Nutrient Metabolism Overview: Carbohydrates, Lipids & Proteins

Question 1

Some Important Terminology

• ADI
• AI
• AMDR
• DRI
• RDA

Answer 1

• ADI – Acceptable Daily Intake
• AI – Adequate Intake
• AMDR – Acceptable Macronutrient
Distribution Range
• DRI – Dietary Reference Intake
• RDA – Recommended Dietary Allowance

Question 2

What are Macronutrients?

Answer 2

• A class of chemical compounds that humans consume in large quantities and provide the majority of our energy
– Carbohydrates, lipids, and protein
• There are also macronutrients that do not provide energy
– Water, fiber
not alcohol as it is a toxin

Question 3

Macronutrients & Daily Energy Metabolism

• A healthful diet is balanced in all 3 macronutrients

Answer 3

• A healthful diet is balanced in all 3 macronutrients
➢AMDR for carbohydrates is 45 – 65%
➢AMDR for fat is 20 – 35%
➢AMDR for protein is 10 – 35%

• A healthy individual is flexible in his ability to
transition between carbohydrates and fats as their
primary energy source between meals and fasting
➢We normally don’t use proteins as an energy source
protein is not storage form of nutrition, we don’t want to break it down for energy *want to use fat and carbs
so protein can support other bodily fxns

Question 4

What are Carbohydrates?

Answer 4

• One of the three macronutrients
• Important source of energy for all cells
• Only energy source for red blood cells
• Preferred energy source for the brain and nerve
cells
• Composed of carbon, hydrogen, oxygen
• Glucose most abundant (produced by plants via
photosynthesis)

plants make sugar through photosynth: chlorophyll absorbs sunlight, water and Co2 absorbed and converted to sugar and O2 released to env

• important for RBCs which dont have mitchondria and only get energy from glycolysis, breakdown glucose for energy
• preferred for energy of brain

Question 5

• Monosaccharides contain one molecule
[• Disaccharides contain two molecules
examples?

Answer 5

• Monosaccharides contain one molecule
➢Glucose, fructose, and galactose
- same chem structure, diff arrangmeent, level of sweetness
fructose is sweetest, galactose in milk\

• Disaccharides contain two molecules
➢Lactose, maltose, and sucrose
- glucose + galactose = lactose (milk sugar)
- glucose + glucose = maltose
- glucose + fructose = sucrose found in sugarcane, honey (sweeten foods)

Question 6

• Complex carbohydrates

what are the storage forms for plants and animals?

Answer 6

➢Oligosaccharides contain 3 to 10
monosaccharides
➢Most polysaccharides consist of hundreds
to thousands of glucose molecules
➢Starch, glycogen, most fibers
- starch is storage form of glucose in plants (grains, legumes, tubers, like yams wheat, rice)
- glycogen is storage form in animals, stored in liver and msucles
- starch is main complex carb we consume as glycogen in animals is mobilized

• fiber: forms the support structures of leaves, stems plant (don’t have the enzymes to break it down so we dont get energy from it)

Question 7

Fiber

soluble vs insoluble

Answer 7

• The body does not easily break down the bonds that
connect fiber molecules.
• Most fibers are not digested and absorbed by our bodies (contribute no energy to our diet)
• Soluble fibers can be digested by bacteria in our colon (e.g. pectins, fructans)
Ø May help reduce risk for cardiovascular disease (lower LDL cholesterol), also absorbs bile and get rid of it when bound to fibre

• Insoluble fibers cannot be digested by bacteria in our
colon (e.g. lignins, cellulose)
Ø Can help promote regular bowel movements (laxatives)
• Sources: Whole grains, vegetables (legumes, broccoli), fruits (blackberries), nuts and seeds

