TABLE 1.

General population selection for studies on gastrointestinal tolerance¹

Criteria	Comments
Male or female	Exclude pregnant and lactating people, and those with irregular bowel habits associated with their menstrual cycle, or plan test days to occur at similar times of their menstrual cycle for acute studies.
Age <18 vs. 18 to 65 y (inclusive)	The age range should reflect the age targeted for the NDC use and could be extended up to 75 y. For children or adolescents, a separate study should be conducted. Validated pediatric-friendly measures should be used in children.
Ethnicity, race	As inclusive as possible to include those who will consume the product and allow for generalizability to the population.
BMI ≥18.5 to <40	There is no specific requirement unless the ingredient or product is targeted for individuals with a particular body mass index range. Inclusion criteria may include those up to 40 kg/m2 but should consider criteria for metabolically healthy obesity (i.e., no components of the metabolic syndrome, except high waist circumference), comorbidities, and medications.
Standard diet	Participant typical diet should contain low-to-average fiber consistent with the population. Participants should maintain habitual dietary patterns, avoid foods that cause gastrointestinal distress and high-fiber foods during the run-in and study periods. Exclude individuals on extreme diets (e.g., vegan, gluten-free, paleo, weight-loss, etc.).
Allergies and food sensitivities	Exclude individuals with allergies to any of the test product components. Reported sensitivities to NDCs should be noted for possible sensitivity analysis or subgroup assessments.
Generally healthy	Exclude individuals with a history or presence of relevant endocrine, cardiovascular, pulmonary, biliary, renal, hepatic, pancreatic, or neurologic disorders. May include individuals at-risk or with certain stable chronic health conditions as long as the disease and treatment would not interfere with the test substance's evaluation. Exclude those with trauma or surgical event within 2 mo or having a cancer diagnosis within 2 y, except for nonmelanoma skin cancer.
Gastrointestinal health	Exclude individuals with diagnosed gastrointestinal disease or conditions, including inflammatory bowel disease, celiac disease, and disorders of the gut–brain interaction such as clinically diagnosed irritable bowel syndrome, as well as individuals with presence or history of gastrointestinal cancer. Exclude individuals with recent history (within 6 wk) of constipation, diarrhea, or other gastrointestinal illness such as nausea or vomiting. For some studies, depending on the participant number and product population target, it may be reasonable to exclude individuals with known irregular bowel habits. Bowel habits and gastrointestinal symptoms should be documented during an appropriate run-in or baseline period.
Psychiatric conditions	Exclude individuals with diagnosed psychiatric disorders that impede their ability to differentiate and communicate symptoms.
Medications	Either exclude individuals on prescribed medications or include those on stable medications, except for medications that have gastrointestinal side effects or affect carbohydrate digestion (e.g., α-glucosidase inhibitors, antidiarrheals, and laxatives). Although most past studies have excluded individuals on cholesterol-lowering medications, proton-pump inhibitors, and metformin, due to the increased use of these medications in the general population, inclusion could be considered, as long as participants have been on the medication for >6 mo, with regular use and not exhibiting gastrointestinal side effects.
Antibiotics	Exclude individuals with recent (within 6 wk) antibiotic use. Exclude from the analysis those who took antibiotics for a medical condition during the study.
Supplements	Willing to avoid fiber, prebiotic, and probiotic supplements, as well as supplements that affect carbohydrate metabolism or gastrointestinal function (e.g., antidiarrheals, laxatives, etc.). Stop usage ≥2 wk before study initiation and during the entirety of the study.
Physical activity	Willing to maintain habitual physical activity patterns. Exclude individuals with extreme physical activity patterns (e.g., marathon training).
Smoking	Exclude heavy smokers (>19 cigarettes/d) and document number of cigarettes per day in smokers enrolled in the study.
Alcohol and unregistered drugs	Exclude those that report alcohol or unregistered drug abuse. Alcohol abuse is defined as >14 drinks per wk (1 drink = 0.6 fluid oz or 14 g of pure alcohol).

¹NDC, nondigestible carbohydrate; vs., versus.