EXAM1 Flashcards
Epidemiological (observational) study
Generate hypothesis and establish complex associations/correlations
Explore or test correlations between exposures and outcomes by diet
Can explore complex relationships but cannot prove a causal relationship
Interventional (Experimental)
Test hypothesis and establish causality
Manipulate one or more factors (ind variables) and measure outcomes (dept variables) in subjects
Distinguish 3 major type of epidemiological studies
Cross-sectional
Measure various exposures and outcomes simultaneously
I.e. The National Health and Nutrition Examination Survey (NHANES)
Distinguish 3 major type of epidemiological studies
Retrospective
Assess outcomes before potential causes
Weakest. Compare those with condition to similar people w/o condition
Case-control: compare people who do and don’t have a condition or disease, closely matching them in age, gender, and other variables so that differences in other factors will stand out. These differences may account for the condition in the group that has it
Distinguish 3 major type of epidemiological studies
Prospective Cohort
Follow a group of people sharing certain characteristics over a long period of time
Framingham Heart Study: smoking and high cholesterol affect heart health
Temporality in establishing causal relationships
potential causes (exposures) must appear before outcomes
Necessary
if cause is not there, outcome won’t occur
Essential nutrients are necessary for health but not sufficient
Essential nutrients
Required for physiological functions but can’t be produced - not at all or not in sufficient quantity - by our body; thus, they must be obtained from diet
Operational definition: When they are removed from diet, health declines; when they are added back into diet, health improves
Sufficient
if the cause is there, the outcome will be to
I.e. Vitamin C is sufficient to cure scurvy
Contributory
the cause is necessary and/or sufficient (and thus has effects) only under certain circumstances
I.e. Niacin is necessary for preventing pellagra only when protein consumption is insufficient
Assessment of exposures challenges
- Lack of reliable measurements
- Potential confounding factors and biases
Assessment of health outcomes of interest
- Indexes/biomarkers of disease are used
- Nutritional Assessments are often not specific
24 hr recall
food and drink recorded over 24 hours
May not represent usual intake
Challenges:
* Recall bias
* Retrospective study
Food frequency questionnaire
Food intake patterns
Limited in accuracy and completeness
Observational study
Food Record (Food Diary)
Recorded when person consumes food
Challenges
* Portion sizes estimated
* Most accurate method of dietary assessment
* May not be representative
* Observer effect
Observational study
ABCD of Nutritional Assessment
Anthropometric measurements
* Weight
Biochemical testing (laboratory tests)
* Best method for detecting nutrient deficiency (ie. iron)
Clinical assessment (physical exam)
* Paleness to access anemia
Dietary assessment (diet and health history)
Primary deficiency caused by inadequate diet.
Secondary deficiency caused by problem inside the body (i.e. crohn’s disease)
Interventional studies:
Randomized human clinical trial limitations
Medrn. diet sufficient in preventing cardiovascular events in high-risk
Clinical trial recruiting those at high risk for cardiovascular disease (smoking, hypertension, high LDL, low HDL, overweight/obese, family history) and applying mediterranean diet (provided olive oil or nuts)
Costly and time consuming
* Provide foods for 5 years
Difficult to control for all confounding factors
* Low subject compliance
Ethics
* Chose to use low fat diet as control over high fat diet
Subjects may not be representative: “Generalizability”?
* Applicable conclusions for general population
Reproducibility?