Question 8

The Importance of

Carbohydrates in the Diet

Answer 8

• Energy
➢Each gram of carbohydrate: 4 kcal
➢Red blood cells can only use glucose for energy
➢Our brain (neurons) are heavy consumers of
glucose
➢Both carbohydrates and fats supply energy for daily
activities
➢Glucose is especially important for energy during
exercise, inital fuel
transitions and fat becomes major fuel source

Question 9

• Carbohydrates spare protein and prevent
ketoacidosis
explain

Answer 9

➢During prolonged starvation the liver makes glucose
from amino acids
➢As this continues the liver will produce ketone bodies to limit muscle proteolysis
- insulin to shut off ketogenesis, carbs cause insulin secretion
- healthy carbs prevent breakdown of muscle into proteins

Question 10

• Fiber helps us stay healthy

explain

Answer 10

➢Promote bowel health (prevent hemorrhoids,
constipation) by keeping stool soft. - gives something to push on
➢Reduces the risk of diverticulosis (increased pressure to push out feces can cause weakening of walls and formation of pockets that can trap stool that leads to infection
➢May reduce risk for colon cancer (binds cancer causing substances)

Question 11

How Much Carbohydrate?

Answer 11

• Recommended Dietary Allowance (RDA) is 130 grams/day to supply adequate glucose to the brain
• Acceptable Macronutrient Distribution Range (AMDR) is 45% to 65% of daily calories
• Focus on fiber-rich carbohydrate foods
- added sugar (fructose and sucrose) should be 25% or less of total energy intake each day (now changed to 10%)

Question 12

What About too Much Carbohydrate?

what does fructose do?

Answer 12

Diets high in simple sugars:
➢Can cause tooth decay, cavitites (bac in mouth thrive on sugar and produce acids)
➢May increase “bad cholesterol” (LDL, decrease HDL)
➢May decrease “good cholesterol”
➢May contribute to obesity (fructose specific for simple sugar)

• Fructose:
➢May increase hepatic de novo lipogenesis (convert carbs into tryglycerides or fat)
➢May increase visceral adiposity (abdominal fat, promotes cardio disease, inflamm cytokines, insulin diabetes)
- fructose absorbed later in GI tract, doesn’t actually promote release of insulin which is a satiety factor
- glucose induces saitry signal in brain but not fructose
• Most of our excess added sugar intake comes
from sugar sweetened beverages

Question 13

What About too Little Carbohydrate?
most ppl only eat half of their fiber intake

enriched foods vs
fortifed foods

Answer 13

• Most Americans eat too little complex carbohydrates
• Adequate Intake (AI) for fiber
➢14 g of fiber for every 1,000 kcal per day (25 g/day for women; 38 g/day for men)
➢It is best to get fiber from food (also a source of vitamins, minerals, and other micronutrients)
• Enriched foods are foods in which nutrients that were
lost during processing have been added back so the
food meets a specified standard
• Fortified foods have nutrients added that did not
originally exist in the food (or existed in insignificant
= amounts)
- dairy fortified with vit D

Question 14

anatomy of a grain

Answer 14

Bran - rich in fibre and vitamins
- outer coating
• Endosperm - rich in carbohydrates & protein
• Germ - rich in unsaturated fats & vitamins

whole grain means entire grain is there
if not whole, grain is milled and most of the bran is removed and will be low in fibre
cannot actually fortify fibre into bread

Question 15

What About Alternative Sweeteners?

Answer 15

• Nutritive sweeteners
➢Sucrose, fructose, honey, and brown sugar contain
4 kcal energy per gram
➢Slow-absorbing sugar alcohols: 2−3 kcal/gm
Causes osmotic diarrhea

• Non-nutritive (alternative) sweeteners
➢Provide little or no energy
➢Safe for adults, children, people with diabetes

still some energy from mannitol
Do not promote tooth decay
• Controversy surrounding whether alternative
sweeteners reduce or contribute to obesity

Question 16

• Acceptable daily intakes (ADI) of alternative sweeteners

Answer 16

➢No ADI for Saccharin
➢50 mg/kg body weight for Aspartame
(not consuming near the ADI for normal use)
➢5 mg/kg body weight for Sucralose

• Saccharin previously linked to cancer
• People with phenylketonuria cannot consume aspartame (cannot breakdown phenylalanine)
- can’t cook with aspartame but can cook with sucralose

Question 17

What are Lipids?

