educating people about

• Carbohydrate content of foods

• Portion sizes

• Serving numbers


Dietary Fiber

Benefits

• Helps lower risk of

- Bowel irregularity

- Obesity

- Heart disease

- Cancer

- Diabetes mellitus

© 2010 Pearson Education, Inc. Figure 4.12

Dietary Fiber

Chronic constipation can lead to diverticulosis and diverticulitis

Prevention of constipation and diverticulosis

• Insoluble fiber helps reduce transit time of foods in the colon

• Soluble fiber helps make stool easier to pass by increasing bulk and softening texture

© 2010 Pearson Education, Inc. Figure 4.13

Dietary Fiber

Prevention of heart disease and diabetes

• Viscous, soluble fiber helps lower elevated blood cholesterol levels

- Interferes with reabsorbtion of bile acid


Dietary Fiber

• Slow moving, viscous, soluble fiber may reduce the rate which fat and carbohydrate are absorbed

- Decreasing level of fat in blood and improving insulin sensitivity, decrease risk of heart disease

• Insoluble fiber has been shown to promote heart health

• Viscous soluble fiber helps slow digestion and absorption helping control blood glucose levels


Dietary Fiber

Fiber helps reduce the incidence of several cancers

• Decreases the amount of time cancer-promoting substances spend in contact with the intestinal lining

• Encourages the growth of colon-friendly bacteria

• Reduces acid in the colon Helps prevent obesity

• Increase satiety

• Reduce food intake

Caution: Increase dietary fiber and fluid intake gradually


Quick Review

Glycemic index (GI) ranks foods according to effects on glucose levels compared to white bread or pure glucose

Glycemic load adjust for serving size Foods that contain high fiber or are eaten with protein and

fat generally have a lower GI. High-fiber diet health benefits include reduced risk of

• Constipation• Diverticulosis• Heart disease• Obesity• Diabetes Mellitus• Cancer

Importance of Whole Grains


Carbohydrate Sources

Best choices should include nutrient-dense, low-saturated fat foods, simple carbohydrates, fiber, complex carbohydrates

Figure 4.14

Food Sources of Carbohydrates

Figure 4.15

Food Sources of Fiber


• Legumes• Low-fat dairy products

• Legumes• Nuts• Seeds

Quick Review

Best sources of carbohydrates are

• Fresh fruits and vegetables

• Whole grains Excellent sources of fiber are

• Whole grains

• Fruits

• Vegetables Packaged foods can be good sources of starch and fiber

• Read label carefully

• Avoid too much sugar, fat, and kilocalories


Diabetes Mellitus

Occurs when an individual either doesn’t make enough, or is unable to utilize, the hormone insulin to regulate blood glucose levels

Epidemic

• Sixth leading cause of death in the United States

• Costs the U.S. almost $100 billion annually

• Number of people with diabetes is rising annually

Liver Breaks Down Glycogen and Produces Glucose from

Non-Carbohydrate

Sources

Consume Carbohydrates

Blood Glucose Rises

Body Uses Fat for Fuel

Ketoadicosis

Blood Glucose Rises

No Insulin Available or

Cells Resistant

Cell Starves

Diabetes Mellitus


Forms of Diabetes

Type 1

• Usually begins in childhood or early adulthood

• 5–10% of diabetics

• Immune system destroys beta cells of the pancreas

- No insulin produced

• Common symptoms of elevated blood sugar

- Polydipsia

- Polyuria

- Polyphagia

• Require insulin and frequent blood glucose monitoring


Forms of Diabetes

Type 2

• Overweight individuals develop this form frequently

• 90–95% of diabetics

• Can go undiagnosed

- Damages vital organs without individual being aware of it

Polycystic ovary syndrome

• Hormonal imbalance in women

• Have higher incidence of insulin resistance and hyperinsulinemia

- Increased risk of developing type 2 diabetes


Forms of Diabetes

Prediabetes

• Impaired glucose tolerance

• Fasting blood sugar between 100 mg/dl and 126 mg/dl

• High risk of developing diabetes and heart disease


• Tooth loss• Gum problems• Kidney disease• Heart disease

Diabetes

Long-term damage from diabetes• Nerve damage• Leg and foot amputations• Eye diseases• Blindness

Slowing of onset of complications• Control level of blood glucose through

- Diet- Insulin or oral medication- Monitoring blood glucose- Regular healthcare visits


Diabetes

Slowing of onset of complications

• Control level of blood glucose through

- Diet

- Insulin or oral medication

- Monitoring blood glucose

- Regular health care visits


Quick Review

Diabetes involves inadequate regulation of blood glucose levels

Type 1 diabetes – inadequate production of insulin Type 2 diabetes – insulin resistance Chronic high blood glucose can damage vital organs Diabetics need medications and/or insulin to manage blood

glucose High-fiber diet and routine exercise play a key role in

managing and preventing diabetes Polycystic ovary syndrome increases the risk of developing

type 2 diabetes


• Confused

• Weak

• Shaky

• Sweaty

Hypoglycemia

A blood glucose level that is too low (usually below 70 mg/dl)

Signs and symptoms

• Hunger

• Nervousness

• Dizziness

• Light-headed Eating or drinking carbohydrate rich foods

• Relieves symptoms

• Raises blood glucose

Figure 4.17

Change in Blood Glucose After Eating a High-Carbohydrate Meal


Fasting Hypoglycemia

Occurs in the morning after an overnight fast Occurs during long stretches between meals or after

exercise May be caused by

• Medications

• Illness

• Drinking too much alcohol

• Certain tumors

• Hormone imbalances


Quick Review

Symptoms of hypoglycemia

• Hungry, nervous, light-headed, shaky, and/or sweaty Diabetics who take medications and/or insulin and do not

eat properly are at risk Individuals without diabetes may experience reactive

hypoglycemia several hours after meals Fasting hypoglycemia may occur upon awaking in the

morning Can be caused by medications, illnesses, hormone

imbalances, or excessive consumption of alcohol


Natural versus Added Sugar

Naturally occurring sugar

• Sugars such as fructose and lactose found naturally in foods

• Tend to be nutrient dense Added sugar

• Sugars added to processed foods and sweets

• Empty calories

Figure 4.18

Slices of an Orange versus Orange Slices


Added Sugar

Reasons sugar is added to foods

• To keep product moist

• To turn pastries a golden brown

• Preservative

• Thickening agent

• Make yeast rise

• Make foods taste sweet

Figure 4.19

Finding Added Sugars on the Label

Figure 4.20

Americans Drink the Majority of Their Sugar


Health Effects of Sugar

Sugar can contribute to

• Dental carries

• Elevated level of fat in the blood

• Lowing of HDL cholesterol Sugar does not cause

• Increased risk of diabetes

• Hyperactivity in children Sugar is not considered an addictive substance


Quick Review

Taste buds do not distinguish between naturally occurring sugar and added sugar

Foods with naturally occurring sugar provide more nutrition and satiation than empty-calorie sweets

There are numerous names for added sugar Soft drinks are the number-one contributor of added sugars

to U.S. diets


Putting It All Together

Carbohydrates are an important part of a healthy diet Whole grains, fruits, vegetables, and lean dairy products

• Provide carbohydrates and vitamins and minerals

• Should be the predominant source of carbohydrates Whole grains, fruits, and vegetables are a good source of

fiber and phytochemicals

• Adequate amounts of these can prevent many chronic disease

Sugary foods should be eaten in moderation

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Chapter 4: Carbohydrates, Sugars, Starches and Fiber