Nutritional status
the health of a person related to how well his/her diet meets the person’s individual nutrient requirements
Both under and overnutrition represent states of malnutrition or poor nutritional status (overnutrition/ toxicity)
Nutrition
The process by which a living organism obtains, assimilates, and uses nutrients or other food components for growth, maintenance of tissues, and reproduction
Human nutrition
science of how dietary intakes affect development, health, and risk of developing diseases later in life
Diet
the foods and beverages a person eats or drinks
Nutrients
Chemical compounds in diet (foods and drinks) that organisms need to sustain life
At an organismal level, nutrients:
Promote growth
Maintain tissues
Regulate physiological processes
* Including reproduction
At a cellular level, nutrients serve as:
Energy substrates
Structural materials
Regulatory agents
Macro vs. micronutrients
Quantity in diet
Macronutrients: carbs, proteins, lipids, water, alcohol
Micronutrients: minerals, vitamins
Organic vs. inorganic nutrients
Organic: compounds containing carbon links
Inorganic: water and minerals
Organic: Vitamins, carbs, proteins, lipids, alcohol
Energy-yielding vs. non-energy-yielding nutrients
Energy-yielding: Carbs (4 kcal/g), proteins (4 kcal/g), lipids (9 kcal/g), alcohol (ethanol)
Non-energy yielding: water, vitamins, minerals
Essential vs. non-essential nutrients vs. conditionally essential nutrients
Operational definition through experiments
I.e. choline depletion/repletion study that established essentiality
Nutrient requirement: lowest intake level of a nutrient that maintains basic physiological functions and supports optimal health
Nutrient requirements differ among individuals
Energy density
a measure of the energy a food provides relative to the weight if the food (kcal per gram)
Nutrient density
the amount of micronutrients and protein of a food item relative to its energy content
Nutrient dense foods- high in nutrients but relatively low in calories
Nutrient-dense foods contain vitamins, minerals, complex carbohydrates, lean protein, and healthy fats
DRI
a set of nutrient intake values for healthy people in the US and Canada. These values are used for planning and assessing diets and include: Estimated Average Requirements (EAR), Recommended Dietary Allowances (RDA), Adequate Intakes (AI), and Tolerable Upper Intake Levels (UL)
Apply to healthy individuals within a specific gender/life stage group
Established when scientific data are sufficient
EAR
the average dietary energy intake that maintains energy balance and good health in a person of a given age, gender, height, and level of physical activity
Amount that covers half of the population
RDA
the average daily amount of a nutrient considered to meet the known nutrient needs of practically all healthy people; a goal for dietary intake by individuals
Derived from EAR
RDA = EAR + 2 Standard Deviations
AI
the average daily amount of a nutrient that appears sufficient to maintain a specified criterion; a value used as a guide for nutrient intake when an RDA cannot be determined
Established when scientific data are insufficient to establish EAR/RDA
Choline has AI data
UL
the maximum daily amount of a nutrient that appears safe for most healthy people and beyond which there is an increased risk of adverse health effects
Monosaccharides
gluctose, fructose, galactose
Disaccharides
Maltose, sucrose, lactose
Polysaccharides
Amylose, amylopectin, glycogen
Glucose
in starch and blood
aldehyde C=O on terminal end
Fructose
sweetest of nutritionally relevant sugars. I.e. fruit
Ketone C=O on internal carbon
Galactose
in dairy products and milk
Aldehyde C=O on terminal end
Structual forms
Have open (Fischer) and closed ring (Hawthorth projection)
* Both glucose and fructose can form a 5-membered (furanose) or 6-membered (pyranose) ring, although one typically predominates
Fructose often depicted as furanose
Anomeric Carbons
- Anomeric carbon is the C=O (carbonyl) is attached to
- Anomeric on second carbon for fructose and first for glucose and galactose
Glycosidic linkage
Formation: condensation (water is released)
* One sugar loses hydrogen and one loses hydroxyl
Breaking: hydrolysis (digestion- water is a reactant)
Maltose
glucose-glucose
Alpha-1,4 glycosidic linkage
Partial digestion
Sucrose
glucose-fructose
Alpha-1-beta-2 glycosidic linkage
* Unique because glycosidic bond between both anomeric Cs; therefore both trapped in cyclic form, and entirely non-reducing because both anomeric Cs used in glycosidic bond
Lactose
galactose-glucose
Beta-1,4 glycosidic bond
* Difficult to digest (i.e. cellulose)
Sweetness ranking
Fructose, sucrose, glucose, maltose, galactose, lactose
Most to least sweet
Amylose
linear chain of alpha-1,4 glucose molecules
Reducing and nonreducing ends
Amylopectin
