Cardiovascular DiseasesNCT03880838

Evaluation of a Letter Intervention Promoting a Plant-based Diet

A study testing Personal testimonial, Forks Over Knives Documentary and Commitment nudge in people with Cardiovascular Diseases and Diabetes Mellitus, run by Geisinger Clinic at 1 site in United States.

Completed

Finished. The study has ended and is not enrolling. Results may be posted on the official record.

Official record

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Trial summary

Who is it for?: Ages 18 years and older
Conditions the study is for: Cardiovascular Diseases, Diabetes Mellitus, Obesity
What is being tested?: Personal testimonial, Forks Over Knives Documentary and Commitment nudge
Type of treatment: Lifestyle or therapy programme
Could I receive a placebo?: No, everyone receives an active treatment
How many people: 11,234 participants
Where: 1 siteUnited States
Study dates: 20 Jun 2019to 30 Jun 2022
Phase: Interventional
Are there results?: Yes, posted in the registrySummary in the doctors' view

Key requirements

Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.

Ages 18 years and older
All sexes
No healthy volunteers
Adult, Older adult

Who may be able to join

Has two out of the three following conditions:
Body mass index over 30
Diagnosis of type 2 diabetes (specifically with at least one medication)
Diagnosis of cardiovascular disease
Has health insurance through Geisinger Health Plan (is an active member with a full 12-month enrollment in the previous year) under one of the following categories:
Medicare with required primary care provider

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Medicaid
Individual policy under the Affordable Care Act
Has visited their primary care provider in the past 12 months

Who cannot join

Is institutionalized
Has active cancer, cirrhosis, renal failure, dementia, or active psychosis
Is in the same household as another selected participant

Trial locations and contacts

1 site in 1 country.

United States1 site

Geisinger Health System
Danville, Pennsylvania, 17822

Other trials in United States

About this study

Official title: 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

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.

Read the 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
Being tested: Personal testimonial, Forks Over Knives Documentary, Commitment nudge, Prevention nudge
Keywords: Plant-based diet, Behavioral nudge, Mail distribution, Randomized controlled trial, Insurance claims, Chronic disease, Letter-based intervention, Health behaviors, Prevention focus, Loss framing, Commitment, Provider testimonial
Medical subject headings: Cardiovascular Diseases, Diabetes Mellitus, Obesity, Chronic Disease, Health Behavior

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

Personal testimonialBehavioural
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.
Forks Over Knives DocumentaryBehavioural
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.
Commitment nudgeBehavioural
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.
Prevention nudgeBehavioural
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.

Study groups in NCT03880838
Study group	Role	What they receive
No contact control	No intervention	Participants are not contacted.
Letter	Experimental	Participants are only contacted through a letter with a personal testimonial. Receives: Behavioral: Personal testimonial
Link and no nudge	Experimental	Participants are sent the Forks Over Knives documentary online link and a letter with a personal testimonial and no nudges. Receives: Behavioral: Personal testimonial; Behavioral: Forks Over Knives Documentary
Link and commitment nudge	Experimental	Participants are sent the Forks Over Knives documentary online link and a letter with a personal testimonial and a commitment nudge. Receives: Behavioral: Personal testimonial; Behavioral: Forks Over Knives Documentary; Behavioral: Commitment nudge
Link and prevention nudge	Experimental	Participants are sent the Forks Over Knives documentary online link and a letter with a personal testimonial and a prevention nudge. Receives: Behavioral: Personal testimonial; Behavioral: Forks Over Knives Documentary; Behavioral: Prevention nudge
Link and both nudges	Experimental	Participants are sent the Forks Over Knives documentary online link and a letter with a personal testimonial and both commitment and prevention nudges. Receives: Behavioral: Personal testimonial; Behavioral: Forks Over Knives Documentary; Behavioral: Commitment nudge; Behavioral: Prevention nudge
DVD and no nudge	Experimental	Participants are sent the Forks Over Knives documentary DVD and a letter with a personal testimonial and no behavioral nudges. Receives: Behavioral: Personal testimonial; Behavioral: Forks Over Knives Documentary
DVD and commitment nudge	Experimental	Participants are sent the Forks Over Knives documentary DVD and a letter with a personal testimonial and a commitment nudge. Receives: Behavioral: Personal testimonial; Behavioral: Forks Over Knives Documentary; Behavioral: Commitment nudge
DVD and prevention nudge	Experimental	Participants are sent the Forks Over Knives documentary DVD and a letter with a personal testimonial and a prevention nudge. Receives: Behavioral: Personal testimonial; Behavioral: Forks Over Knives Documentary; Behavioral: Prevention nudge
DVD and both nudges	Experimental	Participants are sent the Forks Over Knives documentary DVD and a letter with a personal testimonial and both commitment and prevention nudges. Receives: Behavioral: Personal testimonial; Behavioral: Forks Over Knives Documentary; Behavioral: Commitment nudge; Behavioral: Prevention nudge
Link and DVD and no nudge	Experimental	Participants are sent the Forks Over Knives documentary online link and DVD and a letter with a personal testimonial and no behavioral nudges. Receives: Behavioral: Personal testimonial; Behavioral: Forks Over Knives Documentary
Link and DVD and commitment nudge	Experimental	Participants are sent the Forks Over Knives documentary online link and DVD and a letter with a personal testimonial and a commitment nudge. Receives: Behavioral: Personal testimonial; Behavioral: Forks Over Knives Documentary; Behavioral: Commitment nudge
Link and DVD and prevention nudge	Experimental	Participants are sent the Forks Over Knives documentary online link and DVD and a letter with a personal testimonial and a prevention nudge. Receives: Behavioral: Personal testimonial; Behavioral: Forks Over Knives Documentary; Behavioral: Prevention nudge
Link and DVD and both nudges	Experimental	Participants are sent the Forks Over Knives documentary online link and DVD and a letter with a personal testimonial and both commitment and prevention nudges. Receives: Behavioral: Personal testimonial; Behavioral: Forks Over Knives Documentary; Behavioral: Commitment nudge; Behavioral: Prevention nudge

