Research Methodologies

• Cause and effect can be demonstrated via intervention studies by altering consumption of a nutrient, food, or diet in a controlled setting.

Types

• Intervention study designs can range from short-term studies that measure the immediate effect of the intervention.
• Designs measure from minutes to hours as postprandial or post-meal studies, through to long-term studies that evaluate the effects of the intervention over weeks, months, or years.
• The study settings can also vary between free-living populations to studies conducted entirely in research facilities like metabolic words.

Pilot Studies

• Various definitions exist for pilot studies; also sometimes referred to as a feasibility or exploratory study.
• Pilot studies are generally implemented on a small scale to test if all study processes operate as anticipated before undertaking a full-scale trial.
• Pilot study designs vary and may test all or only some aspects of a full-scale study.

Randomized Controlled Trials

• In any controlled study in participants receiving the active nutrient, food, or dietary intervention, the same outcome measurements will be collected in a control group.
• Including a control group, which may receive either a placebo or no intervention, allows control outcomes to be compared with intervention outcomes.
• Without a control group, cause-and-effect statements about an intervention would not be appropriate, as other factors may be responsible for the effects observed.
• Two basic randomized controlled trial (RCT) study designs are parallel group studies and crossover studies.
• For longer-term intervention, parallel studies are generally preferred because of their shorter overall time frame.
• Parallel studies are essential where a washout period may be ineffective at returning outcome measures to baseline.
• Parallel studies are also required where returning to baseline may be unethical, for example, if bodyweight or bone mineral density is the outcome measure.
• Parallel studies do not suit outcomes that show large inter-participant variation.
• Cross-over studies favor where participant availability may be restricted and in short-term studies.

Quasi-experimental studies

• Like RCTs, quasi-experimental studies estimate the impact of an intervention on a group of participants.
• Although similar in design, RCTs, quasi-experimental studies, lack one or more key features of a true experiment.
• Most commonly, random assignment to the intervention or control group is absent, and sometimes the control group is lacking altogether.
• Quasi-experimental studies can provide valuable information about the potential usefulness of an intervention

Population-based fortification studies

• Population-based food-fortification programs are sometimes implemented as part of public health policy to correct dietary deficiencies (e.g., iodized salt to prevent iodine deficiency).
• Can enhance a micronutrient to prevent undesirable health outcomes (e.g., folic acid fortification of flour to prevent neural tube defects).
• Population-based fortification programs require careful planning and consideration of a wide range of background scientific data commenced.
• Monitoring undesirable consequences (e.g., over-exposure in population subgroups resulting in toxic side effects) and desirable effects in the short, medium, and long-term is paramount.

Considerations when Planning Intervention Studies

Factors involved in the planning, conducting, and reporting of intervention studies.

• The primary hypothesis tested statistically should be framed as a null hypothesis, which states there is no difference between the intervention & the control.
• The alternative hypothesis is accepted if the statistical test rejects the null hypothesis, indicating a difference between the two interventions.
• The study duration must be long enough to allow changes in the primary outcome measure.
• It will be determined by data from previous intervention studies and understanding physiology and biochemistry.
• The duration must also relate to the hypothesis's timescale, which may address acute effects.
• Investigators need to decide if participants will substitute the test food for habitual foods, add the test foods to their usual diets, or use some sort of food-exchange model.
• The control is a food, nutrient, substance, or product that does not provide the component being tested.
• The composition of these should be analytically documented.
• Outcomes should be compared between intervention and control groups.

Blinding

• The assessment of study outcomes may be influenced by knowledge of which intervention was received, primarily for subjective outcomes.
• Use of blinded assessment can avoid bias.
• If neither assessor nor participant knows which intervention the participant received, then the study is double blind.
• If only the participant or assessor knows which intervention they received, then the study is single blind.

Size of Study

• A too-small study will fail to detect important differences between interventions, while one that is too large may needlessly waste unethical and resources.

Ethical Approval and Study Registration

• Researchers should determine local ethical approval and research governance procedures required for their study and seek approvals before the study commences.

Statements about research methodologies covering topics like study duration, intervention studies, blinding, statistical power, ethical approval, parallel vs cross-over studies, and quasi-experimental designs. These principles are crucial for designing and interpreting research effectively. Understanding them ensures the validity and reliability of study outcomes.