Remotely Delivered Behavioral Weight Loss Using an Ad Libitum Plant-Based Diet Versus a Balanced Calorie Deficit Diet

Weight loss will be self-reported by participants using a standardized weighing procedure. Participants will weigh themselves in lightweight clothes without shoes with a digital scale accurate to 0.1 kg. Percent weight loss at 6-months will be calculated as the percentage loss in initial body weight at baseline by the time of the post-treatment assessment.

Subjective appetite will be assessed using 6 visual analogue scale items (VAS) inquiring about past-week hunger, fullness, the degree to which hunger made it difficult to follow the prescribed diet, preoccupation with thoughts of food, and being bothered by hunger on a visual analogue scale of 0-100. Scores on the fullness item will be reversed, such that higher scores will indicate greater subjective appetite.

Dietary adherence in the whole food plant-based diet (WFPBD) condition will be assessed with an adapted 7-item food frequency questionnaire (FFQ). Each day for 7 days, participants will indicate whether they ate each of the "green zone" food categories (veggies/fruits, leafy greens, whole gains/starches, beans/lentils), whether they ate less than 3 servings of "yellow zone" foods, the "red-zone" foods consumed (and servings of). To evaluate whether intake of green/yellow/red-zone foods changes more in the WFPBD condition than in the balanced calorie deficit diet (BCDD) condition, those in the BCDD condition will complete the FFQ at each assessment point. To evaluate dietary adherence in the BCDD condition, calorie-tracking adherence will be examined. Dietary adherence on a given day will be defined as the overall number of days participants tracked at least two eating occasions.

Quality of life will be assessed using the 36-item Short-Form General Health Survey (SF-36; Ware, Kosinski, & Keller, 1994; Ware & Sherbourne, 1992), which assesses eight domains: physical functioning, limits due to physical health, pain, general health, energy/fatigue, social functioning, emotional wellbeing, and mental health. Scores will be converted to a 0 to 100 scale, with higher scores indicating better functioning. This scale produces both physical health (PH) and mental health (MH) component summaries.

Intentions to continue adhering to dietary prescription will be assessed with a 3-item self-report measure ("Future Intentions Questionnaire"). On a Likert scale ranging from 1 (Not at all) to 5 (Completely), participants will respond to face-valid questions asking about plans to continue adhering to the prescribed program diet (sample item: "I plan to follow the diet from this program moving forward") and the feasibility of the program diet (sample item: "The diet in this program is straightforward to follow moving forward"). Accompanying the measure, participants will receive a brief reminder of their dietary prescription (i.e., the traffic light diet chart in the whole food plant-based diet condition, or the calorie goal and daily calorie tracking requirement in the balanced calorie deficit diet condition). Items will be averaged to create a measure of intentions to adhere to the prescribed diet; higher scores indicate greater adherence.

To assess depressive symptoms, the Beck Depression Inventory-II (BDI-II; Dozois et al., 1998) will be administered-a 21-item measure of somatic (e.g., appetite), affective (e.g., sadness) and cognitive (e.g., self-criticalness) dimensions of depressive symptomology. Participants will indicate how they have been feeling during the past week and make responses on a Likert scale ranging from 0 (e.g., I don't cry any more than I used to) to 3 (e.g., I feel like crying but I can't), with higher scores indicating greater levels of depressive symptoms.

Overall program acceptability will be assessed post-treatment with a questionnaire adapted from prior work (Bradley et al., 2017) that will ask participants to report how satisfied they were with the program, the degree to which they found the program helpful, and the likelihood they would recommend it to family or friends using a Likert scale ranging from 1 (Not at all) to 5 (Very much). Scores will be averaged across conditions to create mean program acceptability scores. Higher scores will indicate greater program acceptability.

Participants will indicate the degree to which they found their diet to be acceptable by indicating, on a Likert scale, how difficult they found the diet to follow (1-Very Easy - 5-Very difficult) with regards to: following the diet as a whole, cooking, dietary tracking, staying full, and managing cravings. Participants will also indicate how time-consuming they found their diet (1-Not at all time-consuming - 5-Very time-consuming), and how confident they felt in their ability to follow their diet (1-Not at all - 5-Very much so). Scores will be averaged across items to create mean dietary acceptability scores.

To assess social support vs. social sabotage, participants will complete the Social Support and Sabotage Scale from Ball & Crawford (2006). On this measure, participants separately rate the degree to which friends and family act in ways that support or hinder their healthy eating efforts with a Likert scale ranging from 1 (Almost never) to 5 (Almost always). Scores will be averaged for each subscale to compute: 1) support for health behaviors from friends, 2) support for health behaviors from family, 3) sabotage for health behaviors from friends, and 4) sabotage for health behaviors from family.

Self-reported fatigue will be measured using the Functional Assessment of Chronic Illness Therapy - Fatigue Scale (FACIT Fatigue), a 13-item self-report questionnaire that assesses level of fatigue during an individual's usual daily activities over the past week on a Likert scale ranging from 4 (not at all fatigued) to 0 (very much fatigued) (Webster et al., 2003). Scores will be reversed such that higher scores indicate greater levels of fatigue.