What is being measured

The primary outcome is the main question the study is designed to answer.

Medical Cost in US Dollars From One Year Before to One Year After Intervention
Total annual amount of medical and pharmacy costs (sum) as reported by Geisinger Health Plan. General linear models are used to model change between the data from the year before the intervention and the data from one year after intervention. Lower costs is the desirable outcome.
Measured: 2 years
Number of Visits From One Year Before to One Year After Intervention
Total number of primary care physician and specialist visits (sum) as reported by Geisinger Health Plan. General linear models are used to model change between the data from the year before the intervention and the data from one year after intervention. Fewer visits is the desirable outcome.
Measured: 2 years
Number of Prescriptions From One Year Before to One Year After Intervention
Total number of prescriptions (fills) as reported by Geisinger Health Plan. General linear models are used to model change between the data from the year before the intervention and the data from one year after intervention. Fewer prescriptions is the desirable outcome.
Measured: 2 years
Number of Unique Prescribed Medication From One Year Before to One Year After Intervention
Total number of unique prescribed medication in the past year as reported by Geisinger Health Plan. General linear models are used to model change between the data from the year before the intervention and the data from one year after intervention. Less unique prescribed medication is the desirable outcome.
Measured: 2 years
Body Mass Index From One Year Before to One Year After Intervention
Taken from annual checkup with primary care provider. Computed from height (in meters) and weight (in kilograms) data with the formula kilograms/meters^2. General linear models are used to model change between the data from the year before the intervention and the data from one year after intervention. A body mass index between the range of 18.5 to 25 is the desirable outcome.
Measured: 2 years
Systolic Blood Pressure From One Year Before to One Year After Intervention
Taken from annual checkup with primary care provider. General linear models are used to model change between the data from the year before the intervention and the data from one year after intervention. Systolic blood pressure that is 120 millimeters of mercury (mmHg) or less is the desirable outcome.
Measured: 2 years
Diastolic Blood Pressure From One Year Before to One Year After Intervention
Taken from annual checkup with primary care provider. General linear models are used to model change between the data from the year before the intervention and the data from one year after intervention. Systolic blood pressure that is 80 millimeters of mercury (mmHg) or less is the desirable outcome.
Measured: 2 years

Secondary outcomes (19)

