Superfoods Research & Evidence-Based Practice 3 — Questions and Answers
Question 1: Which type of study design is most prone to 'healthy user bias' when evaluating superfood consumption?
- Prospective cohort studies (Correct answer)
- Double-blind RCTs
- Crossover trials
- N-of-1 trials
Correct answer: Prospective cohort studies
Prospective cohort studies cannot fully control for the fact that people who eat superfoods often also exercise, avoid smoking, and follow other healthy behaviors that independently reduce disease risk.
Question 2: Sulforaphane bioavailability from broccoli is substantially reduced by boiling compared to lightly steaming. This finding best illustrates which research consideration?
- Preparation method critically alters phytochemical content (Correct answer)
- Cooking always destroys beneficial compounds
- Raw vegetables are always superior to cooked
- Sulforaphane is not a meaningful bioactive
Correct answer: Preparation method critically alters phytochemical content
Boiling leaches water-soluble glucosinolates and inactivates myrosinase (the enzyme that converts glucosinolates to sulforaphane), so preparation method is a key variable in superfood research.
Question 3: The Women's Health Initiative Dietary Modification Trial failed to show that a low-fat diet reduced breast cancer risk. What does this illustrate about superfood/diet research?
- Short intervention periods and imperfect adherence can mask true long-term effects (Correct answer)
- Low-fat diets are definitively safe for breast cancer
- Observational data always overestimates dietary benefits
- Only supplements can produce measurable health effects
Correct answer: Short intervention periods and imperfect adherence can mask true long-term effects
Despite a large sample, the trial's 8-year follow-up may have been too short and dietary change too modest to detect effects on cancer incidence, highlighting limitations of large dietary RCTs.
Question 4: A researcher measures resveratrol blood levels after participants eat red grapes. This type of measurement is called a:
- Pharmacokinetic bioavailability study (Correct answer)
- Dietary recall validation
- Nutrient density analysis
- Bioelectrical impedance assessment
Correct answer: Pharmacokinetic bioavailability study
Measuring plasma concentrations of a compound over time after ingestion is a pharmacokinetic study, which determines how much is absorbed, how quickly, and how long it persists.
Question 5: Which methodological issue is most common in cell culture (in vitro) studies of superfood antioxidants?
- Concentrations used far exceed what is achievable in human blood after normal food intake (Correct answer)
- Cell lines respond differently than gut bacteria
- Results cannot be published in peer-reviewed journals
- Antioxidants are toxic to cells at low concentrations
Correct answer: Concentrations used far exceed what is achievable in human blood after normal food intake
In vitro studies often expose cells to antioxidant concentrations 10–100× higher than physiological levels, making results difficult to translate to dietary recommendations for humans.
Question 6: Food frequency questionnaires (FFQs) used to assess superfood intake are subject to which primary limitation?
- Recall bias and tendency to underreport or overreport consumption (Correct answer)
- Inability to measure macronutrients
- Requirement for blood samples from participants
- Cost that limits their use to industry-funded studies
Correct answer: Recall bias and tendency to underreport or overreport consumption
FFQs rely on participants accurately remembering typical eating patterns over months or years, introducing recall bias that can misclassify dietary exposures.
Question 7: In the NHANES database, a positive correlation between açaí supplement use and BMI could be explained by which phenomenon?
- Reverse causation — heavier individuals may be more likely to take supplements to lose weight (Correct answer)
- Açaí supplements cause weight gain
- NHANES excludes supplement users from analysis
- Correlation in NHANES always implies biological causation
Correct answer: Reverse causation — heavier individuals may be more likely to take supplements to lose weight
Reverse causation means the outcome (higher BMI) precedes and causes the exposure (supplement use), not the other way around — a common issue in cross-sectional nutrition data.
Superfoods Research & Evidence-Based Practice 3
Which type of study design is most prone to 'healthy user bias' when evaluating superfood consumption?