branching chain of alpha-1,4 glucose, with alpha-1,6 branches
One reducing end
Glycogen
Branching chain of alpha-1,4 glucose with alpha-1,6 branches (but generally more branches than amylopectin)
* Storage form of glucose in your body- found in muscle and liver
* Liver is blood glucose buffer system: helps maintain blood glucose (thus, glycogen in liver can be mobilized and pushed out into circulation)
Muscle uses it for energy reserve (it cannot contribute to maintenance of blood glucose)
Several nonreducing and one reducing end
Non-digestible or incompletely digestible polysaccharides
Oligosaccharides (3-10 monosaccharides): typically have both alpha and beta glycosidic bonds
Cellulose
Insoluble carbohydrate
beta-1,4 glycosidic bonds which can’t be hydrolyzed
Hemicellulose
Soluble or insoluble, depending on type/structure
Adds bulk to fecal matter and decreases intestinal transit time
Lignins
Polycyclic alcohol (non-carbohydrate)
Insoluble fiber
Provide bulk to fecal material
Soluble carbohydrate fibers
Pectins, gums, and mucilages
Absorbs water (gel-like consistency)
Used as food additives, thickening agents, etc. because they absorb water
Delays gastric emptying, slows glucose absorption, and lowers blood cholesterol
Diverticulosis
Diverticula are little pouches of epithelial lining that pushes out in between the layers of muscle
Diverticulitis
Material from the intestine becomes trapped in the diverticula (particularly bacteria)
This can trigger inflammation and lead to internal bleeding
Soluble Fiber Lowering Blood Cholesterol
Mechanism:
* Soluble fiber blocks enterohepatic circulation of bile acids
* Soluble fiber is metabolized into short-chain fatty acids that travel to the liver and reduce cholesterol synthesis
Fatty Acid Structure
Methyl group on one end (⍵ omega); carboxylic acid on the other end (ɑ alpha)
4-24 carbons long
16 and 18 carbons are most common in food
I.e. nomenclature 18:3 means 18 carbons, 3 double bonds
Saturation
- Presence or absence of C=C
1. Saturated fatty acid: No C=C
2. Monounsaturated fatty acid (MUFA): A single C=C
3. Polyunsaturated fatty acid (PUFA): > 1 C=C
Unsaturations
Each C=C also means loss of 2 H atoms
unsaturated fatty acids does not stack, therefore liquids
If oleic acid (C18:1) has a chemical formula of C18H34O2 and an additional unsaturation is introduced, the chemical formula will become:
C18H32O2
Texture and Firmness
- Degree of unsaturation and length of chains decide texture
- Most polyunsaturated are liquid at room temperature
- Saturated animals fats are solid at room temperature
- Some fats such as cocoa butter, palm oil, and coconut oil are firmer than vegetable oils because of saturation, but softer than animal fats because of shorter carbon chains
linoleic acid
ω-6; C18:2
Used to make series 1 and 2 eicosanoids
Stimulates blood clotting
Dangerous in heart disease
α-linolenic
ω-3; C18:3
Used to make series 3 eicosanoids
Decrease blood clotting by reducing the synthesis of Group 2 series eicosanoids
Abuse may lead to hemorrhagic stroke
Rancidification
autoxidation/hydrolysis
* Produces short-chain aldehydes, ketones, and fatty acids
* Oxidation in lipids occurs at the unsaturations – more double bonds means more likely for this to occur
* Contributed to the use of hydrogenation
more common in PUFAs than MUFAs
antioxidants is also a strategy to prevent : Vit E, BHA, BHT
Triglycerides
Glycerol head group + 3 fatty acid chains
TGs do not cross cell membranes
TGs must first be hydrolyzed (de- esterified) by a class of enzymes called lipases
Phospholipids
Somewhat similar to TGs but they only contain 2 fatty acid chains (instead of 3)
Primary component of cellular membranes
Also used as emulsifiers due to amphiphilic nature
Sterols
From cholesterol
Precursor to the steroid hormones and fat-soluble vitamins
Animal sources
Emulsification
Lecithins
Phosphatidylcholine
Polysorbate 60
Monoacylglycerol
Egg yolk
Fed state
Clearance of blood lipids (10-14 hr)
Lipoprotein lipase is insulin sensitive and acts on chylomicrons and VLDL
Lipids are delivered to muscle and adipose (adipose contains 3,500 kcal/lb)
Fasting state
Hormone sensitive lipase is activated in adipose tissue (glucagon, norepinephrine)
Triglyceride breakdown and mobilization of glycerol and FFAs
FFA from adipose are delivered to liver and muscle via albumin
Chylomicrons
Transports diet derived lipids from small intestine to lymphatics and then to blood and eventually to liver (losing TGs to muscle and adipose along the way)
Dietary lipids and cholesterol
Very low-density lipoprotein (VLDL)
Lots of TGs. Bigger but less dense
Travel from liver to other tissues through blood, interacting with Lipoprotein lipase
Deliver TGs and cholesterol
Low density lipoprotein (LDL)
Mostly cholesterol
A lipoprotein that is derived from VLDL as triglycerides are removed.
