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
Assessment of health outcomes of interest
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