Lecture notes, 9/28
Nutrition is a relatively young science
•Vitamin A and thiamin were first identified as essential nutrients in 1911
•Researchers are still debating which nutrients and how much of them humans require
The nutrition knowledge base is constantly changing
•Focus of nutrition in US is shifting from deficiency diseases to diseases of excess
(obesity, type 2 diabetes)
•“What were once vices are now habits”-and vice versa
Q:
How does the science of nutrition advance?
A: Practice and research
Practice (what’s seen in the real world)
•Can lead to new research questions
•Breastfed babies in Indonesia whose moms eat greens (a “good” source of vitamin A)
still have signs of low vitamin A status
Research
•Attempts to answer specific questions in a controlled experimental framework
•How long does it take to deplete a healthy person of vitamin C in an inpatient setting?
•And how much vitamin C will it take to restore normal function after depletion?
The Research Process
Types of Research Studies
•Observational vs. Intervention
•Epidemiologic
•Short-term vs. Longitudinal
•Retrospective vs. Prospective
•Gold Standard-Randomized, placebo-controlled, double-blind
No Study is Perfect
•Humans are notoriously bad research subjects
•Not everything can be controlled for in an experiment
•As a result, different study designs may yield different results for the same research
question
Experimental Models
•Cells or tissues
•Animals
Most control
•Humans
Least control
Observational Studies
•Can include case reports
•What is going on in a particular setting
•How many NTR 150 students take herbal supplements?
•What is the incidence of anorexia nervosa among Pacific Northwest Ballet dancers?
Intervention Studies
•A variable is manipulated and the outcome (health status, lab values) is compared to a
control group
•Dietary Approaches to Stop Hypertension (DASH)-diets high in fruits, vegetables, &
low fat dairy products reduced blood pressure
Balance Study
•Most rigorous, but most expensive form of intervention study
•Scientists know exactly what goes in and measure what comes out
•Blood measurements may also be taken
Epidemiologic Studies
–Calculates risk of disease based on dietary and other lifestyle factors in a group
–Nurses’ Health Study (all women) and Health Professionals’ Follow-Up Study (all men)
are two examples
–Correlation ≠ Cause
Credible Sources of Nutrition Information
•Studies in peer-reviewed journals
–Journal of Nutrition
–American Journal of Clinical Nutrition
–Journal of the American Dietetic Association
–New England Journal of Medicine
–Specialty medical journals
Credible Sources of Nutrition Information
•Researchers at accredited universities
•Look for credentials (MD, PhD, RD)
•Science sections of the New York Times, Washington Post, Seattle Times and P-I
Less Credible Sources
•Websites or health care professionals that are selling what they’re touting
•Testimonials and anecdotes without hard data
•Lots of exclamation points-“Breakthrough!!!”
•Pseudoscientific terms-cleansing, cellular detoxification, dysbiosis
•Multi-level marketing schemes
Nutrition Assessment
•The A’s, B’s, C’s, and D’s
A is for Anthropometric
•The measure of (hu)man
•Height or length
•Weight
•Measurement of body fat by skinfolds, underwater weighing, or other means
B is for Biochemical
•Blood/urine/fecal measurements
•May be the nutrient or a metabolite, OR activity of an enzyme dependent on the nutrient
•Red blood cell measures also fall under this category
C is for Clinical
•What a doctor or dietitian can “see”
•Hair and skin can show important signs of malnutrition
D is for Dietary
•What does the person eat or drink?
•24-hour recall
•3 (or more)- day food records
•Food frequency questionnaires
•Diet history