Triglyceride Levels From One Year Before to One Year After Intervention
One component of cholesterol, used if data is on health record. A triglyceride level of 150 milligrams per deciliter (mg/dl) or lower is the desirable outcome.
Measured: 2 years
Low-density Lipoprotein (LDL) Levels From One Year Before to One Year After Intervention
One component of cholesterol, used if data is on health record. An LDL level of 100 milligrams per deciliter (mg/dl) or lower is the desirable outcome.
Measured: 2 years
Five Years Before to Two Years After Intervention in Depressed Mood and Anhedonia as Assessed by the Patient Health Questionnaire-2 (PHQ-2) (Extended Time Frame)
Assesses depressed mood and anhedonia in the past two weeks; used if data is on health record. The sum of two items (each scored 0-3) is computed with a total score range of 0-6. A lower score is the desired outcome.
Measured: 7 years
Hemoglobin A1c (hbA1c) From Five Years Before to Two Years After Intervention (Extended Time Frame)
Test for diabetes, used if data is on health record. Percentage score reflects blood-glucose levels. An hbA1c level of 5.7% and below is the desirable outcome.
Measured: 7 years
Low-density Lipoprotein/High-density Lipoprotein (LDL/HDL) Ratios From Five Years Before to Two Years After Intervention (Extended Time Frame)
Computed as the ratio of LDL/HDL. An LDL/HDL ratio of 3 or less for men and 2.5 or less for women is the desirable outcome.
Measured: 7 years
High-density Lipoprotein (HDL) Levels From Five Years Before to Two Years After Intervention (Extended Time Frame)
One component of cholesterol, used if data is on health record. An HDL level of 60 milligrams per deciliter (mg/dl) or higher is the desirable outcome.
Measured: 7 years
Low-density Lipoprotein (LDL) Levels From Five Years Before to Two Years After Intervention (Extended Time Frame)
One component of cholesterol, used if data is on health record. An LDL level of 100 milligrams per deciliter (mg/dl) or lower is the desirable outcome.
Measured: 7 years
Triglyceride Levels From Five Years Before to Two Years After Intervention (Extended Time Frame)
One component of cholesterol, used if data is on health record. A triglyceride level of 150 milligrams per deciliter (mg/dl) or lower is the desirable outcome.
Measured: 7 years
Diastolic Blood Pressure From Five Years Before to Two Years After Intervention (Extended Time Frame)
Taken from annual checkup with primary care provider. Systolic blood pressure that is 80 millimeters of mercury (mmHg) or less is the desirable outcome.
Measured: 7 years
Systolic Blood Pressure From Five Years Before to Two Years After Intervention (Extended Time Frame)
Taken from annual checkup with primary care provider. Systolic blood pressure that is 120 millimeters of mercury (mmHg) or less is the desirable outcome.
Measured: 7 years
Body Mass Index From Five Years Before to Two Years After Intervention (Extended Time Frame)
Taken from annual checkup with primary care provider. Computed from height (in meters) and weight (in kilograms) data with the formula kilograms/meters^2. A body mass index between the range of 18.5 to 25 is the desirable outcome.
Measured: 7 years
Number of Unique Prescribed Medication From Five Years Before to Two Years After Intervention (Extended Time Frame)
Total number of unique prescribed medication in the past year as reported by Geisinger Health Plan. Less unique prescribed medication is the desirable outcome.
Measured: 7 years
Number of Prescriptions From Five Years Before to Two Years After Intervention (Extended Time Frame)
Total number of prescriptions (standard unit is prescription per number of days supplied) as reported by Geisinger Health Plan. Fewer prescriptions is the desirable outcome.
Measured: 7 years
Number of Visits From Five Years Before to Two Years After Intervention (Extended Time Frame)
Total number of primary care physician and specialist visits (sum) as reported by Geisinger Health Plan. Fewer visits is the desirable outcome.
Measured: 7 years
Medical Cost in US Dollars From Five Years Before to Two Years After Intervention (Extended Time Frame)
Total annual amount of medical and pharmacy costs (sum) as reported by Geisinger Health Plan. Lower costs is the desirable outcome.
Measured: 7 years
Values From One Year Before to One Year After Intervention of Depressed Mood and Anhedonia as Assessed by the Patient Health Questionnaire-2 (PHQ-2)
Although originally listed as secondary, this outcome measure was intended to be exploratory. Due to the largely null pattern of results on the primary outcomes, it was decided to forgo additional analysis at this time.
Measured: 2 years
Hemoglobin A1c (hbA1c) From One Year Before to One Year After Intervention
Test for diabetes, used if data is on health record. Percentage score reflects blood-glucose levels. An hbA1c level of 5.7% or lower is the desirable outcome.
Measured: 2 years
Low-density Lipoprotein/High-density Lipoprotein (LDL/HDL) Ratios From One Year Before to One Year After Intervention
Computed as the ratio of LDL/HDL. An LDL/HDL ratio of 3 or less for men and 2.5 or less for women is the desirable outcome.
Measured: 2 years
High-density Lipoprotein (HDL) Levels From One Year Before to One Year After Intervention
One component of cholesterol, used if data is on health record. An HDL level of 60 milligrams per deciliter (mg/dl) or higher is the desirable outcome.
Measured: 2 years

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

20 Jun 201930 Jun 2022

First posted19 Mar 2019
Study start20 Jun 2019
Primary completion30 Jun 2020
Study completion30 Jun 2022

Resources

Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
Posted resultsParticipant flow, outcome measures and adverse events reported by the sponsor.
Publications (2)Papers the sponsor has linked to this study.
Other trials for Cardiovascular DiseasesStudies of the same condition, open and under way.
What the trial phases meanHow a treatment moves from first tests in people to approval.

More details

For doctors and researchers: how the study is designed, who runs it, and its registry IDs.

