The Carbohydrates:
Sugars, Starches, and
Fibers
Lancelot McLean, PhD
[email protected]
Whitney & Rolfes – Understanding Nutrition, 12th
Edition
Introduction

Brain use:
 Glucose

Muscles use:
 Glucose
 Glycogen
 Fat

Sources of carbohydrates
 All plant foods: whole grains, vegetables, legumes and fruits
 Milk also contains carbohydrates
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Carbohydrates

Carbohydrate family
 Monosaccharides
 Glucose, fructose, galactose
 Disaccharides
 Maltose = glucose + glucose
 Sucrose = glucose + fructose
 Lactose = glucose + galactose
 Polysaccharides
 Glycogen = glucose units
 Starches (amylose and amylopectin) = glucose units
 Fibers (soluble and insoluble)
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Carbohydrates
Monosaccharides
•
Glucose and fructose
– principal monosaccharides found in food
•
Glucose
– abundant in fruits, sweet corn, corn syrup and honey
•
Free fructose
– found together with free glucose and sucrose in honey and fruits
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Carbohydrates
Monosaccharides
 High fructose corn syrup (HFCS)
– Corn syrups that have undergone enzymatic processing to
convert their glucose into fructose and have been mixed with
pure corn syrup (100% glucose) to produce a desired sweetness
– In the US HFCS 55 (55% fructose and 42% glucose) is
commonly used as a substitute for sucrose in beverages,
including soft drinks
– HFCS 42 (42% fructose and 53% glucose) used in processed
foods
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Carbohydrates
Disaccharides
•
Sucrose
– Table sugar
•
Lactose
– Principal sugar in milk
•
Maltose
– Found in significant quantities in beer and malt liquors
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Carbohydrates
Polysaccharides
•
Complex carbohydrates
– do not have a sweet taste
•
Examples:
– Starch found in plants
– Glycogen in animals
•
Common sources of starch:
–
–
–
–
wheat and other grains
potatoes
dried peas and beans
vegetables
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Carbohydrates
Fiber
•
Nondigestible carbohydrates and lignin (complex polymer of
phenylpropanoid subunits) present intact in plants
•
Provides little energy but has several beneficial effects
– Adds bulk to the diet
– Can absorb 10-15 times its own weight in water drawing fluid into the lumen
of the intestine and increasing bowel motility
– Delays gastric emptying
– Lower LDL cholesterol by increasing fecal bile acid excretion and interfering
with bile acid absorption
– Decrease risk of constipation, hemorrhoids and diverticulitis
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Carbohydrate Digestion

Ultimate goal
 Glucose for absorption and use

Hydrolysis via enzymes

Mouth
 Amylase hydrolyze starch to shorter polysaccharides and to maltose

Stomach
 Stomach acid & protein-digesting enzymes
 Fiber delay gastric emptying; provides a feeling of fullness
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Carbohydrate Digestion

Small intestine
 Most carbohydrate digestion
 Pancreatic amylase
 Continues breakdown of polysaccharides to shorter glucose chains
and maltose
 Specific disaccharide enzymes
 Maltase breaks down maltose
 Sucrase breaks down sucrose
 Lactase breaks down lactose

Large intestine
 Fibers attract water which soften stools for passage without
straining
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Carbohydrate Absorption
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Breaking Down Nutrients for Energy
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Lactose Intolerance

Lactase activity
 Highest immediately after birth
 Declines with age

Symptoms of intolerance
 Bloating, abdominal discomfort, and diarrhea

Prevalence
 Genetically determined
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Blood Glucose Homeostasis
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Blood Glucose Homeostasis

Diabetes
 Blood glucose rises after a meal and remains above normal levels
 Insulin is either inadequate or ineffective
 Type 1 diabetes:
 Pancreas fails to produce insulin
 Type 2 diabetes
 Cells fail to respond to insulin
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Blood Glucose Homeostasis

Hypoglycemia
 Blood glucose below normal level
 Poorly managed diabetes is most common cause
 Too much insulin
 Strenuous physical activity
 Inadequate food intake
 Illness that causes blood glucose levels to plummet
 Rare in healthy people
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Glycemic Index

Glycemic response
 How quickly glucose is absorbed after a person eats, how high
blood glucose rises, and how quickly it returns to normal
 Low glycemic response
 Desired
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Glycemic Index
•
Some carbohydrate-containing foods produce a rapid rise followed by a
steep fall in blood glucose concentration, whereas others result in a
gradual rise followed by a slow decline (differ in glycemic index)
Glycemic index (GI) is a method of
classifying foods according
to their
potential to raise blood glucose.
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Glycemic Index
•
Low glycemic index foods tend to create a sense of satiety
over a longer period of time
•
How much a typical serving size of a food raises blood glucose is
termed glycemic load (GL)
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Glycemic Index of Selected
Foods
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Effects of Sugars on the tooth

