Glossary of Commonly Used Terms in Nutrition Research

Terms in the following glossary were compiled from various sources and modified for nutrition research use.  

Adverse Reaction (Adverse Event):  Any noxious and unintended response caused by a nutrient or drug.  Onset may be sudden or develop over time.

Amino Acids: Organic molecules that contain an amino (NH2) and carboxy (COOH) groups.  Normally link together to form protein.

Analog: In chemistry, a derivative of a parent compound that often differs from it by a minor part of the formula.

Animal Study:  A study in which animals are used to test a theory.  While animal studies can be useful as preliminary studies to test the safety and effectiveness of a treatment, they cannot reliably predict effects in humans.

Antimicrobial: Compounds that can either destroy, prevent the development of, or prevent the pathogenic actions of microorganisms.

Antioxidant: An organic molecule that can counteract the damaging effects of oxygen in tissues.

Apoptosis: A genetically directed mechanism for cells to self-destruct to reduce damaged or unwanted cells.

Arm:  Any of the treatment groups in a randomized trial.  Most randomized trials have two “arms”, but some have three or more. See Randomized Trial.

Arteriosclerosis: Hardening and thickening of the walls of the arteries.  Arteriosclerosis can occur because of fatty depositis on the inner lining of arteries (arteriosclerosis), calcification of the wall of the arteries, or thickening of the muscular wall of the arteries from chronically elevated blood pressure (hypertension).

Attenuate: To reduce the severity of a substance, an ailment or disease, or harmful agent.

BAP (Benzoalphapyrenes or Benzo(a)pyene): Harmful benzene family products created by high temperature processing suspected of causing cancer in humans.

Baseline: Information gathered at the beginning of a study from which variations found in the study are measured.

Bias:  When a point of view prevents impartial judgment.  In clinical studies, bias is controlled by blinding and randomization (See Blind and Randomization).

Blind: A randomized trial is “Blind” if participants are not told which arm of the trial they are on.  A clinical trial is “Blind” if participants are unaware of whether they are in the experimental or control arm of the study; also called “masked”.  See Single-Blind Study and Double-Blind Study.

Blood Brain Barrier: A barrier forned by epithelial cells in the capillaries that supply the brain and central nervous system.  This barrier selectively allows entry of substances needed for metabolic functions, but excludes or slows other substances, such as certain drugs, chemical compounds, or microorganisms.

Blood Pressure: The pressure exerted by circulating blood on the walls of blood vessels. For each heartbeat, blood pressure varies between systolic and diastolic pressures:

• Systolic pressure is the peak pressure in the arteries, which occurs near the end of the cardiac cycle, when the ventricles are are contracting.   It is the higher number of the two blood pressure readings.
• Diastolic pressure is the minimum pressure in the arteries, which occurs near the beginning of the cardiac cycle.  It is the lower number of the two blood pressure readings.

Capillaries - Minute, thin walled vessels in the body, especially those that connect the small ends of arteries to the small veins ends.

Catalyst: A substance, usually used in small amounts, that modifies and increases the rate of a reaction without being consumed in the process.

Cell Study: A trial done in test tubes with cells kept alive artificially. These trials are considered screening tests and should be followed by animal and human tests.

Chemistry Panel: A group of chemical tests performed on serum (the protion of blood without cells). These tests include total cholesterol, total protein, various electrolytes, and chemicals that help evaluate liver and kidney function.

Clinical: Pertaining to or founded on observation and treatment of participants, as distinguished from theoretical or basic science.

Clinical Investigator: A researcher in charge of carrying out a clinical trial’s protocol.

