Chapter Four

Monosaccharides - single sugars

Example.

glucose - blood sugar

  • essentially energy source for all the body’s activities, including the brain

  • part of every disaccharide

fructose - sweetest of the sugars (occurs naturally in fruits and honey)

galactose - found naturally in only a few foods

Disaccharides (and what monosaccharides are in each pair) -

Formed when

maltose - two glucose units

  • produced whenever starch breaks down

Sucrose - glucose and fructose

  • “table sugar” and other added sugars

Lactose - galactose and glucose

  • the primary carbohydrate of milk

Polysaccharides - contain many glucose units and in some case mix of monosaccharides linked together

Three types

  • glycogen - human storage form of glucose (liver and skeletal muscles)

  • starches - plant energy storage form of glucose (chroloplasts)

  • fibers - structural part of plants found naturally in all plant-based foods

Simple Carbohydrates vs Complex Carbohydrates

Simple carbohydrates are only composed of one sugar. Complex carbohydrates are long chains of sugar molecules.

Digestion of Carbohydrates and Enzymes Associated With It

In the mouth

  • the enzyme salivary amylase starts to work in the mouth hydrolyzing starch to shorter polysaccharides and to the disaccharide maltose

In the stomach

  • the stomach acid inactivates salivary amylase, halting starch digestion

  • the stomach’s digestion juices contain NO enzymes to break down carbohydrates

  • carbohydrate digestion pauses in the stomach

In the small intestine

  • the small intestine performs most of the work of carbohydrate digestion

  • pancreatic amylase, enters the intestine and continues breaking down the polysaccharides

  • maltase breaks maltose into two glucose molecules

  • sucrase breaks sucrose into one glucose and one fructose molecule

  • lactase breaks lactose into one glucose and one galactose molecule

In the large intestine

  • most fiber arrives intact to the large intestine

  • bacterial enzymes digest some fiber

  • fiber holds water, regulates bowel activity and binds with bile, cholesterol and some minerals for the body to excrete

Sources of Carbohydrates in the Diet

Grains, vegetables, fruits, and legumes

Condensation vs Hydrolysis

Condensation - a chemical reaction in which water is released as two molecules combine

Hydrolysis - breaks a disaccharide into two, occur commonly during digestion. Water is added breaking the bond.

Glucose in the Body - hormones that maintain glucose balance

Insulin - moves glucose from blood into cels

Glucagon and Epinephrine - brings glucose out from storage

Alternatives to Glucose When it is Not Available

Proteins - when a person doesn’t replenish glucose by eating carbohydrate, body proteins are broken down to make glucose to fuel the brain and other nerve cells

Fat ketone bodies - ketone bodies formed from fat fragments are metabolized to create non-carbohydrate energy source

  • provides alternative fuel source during starvation

  • disturbs body’s normal acid-base balance

Health Benefits of Starch and Fiber - best sources of fiber from each carbohydrate-rich food group

Grains - whole grain breads > 3g fiber per serving and > 5g fiber per serving whole grain cereal

Vegetables - raw vegetables (potatoes and zucchini with the skin)

Fruits - fresh and dried fruit for snacks (apples and pears with the skin)

Legumes - add to soups, salads, and casseroles