Study design

Study type: Interventional
Phase: Phase N/A
Primary purpose: Supportive care
Allocation: Randomised
Intervention model: Factorial
Model description: One group of participants will not be contacted at all (n = 6200). One group will only received a letter promoting a plant-based diet (n = 2200). Twelve groups (n = 550 for each group) will receive the letter promoting a plant-based diet, along with the Forks Over Knives documentary. The documentary will be delivered through 3 different methods, and the accompanying letter will contain 4 different combinations of behavioral nudges. * 1 primary control group (no contact) * 1 group contacted by letter * 3 groups (documentary distribution: online link, DVD, online link + DVD) x 4 groups (behavioral nudges in the letter: no nudge, commitment nudge, prevention nudge, commitment and prevention nudges) Note: The control group size is an estimate of number of participants who match the eligibility criteria but were not randomly assigned to an experimental group.
Masking: Triple blind
Who is masked: Participant, Care provider, Outcomes assessor
Enrolment: 11,234 participants (actual)

IDs, dates and publications

ClinicalTrials.gov ID: NCT03880838
Sponsor's protocol ID: 2019-0179
Status last verified: May 2025
First submitted: 14 Mar 2019
Last updated: 20 May 2025
Results posted: Yes, on ClinicalTrials.gov
Data monitoring committee: No
FDA-regulated drug: No
FDA-regulated device: No
Individual data sharing: Yes: Data with no personally identifiable information will be made available to other researchers on the Open Science Framework for transparency. This will include preregistered hypotheses, analysis plan and code, and the essential data needed to replicate the analysis that yielded reported findings.

Publications

Milkman KL, Beshears J, Choi JJ, Laibson D, Madrian BC. Using implementation intentions prompts to enhance influenza vaccination rates. Proc Natl Acad Sci U S A. 2011 Jun 28;108(26):10415-20. doi: 10.1073/pnas.1103170108. Epub 2011 Jun 13.
PubMed 21670283
Tversky A, Kahneman D. The framing of decisions and the psychology of choice. Science. 1981 Jan 30;211(4481):453-8. doi: 10.1126/science.7455683.
PubMed 7455683

Want to know more?

The sponsor has not listed a contact. The official record may have more details.

Talk to your doctor first and take this page with you. Only the study team can confirm whether you can join.

Questions to ask the study team

What is the study trying to find out?
What would I need to do, and how often would I visit?
Could I receive a placebo instead of the treatment?
What are the possible risks and benefits for me?
Will it cost me anything? Are travel or time paid for?
Can I keep seeing my own doctor during the study?
What happens when the study ends?

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Study at a glance

From the registry record, last updated by the sponsor on 20 May 2025. Recruitment status is as the sponsor reported it: confirm with the study team.

Official title: 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
ClinicalTrials.gov ID: NCT03880838
Acronym / sponsor ID: 2019-0179
Conditions: Cardiovascular Diseases, Diabetes Mellitus, Obesity
Keywords: Plant-based diet, Behavioral nudge, Mail distribution, Randomized controlled trial, Insurance claims, Chronic disease, Letter-based intervention, Health behaviors
Study type: Interventional
Recruitment status: Completed
Enrolment: 11,234 participants (actual)
Lead sponsor: Geisinger ClinicUniversity, hospital or other
Study start: 20 Jun 2019 (actual)
Primary completion: 30 Jun 2020 (actual)
Study completion: 30 Jun 2022 (actual)
First posted: 19 Mar 2019 (actual)
Results: Posted 7 Sep 2023

Clinical summary

The research question as the sponsor registered it. This describes what the study plans to test, not what it found.

Detailed description

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.

Study design

Primary purpose: Supportive care
Allocation: Randomised
Intervention model: Factorial
Masking: Triple blind (participant, care provider, outcomes assessor)
Number of arms: 14
Model description: One group of participants will not be contacted at all (n = 6200). One group will only received a letter promoting a plant-based diet (n = 2200). Twelve groups (n = 550 for each group) will receive the letter promoting a plant-based diet, along with the Forks Over Knives documentary. The documentary will be delivered through 3 different methods, and the accompanying letter will contain 4 different combinations of behavioral nudges. * 1 primary control group (no contact) * 1 group contacted by letter * 3 groups (documentary distribution: online link, DVD, online link + DVD) x 4 groups (behavioral nudges in the letter: no nudge, commitment nudge, prevention nudge, commitment and prevention nudges) Note: The control group size is an estimate of number of participants who match the eligibility criteria but were not randomly assigned to an experimental group.

