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Paper 1 Discussion (Diet, Dyslipidemia, and CVD)

Lecture Details

  • Lecture Title: Paper 1 Discussion (Diet, Dyslipidemia, and CVD)

  • Course: KHPM324 Chronic Diseases of Modern Society (영강) (현대인의 만성질환)

  • Presenter: Hannah Oh, ScD

  • Division: Health Policy & Management

  • Institution: College of Health Sciences, Korea University

Reading Assignment

  • Paper Reference:

    • Appel LJ et al. (2005)

    • Title: "Effects of protein, monounsaturated fat, and carbohydrate intake on blood pressure and serum lipids: results of the OmniHeart randomized trial."

    • Journal: JAMA

    • Volume: 294(19)

    • Pages: 2455-2464

Guiding Questions

  1. Knowns and Unknowns in Diet-CVD Relationship:

  2. Inclusion Criteria for Study Participants: Why were prehypertension and stage I hypertension included?

  3. Three Dietary Patterns of Interest: What are they?

  4. Study Design: Overview, strengths, and limitations.

  5. Reason for Wash-out Period: Why is it important?

  6. Summary of Main Findings: Personal interpretation.

  7. Personal Reaction to the Paper: Thoughts and reflections.

Known and Unknown Relationships

  • Knows:

    • Reduction in saturated fat intake lowers CVD risk.

  • Unknowns:

    • The optimal type of macronutrient (protein, unsaturated fat, carbohydrate) to replace saturated fat.

  • Objectives:

    • To compare effects of three healthful diets substituting saturated fat for one of the macronutrients on blood pressure and serum lipids (LDL, HDL).

Dietary Fat Types and Sources

  • “Good” Fats:

    • Monounsaturated Fat:

    • Sources: Olive oil, avocado, nuts.

    • Polyunsaturated Fat:

    • Sources: Most vegetable oils, nuts.

    • Plant Omega-3:

    • Sources: Soybean and canola oils, walnuts.

    • Fish Omega-3:

    • Sources: Marine fish, seafood.

  • “Bad” Fats:

    • Saturated Fat:

    • Sources: Meats, dairy, butter.

    • Trans Fat:

    • Sources: Stick margarines, vegetable shortenings, commercial bakery and deep-fried foods.

Fatty Acids Structures

  • Saturated Fat: No double bond (No C=C).

  • Monounsaturated Fat: One C=C double bond.

  • Polyunsaturated Fat: More than one C=C double bond.

Cholesterol and Triglycerides

  • Cholesterol Types:

    • LDL (Low-Density Lipoprotein): Leads to deposition of plaque in blood vessels.

    • HDL (High-Density Lipoprotein): Transports cholesterol from blood vessels to liver for elimination.

  • Impact of High LDL Levels:

    • High LDL leads to plaque formation in arteries, which restricts blood flow and can cause coronary heart disease (CHD).

Study Population and Inclusion Rationale

  • Importance of Study Population Characteristics: Essential for understanding what impact diet has on CVD and to ensure representativeness.

  • Rationale for Including Prehypertensive Participants:

    • To evaluate diet impact on individuals at risk for developing hypertension.

Dietary Patterns of Interest

  • Three Dietary Patterns:

    • Carbohydrate-Rich Diet (similar to DASH diet).

    • Protein-Rich Diet.

    • Unsaturated Fat-Rich Diet.

    • Each diet: Reduced in saturated fat, cholesterol, and sodium; rich in fruits/vegetables, fiber, potassium, and other vitamins and minerals.

Study Design

  • Controlled Feeding Study:

    • Structure: 7-day menu cycle at 5 caloric levels (1600, 2100, 2600, 3100, and 3600 kcal).

    • Preparation of Menus: Designed with commonly available foods, meals provided in research kitchens.

    • Diet Compliance Monitoring: Participants completed a diary on food consumption and studied adherence.

    • Weight Measurement: Conducted weekly to maintain participants within 2% of baseline weight.

Participant Flow in OmniHeart Trial

  • Details of the Trial: 930 individuals screened; 716 excluded for various reasons. 191 randomly assigned into one of six diet sequences.

  • Crossover Design:

    • Participants receive all treatments at different times, acting as their own control.

Strengths and Limitations of Study Design

  • Strengths:

    • Within-person comparisons that reduce non-time varying confounders (sex, genetic factors).

    • Requires fewer subjects for comparable statistical power.

  • Limitations:

    • Does not eliminate effects of time-varying confounders (physical activity, alcohol).

    • Possibility of carryover effects from one treatment to another.

Wash-out Period

  • Definition: Time between treatment periods where participants eat their own food.

  • Implementation: 2-4 weeks between feeding periods to allow for treatment effect to wash out.

  • Purpose:

    • To mitigate carryover effects and return to baseline conditions for accurate comparison.

Study Findings and Data Tables

Table Summaries

  • Adherence and Confounders (Table 4): Measures of adherence and confounding variables across diets, showing similar caloric intake and weight maintenance across the dietary patterns.

  • Change from Baseline by Diet (Table 5): Measures of blood pressure, cholesterol, and triglycerides, indicating significant reductions in both systolic and diastolic blood pressures and lipid levels across all diets.

Diet Efficacy Comparison (Figures and Tables)

  • Outcome Differences Shown (Figures 2 A-F): Differences between diets in terms of blood pressure and cholesterol levels.

  • General Observations: All diets lowered CVD risk factors, with protein and unsaturated fats showing greater reductions in blood pressure and LDL cholesterol compared to carbohydrate-rich diets.

Risk Prediction Models

  • Framingham Risk Score: Predicts 10-year CHD risk using age, systolic BP, total cholesterol, HDL cholesterol, hypertension treatment, and smoking status.

  • PROCAM Score: Predicts 10-year CHD risk in men based on 8 variables, including triglycerides.

Side Effects of Diets

  • Protein-Rich Diet: Notable side effects include poor appetite, bloating, fullness, and dry mouth.

Summary of Study

  • Overall Findings: All three diets (high-carbohydrate, high-protein, high-unsaturated fat) resulted in lowered CVD risk factors. Substituting saturated fat with protein or unsaturated fat appears more beneficial in reducing CVD risk factors overall, enlightening potential public health dietary guidelines.