The scoping review of available functional foods, beverages, and supplements will be conducted in databases (ie, Medline, Embase, PsycINFO, and Web of Science) and search engines (ie, Google and Bing). Well-known publicly available travel catering gray literature (ie, PAX International, APEX, and Onboard Hospitality) that includes articles and advertisements of relevant functional foods, beverages, and supplements will also be searched. Search terms will include combinations, truncations, and synonyms of: “drinks”, “beverages”, “food”, “snacks”, “nutrition”, or “supplements” combined with “airplane”, “aviation”, “deep vein thrombosis”, “flight”, “hydration”, “jetlag”, or “sleep”.

Products identified in the scoping review will be included in the database if they meet any one of the following inclusion criteria.

Products will be excluded from the database if they were discontinued at the time of the search.

The following information will be transcribed into Microsoft Excel 2011 (Microsoft, Redmond, WA).

Active ingredients of functional foods and nutrients will be extracted and sorted according to the following categories: vitamins, minerals, macronutrients, consumption method, and other. Ingredients with possible beneficial effects on symptoms relating to flight will be further examined by a systematic literature review.

Search terms will be the ingredients of products within the database. These will be combined with synonyms and truncations of aviation terms such as air travel, aviation, cabin crew, and travel medicine. The Medline Thesaurus MeSH (Medical Subject Headings) term will be refined according to each database. The Scottish Intercollegiate Guidelines Network (SIGN) randomized controlled trial study filter [15] will be adapted to capture nonrandomized controlled trials and applied to searches conducted within Medline, Embase, and Cumulative Index to Nursing and Allied Health Literature (CINAHL).

The databases CINAHL, Cochrane Central Register of Controlled Trials (CENTRAL), Embase, Medline (including PreMedline), and PsycINFO will be searched from inception for studies. Any published scientific articles referenced by products in the database and the reference lists of included studies will be hand searched for additional citations.

Eligibility criteria for studies have been selected based on PICOS (participants, interventions, comparisons, outcomes, and study designs) standards.

The target age group for included studies is adults aged 18 years or older. No animal studies will be included. Participants should be healthy with no pre-existing health conditions that could impact the primary outcome of intervention, such as hematological abnormalities. Studies that involve pregnant women or participants aged 18 years or younger are not eligible for inclusion. There will be no limitations placed on gender or ethnicity.

Intervention must involve administration of a functional food, beverage, or nutritional supplement to participants at any time before, during, or after a commercial flight or flight simulation that is intended to improve the well-being of the participant. No limitations will be placed on length of intervention or follow-up period. Studies that solely involve the use of pharmacological agents (with the exception of melatonin and caffeine) or nonpharmacological treatments other than nutrition such as physical activity will be excluded. Interventions that use a combination of nonpharmacological treatments but also test functional foods, beverages, or nutritional supplements will be eligible for inclusion if the effect of the functional or nutritional products can be isolated.

Studies must make a comparison between those who received intervention and those who did not receive intervention or were given a placebo, and both groups must have undergone the same in-flight or flight simulation.

The primary outcome of this systematic literature review is to determine if there is an improvement in the physical or cognitive symptoms associated with air travel between participants that received intervention and the controls. This can be reported using valid qualitative and quantitative measures.

The secondary outcomes that will be investigated are the incidence of toxicity or negative effects within the intervention or control groups, study funding sources, and the prevalence of industry funding.

Studies will be limited to randomized and nonrandomized controlled trials conducted using in-flight or flight simulation settings. All other study types and non-English studies will be excluded. Studies completed under space or military flight conditions will also be excluded, as the conditions of speed and altitude are not comparable to commercial air travel.

Bibliographic records for all papers will be exported into Endnote X9 reference management software (Clarivate Analytics, Philadelphia, PA). After duplicates are removed, the titles and abstracts of studies will be screened against the eligibility criteria and placed into two groups: further review or excluded. The full text of studies classified for further review will be obtained and reviewed again against the eligibility criteria. The reasons for exclusion of studies will be recorded in a PRISMA diagram. Two reviewers will independently complete each step of the process. Any disagreements between the two reviewers will be resolved through discussion. In the instance that a resolution cannot be reached, a third reviewer will be consulted to reach a final decision.

The data extraction table will be designed using the principles of the PRISMA statement for reporting systematic reviews. The items to be extracted from the included papers are study details (ie, authors, year, country of publication, funding, and affiliations), participants (ie, characteristics, flight and simulation details, inclusion and exclusion criteria, attrition, and blinding), intervention and comparator details (ie, intervention, sample size, length of intervention and follow-up, and retention rate), and outcomes (ie, qualitative and quantitative measures of symptoms associated with flight and adverse effects).

A narrative synthesis of findings structured around the nutrients and herbal compounds investigated will be provided. Tests of heterogeneity between the studies will be conducted using the I² statistic. Meta-analysis by nutrients or supplements will be conducted using Stata software provided there is low heterogeneity (I² value <40%) between two or more studies [16]. The strength of evidence will be judged using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) approach [17].

Two review authors will independently assess the risk of bias of the included studies using the appropriate Cochrane Collaboration tool (Risk of Bias for Randomized Control Trials II or Robins I for Other Non-Randomized Interventions) [18,19]. The body of evidence from studies with a high risk of bias will be interpreted with caution.