NCT03880838

Evaluation of a Letter Intervention Promoting a Plant-based Diet

Evaluation of a Letter Intervention Among At-risk Adults Promoting a Plant-based Diet Using a Combination of Provider Testimonials, the Forks Over Knives Documentary, and Commitment- or Prevention-focused Behavioral Nudges

• Status: Completed
• Phase: N/A
• Study type: Interventional
• Enrollment: 11,234 (actual)
• Sponsor: Geisinger Clinic · Academic / Other
• Sex: All
• Age: 18 Years
• Healthy volunteers: Not accepted

Summary

The researchers' mission is to promote healthier eating behavior and to reduce costs associated with healthcare. The purpose of this study is to evaluate the effects of mailing randomly selected participants a letter promoting a plant-based diet. Depending on the experimental condition, participants may additionally receive a free documentary, Forks Over Knives, and they may also get letters which use commitment- or prevention-focused messages to encourage watching the documentary and changing their eating behavior. The researchers hypothesize that receiving the documentary will be associated with lower insurance claims and improved health outcomes one and two years later. The researchers also hypothesize that using either commitment- or prevention-focused messages will also contribute to lower insurance claims and improved health outcomes compared to experimental conditions where materials did not include these messages. This study will help the researchers design evidence-supported programs that can improve people's health.

Detailed description

Note that participant selection and assignment will be done at the level of the household, but analysis of outcomes will include individual-level analysis. This analytic decision was made because the researchers assume that the intervention may potentially affect other members of the household. While one person in a household will be selected for matching the eligibility criteria, the mailed materials will be addressed to all adult members of the household (defined as adults 18+ who are the spouse or child of the selected member) who are members of the Geisinger Health Plan. Outcome data will be pulled from all adult members of the household who have data through the Geisinger Health Plan. The researchers will analyze the data using standard survey research analyses methods, including computing bivariate correlations, using general linear models, using non-parametric models for non-normally distributed insurance data, and entering variables as independent predictors in regression models to attempt to predict desired outcomes. The researchers will also use multilevel models to account for household- and individual-level data. The analysis of primary outcomes will focus on data one year after the intervention begins. Follow-up analysis on secondary outcomes will be conducted two years after the intervention begins. The researchers will conduct separate analyses of the selected participant (i.e., the individual who met the eligibility criteria) and other members of that participant's household. This will test whether there are any spillover effects of the intervention to other people in the household. For clarity in this record, any discussion of sample size and participants refers to households, as this is the primary level for participant selection and assignment.

Conditions

• Cardiovascular Diseases
• Diabetes Mellitus
• Obesity

Interventions

Type	Name	Description
BEHAVIORAL	Personal testimonial	Participants will receive a letter promoting a plant-based diet. This letter will feature a personal testimonial about the benefits of a plant-based diet. Presenting this information to participants might encourage them to make behavioral changes to improve their health.
BEHAVIORAL	Forks Over Knives Documentary	Participants will be mailed the documentary Forks Over Knives, which provides scientific arguments promoting a plant-based and whole foods diet. The behavioral effect of this documentary comes from watching the documentary and potentially choosing to order a free cookbook (participants are given this opportunity in the letter accompanying the documentary). The effect of the diet itself is not a central part of the intervention, as people can choose to adopt or not adopt any part of the diet.
BEHAVIORAL	Commitment nudge	At the end of the letter promoting a plant-based diet, participants will be asked to write dates and personal signatures committing to watching the documentary. They will be asked to mail back this written commitment. Stating one's intentions to implement certain behavior is meant to increase the likelihood of follow-up behavior. This request might nudge more people to watch the documentary and make some behavioral changes to prevent negative health outcomes.
BEHAVIORAL	Prevention nudge	As part of the letter promoting a plant-based diet, one paragraph will describe the risks of not taking action. This phrasing reframes the status quo as contributing to future loss (e.g., costs of medication and operations). In effect, the letter encourages participants to focus on preventing this loss by taking action. This additional text might nudge more people to watch the documentary and make some behavioral changes to prevent negative health outcomes.

Timeline

• Start date: 2019-06-20
• Primary completion: 2020-06-30
• Completion: 2022-06-30
• First posted: 2019-03-19
• Last updated: 2025-05-20
• Results posted: 2023-09-07

Locations

1 site across 1 country: United States