Arm	Type	Receives
No contact control	No intervention	–Participants are not contacted.
Letter	Experimental	Behavioral: Personal testimonialParticipants are only contacted through a letter with a personal testimonial.
Link and no nudge	Experimental	Behavioral: Personal testimonial, Behavioral: Forks Over Knives DocumentaryParticipants are sent the Forks Over Knives documentary online link and a letter with a personal testimonial and no nudges.
Link and commitment nudge	Experimental	Behavioral: Personal testimonial, Behavioral: Forks Over Knives Documentary, Behavioral: Commitment nudgeParticipants are sent the Forks Over Knives documentary online link and a letter with a personal testimonial and a commitment nudge.
Link and prevention nudge	Experimental	Behavioral: Personal testimonial, Behavioral: Forks Over Knives Documentary, Behavioral: Prevention nudgeParticipants are sent the Forks Over Knives documentary online link and a letter with a personal testimonial and a prevention nudge.
Link and both nudges	Experimental	Behavioral: Personal testimonial, Behavioral: Forks Over Knives Documentary, Behavioral: Commitment nudge, Behavioral: Prevention nudgeParticipants are sent the Forks Over Knives documentary online link and a letter with a personal testimonial and both commitment and prevention nudges.
DVD and no nudge	Experimental	Behavioral: Personal testimonial, Behavioral: Forks Over Knives DocumentaryParticipants are sent the Forks Over Knives documentary DVD and a letter with a personal testimonial and no behavioral nudges.
DVD and commitment nudge	Experimental	Behavioral: Personal testimonial, Behavioral: Forks Over Knives Documentary, Behavioral: Commitment nudgeParticipants are sent the Forks Over Knives documentary DVD and a letter with a personal testimonial and a commitment nudge.
DVD and prevention nudge	Experimental	Behavioral: Personal testimonial, Behavioral: Forks Over Knives Documentary, Behavioral: Prevention nudgeParticipants are sent the Forks Over Knives documentary DVD and a letter with a personal testimonial and a prevention nudge.
DVD and both nudges	Experimental	Behavioral: Personal testimonial, Behavioral: Forks Over Knives Documentary, Behavioral: Commitment nudge, Behavioral: Prevention nudgeParticipants are sent the Forks Over Knives documentary DVD and a letter with a personal testimonial and both commitment and prevention nudges.
Link and DVD and no nudge	Experimental	Behavioral: Personal testimonial, Behavioral: Forks Over Knives DocumentaryParticipants are sent the Forks Over Knives documentary online link and DVD and a letter with a personal testimonial and no behavioral nudges.
Link and DVD and commitment nudge	Experimental	Behavioral: Personal testimonial, Behavioral: Forks Over Knives Documentary, Behavioral: Commitment nudgeParticipants are sent the Forks Over Knives documentary online link and DVD and a letter with a personal testimonial and a commitment nudge.
Link and DVD and prevention nudge	Experimental	Behavioral: Personal testimonial, Behavioral: Forks Over Knives Documentary, Behavioral: Prevention nudgeParticipants are sent the Forks Over Knives documentary online link and DVD and a letter with a personal testimonial and a prevention nudge.
Link and DVD and both nudges	Experimental	Behavioral: Personal testimonial, Behavioral: Forks Over Knives Documentary, Behavioral: Commitment nudge, Behavioral: Prevention nudgeParticipants are sent the Forks Over Knives documentary online link and DVD and a letter with a personal testimonial and both commitment and prevention nudges.

Who may qualify

Ages: 18 years and older
Sex: All
Healthy volunteers: Not accepted
Age groups: Adult, Older adult

Key inclusion criteria (9 listed)

Has two out of the three following conditions:
Has health insurance through Geisinger Health Plan (is an active member with a full 12-month enrollment in the previous year) under one of the following categories:
Has visited their primary care provider in the past 12 months

Key exclusion criteria (3 listed)

Is institutionalized
Has active cancer, cirrhosis, renal failure, dementia, or active psychosis
Is in the same household as another selected participant

Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.

Interventions

Intervention	Type	Arms
Personal testimonialParticipants 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.	Behavioural	DVD and both nudges, DVD and commitment nudge, DVD and no nudge, DVD and prevention nudge, Letter, Link and DVD and both nudges, Link and DVD and commitment nudge, Link and DVD and no nudge, Link and DVD and prevention nudge, Link and both nudges, Link and commitment nudge, Link and no nudge, Link and prevention nudge
Forks Over Knives DocumentaryParticipants 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.	Behavioural	DVD and both nudges, DVD and commitment nudge, DVD and no nudge, DVD and prevention nudge, Link and DVD and both nudges, Link and DVD and commitment nudge, Link and DVD and no nudge, Link and DVD and prevention nudge, Link and both nudges, Link and commitment nudge, Link and no nudge, Link and prevention nudge
Commitment nudgeAt 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.	Behavioural	DVD and both nudges, DVD and commitment nudge, Link and DVD and both nudges, Link and DVD and commitment nudge, Link and both nudges, Link and commitment nudge
Prevention nudgeAs 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.	Behavioural	DVD and both nudges, DVD and prevention nudge, Link and DVD and both nudges, Link and DVD and prevention nudge, Link and both nudges, Link and prevention nudge

