Glossary: Health & Research Terms Defined

This page defines terms you'll encounter across Proco's content and in consumer health writing more broadly. It is reference material, not medical advice.

Health and research writing uses a lot of specialised vocabulary. Most of it has precise meanings that get distorted in consumer translation. This glossary defines the terms we use most often, with links to the deeper coverage where it exists.

Terms are grouped by category. Use Ctrl/Cmd+F to find a specific term.

Research methodology

Randomised controlled trial (RCT). A study in which participants are randomly assigned to receive an intervention or a control (typically a placebo or alternative treatment). Random assignment is the gold-standard method for establishing causal effects. See How to read a clinical trial.

Meta-analysis. A statistical synthesis of multiple individual studies on the same question, weighted by quality and sample size. Provides more precise effect estimates than any single trial.

Systematic review. A structured review of all available studies on a question using predefined inclusion criteria and risk-of-bias assessment. Often paired with a meta-analysis.

Cohort study. A prospective observational study that follows a group of people over time, measuring exposures and outcomes. Cannot establish causation but is informative for long-term outcomes.

P-value. The probability of observing the data (or more extreme data) if the null hypothesis were true. A p-value below 0.05 is conventionally "statistically significant" but says nothing about effect size or clinical importance.

Effect size. The magnitude of an effect, independent of statistical significance. Cohen's d, hazard ratio, relative risk, and mean difference are common effect size measures.

Confidence interval. A range within which a study's estimate of an effect is statistically expected to lie with a given level of certainty (typically 95%). Wide intervals indicate substantial uncertainty.

GRADE. A structured framework for grading evidence quality based on study design, risk of bias, consistency, directness, and precision. Used in systematic reviews to rate evidence as high, moderate, low, or very low quality.

CONSORT. Consolidated Standards of Reporting Trials. A 25-item checklist for reporting RCTs that strengthens transparency and quality assessment.

PRISMA. Preferred Reporting Items for Systematic Reviews and Meta-Analyses. The corresponding reporting standard for systematic reviews.

Cochrane review. A systematic review published under Cochrane's strict methodology. Considered among the highest-quality evidence syntheses in healthcare.

Surrogate endpoint. A measurable biomarker used as a proxy for a clinical outcome that is harder to measure directly. Surrogate endpoints don't always predict clinical outcomes well.

Pre-registration. Publicly committing to a study's design, primary outcomes, and analysis plan before data collection. Reduces the risk of post-hoc data analysis distorting findings.

Funder effect. The tendency for industry-funded studies to report findings more favourable to their funders' products than independent studies of the same questions. Replicated across many fields.

Cardiovascular

VO2 max. Maximum rate at which the body can take in and use oxygen, measured in ml/kg/min. The most-used measure of cardiorespiratory fitness.

Cardiopulmonary exercise testing (CPET). Direct laboratory measurement of VO2 max using gas analysis during incremental exercise. The gold standard.

Heart rate variability (HRV). Variation in time between consecutive heartbeats. Reflects autonomic nervous system balance. Higher HRV typically reflects better recovery and parasympathetic dominance.

RMSSD. Root Mean Square of Successive Differences. The most common HRV calculation; reflects short-term, primarily parasympathetic variation.

SDNN. Standard Deviation of Normal-to-Normal intervals. Captures longer-term HRV variation. Used differently from RMSSD.

MET (metabolic equivalent). Unit of energy expenditure. 1 MET = resting metabolic rate (approximately 3.5 ml/kg/min of oxygen consumption). A 5 MET activity uses 5× resting energy.

Nutrition

Macronutrient. Protein, carbohydrate, or fat. The nutrients required in large quantities.

Micronutrient. Vitamin or mineral. Required in small quantities.

RDA (Recommended Dietary Allowance). The average daily intake of a nutrient sufficient to meet the requirements of 97-98% of healthy individuals. Established by national bodies (Institute of Medicine in the US; EFSA in the EU).

AI (Adequate Intake). Used when RDA cannot be determined; reflects observed mean intake in healthy populations.

UL (Tolerable Upper Intake Level). Highest daily intake unlikely to cause adverse health effects in the general population. Important for supplement safety.

Bioavailability. The proportion of an ingested nutrient that reaches the systemic circulation. Varies dramatically by form (magnesium oxide vs glycinate, vitamin K1 vs K2).

EFSA. European Food Safety Authority. The EU body that evaluates health claims for food and supplements.

NOVA classification. A four-tier framework categorising foods by degree of industrial processing. Group 4 (ultra-processed) is the contested category. See Ultra-processed food research.

Glycemic index (GI). A ranking of carbohydrate foods by their effect on blood glucose. Higher GI = faster glucose rise.

FODMAP. Fermentable Oligosaccharides, Disaccharides, Monosaccharides, And Polyols. Short-chain carbohydrates that can trigger digestive symptoms in some people.

Probiotic. Live microorganisms intended to provide a health benefit when consumed. Evidence varies enormously by strain and indication.

Prebiotic. A non-digestible food component that selectively stimulates the growth of beneficial gut bacteria.

Postbiotic. Bacterial metabolites with potential health effects, including short-chain fatty acids.

Supplements & ingredients

Form. The chemical version of a nutrient (e.g. magnesium glycinate vs magnesium oxide; vitamin K1 phylloquinone vs vitamin K2 menaquinone). Different forms have different bioavailability and uses.

Chelated. A nutrient bound to an organic molecule (typically an amino acid) to improve absorption. Magnesium glycinate is chelated; magnesium oxide is not.

Synergistic combination. A combination of ingredients where the combined effect exceeds the sum of individual effects. Often claimed in marketing; less often demonstrated in research.

Bioactive. Having biological effects beyond basic nutrition. Polyphenols, omega-3 fatty acids, and creatine are examples.

Pharmaceutical-grade. A vague marketing term sometimes used to imply higher quality. The term has no formal definition for supplements outside specific manufacturing standards.

Third-party tested. Independently verified for ingredient identity, purity, and potency. NSF Certified for Sport, USP Verified, and ConsumerLab are common third-party programs.

DSHEA. Dietary Supplement Health and Education Act of 1994. The US law governing supplement regulation. See How supplements are regulated: EU vs US vs UK.

Structure/function claim. A claim about how a supplement affects normal body structure or function (e.g. "supports immune function") permitted under US DSHEA without FDA pre-approval.

Disease claim. A claim that a product prevents, treats, cures, or mitigates a disease. Not permitted on supplement labels in the US, EU, or UK.

Regulatory & compliance

EFSA. European Food Safety Authority. Evaluates health claims for food and supplements in the EU.

Health Claims Regulation (EC 1924/2006). EU regulation controlling what health claims can be made on food and supplement labels.

ASAI Code. Code of Standards for Advertising and Marketing Communications in Ireland. Governs health claims in Irish advertising.

FSA. Food Standards Agency. The UK food regulator.

MHRA. Medicines and Healthcare products Regulatory Agency. The UK medical device regulator.

FDA. Food and Drug Administration. The US regulator of food, drugs, supplements, and medical devices.

GDPR. General Data Protection Regulation. EU data protection law applying to processing of EU residents' personal data.

Acronyms quick reference

Missing a term?

If you encountered a term in our content (or elsewhere) that should be in this glossary, email hello@procohq.com (subject: GLOSSARY) and we'll add it.