Answer 17

• Lipids
➢Diverse group of molecules that are insoluble in water
• Fats
➢Foods – lipids occur as fats and oils
➢Animal fat is solid at room temp.
➢Plant fat (oils) are liquid at room temp.

Question 18

Three types of lipids are found in foods

and in body cells and tissues:

Answer 18

➢Triglycerides: 90-95% of fat we consume
➢Phospholipids: egg yolks, peanuts
➢Sterols: choesterol

Question 19

Triglycerides contain

fatty acids are classified by?

Answer 19

Triglycerides (triacylglycerols) contain:
➢Three fatty acid molecules
➢attached to One glycerol molecule (backbone)

Fatty acids are classified by:
➢Carbon chain length – How many C
➢Saturation level – How many double bonds
➢Shape – Straight and rigid or bent and
kinked

Question 20

TG

• Carbon Chain Length

Answer 20

➢Short- (<6), medium- (6-12), or long-chain FAs (14+)
➢Carboxyl end (COOH): α-carbon (alpha—first)
➢Methyl end (CH3): Ω-carbon (omega—last)
➢Determines method of lipid digestion, absorption,
metabolism, and use

• short and medium chain are absorbed much faster as they bind albumin
• long chain packaged as chylomicrons and enter lymphatic system before circulation

Question 21

Triglyceride

Saturation

Answer 21

➢Saturated fatty acids (SFA) have hydrogen atoms
surrounding every carbon in the chain
➢Monounsaturated fatty acids (MUFA) lack two
hydrogen atoms (one double bond)
➢Polyunsaturated fatty acids (PUFA) have more than
one double bond

double bond introduces kinks, (seen in plant based oils have a liquid shape, can’t be compacted together unlike animal which is solid)

• animal based fat contains a lot of saturated fat: butter, milk, beef, egg, chicken breast –> ceramides leading to insulin resistance
• plant based lots of unsaturated (more healthful fat)

Question 22

Triglyceride

how chan sat fat become packed tightly together?

Answer 22

Shape
➢Saturated fatty acids pack tightly together and are
at solidroom temp.
➢Unsaturated fatty acids do not pack tightly together and are more often liquid at room temp.
➢Hydrogen atoms at the unsaturated part can be
arranged in different positions:
❑Cis: same side of the carbon chain
❑Trans: opposite sides of the chain

natural is cis, opposite is trans which straightens the kink

Question 23

Triglyceride

Hydrogenation:

Answer 23

Hydrogenation: hydrogen atoms are added to
unsaturated fatty acids
➢Make oils more solid and more like a saturated fat
➢Create trans fatty acids
➢Also known as a partially hydrogenated oil
➢Reduce oxidation; resist rancidity –> longer shelf life
➢Increase risk of cardiovascular disease
➢Some trans fats found naturally in cow’s milk and
meat if less than 0.5g of trans fat, will show as 0 but may still contain it, need to see ing list of partially hydrogenated vegetable oil

Question 24

• Essential fatty acids (EFAs)

Answer 24

– Cannot be made by our body and must be obtained
in the diet

– Linoleic acid (omega-6 fatty acid)
❑Found in vegetable and nut oils (safflower, sunflower,
corn, soy and peanut oil)

– Alpha-linolenic acid (omega-3 fatty acid)
❑Found in vegetables (dark leafy), soy, flaxseeds and flaxseed oil, soybeans and soybean oil, walnuts, walnut oil, and canola oil

double bond at 3 or 6 carbons counting from omega end
we don’t have enzymes to create double bond before 9 carbon