Primary outcome

Medical Cost in US Dollars From One Year Before to One Year After Intervention
Time frame: 2 years
Total annual amount of medical and pharmacy costs (sum) as reported by Geisinger Health Plan. General linear models are used to model change between the data from the year before the intervention and the data from one year after intervention. Lower costs is the desirable outcome.
Number of Visits From One Year Before to One Year After Intervention
Time frame: 2 years
Total number of primary care physician and specialist visits (sum) as reported by Geisinger Health Plan. General linear models are used to model change between the data from the year before the intervention and the data from one year after intervention. Fewer visits is the desirable outcome.
Number of Prescriptions From One Year Before to One Year After Intervention
Time frame: 2 years
Total number of prescriptions (fills) as reported by Geisinger Health Plan. General linear models are used to model change between the data from the year before the intervention and the data from one year after intervention. Fewer prescriptions is the desirable outcome.
Number of Unique Prescribed Medication From One Year Before to One Year After Intervention
Time frame: 2 years
Total number of unique prescribed medication in the past year as reported by Geisinger Health Plan. General linear models are used to model change between the data from the year before the intervention and the data from one year after intervention. Less unique prescribed medication is the desirable outcome.
Body Mass Index From One Year Before to One Year After Intervention
Time frame: 2 years
Taken from annual checkup with primary care provider. Computed from height (in meters) and weight (in kilograms) data with the formula kilograms/meters^2. General linear models are used to model change between the data from the year before the intervention and the data from one year after intervention. A body mass index between the range of 18.5 to 25 is the desirable outcome.
Systolic Blood Pressure From One Year Before to One Year After Intervention
Time frame: 2 years
Taken from annual checkup with primary care provider. General linear models are used to model change between the data from the year before the intervention and the data from one year after intervention. Systolic blood pressure that is 120 millimeters of mercury (mmHg) or less is the desirable outcome.
Diastolic Blood Pressure From One Year Before to One Year After Intervention
Time frame: 2 years
Taken from annual checkup with primary care provider. General linear models are used to model change between the data from the year before the intervention and the data from one year after intervention. Systolic blood pressure that is 80 millimeters of mercury (mmHg) or less is the desirable outcome.

19 secondary outcomes

Triglyceride Levels From One Year Before to One Year After Intervention
Time frame: 2 years
Low-density Lipoprotein (LDL) Levels From One Year Before to One Year After Intervention
Time frame: 2 years
Five Years Before to Two Years After Intervention in Depressed Mood and Anhedonia as Assessed by the Patient Health Questionnaire-2 (PHQ-2) (Extended Time Frame)
Time frame: 7 years
Hemoglobin A1c (hbA1c) From Five Years Before to Two Years After Intervention (Extended Time Frame)
Time frame: 7 years
Low-density Lipoprotein/High-density Lipoprotein (LDL/HDL) Ratios From Five Years Before to Two Years After Intervention (Extended Time Frame)
Time frame: 7 years
High-density Lipoprotein (HDL) Levels From Five Years Before to Two Years After Intervention (Extended Time Frame)
Time frame: 7 years
Low-density Lipoprotein (LDL) Levels From Five Years Before to Two Years After Intervention (Extended Time Frame)
Time frame: 7 years
Triglyceride Levels From Five Years Before to Two Years After Intervention (Extended Time Frame)
Time frame: 7 years
Diastolic Blood Pressure From Five Years Before to Two Years After Intervention (Extended Time Frame)
Time frame: 7 years
Systolic Blood Pressure From Five Years Before to Two Years After Intervention (Extended Time Frame)
Time frame: 7 years
Body Mass Index From Five Years Before to Two Years After Intervention (Extended Time Frame)
Time frame: 7 years
Number of Unique Prescribed Medication From Five Years Before to Two Years After Intervention (Extended Time Frame)
Time frame: 7 years
Number of Prescriptions From Five Years Before to Two Years After Intervention (Extended Time Frame)
Time frame: 7 years
Number of Visits From Five Years Before to Two Years After Intervention (Extended Time Frame)
Time frame: 7 years
Medical Cost in US Dollars From Five Years Before to Two Years After Intervention (Extended Time Frame)
Time frame: 7 years
Values From One Year Before to One Year After Intervention of Depressed Mood and Anhedonia as Assessed by the Patient Health Questionnaire-2 (PHQ-2)
Time frame: 2 years
Hemoglobin A1c (hbA1c) From One Year Before to One Year After Intervention
Time frame: 2 years
Low-density Lipoprotein/High-density Lipoprotein (LDL/HDL) Ratios From One Year Before to One Year After Intervention
Time frame: 2 years
High-density Lipoprotein (HDL) Levels From One Year Before to One Year After Intervention
Time frame: 2 years

Results and safety

Results posted to the registry on 7 Sep 2023, as reported by the sponsor. Figures are copied from the record, not re-analysed. Full results on ClinicalTrials.gov.

