The Carbohydrates: Sugars, Starches, and Fibers Chapter 4
The Carbohydrates: Sugars, Starches, and Fibers
Chapter 4
Introduction
Brain Glucose as E source
Muscles ½ Glucose & Glycogen (storage form of glucose) ½ Fat
Sources of carbohydrates
“Fattening” – mistaken thinking
CHEMIST’S VIEW OF CARBOHYDRATES
CHO cmpds composed of C, O, H arranged as mono or multiple mono
Dietary CHOs Monosaccharide Disaccharides Polysaccharides
CHEMIST’S VIEW OF CARBOHYDRATES
CHEMIST’S VIEW OF CARBOHYDRATES
Monosaccharides – three kinds Same numbers and kinds of atoms Differ in arrangements 1.Glucose – blood sugar2.Fructose3.Galactose
CHEMIST’S VIEW OF CARBOHYDRATES
Disaccharides Pairs of three monosaccharides
1. Maltose – two glucose* units2. Sucrose – glucose* and fructose3. Lactose – glucose* and galactose
CHO-put together & taken apart by similar chemical rxns:
Condensation (to make) Links two monosaccharides together
CHO-put together & taken apart by similar chemical rxns:
Hydrolysis (to take apart) Breaks a disaccharide in two Commonly occurs during digestion
CHEMIST’S VIEW OF CARBOHYDRATES
Polysaccharides Contain many glucose units sometimes few mono strung together Three types important in nutrition: glycogen, starch, fiber.
1.Glycogen Storage form of energy Many glucose units linked Hormonal message
CHEMIST’S VIEW OF CARBOHYDRATES
2. Starch• Storage form of E (glucose) in plants• Long, branched, or unbranched glucose molecules • Consume a plant body hydrolyzes starch to glucose glucose as E• All come from plants (grains richest source)
CHEMIST’S VIEW OF CARBOHYDRATES
3. Fibers Structural part in plant; found in all plant derived
foods Differ from starches
bonds between monos can’t be broken down by digestive enzymes
Soluble fibers (dissolve in water)- form gels easily digested heart protective and diabetes
Insoluble fibers (do not dissolve in water)-3. do not form gels less readily fermented promote bowel
movement, aid constipation
Functional fibers Resistant starches Phytic acid
Carbohydrate Digestion
Ultimate goal Glucose for absorption and use**
Hydrolysis via enzymes
Mouth Salivary enzyme- amylase starch to poly to maltose
Stomach Stomach acid & protein- inactivate amylase No enzymes to significantly further breakdown Role of fiber
lingers in stomach, delaying gastric emptying fullness/satiety
Carbohydrate Digestion
Small intestine Most carbohydrate digestion Pancreatic amylase
major CHO digesting enzyme Specific disaccharide enzymes
Maltase: maltose 2glucose Sucrase: sucrose glucose + fructose Lactase : lactose glucose + galactose
Large intestine Fibers only remaining
(sugars & starches digested) Aid in healthy bowel functions/movements
Carbohydrate Absorption
Takes place in small intestine
Active transport Glucose Galactose
Facilitated diffusion Fructose
Carbohydrate Absorption
Lactose Intolerance
Lactase activity
Symptoms of intolerance
Causes of intolerance beyond age
Prevalence
Lactose Intolerance
Dietary changes Manage dairy consumption rather than restriction Fermented milk products Individualized diets Potential nutrient deficiencies
Riboflavin, vitamin D, and calcium
Carbohydrate Metabolism
Glucose is key player
Storing glucose as glycogen Liver storage Muscle storage
Carbohydrate Metabolism
Glucose for energy Fuels most of body’s cells Cellular breakdown of glucose into carbon dioxide and water
Making glucose from protein Amino acid conversion to glucose in some extent Gluconeogenesis- conversion of protein to glucose (not ideal)
Carbohydrate Metabolism
Ketone bodies from fat fragments Inadequate supply of carbohydrates
Carbohydrate needs for protein sparing and prevention of ketosis (50-100g CHO daily)
Using glucose to make fat
The Constancy of Blood Glucose
Steady supply in blood stream Intestines – food consumption Liver – glycogen breakdown
Blood glucose homeostasis Insulin Glucagon & epinephrine
Blood Glucose Homeostasis
The Constancy of Blood Glucose
Balancing within the normal range Balanced meals at regular intervals
Diabetes Blood glucose levels rises after a meal and remains above
normal levels because Insulin is either inadequate or ineffective Type 1 diabetes Type 2 diabetes
Hypoglycemia Blood glucose levels fall below normal Symptoms Seen in poorly managed diabetes, too much insulin, strenuous
exercise, inadequate food intake, or illness
The Constancy of Blood Glucose
Glycemic response Speed of glucose absorption, how high level of blood glucose rises,
and how quickly it returns to normal glucose levels Important in diabetes Low glycemic response
Desired High glycemic response Glycemic index-method of classifying food according to their
potential to raise blood glucose
Health Effects of Sugars
Pleasure in moderate amounts without harming health
Nutrient deficiencies Energy with few other nutrients (empty calories) Some sugar sources are more nutritious than other
Dental caries Bacteria in mouth ferment sugars producing an acid that erodes
tooth enamel, causing tooth decay
Practicing good oral hygiene and minimize consuming sugar and starch containing foods and beverages
Recommended Intakes of Sugars
Dietary Guidelines Choose and prepare foods with little added sugar
DRI Added sugars
No more than 25% of day’s total energy
WHO and FAO recommendations Suggest restricting consumption of added sugars to less than 10% of
total energy.
Alternative Sweeteners
Artificial sweeteners Sometimes called Non-nutritive sweeteners
Provide virtually no E Large doses and adverse effects
Stevia – an herbal product Derives from a plant Generally recognized as safe (GRAS)-used as additive in variety of food and
drinks
Sugar alcohols Found in “sugar-free” or reduced-calorie products Provide kcalories, but fewer than CHO sugars (nutritive sweetener) Benefits and side effects
Health Effects of Starch and Fibers
Heart disease Whole grains
Soluble fibers Sources Bind with bile acids in GI tract increasing excretion
Protect against heart disease and stroke
Health Effects of Starch and Fibers
Diabetes High-fiber foods
trap nutrients and delay transit time in GI tract glucose absorption slowed
GI health High-fiber foods
increase stool wt, easing passage, reduce transit time Ample fluids easier passage Protects against colon cancer
Weight management High-fiber foods and whole grains help with healthy body weight
Health Effects of Starch and Fibers
Excessive fiber Insufficient energy or nutrient needs Abdominal discomfort, gas, diarrhea GI obstruction Nutrient absorption Dietary goals
Balance, moderation, variety
Recommended Intakes of Starch & Fibers
DRI for carbohydrates 45 to 65% of energy requirement
RDA for carbohydrates 130 grams per day
Fiber DV: 11.5 grams per 1000-kcalories DRI: 14 grams per 1000-kcalories No UL