Clinical Trial:  A clinical trial is a research study to answer specific questions on new therapies or new ways of using known treatments.   Clinical trials are used to determine whether treatments are both safe and effective. Trials are in four phases: 

• Phase I tests a new treatment in a small group to determine metabolism, dose, and effectiveness of treatment.
• Phase II expands the study to a larger group of people.  Phase II trials are more controlled and in groups at risk of ailments.  They study side effects and safety of treatments.
• Phase III expands the study to an even larger group of people and evaluates dose, effectiveness, risks and benefits of treatment.
• Phase IV takes place after the product or treatment has been licensed and marketed to obtain more information on dose, risks and benefits.

See Phase I, II, III, and IV Trials.

Cohort:  A group of individuals with some characteristics in common.

Compassionate Use:  A method of providing experimental treatments prior to final FDA approval for use in humans.   This procedure is used with very sick patients who have no other treatment options.  Often, case-by-case approval must be obtained from the FDA for “compassionate use” of a treatment.

Complementary and Alternative Therapy:  Broad range of healing philosophies, approaches, and therapies that Western (conventional) medicine does not commonly use.   Examples include acupuncture and herbs.

Contraindication:  A specific circumstance when the use of certain treatments could be harmful.

Control:

1. A subject in a study within a Control Group.
2. A factor that needs to be controlled during the trial period, such as exercise, calorie intake, diet, or smoking.

Control Group:  The standard by which experimental observations are evaluated.  In many clinical trials, one group of participants is given an experimental treatment, while another group (such as the control group) is given either a standard treatment for the condition or a placebo.

Cystic Fibrosis: A genetic disease that affects the body’s ability to move salt and water in and out of cells.  This defect causes the lungs and pancreas to secrete thick mucus, blocking passageways and preventing proper function.

Data Safety and Monitoring Board (DSMB): An independent committee, composed of community representatives and clinical research experts, that reviews data while a clinical trial is in progress to ensure that participants are not exposed to undue risk. A DSMB may recommend that a trial be stopped if there are safety concerns or if the trial objectives have been achieved.

Detoxification: The removal of a poison or its effects from the body.

Dextro or (D): One form of a molecule that can occur in another shape that would appear if the molecule was placed before a mirror.

Diagnostic Trials:  Trials that are conducted to find better tests or procedures for diagnosing a particular disease or condition.   Diagnostic trials usually include people who have signs or symptoms of the disease or condition being studied.

Dilation: The action of stretching or enlarging an organ or part of the body.

DNA (Deoxyribonucleic Acid): Double-stranded linear macromolocule which encodes an organism’s genetic information.

Dose-Ranging Study:  A clinical trial in which two or more doses of a substance are tested against each other to determine which dose works best and is least harmful.

Double-Blind Study:  A clinical trial in which neither the participants nor the study staff knows which participants are receiving the test materials or conditions. 

Double-Blind Crossover Study: A double-masked study in which the control group and the test group are reversed after equilibrium is reached.

Double-Masked Study:  See Double-Blind Study.

Downregulation: The process by which a cell decreases the amount of a cellular component, such as RNA or protein, in response to external variables.

Efficacy: The ability of a treatment to produce a positive result.

Eligibility Criteria: Summary criteria for participant selection; includes inclusion and exclusion criteria. 

Empirical:  Based on observational or experimental data, not on a theory.

Endothilial: Relating to the thin, flattened cell layer that lines internal body cavities.

Endpoint: Overall outcome that the protocol is designed to evaluate.   Common endpoints are severe toxicity, disease progression, or death.

Enrolling: Signing up participants for a study.  Generally, this process involves evaluating participants with respect to the eligibility criteria of the study and going through the informed consent process.

Epidemiology: The branch of medical science that deals with the study of the incidence, distribution, and control of a disease in a population.

Epidemiological Study:  A study on human populations that attempts to link human health effects (e.g. cancer) to a cause, such as exposure to a specific chemical.

Equilibrium: A steady state in which there are no changes in the controls or results.  This is gradually reached with time.

Epithelial Cells:  Cells that help to protect or enclose organs.

Etiology: Science to determine the origin or causes of a desease.

