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Chapter 10
Nutrients and
Phytochemicals
That Function
as Antioxidants
Copyright © 2015 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Student Learning Outcomes 1
10.1 Understand oxidation and reduction, and how free
radicals can alter normal cell function.
10.2 Describe how antioxidants function to neutralize
free radicals.
10.3 Summarize the functions of vitamin E and describe
its food sources and deficiency and toxicity symptoms.
10.4 Describe the functions of vitamin C as well as its
dietary sources and deficiency symptoms.
Student Learning Outcomes 2
10.5 Explain the functions and food sources of
carotenoids.
10.6 Describe the role of antioxidant phytochemicals.
10.7 Summarize the functions of selenium and
describe its food sources and deficiency and toxicity
symptoms.
10.8 Describe how calorie and fat intakes contribute
to cancer risk and the role other food constituents play
in inhibiting cancer.
Nutrients and Phytochemicals
That Function as Antioxidants
• Some vitamins, minerals, plant compounds
function as antioxidants
• Protect cells against free radicals
• Nutrients that function as antioxidants:
– Vitamin E (tocopherol)
– Vitamin C (ascorbic acid)
– Vitamin A (retinoids & carotenoids)
– Phytochemicals
– Selenium (Se)
10.1 Oxidation and
Reduction
1. What happens to electrons during the
processes of reduction and oxidation?
2. What is a free radical?
3. Why are free radicals thought to be
harmful to cells?
Protons and Electrons
• Protons and neutrons are found in the
nucleus
• Electrons circle the nucleus in pairs
• Nucleus is positively (+) charged
• Electrons are negatively (-) charged
• Positive and negative charges balance
– atom has no overall charge
Oxidative Stress
• Atoms bond together in molecules
• Oxidative stress
– imbalance between production of reactive
compounds and body’s ability to protect against
their adverse effects
• Reduction
– gain of a negatively charged electron
Oxidation and Reduction
• Oxidation
– loss of a negatively charged electron
• We derive energy from food in the form of
ATP and other high-energy compounds
• Sharing electrons in outer shell makes
bonds between atoms or molecules strong
• Oxidation of these bonds produces stable
compounds
Free Radical Formation
• A weak bond between atom or molecule
produces possible molecule or atom left
with an unpaired electron in its outer shell
• Free radical
– unstable atom with unpaired electron in its
outermost shell
• Overproduction of free radicals can be
harmful to healthy cells
Redox Reaction
10.2 Defense Against Free
Radicals
1. Which micronutrients are known to have
antioxidant roles?
2. How do antioxidant chemicals reduce
cellular damage?
Defense Against
Free Radicals
• Body has two defense mechanisms
– Enzyme systems and antioxidant chemicals
– Work together to limit free radical formation
• Enzyme activity
– requires presence of minerals selenium,
manganese, zinc, iron, copper
• Antioxidant
– substance has ability to prevent or repair damage
caused by oxidation
– Derived from food nutrients
Antioxidants Protect DNA
More Fruits and Vegetables
• 2010 Dietary Guidelines, MyPlate and
Fruits & Veggies: More Matters©
campaigns
• Premise to increase consumption of fruits
and vegetables
– Increases fiber, vitamins, minerals,
phytochemicals detoxifying reactive
molecules including free radicals
Dietary Antioxidants
• Dietary antioxidant
– substance in foods that significantly
decreases adverse effects of reactive species
such as reactive oxygen and nitrogen species
on normal physiological function in humans
(from DRI)
Antioxidant Activity
10.3 Vitamin E
(Tocopherols)
1. How does vitamin E work to prevent oxidative
damage?
2. What are some rich food sources of vitamin E?
3. Why are preterm infants, smokers, and people with
fat malabsorption particularly susceptible to
oxidative damage to cell membranes?