Dental caries
 Bacteria ferment sugars producing acid
 Food factors associated with tooth decay
 Time of food in mouth
 Sticky foods stay on teeth longer
 Sugar in juice consumed quickly is less likely to cause caries than
sugar in pastries
 Frequency of sugar consumption
 Bacteria produce acid for 20-30 minutes after each exposure
 It’s better to eat 3 pieces of candy at once than at 3
separate times
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Effects of Sugars on the tooth

Dental caries
 Nonsugary foods can help remove sugar from tooth surfaces
 Better to eat sugar with meals than between meals
 Foods such as milk and cheese are helpful against caries




Neutralize acids
Stimulates salivary flow
Inhibit bacterial activity
Promote remineralization of damaged enamel
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Effects of Sugars on the tooth

Drinks that contribute to caries
 Soft drinks
 Orange Juice
 Sports Drinks
 Contain sugar as well as have a low pH
 Acidic drinks can erode tooth enamel and may explain why the
prevalence of dental erosion is steadily growing
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Oral microbi0ta and sugars
•
The oral microbiota is predominantly saccharolytic and the major
fermentation end product is lactic acid
•
Bacteria metabolizing aerobically exude CO2 and H20.
•
Bacteria metabolizing anaerobically exude Lactic acid
•
The deeper the plaque, the more anaerobic, the more acid and the lower
the pH
•
At pH 5.5 the enamel begins to dissolve- Demineralization!!!!!!!
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Oral microbi0ta and sugars
•
These lactic acid forming bacteria have a think outer cell wall (gram +ve)
which allows them to tolerate the low pH caused by the lactic acid they are
producing

Primary causative agents
 Streptococcus mutans
 Lactobacillus spp
 Lactobaillus casei can survive pH 1 for a few hours
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Sucrose
It is evident that European populations suffered little from caries before the late 18th
century
The rise of caries coincided with increased sucrose consumption
The most compelling evidence for sucrose causing caries was obtained by comparing
the sucrose intake in 12-year old children from 47 countries (obtained from the
WHO’s Global Oral Epidemiology Bank during the 1970s) with the DMFT (decayed,
missing, and filled teeth) during this period
The number of affected teeth increased by about 1 DMFT for every 25g of sugar
consumed daily
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Sucrose and Dental Caries
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Effects of Sugars on the tooth
•
Sucrose is required for growth of Streptococcus mutans, the
causative agent for dental caries.
•
Frequent sucrose consumption causes a 100 fold increase in S. mutans
which are the cause of caries
•
In populations which have inadequate fluoride, the frequent consumption of
sucrose guarantees endemic universal caries
Whitney & Rolfes – Understanding Nutrition, 12th Edition
The mineral in teeth is a highly substituted
hydroxyapatite
Acid makes
hydroxyapatite more
soluble
Flourine makes it
more insoluble
The unit cell has the formula Ca10 (PO4)6(OH)2
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Dental Caries
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Effects of Sugars on the tooth

Good oral hygiene
 Regular brushing and
flossing
 At least twice a day with a
fluoride toothpaste
 Restricting sugary food and
drink intake
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Recommended intakes for carbohydrate
•
The absence of dietary carbohydrate leads to ketone body production, and
degradation of body protein whose constituent amino acids provide carbon
skeletons for gluconeogenesis
•
Adults should consume 45-65% of their calories from carbohydrates
•
Recommended that added sugar represent no more than 25% of total energy
because of concerns that sugar may displace nutrient-rich foods from the diet
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Alternative sweeteners

Artificial sweeteners (non-nutritive sweeteners)
 Provide virtually no energy
 Acesulfame potassium, aspartame, cyclamate, neotame, saccharin,
sucralose, tagalose

Herbal products
 Stevia

Sugar alcohols (polyols)
 Provide kcalories, but fewer than their carbohydrate cousins, the sugars
 Also referred to as nutritive sweeteners because they yield energy
 Erythriol, isomalt, lactitol, maltitol, mannitol, sorbitol, xylitol
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Health Effects of Starch and Fibers

Heart disease
 Whole grains and soluble fiber

Diabetes
 High-fiber foods

Cancer
 Dietary fiber and colon cancer

GI health
 High-fiber foods
 Ample fluids

Weight management
 High-fiber foods and whole grains
 Feeling of fullness
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Health Effects of Starch and Fibers

Excessive fiber
 Insufficient energy or nutrient needs
 Abdominal discomfort, gas, diarrhea
 GI obstruction
 Limit nutrient absorption
Whitney & Rolfes – Understanding Nutrition, 12th Edition