Exclusion/Inclusion Criteria: The standards determining whether a person may or may not be allowed to enter a clinical trial.   These criteria are based on such factors as age, gender, the type and stage of a disease, previous treatment history, and other medical conditions.

Expanded Access:  Any of the FDA procedures, such as compassionate use, parallel track, and treatment IND that distribute experimental drugs to participants who are failing on currently available treatments for their condition and also are unable to participate in ongoing clinical trials.

Experimental Drug: A drug that is not FDA-licensed for use in humans or as a treatment for a particular condition.  See Off-Label Use.

Fasting Level: The body levels of a test substance after a fasting period, often overnight.

FDA (Food and Drug Administration): The U.S. Department of Health and Human Services agency responsible for the safety and effectiveness of foods, cosmetics, nutraceuticals, drugs, biologics, vaccines, and medical devices, including those used in the diagnosis, treatment, and prevention of various conditions and diseases.

Glutathione: An antioxidant made from the combination of the amino acids cysteine, glycine, and glutamic acid.

Hypothesis:  A supposition or assumption advanced as a basis for reasoning or argument, or as a guide to experimental investigation.

Inclusion/Exclusion Criteria:  The standards determining whether a person may or may not be allowed to enter a clinical trial.   These criteria are based on such factors as age, gender, the type and stage of a disease, previous treatment history, and other medical conditions. 

Incubation: The process of preparing test materials to be ready for testing or culturing materials.

Induction Period: The initial slow phase of a chemical reaction which later accelerates.

Informed Consent:  The process of learning the key facts a bout a clinical trial, such as its purpose, duration, and required procedures; before deciding whether or not to participate.  It is also a continuing process throughout the study to provide information for participants.

Institutional Review Board (IRB):  A committee of physicians, statisticians, researchers, community advocates and others that ensures that a clinical trial is ethical and that the rights of study participants are protected.   All clinical trials in the U.S. must be approved by an IRB before they begin.

Insulin Resistance: The reduced sensitivity to insulin by body processes that is usually, but not always, found in Type II diabetics.

Intent to Treat:  Analysis of clinical trial results that includes all data from participants in the groups to which they were randomly assigned, even if they never received the treatment.  See Randomization.

Intervention Name:  The generic name of the intervention being studied.

Intervention:

1. The treatment being studied, such as diet, nutrient, or exercise.
2. Adding a specific test factor to a group normally receiving significantly less or more in their normal lifestyle.

Inverse Association: An effect which decreases as the dose increases, or which increases as the dose decreases.

Isomers: Compounds that have the same chemical constituents but different shapes.

Levo or (L): One form of a substance which has an identically shaped twin but in reverse order, like an image in a mirror. 

Lipid: A fat or oil.

Loading: Continuing with the use of a substance until equilibrium or desired levels are reached.

Lymphatic: Refers to secondary circulatory system that transfers blood-insoluble materials.

Malignant: Harmful to cells, human or animal life.

Masked:  The knowledge of intervention assignment.

Mediation: Transmitting or carrying out a physical process or effect; an intervention.

Meta-Analysis: A system of evaluation in which the researcher chooses a statistical model and combines work done in previously published studies.

Metabolism: The chemistry going on in cells.

Metastatic: Changing to a new location in the body.  Normally refers to cancer cells spreading to a new location.

Methyl Donor: Compounds that have methyl groups that can become added to other compounds (methylation).

Microorganism: Small living organisms that come in various forms such as yeast, molds, and bacteria.

Modulating: Keeping in proper proportion.

Natural History Study: Study of the natural development of something, such as an organism or a disease, over a period of time.

Off-Label Use:  A substance prescribed for conditions other than those approved by the FDA.

Open-Label Trial:  A clinical trial in which researchers and participants know which treatment is being administered.

ORAC: A leading system of measuring the antioxidant potential of various substances.  Some authorities find problems with this in vitro ystem.