4. What are the possible results of vitamin E toxicity?
Functions of Vitamin E
• Compound identified as essential for rat
fertility, 1920s
– No corresponding fertility effect in humans
• Compound named tocopherol
• Development of muscles
• Development of central nervous system
• Antioxidant
• Maintains nervous tissue and immune
function
Vitamin E as an Antioxidant
• Fat-soluble vitamin found in adipose tissue and
cell membrane
• Lipids in these membranes are polyunsaturated
fatty acid (PUFA)
– PUFAs susceptible to oxidative attack
• Vitamin E donates electrons or hydrogens to free
radicals to make cell more stable
• Vitamin E important in areas exposed to ↑ levels of
oxygen
– RBCs and lungs
Vitamin E Protects Cell Membranes
• Vitamin E can
insert itself into
cell membranes
• It helps stop freeradical chain
reactions
Vitamin E: Deficiency
• Deficiency is rare because primary source
of Vitamin E is plant oils and our diets are
high in fat
• Deficiency can be problem in preterm
infants as transfer from mother occurs late
in pregnancy
Getting Enough Vitamin E
• Plant products best sources, especially
oils
• RDA for adults:
15 mg/day of alpha-tocopherol (the most active form of
vitamin E)
• DV on labels is based on
30 mg
Food Sources of Vitamin E
• Only synthesized by plants, particularly
their oils
• Good sources include:
– Salad oils
– Margarines
– Shortening
– Fortified cereals
– Nuts and seeds
Bar Graph: Sources of Vitamin E
MyPlate: Sources of Vitamin E
Calculating Vitamin E Content
of Dietary Supplements
• Vitamin E content on Supplement Facts
labels given in international units (IU)
– measure of biological activity of a nutrient
rather than its absolute quantity
• Supplements contain variety of chemical
forms
– usually less bioactivity than natural or dietary
vitamin E
Avoiding Too Much Vitamin E
• Megadosing does not provide significant
health benefits or prevent against
oxidative damage
• Not stored in the liver – stored in fat tissue
• UL is 1,000 mg/day
• Excess can interfere with vitamin K and
anticoagulant medications causing
hemorrhage (Coumadin & aspirin)
10.4 Vitamin C
(Ascorbic Acid)
1. How does vitamin C function as an
antioxidant and regenerate vitamin E?
2. How do the signs of vitamin C deficiency
relate to the many roles of the vitamin
discussed in this chapter?
3. Why are fresh foods the best sources of
vitamin C?
Functions of Vitamin C
• Collagen synthesis, most abundant protein in body
• Carnitine synthesis, transports fatty acids
• Serotonin and norepinephrine synthesis
• Antioxidant
• Increases iron absorption
• Vital for immune function
• May decrease formation of carcinogen nitrosamines
in the stomach
• Doesn’t prevent colds but may decrease severity
Getting Enough Vitamin C
• Adult RDA:
– 75 mg/day for women
– 90 mg/day for men
• Smokers need an extra 35 mg because of
increased oxidation by tobacco smoke in
lungs
• Average U.S. consumption: 70-100
mg/day
Vitamin C Deficiency - Scurvy
• Causes scurvy due to reduced collagen
synthesis, causing bruising, bleeding gums
• 1700s half of sailing crew on long voyages
died
• British physician discovered citrus fruits
prevented and restored health of sailors
• Future food rations included limes, resulting
in nickname “limeys”
Pinpoint Hemorrhages
Early Scurvy Sign
Food Sources of Vitamin C
• Citrus fruits
• Strawberries
• Green peppers
• Cauliflower & broccoli
• Cabbage
• Papaya
• Romaine, darker color lettuce
• Brighter fruits and vegetables = more vitamin C
• Ready to eat breakfast cereals
Avoiding Too Much Vitamin C
• Increased iron absorption: problematic
with hemochromatosis
• Increased kidney function and urination
above 100 mg per day
• UL is 2,000 mg/day
• Stomach inflammation and diarrhea
• GI distress
Bar Graph: Sources of Vitamin C
MyPlate: Sources of Vitamin C
10.5 Carotenoids
1. What are the names of four carotenoids known
to have antioxidant functions?
2. How are the carotenoids related to vitamin A?
3. What are some rich food sources of
carotenoids?