Internalized by a receptor pathway in liver and a few other tissues
May be scavenged by white blood cells
Attach to blood vessels and oxidize lipids. Ultimately become arterial plaques (atherosclerosis)
High density Lipoprotein (HDL)
“Good” cholesterol
Mostly protein
Synthesized in the liver and intestine
Picks up cholesterol from dying cells and transfers it to other lipoproteins and deposits it in the liver for excretion
Lipoprotein lipase
Made in liver and small intestine
Enzyme attached to blood vessels that hydrolyze TGs, yielding glycerol and free fatty acids (FFAs) and thus delivering lipids to surrounding tissues (adipose, muscle)
* Picks up cholesterol from dead/dying cells, delivers to liver for excretion
Essential Fatty Acids
Omega-3: Rich in fatty fish (salmon, tuna, sardines), canola or soybean oil
Omega-6: 1 tbsp of plant oil/day is enough to meet most people’s needs
* Polyunsaturated fatty acids (PUFA) that must be provided by foods because these cannot be synthesized in the body yet are necessary for health
Trans fats
Most fatty acids with unsaturations are cis – the hydrogens are on the same side, and the chain is therefore “kinked”
A small percentage are trans, H atoms on opposite sides
* The chain is more linear and can behave more like a saturated fat
There is some evidence that there are negative health effects from intake of higher than naturally-occurring amounts of trans fats
Amino Acids
Amino – nitrogen containing
Amphoteric - Can carry both positive and negative charge
Primarily L-isomer amino acids
Carbon with acid group, amino group, and varying side group
Amino acid side chains
There is a wide variety of side chain structures. This is necessary because of the wide variety of functions that proteins have.
Basic, acidic, sulfur containing, aliphatic, hydroxyl, aromatic, N containing
Essential amino acids
Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine
Non-essential (dispensable) amino acids
Alanine, arginine, asparagine, aspartate, glutamate, glutamine, glycine, proline, serine
Conditionally dispensable amino acids
Cysteine, tyrosine
Phenylketonuria (PKU): Mutation in the enzyme that converts phenylalanine to tyrosine
Transamination
Transamination reactions are used to transfer nitrogen between amino acid backbones
Deamination
Removal of amino group
Ammonia, however, is a problem for the AA pool (except protein synthesis as it is toxic (acts as a solvent: Windex)
Ammonia converted to urea in liver, goes to kidney, and excreted in urine
All-or-nothing rule
Protein turnover
If an essential amino acid is deficient, you cannot make proteins that have that amino acid
A protein will not be made if any single amino acid in its primary structure is not available
Protein Structure
Primary
* Sequential order of amino acids
* Example: MADQRKSSCTPGAECN
Secondary
* Local 3-dimensional structure
Tertiary
* Arrangement of local structures into full macromolecular structure
Quaternary
* Protein-protein interactions
Nitrogen balance equation
I.e. (50g protein0.16)-(3 urinary N)-(0.23 urinary N)-2g= 2.4
Total N intake - urinary urea output - other DNA/RNA fudge factor - skin/feces fudge factor
Protein
Polymers of amino acids joined by peptide bonds
Bonds formed via condensation and break via hydrolysis
Protein digestibility
A measure of the amount of amino acids absorbed from a given protein source
Reference protein
a standard used to measure the quality of other proteins (egg protein)
Biological value (BV)
amount of protein nitrogen retained for growth and maintenance expressed as a % of protein nitrogen digested and absorbed
Protein Efficiency Ratio (PER)
a determination of how well a given protein supports weight gain in growing rats over a given period of time
Chemical score
lowest ratio for any essential amino acid
Protein Digestibility Corrected amino acid score (PDCAAS)
PDCAAS = chemical score * digestibility of a protein
Chemical score [0 – 1]
Digestibility [0.8 – 1]
Identify the glycosidic bond type that humans cannot generally breakdown or digest
Beta-1,4
The two major polysaccharides we discussed are _____ and _; amylopectin is an example of #2 that contains ____ and _____ bonds.