Oxidant: An agent which oxidizes substances. Normally this increases spoilage in foods and accelerates aging,  

Oxidized: The change that occurs when a substance reacts with oxygen or an oxidant.

P-Value: A value ranging from zero to one that measures the probability that a difference between groups during an experiment happened by chance.  The lower the p-value, the more significant the result; that is, the more likely it is that the difference between groups was caused by treatment. 

Peer Review:  Review of a clinical trial by experts chosen by the study sponsor. These experts review the trials for scientific merit, participant safety, and ethical considerations.

Peer-Reviewed Publications: Journals in which articles to be published are sent to experts in that field before publishing.

Peridontal: Pertaining to the gums.

Pharmacokinetics:  The processes (in a living organism) of absorption, distribution, metabolism, and excretion of a substance.

Phase I Trials:  Initial studies to determine the metabolism and pharmacologic actions of substances in humans, the side effects associated with increasing doses, and to gain early evidence of effectiveness; may include healthy participants and/or patients.

Phase II Trials:  Controlled clinical studies conducted to evaluate the effectiveness of the substance for a particular ailment in patients with the disease or condition under study and to determine the common short-term side effects and risks.

Phase III Trials:  Expanded controlled and uncontrolled trials after preliminary evidence suggesting effectiveness of the substance has been obtained, and are intended to gather additional information to evaluate the overall benefit-risk relationship of the substance.

Phase IV Trials: Post-marketing studies to delineate additional information including the substance’s risks, benefits, and optimal use.

Pilot Study: A preliminary, small study to obtain information to see if further testing is warranted and controls and doses needed.

Placebo:  An inactive pill, liquid, or powder that has no treatment value. In clinical trials, experimental treatments are often compared with placebos to assess the treatment’s effectiveness. See Placebo-Controlled Study.

Placebo-Controlled Study:  A method of investigation in which an inactive substance (the placebo) is given to one group of participants, while the substance being tested is given to another group. The results obtained in the two groups are then compared to see if the investigational treatment is more effective in treating the condition.

Placebo Effect: A physical or emotional change, occurring after a substance is taken or administered, that is not the result of any special property of the substance. The change may be beneficial, reflecting the expectations of the participant or the expectations of the person giving the substance.

Plaques: Localized, abnormal patches on a body part or surface.

Polyphenols: A class of antioxidants, such as grape antioxidants, that have multiple active OH groups.

Pre-Clinical: The testing of experimental substances in the test tube or in animals that occurs before trials in humans may be carried out.  See Cell Study and Animal Study.

Prevention Trials: Trials to find better ways to prevent disease in people who have never had the disease or to prevent a disease from returning. These approaches may include medicines, vaccines, vitamins, minerals, or lifestyle changes.

Prostate Gland: A firm, muscular, partly glandular body located about the base of the male urethra.

Protocol: A study plan on which all clinical trials are based. The plan is carefully designed to safeguard the health of the participants as well as answer specific research questions. A protocol describes what types of people may participate in the trial; the schedule of tests, procedures, medications, and dosages; and the length of the study. While in a clinical trial, participants following a protocol are seen regularly to monitor their health and to determine the safety and effectiveness of their treatment. 

Prototype: An original or early version that serves as a basis or standard for later stages.

Psoriasis: A skin disease with red patches covered with white scales.

Randomization: A method based on chance by which study participants are assigned to a treatment group. Randomization minimizes the differences among groups by equally distributing people with particular characteristics among all the trial arms. See Arm.

Randomized Trial: A study in which participants are randomly (by chance) assigned to one of two or more treatment arms of a clinical trial.  Placebos are occasionally utilized. See Arm and Placebo.

Range: The difference between the bottom and top values in a trial.

Reactive Oxygen Species: Molecules and ions of oxygen that have an unpaired electron, rendering them extremely reactive oxidizing agents.

Recruiting: The period during which a trial is attempting to identify and enroll participants. Recruitment activities can include advertising and other ways of soliciting interest from possible participants. See Recruitment Status and Enrolling.