Participant flow

Group	Started	Completed
No Contact Control	2,434	2,434
Letter	2,200	2,200
Link and no Nudge	550	550
Link and Commitment Nudge	550	550
Link and Prevention Nudge	550	550
Link and Both Nudges	550	550
DVD and no Nudge	550	550
DVD and Commitment Nudge	550	550
DVD and Prevention Nudge	550	550
DVD and Both Nudges	550	550
Link and DVD and no Nudge	550	550
Link and DVD and Commitment Nudge	550	550
Link and DVD and Prevention Nudge	550	550
Link and DVD and Both Nudges	550	550

Primary outcome: Medical Cost in US Dollars From One Year Before to One Year After Intervention

Time frame: 2 years. Mean (Standard Deviation). Unit: dollars

Measure	No Contact Control n = 1997	Letter n = 1849	Link and no Nudge n = 434	Link and Commitment Nudge n = 466	Link and Prevention Nudge n = 459	Link and Both Nudges n = 447	DVD and no Nudge n = 453	DVD and Commitment Nudge n = 453	DVD and Prevention Nudge n = 458	DVD and Both Nudges n = 458	Link and DVD and no Nudge n = 472	Link and DVD and Commitment Nudge n = 454	Link and DVD and Prevention Nudge n = 451	Link and DVD and Both Nudges n = 457
2019	6123.39 (9447.33)	5863.82 (11818.81)	5901.99 (11124.11)	5630.26 (7461.85)	6427.50 (9412.89)	6343.24 (9206.43)	6270.08 (9647.26)	6336.36 (9452.46)	6129.37 (10795.32)	5542.03 (7632.87)	6681.14 (10538.91)	6850.98 (11812.93)	6202.43 (8509.40)	5305.93 (6743.15)
2020	6101.54 (10076.51)	6309.49 (13727.90)	5754.70 (11157.93)	5932.12 (8279.96)	6078.06 (9847.06)	7047.98 (14827.87)	6284.85 (10203.78)	6772.89 (10159.36)	6709.80 (14548.68)	5753.38 (7720.93)	6723.81 (13785.71)	6795.82 (12895.57)	6275.88 (9067.47)	5260.87 (6808.98)

Population analysed: Number of participants analyzed was based on the number of baseline (2019) records with no missing data for this outcome.

Primary outcome: Number of Visits From One Year Before to One Year After Intervention

Time frame: 2 years. Mean (Standard Deviation). Unit: visits

Measure	No Contact Control n = 1997	Letter n = 1849	Link and no Nudge n = 434	Link and Commitment Nudge n = 466	Link and Prevention Nudge n = 459	Link and Both Nudges n = 447	DVD and no Nudge n = 453	DVD and Commitment Nudge n = 453	DVD and Prevention Nudge n = 458	DVD and Both Nudges n = 458	Link and DVD and no Nudge n = 472	Link and DVD and Commitment Nudge n = 454	Link and DVD and Prevention Nudge n = 451	Link and DVD and Both Nudges n = 457
2019	5.59 (6.31)	5.57 (6.12)	5.17 (5.91)	5.66 (6.76)	5.69 (6.12)	5.77 (5.84)	5.69 (5.49)	5.43 (6.08)	5.60 (6.74)	5.88 (6.13)	5.71 (6.25)	5.59 (7.87)	5.53 (5.89)	5.26 (6.15)
2020	4.77 (5.65)	4.80 (5.56)	4.26 (5.30)	4.88 (5.78)	4.89 (5.52)	5.13 (5.36)	4.82 (5.29)	4.51 (5.31)	4.49 (5.49)	5.27 (5.80)	5.15 (5.85)	4.69 (6.24)	4.63 (5.18)	4.34 (5.06)

Population analysed: Number of participants analyzed was based on the number of baseline (2019) records with no missing data for this outcome.

Primary outcome: Number of Prescriptions From One Year Before to One Year After Intervention

Time frame: 2 years. Mean (Standard Deviation). Unit: prescriptions

Measure	No Contact Control n = 1735	Letter n = 1580	Link and no Nudge n = 381	Link and Commitment Nudge n = 403	Link and Prevention Nudge n = 391	Link and Both Nudges n = 404	DVD and no Nudge n = 403	DVD and Commitment Nudge n = 395	DVD and Prevention Nudge n = 399	DVD and Both Nudges n = 411	Link and DVD and no Nudge n = 413	Link and DVD and Commitment Nudge n = 395	Link and DVD and Prevention Nudge n = 382	Link and DVD and Both Nudges n = 399
2019	48.96 (49.89)	48.02 (48.47)	47.44 (49.70)	50.85 (46.95)	50.50 (46.08)	49.66 (43.44)	49.14 (54.80)	52.71 (53.75)	48.66 (43.52)	49.34 (48.53)	48.82 (51.30)	50.02 (49.10)	50.26 (49.83)	43.81 (44.03)
2020	29.87 (47.45)	26.82 (31.06)	29.09 (62.85)	29.86 (32.26)	29.32 (33.00)	30.35 (32.78)	28.05 (32.78)	30.24 (51.07)	30.32 (35.34)	31.70 (34.24)	29.83 (36.16)	27.83 (29.20)	31.69 (36.72)	27.30 (32.97)

Population analysed: Number of participants analyzed was based on the number of baseline (2019) records with no missing data for this outcome.