Carotenoids
• Plants contain pigments called carotenoids
• Carotenoids are phytochemicals with
health promoting chemicals
• Precursors of vitamin A, antioxidant
properties
Carotenoids
• Three carotenoids are provitamins - can
be turned into vitamin A:
– Beta-carotene
– Alpha-carotene
– Beta-cryptoxanthin
• Other carotenoids that may have health
benefits:
– Lycopene
– Zeaxanthin
– Lutein
Functions of the Carotenoids
• Vision, reduce macular degeneration
– Leading cause of legal blindness in North
America
• Cardiovascular disease prevention
– May inhibit oxidation of low-density
lipoproteins
• Cancer prevention, lung,
oral, skin, prostate
Age-Related Macular Degeneration
(a)Age-related
degeneration of the
macular region as
noted by the black
arrow
(b)The blurry center of
the image simulates
the vision of a person
with macular
degeneration
Getting Enough Carotenoids
• Dark green and yellow-orange vegetables
and fruits
• Green leafy vegetables, spinach, kale
– lutein and zeaxanthin
• Tomato products, juice,
sauce
– lycopene
• Cooking frees carotenoids
for better absorption
Avoiding Too Much
Carotenoids
• Excess dietary
consumption, no toxic
effects
• Hypercarotenemia, too
many carrots or betacarotene supplements/pills
– Skin may turn yelloworange
10.6 Other Phytochemicals
1. What categories of phytochemicals function as
antioxidants?
2. Which food group has the richest supply of
antioxidant phytochemicals?
3. What phytochemical group is responsible for the
color of berries?
4. What is the ORAC assay, and what are the
limitations to using its values to estimate antioxidant
activity?
5. Diets rich in phytochemicals have been associated
with a decreased risk of which diseases?
Phytochemicals
• Thousands of food substances in addition to
45 essential nutrients
• Functional foods
– have health benefits beyond basic nutrition
• Zoochemicals
– found in animal products that have health protective
actions
• Phytochemicals
– health-promoting compounds found in plant food
• Many foods contain hundreds of phytochemicals
• Not essential nutrients, no deficiency disease
when removed from diet
Functions of Phytochemicals
• Antioxidants
• Inhibit cancer and cell death
• Alter absorption, production,
and metabolism of cholesterol
• Mimic or inhibit hormones and enzymes
• Decrease formation of blood clots
• Decrease inflammation, affecting immunerelated disorders
Antioxidant Activity of Food
• 326 foods analyzed by USDA
– oxygen radical absorption capacity (ORAC)
– ORAC measures antioxidant capacity in test tube,
not humans
– USDA reports results may be abused by
supplement manufacturers to promote products
• Dietary Guidelines
– eat variety of fruits, vegetables,
and whole grains
• 5-A-Day program results
associated with lower
oxidative stress, improved
antioxidant status
Antioxidant Activity of Foods 1
Antioxidant Activity of Foods 2
Antioxidant Activity of Foods 3
Getting Enough
Phytochemicals
• No specific recommendation for amount
• Typical U.S. consumption is 3000-5000
ORAC units
• Should be closer to 12,000 ORAC units
– This would be 8-9 fruit,
vegetable servings/day
• Very little evidence
supporting use of
antioxidant supplements
10.7 Selenium (Se)
1. How does selenium play an antioxidant role?
2. What other functions does selenium play in
the body?
3. What are the signs of a selenium deficiency?
4. What food groups are the best sources of
selenium?