Recruitment Status: Indicates the current stage of a trial, whether it is planned, ongoing, or completed. Possible values include:

• Not Yet Recruiting: Participants are not yet being recruited or enrolled
• Recruiting: Participants are currently being recruited and enrolled
• Enrolling by Invitation: Participants are being (or will be) selected from a predetermined population
• Active, Not Recruiting: Study is ongoing (i.e., patients are being treated or examined), but enrollment has completed
• Completed: The study has concluded normally; participants are no longer being examined or treated (i.e., last patient’s last visit has occurred)
• Suspended: Recruiting or enrolling participants has halted prematurely but potentially will resume
• Terminated: Recruiting or enrolling participants has halted prematurely and will not resume; participants are no longer being examined or treated
• Withdrawn: Study halted prematurely, prior to enrollment of first participant

Referee: One of the participants in the peer review of an article for a journal, normally done by an experienced researcher in the same field.

Renal: Pertaining to the kidneys.

Retina: The sensory membrane that lines most of the back part of the eye chamber.

Risk-Benefit Ratio: The risk to individual participants versus the potential benefits.

Screening Trials: Trials that test the best way to detect certain diseases or health conditions.

Side Effects: Any undesired actions or effects of a treatment. Negative or adverse effects may include headache, nausea, hair loss, skin irritation, or other physical problems. Experimental treatments must be evaluated for both immediate and long-term side effects. See Adverse Reaction.

Single-Blind Study: A study in which one party, either the investigator or participant, is unaware of what treatment is applied to the participant (also called single-masked study). See Blind and Double-Blind Study.

Single-Masked Study: See Single-Blind Study.

SOD (Superoxide dismutase): An enzyme whose function is to clear highly active superoxide free radicals from the body.

Standard Treatment: A treatment currently in wide use and approved by the FDA, considered to be effective in the treatment of a specific disease or condition.

Statistical Significance: Whether an observed effect occurred by chance alone. The level of statistical significance depends on the number of participants studied and the observations made, as well as the magnitude of differences observed.

Study Endpoint: A primary or secondary outcome used to judge the effectiveness of a treatment.

Study Type: The primary investigative techniques used in an observational protocol; types are Purpose, Duration, Selection, and Timing.

Subclinical: Effects too small to be noticed or to reach statistical significance in a clinical study.

Suspended: A trial status indicating that recruiting or enrolling participants has halted prematurely, but potentially will resume.

Synergistic: An agent that increases the effectiveness of a nutrient.

Suspended: A trial status indicating that recruiting or enrolling participants has halted prematurely, but potentially will resume.

TBARS (Thiobutyric Acid Reactive Species): Harmful free radicals created when cells are damaged by oxidation.  A TBARS Assay is often used to measure antioxidant capacity.

Terminated: a trial status indicating that recruiting or enrolling participants has halted prematurely and will not resume; participants are no longer being examined or treated.

Threshold: The point at which a physiological or psychological effect begins to be produced.

Time to Progression:  A measure of time after a disease is diagnosed (or treated) until the disease starts to get worse. Also called TTP. 

Toxicity: An adverse effect produced by a substance that is detrimental to the participant’s health. Normally, there is a threshold level at which the body’s normal defense mechanisms are not adequate for protection.

Trolox Equivalent: A measure of the antioxidant strength of a substance compared to Trolox, a vitamin E analogue.

Upregulation: The process of increasing the response to a stimulus.

Uvea: The middle layer of the eye.

Vascular: Related to the system of tubes to transport blood or lymph.

Vital Signs: Signs of life, such as pulse rate, body temperature, and respiation rate.

Washout Period: An initial period in which variances in the test groups are washed out and test values come to an equilibrium before the test period begins.

Withdrawn: A trial status indicating that a study was halted prematurely, prior to enrollment of the first participant.

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Understanding Nutrition Research