Question 25

• EFAs (fish & fish oil omega-3 fatty acids)
2 types
effects

Answer 25

➢Eicosapentaenoic acid (EPA)
➢Docosahexaenoic acid (DHA)
more in salmon and tuna, less in lean fish

• Eicosanoid precursors (prostaglandins, thromboxanes, and leukotrienes)
➢reduce inflammatory responses, reduce plasma
triglycerides
➢regulate GI motility, blood clotting, vasodilation,
vasoconstriction, vascular permeability, and inflammation
➢Reduce risk of heart disease

Question 26

• Phospholipids consist of the following:

Answer 26

➢Glycerol backbone, two fatty acids, phosphate is 3rd entity which is water sol
➢ Hydrophobic end, which is their lipid “tail”, and a
hydrophilic end, which is their phosphate “head”
➢Transport substances in and out of the cell

Question 27

Phospholipids fxn and where they are found

Answer 27

• In the liver called lecithins (combine with bile salts and electrolytes to make bile)
➢ Aids in digestion of fat
• Transport fat in the bloodstream
• Manufactured in our bodies (not required from diet)
phosphorus is essential
• Egg yolks, peanuts, and soybeans and are present in processed foods containing emulsifiers (additives that help foods stay blended)

Question 28

Sterols

roles
where they are found

Answer 28

• Contain multiple rings of carbon atoms
• Found in both plant and animal foods and
produced in the body
• Food: primarily found in fatty part of animal
products
➢Butter, egg yolks, whole milk, meats and poultry
–> also contain a lot of saturated fat

• Cholesterol (exogenous vs. endogenous)

• Not necessary in the diet, made in our body
• Plant sterols (Phytoesterols) → block the
absorption of dietary cholesterol, ↓ cholesterol
• Sex hormones (estrogen, androgens), vitamin D, bile
- adds fluidity in membrane for bending

Question 29

The Importance of Fats in the Diet

guideliens want to switch fats, not to reduce

Answer 29

• Fats are a major fuel source at rest
➢9 kcal/g
➢30 – 70% of our daily energy
➢Primary fuel source for the heart (needs a lot of energy)
• Important for energy storage, adipose tissue

• Essential fatty acids
➢Important constituents of cell membranes
➢Anti-inflammatory
• Fat-soluble vitamins
➢Assist with the transport of vitamins A/D/E/K, require dietary fat to digest and absorb

• Protects the body
➢Cushions our organs
• Provides flavors and textures of foods
• Helps us feel satiated
➢Fats are less satiating than protein but more
satiating than carbohydrate

Question 30

How Much Fat?

• DRIs set for essential fatty acids
➢Linoleic acid: AMDR of 5−10% of energy (AI: 14 to
17 g/d men and 11 to 12 g/d women, adults)
➢Alpha-linolenic acid: 0.6−1.2% of energy (AI:
1.6g/d men and 1.1 g/d women, adults)

Answer 30

• Acceptable Macronutrient Distribution Range
(AMDR) for fat: 20−35% of calories, not less than 20%
• Active people may need more energy from
carbohydrates and can reduce their fat intake
to 20−25% of total calories
• Minimize saturated and trans fatty acid intake
to lower risk of heart disease
➢Saturated fat (<7% of energy)
➢Trans fat (reduce to the absolute minimum)

5:1 to 10:1 ratio of linoleic:alpha-linolenic acid
➢These fats compete for the same enzymes to
produce various eicosanoids that regulate body
functions. This ratio helps ensure eicosanoids are
produced in balance

Question 31

What About Reduced Fat Foods

read

Answer 31

• Fat-free < 0.5 g fat per serving
• Low-fat ≤ 3 g fat per serving
• Reduced-fat or less fat: at least 25% less fat
compared to a standard serving
• Light: 50% less fat compared to a standard
serving
• Reduced/lower fat alternatives may not always
be lower in calories