Primary outcome: Number of Unique Prescribed Medication From One Year Before to One Year After Intervention

Time frame: 2 years. Mean (Standard Deviation). Unit: prescriptions

Measure	No Contact Control n = 1735	Letter n = 1580	Link and no Nudge n = 381	Link and Commitment Nudge n = 403	Link and Prevention Nudge n = 391	Link and Both Nudges n = 404	DVD and no Nudge n = 403	DVD and Commitment Nudge n = 395	DVD and Prevention Nudge n = 399	DVD and Both Nudges n = 411	Link and DVD and no Nudge n = 413	Link and DVD and Commitment Nudge n = 395	Link and DVD and Prevention Nudge n = 382	Link and DVD and Both Nudges n = 399
2019	8.12 (6.08)	8.15 (6.22)	7.90 (6.08)	8.50 (6.25)	8.47 (6.29)	8.48 (5.76)	7.84 (6.18)	8.77 (7.52)	8.32 (6.11)	8.39 (7.07)	8.25 (6.17)	8.45 (6.43)	8.53 (6.63)	7.50 (6.15)
2020	5.92 (4.86)	5.82 (5.05)	5.80 (4.93)	6.27 (5.28)	6.00 (5.31)	6.28 (5.36)	5.70 (4.77)	5.98 (6.18)	6.13 (5.43)	6.44 (5.99)	6.28 (5.28)	5.88 (4.68)	6.39 (5.47)	5.66 (4.96)

Population analysed: Number of participants analyzed was based on the number of baseline (2019) records with no missing data for this outcome.

19 secondary outcomes are reported in the full results.

Adverse events

Time frame: We did not report a time frame as we did not actively collect adverse event data.. Other adverse events reported at 0% frequency or more

Group	Serious adverse events	Other adverse events
No Contact Control	0 of 0	0 of 0
Letter	0 of 0	0 of 0
Link and no Nudge	0 of 0	0 of 0
Link and Commitment Nudge	0 of 0	0 of 0
Link and Prevention Nudge	0 of 0	0 of 0
Link and Both Nudges	0 of 0	0 of 0
DVD and no Nudge	0 of 0	0 of 0
DVD and Commitment Nudge	0 of 0	0 of 0
DVD and Prevention Nudge	0 of 0	0 of 0
DVD and Both Nudges	0 of 0	0 of 0
Link and DVD and no Nudge	0 of 0	0 of 0
Link and DVD and Commitment Nudge	0 of 0	0 of 0
Link and DVD and Prevention Nudge	0 of 0	0 of 0
Link and DVD and Both Nudges	0 of 0	0 of 0

Limitations and caveats (from the sponsor): Due to limited data access, only information related to mailing and the outcomes were given to the researchers.

Loading the posted results from ClinicalTrials.gov…

Research links

Official record on ClinicalTrials.govLast updated by the sponsor 20 May 2025.
Posted resultsParticipant flow, baseline, all outcome measures and adverse events.
Background: PubMed 21670283Milkman KL, Beshears J, Choi JJ, Laibson D, Madrian BC. Using implementation intentions prompts to enhance influenza vaccination rates. Proc Natl Acad Sci U S A. 2011 Jun 28;108(26):10415-20. doi: 10.1073/pnas.1103170108. Epub 2011 Jun 13.
Background: PubMed 7455683Tversky A, Kahneman D. The framing of decisions and the psychology of choice. Science. 1981 Jan 30;211(4481):453-8. doi: 10.1126/science.7455683.
The trailer for the Forks Over Knives Documentary that will be sent for free to participants in the relevant armsLink provided by the sponsor.
Individual participant dataSharing planned: Yes. Data with no personally identifiable information will be made available to other researchers on the Open Science Framework for transparency. This will include preregistered hypotheses, analysis plan and code, and the essential data needed to replicate the analysis that yielded reported findings.

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Referral and contact

AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.

Amir Goren, PhD principal investigator

Program Director

Henri Carlo Y Santos, PhD study director

Post-doctoral Fellow

Christopher Chabris, PhD study director

Professor

1 site in 1 country: see every site and its status.

Questions about this trial

What is this clinical trial studying?

The full registered description is in the About this study section and the official record.

Who may be eligible to take part?

The sponsor lists 9 inclusion and 3 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.

Is this clinical trial currently recruiting?

The record says: finished, as of the sponsor's last update on 20 May 2025. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 1 site in United States. Whether a site is taking part right now should be confirmed with that site. See every site.

What are the possible benefits and risks?

They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.

Are results available for this study?

Yes. Results are posted in the registry (first posted 7 Sep 2023). A summary is in the For doctors view, and the full results are on ClinicalTrials.gov.

How can a doctor refer a patient or contact the research team?

The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

Medical Cost in US Dollars From One Year Before to One Year After Intervention (time frame: 2 years). The study lists 7 primary outcomes in all. It is what the study was designed to measure, not a finding.

Where can I read the original study information?

On the ClinicalTrials.gov record for NCT03880838, which also lists 2 linked publications.

Does a listing mean the treatment is approved or proven to work?

No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.

How often is this information updated?

AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 20 May 2025; AzTrials last refreshed its copy on 6 Nov 2026.