The two major polysaccharides we discussed are GLYCOGEN and STARCH; amylopectin is an example of #2 that contains ALPHA-1, 4 and ALPHA-1, 6 glycosidic bonds.
What is a key difference between the structures of glucose and fructose?
One is an aldose and one is a ketose
Match the polysaccharide with its correct description:
* Cellulose ->
* Oligosaccharides ->
* Lignin ->
- Cellulose -> non-digestible polysaccharide
- Oligosaccharides -> soluble non-digestible polysaccharide
- Lignin -> insoluble non-carbohydrate
Functions of triglycerides in the body?
- A condense source of energy
- Storage of metabolic energy
- Transport of lipid-soluble vitamins
- Aid in bodily insulation and protection
Most commonly associated with a reduced risk of having arterial plaques?
HDL
Just like the formation of ____ bonds between carbohydrates, the formation of a peptide bond is an example of a ____ reaction because ____ is given off as a product.
Just like the formation of GLYCOSIDIC bonds between carbohydrates, the formation of a peptide bond is an example of a CONDENSATION reaction because WATER is given off as a product.
There are two conditionally essential amino acids, ____. They can by synthesized from two completely essential amino acids, _____, respectively.
There are two conditionally essential amino acids, CYSTEINE or TYROSINE. They can by synthesized from two completely essential amino acids, METHIONINE and PHENYLALANINE, respectively.
A 30 year old woman consumes 50 g of a complete protein source and over the next 24 hours produces 3 g of urinary nitrogen. Identify the correct nitrogen balance value and direction from the following:
2.4 g; in positive nitrogen balance
One common limitation of epidemiological (observational) studies is that the findings can rarely establish __________
One common limitation of epidemiological (observational) studies is that the findings can rarely establish CAUSAL RELATIONSHIPS
Unit of energy density?
kcal/g
Essential nutrients are __ but not _for health
Essential nutrients are NECESSARY but not SUFFICIENT for health
A 24-hour dietary recall (24HR) is a structured interview intended to capture detailed information about all foods and beverages (and possibly, dietary supplements) consumed by the respondent in the past 24 hours. What type of dietary assessment tool is 24-hour recall?
Retrospective
To determine if performances in NS332 predict career choices of students, a study was performed to collect relevant information, including exam scores, age, gender, major, attitude and perception of the subject, and professions … etc) from the same group of NS332 students annually for 10 years after their completion of the course. What type of study is this?
prospective cohort study
Which of the following observations is considered the strongest evidence to reject the hypothesis that pellagra was a germ-based, infectious disease?
Dr. Goldberger exposed healthy individuals with body fluids and other potential infectious agents from patients and found that none of them developed pellagra.
In his search for a cure of pellagra, Dr. Goldberger performed an interventional trial, in which sick orphans were fed a nutritious diet (and orphans eventually recovered from the disease). Which one of the following statements BEST describes the hypothesis being tested in this trial?
A nutritious diet is sufficient to cure pellagra.
The requirement levels for the nutrient X in the general population exhibit a normal distribution, with an average of 200 mg/day and a standard deviation (SD) of 20. What is the RDA for nutrient X?
RDA = 240
Which of the following are aldo monosaccharides?
galactose and glucose
Describe D-fructose
- Very sweet
- Part of sucrose
- Rich in corn syrup
- Also known as levulose
Why is it important to include omega-6 and omega-3 fatty acids in the diet?
- These fatty acids are precursors of eicosanoids.
- The human body is unable to synthesize these fatty acids, because human cells cannot create double bonds between the CH3 end and the 9th carbon of fatty acids
- These fatty acids serve important roles that cannot be compensated fully by other nutrients.