5. What are the signs of selenium toxicity?
Selenium (Se) Functions
• Trace mineral
• Helps glutathione peroxidase:
– Glutathione peroxidase chemically converts
dangerous peroxides → water
• Selenium spares vitamin E and helps
maintain cell-membrane integrity
• Activates thyroid hormone
• Helps immune function
Getting Enough Selenium
• RDA: 55 mcg per day for adults
• DV used on supplement and food labels is
70 mcg
• Adults generally meet selenium needs
Selenium Deficiency
• Low blood levels linked to ↑ risk of some
types of cancer (ex: prostate)
• Muscle pain, wasting, heart damage
• China’s Keshan province’s soil is known to
be deficient in selenium
Food Sources of Selenium
• Selenium content of soil where plant or
animal food comes from predicts selenium
content in plant or animal food
• Brazil nuts, fish, meat and organ meats,
shellfish, eggs
• Some grains and seeds grown in selenium
rich soil
Bar Graph: Sources of Selenium
Avoiding Too Much Selenium
• Selenium toxicity has not
been reported from food
sources
• Supplementation for long
periods of time is toxic
• UL is 400 mcg
• Toxicity signs: hair loss,
weakness, cirrhosis
Portion of 10 Brazil nuts
contains 960 mcg of
selenium, which exceeds
the Upper Limit
Nutrition and Your Health
Nutrition and Cancer
Detecting Cancer
• Undetected, it can spread quickly – early detection
• Use CAUTION acronym
Change in bowel or bladder habits
A sore that does not heal
Unusual bleeding or discharge
Thickening or lump in the breast or elsewhere
Indigestion or difficulty in swallowing
Obvious change in a wart or mole
Nagging cough or hoarseness
– unexplained weight loss an additional warning sign
Detecting Cancer
• Routine screenings important for early
detection
• Colonoscopy examinations
– middle-aged and older adults
• Prostate-specific antigen (PSA) tests
– middle-aged, older men
• Papanicolaou tests (Pap smears) and regular
breast examinations
– mammograms about age 40 for women (ACS)
Cancer Statistics
• Second leading cause of death, North
America
• Estimated 1600 die each day in U.S.
• Four cancers, more than 50% of cancer
deaths, lung, colorectal, breast, prostate
cancers
• Cancer is many diseases, by types of cells
and contributing factors
• Treatments vary
Cancer Terminology
• Tumor
– mass of cells; cancerous or noncancerous
• Benign
– noncancerous; tumors that do not spread
• Malignant
– property of spreading locally and to distant sites
• Metastasize
– spreading of disease from one part of body to
another, even parts of body that are remote from
site of original tumor
– cells spread via blood vessels, lymphatic system,
or direct growth of tumor
Factors That Influence
Development of Cancer
• Genetics, environment, lifestyle
• Genetic role in colon, breast, and prostate
cancer
• Experts estimate that only 5% of most
cancers can be explained by the
inheritance
• Diet likely to account for 30-40% of all
cancers
Contributions of Calorie and
Fat Intakes to Cancer Risk
• Food constituents may contribute to cancer
development, some are protective
• Excess calorie intake and obesity responsible
for 14% of cancer death in men, 20% women
– Increased estrogen and insulin output suspected
• Nation Cancer Institute recommends reducing
fat intake to 20% of total calories
• Some researcher say to reduce calories to 70%
of usual intake, increases longevity
Cancer Deaths
Cancer-Inhibiting
Constituents of Foods
• Include antioxidants and some
phytochemicals
• Some help prevent DNA mutations
• Vitamin C and E help prevent formation of
nitrosamines (carcinogen) in GI tract
• Fruit and vegetable intake reduces risk of
nearly all types of cancer
• Use MyPlate guidelines
to form diet
Nutrition Concerns During
Cancer Treatment
• Overall goals of medical nutrition therapy to
minimize weight loss, prevent nutrient
deficiencies
– Preserve muscle mass
• Fatigue, mouth sores, dry mouth, taste
abnormalities, nausea, diarrhea lead to poor
food intake
• Best food…any patient tolerates
• Small, frequent, nutrient dense
– Liquid nutritional supplements often needed
American Institute for Cancer
Research Recommendations
for Cancer Prevention
1. Be as lean as possible without becoming
underweight
2. Be physically active for at least 30 minutes every day
3. Avoid sugary drinks. Limit consumption of energydense foods
4. Eat more of a variety of vegetables, fruits, whole
grains, and legumes
5. Limit consumption of red meats
American Institute for Cancer
Research Recommendations
for Cancer Prevention
6. If consumed at all, limit alcoholic drinks to two per
day (men) or one per day (women)
7. Limit consumption of salty foods, foods processed
with salt
8. Don’t use supplements to protect against cancer
9. It is best for mothers to breastfeed exclusively for
up to 6 months and then add other liquids and
foods
10. After treatment, cancer survivors should follow the
recommendations for cancer prevention
– Don’t smoke or chew tobacco