Chapter 4: Carbohydrates

Carbohydrate

• Body’s favorite source of energy

• Consists of Monosaccharides, Disaccharides, & Poly- saccharides

• Protein sparing. Prevents ketosis

• Carbon, Oxygen and

Hydrogen

CHO in Food

Dietary Carbohydrate Requirement

►55% to 70% of total kcal intake should come from Carbohydrate.

►This is approximately 275 grams to 350g daily if you consume 2000 kcal per day.

Less than 50 grams should be from added sugar (sucrose, HFCS).

Monosaccharides “Simple Sugars”

• Glucose: Is present in every disaccharide. Makes up polysaccharides exclusively. Blood sugar. All MS are converted to glucose in liver

• Fructose: Sweetest of MS. Honey, Fruit• Galactose: Most always bound with glucose.

Found in milk. Not very sweet.

Disaccharides “Sugars”

• Maltose (Gluc + Gluc) – Fermentation– Alcohol production

• Sucrose (Gluc + Fruc)– Sugar

• Lactose (Galactose + Gluc) – Milk products

Formation of Disaccharide

• Condensation creates water

How Disaccharides are split

• Hydrolysis uses water to separate monosaccharides from disaccharides.

High Sugar Diets

• Empty calories• Soda replacing milk• Calories adding to excess• Dental caries

– exposure to teeth

• High glycemic index– Blood glucose response of a given food– Influence by various factors

Recommendation for Simple Sugar Intake

• No more than 10% of total kcal/day around 50 grams

• Reduce intake of fruit juices, fruit “drinks”, and soda.

• Avoid sweet, processed food including: – Cakes, pastries, muffins, doughnuts.

• Check labels! Sugar is added to a wide range of food and beverages during processing

Complex Carbohydrates

• Complex Carbohydrates are called “Polysaccharides” There are 3 kinds:

• Starch

• Glycogen

• Dietary fiber

Starch

• Many monosaccharides bound together

Storage form of carbohydrate in plants

Glycogen

• Storage form of CHO for animals and human• Highly Branched. More sites for enzyme action• Found in the liver and muscles

Dietary Fiber(Non-starch polysaccharides)

Body cannot break the bonds• Types:

– Insoluble (fermentable) • Cellulose • hemicellulose • lignin

– Soluble (viscous) • gums,• mucilages• pectin

– Resistant starches: beans, unripe bananas, raw potatoes.

Foods that Provide Fiber

• Insoluble Fiber– Wheat bran– Whole grain breads, cereals– Vegetables

• Soluble Fiber– Fruits– Oats– Legumes

• However, most foods contain a little of both

Soluble and Insoluble Fiber

Actions And Benefits of Dietary Fiber

• Softens stool and bulks stool• Promotes peristalsis exercise for the

intestines. Prevents Diverticulosis.• Fermentation provides SCFA• Delays glucose absorption• Affects transit time of food in GI tract

– Insoluble accelerate transit– Soluble slows transit

• Soluble fiber can lower blood cholesterol

Diverticula

Recommended Dietary Fiber Intake

• 20-35 gm of fiber/day (10-13 gm/1000 kcals)• Children: age +5gm/day• Ave. U.S. intake: ~16 gm/day• Too much fiber (>80 gm/d) will:

– require extra intake of fluid – bind to some minerals– develop phytobezoars– Will cause cramps, gas, diarrhea.

Phytate

• Anti-nutrient

• Found in foods high in fiber, soy, wheat, seeds, legumes

• Binds to ZN, CA, FE, MG, CU

• A problem when consuming too much fiber, especially when not use to it.

Blood Glucose Regulation• Blood Glucose Regulated by:

– Insulin: Stimulates uptake of glucose into the cells. Facilitates storage of glycogen and the conversion of excess carbohydrates to fat

– Glucagon: Stimulates liver cells to break down glycogen for glucose or to produce glucose from protein and glycerol. This is called “gluconeogenesis”.

• Hypoglycemia– Reactive hypoglycemia– Occurs 2-4 hours after eating a meal – Possibly due to release of epinephrine.

• Fasting hypoglycemia– Can occur in healthy people.

– Insufficient glucagon.• Hyperglycemia. Too much glucose in the blood stream.

Indicative to diabetes.

You are a pediatric nurse at a private practice. A long time patient of yours comes in for a physical. Although Leticia is a healthy and energetic adolescent, today she looks a little pale and fatigued. When you ask her how she is feeling Leticia states that she’s feeling a little shaky and light headed. She also states that she tends to feel this way almost every morning about 2 hours after breakfast, then the symptoms subside within an hour. Concerned with resolving her problem, your ask her what she usually has for breakfast. Leticia replies that she usually has a large plain bagel with jelly, and a glass of juice.

Assume Leticia is telling the truth about what she ate, and that she does not have a biological disorder, what is the likely cause of her light-headedness? What advice would you give her?

Glycemic Index• A measurement of glucose response to a

particular type of food.• The greater the glucose response, the

higher the value. (White bread = 100)• High glycemic foods create high insulin

levels– increases fat synthesis and storage– Increases blood triglycerides– Increases hunger– Increases insulin resistance

Digestion of Carbohydrates

Digestion of Carbohydrate in the Mouth

• Saliva contains amylase

• Starch is broken down to shorter saccharides

• Taste the sweetness with prolong chewing

• Proceeds down the esophagus

Digestion of Carbohydrate in the Stomach

• The acidic environment stops the action of salivary amylase

• No further starch digestion occurs

In the Small Intestine

• Pancreatic amylase is released• Intestinal cells release enzymes Maltose + maltase glucose + glucose Sucrose + sucrase glucose + fructose Lactose + lactase glucose + galactose

• Monosaccharides are absorbed

CHO Digestion

Portal Vein

• Transport absorbed monosaccarhides

• Delivers them to the liver

Liver can:

• transform them into glucose

• release them back into the blood stream

• store as gylcogen (or fat)