True or false:
Humans do not have the enzyme required to break beta-1-4-glycosidic linkages found in lactose.
FALSE
Select all correct statements regarding polysaccharides:
- Amylose and amylopectin both have 𝛼-1-4 linkages.
- Liver glycogen contributes to the maintenance of blood glucose.
- Glycogen is found in the liver and muscle. It has a similar structure to amylopectin except that it has more branch points.
Match the following with the best description for each chain length saturated FA
Long chain saturated fatty acids (> 12 C)
* Solid at room temp
Short chain saturated fatty acids (< 6 C)
* Liquid at room temp
Medium chain saturated fatty acids (6-10 C)
* Solid or liquid at room temp
True or false: Diverticula are polyps and are a precursor to colon cancer.
FALSE
Function of soluble fiber
- Promotes satiety by delaying gastric emptying
- Can protect against diabetes by preventing the rapid increase of blood glucose post meal
In what ways do Dietary Guidelines for Americans (DGA) and Dietary Reference Intakes (DRIs) differ?
- DRIs are a set of values focusing on assessing nutrient intake
- DGAs focus on food groups, nutrients and eating patterns
- DGAs are published by the U.S. Departments of Health and Human Services (HHS) and of Agriculture (USDA
Which of the following recommendations are included in the 2020-2025 DGA?Which of the following recommendations are included in the 2020-2025 DGA?
- Meet your food group needs with nutrient dense foods
- Limit foods and beverages higher in added sugars, saturated fat, and sodium, and limit alcoholic beverages
- For the first 6 months of life feed infants human milk or iron-fortified milk when human milk is not available
Which of the following statements about Dietary Reference Intakes (DRIs) are correct:
- DRIs differentiate populations by age, sex and other lifespan characteristics
- DRIs include a set of value that includes Recommended Dietary Allowance (RDA), Adequate Intake ( AI) and Upper Intake Level (UL) for each of the micronutrient
- DRIs are more likely used by health professionals to assess individual nutrient status in patients and people who need assessment.
The 2020-2025 edition of the Dietary Guidelines for Americans is unique because it is the first time they have
provided guidance by stages of life
According to the NYT article, U.S. Diet Guidelines Sidestep Scientific Advice to Cut Sugar and Alcohol, which of the following are her critiques of the new DGA?
- the guidelines did not make a quantitative change on added sugars and alcoholic beverages
- the guidelines ignore the current pandemic
- the guidelines ignore climate change and how modern food production affects this
True or False: The DGA are updated every five years by the US Departments of Agriculture and Health and Human Services.
TRUE
Which of the following are the three ways main ways that the Dietary Guidelines for Americans has evolved?
- The lifespan approach: encouraging healthy dietary patterns at every stage of life
- Since nutrients and food are not consumed in isolation, the DGA recommend a healthy dietary pattern
- Recent editions have focused on both healthy people and those affected by chronic disease since these diseases affect many Americans
Proteins are the body’s main source of:
Nitrogen
Cysteine can be synthesized from:
Tyrosine can be synthesized from:
Cysteine can be synthesized from methionine
Tyrosine can be synthesized from phenylalanine
Which of the following are true about essential amino acids?
- Valine is an example of one
- The body does not contain enzymes to produce them.
- They are obtained from the diet
True/false: All proteins contain an amino group and a carboxyl group
TRUE
Proteins:
- Proteins are amino acids joined together by peptide bonds
- Tertiary protein structure is determined by R group interactions
- Proteins have many functions in the body. Some of these functions include: growth, enzymes, hormones, antibodies, energy, and acid-base balance to name a few.
- Heat, acid, salt, and alkali conditions can cause denaturation of protein structure.
Why do you subtract 2 in the nitrogen balance equation?
To account for nitrogen lost in other routes such as skin cells and feces.
True/False: Lipoprotein lipase is activated by insulin and acts on chylomicrons and VLDL.
TRUE
Select all of the following that are true about Phenylketonuria (PKU):
- Affected individuals cannot synthesize tyrosine
- The toxic byproducts that build-up cause severe retardation
- Treatment includes a special diet low in phenylalanine
