Description

Background. The popularity of anti-obesity medications, particularly glucagon-like peptide-1 receptor agonists (GLP-1RAs) like semaglutide and dual GLP-1/GIP receptor agonists like tirzepatide, has increased dramatically over the past several years. These medications are routinely prescribed in obesity management clinics and other medical settings. While controlled clinical trials have been conducted for specific drugs, many of these have not reported relevant outcomes, such as body composition changes, muscular performance, and nutritional intake. Additionally, these controlled clinical trials may not fully represent the "real world" effects of treatment in varied settings. As such, there is a need for observational, real-world evaluations of the effects of GLP-1RA and GLP-1/GIP drugs on body composition, muscular performance, nutritional intake, and routine clinical markers. Additionally, the influence of lifestyle factors, such as exercise participation, on the observed changes in these outcomes should be evaluated.

Overview. Eligible participants beginning treatment with selected obesity medications (semaglutide or tirzepatide) at a specified virtual health clinic will undergo periodic body composition and muscular performance testing, as well as complete online surveys about their nutritional intake and physical activity and exercise participation. Additionally, routinely collected clinical information will be evaluated.

Body Composition Assessment. Participants will be asked to report an approved local DXA testing facility for a baseline body composition assessment as close as possible to the beginning of their anti-obesity medication treatment. Participants will be requested to report for another scan after ~6 months of treatment, as well as after ~17 months of treatment (provided they are still undergoing treatment at this point).

Handgrip Strength Testing. Handgrip testing will take place using a standard, consumer-grade at-home handgrip dynamometer, which will be provided to each participant. Participants will be provided with instructions for conducting the handgrip testing. This testing will be completed at baseline (as close as possible to the initiation of anti-obesity medication), and after ~3, ~6, and ~17 months of treatment (provided they are still undergoing treatment at these time points).

Questionnaires. The following questionnaires will be completed at baseline (as close as possible to the initiation of anti-obesity medication), and after ~3, ~6, and ~17 months of treatment (provided they are still undergoing treatment at these time points):

1. Automated Self-Administered 24-hour (ASA24®) Dietary Assessment Tool
2. The International Physical Activity Questionnaire (IPAQ)
3. The Muscle-Strengthening Exercise Questionnaire (MSEQ)

Standard Clinical Markers. Some clinical markers routinely collected during standard medical treatment will also be evaluated, including a lipid panel (total cholesterol, HDL cholesterol, LDL cholesterol, triglycerides), hemoglobin A1C, glucose, and blood pressure.

Power Analysis. A priori power analyses were conducted for repeated-measures ANOVA (within-subjects factors) using GPower to determine the required sample size. The analyses used a conservative effect size (f = 0.25; "medium" strength), an alpha error probability (α) of 0.05, a desired statistical power (1-β) of 0.8, and specified one group. Ranges of number of repeated measures (2 to 4), correlations between repeated measures (0.25 to 0.5), and nonsphericity corrections (ε; 0.8 to 1) were implemented. These analyses indicated the total sample size required to achieve adequate power ranged from 24 to 50 participants. A priori power analyses were conducted for linear multiple regression (R2 deviation from zero) using GPower to determine the required sample size for analyses examining predictors of variation in changes in outcome variables. A medium strength effect size (f2=0.15), an alpha error probability (α) of 0.05, and a desired statistical power (1-β) of 0.8 were specified. This analysis indicated that up to 6 predictors could be included in the regression model at a sample size of 98 participants. Based on consideration of these analyses, a target sample size of 100 was specified.

Statistical Analysis. Comprehensive descriptive data will be presented. Changes in all outcome variables over time will be quantified using appropriate statistical methods (e.g., repeated-measures ANOVA or a similar linear model). Additionally, the potential influence of lifestyle factors - particularly nutritional intake, physical activity level, and participation in muscle-strengthening activities - and medication type (semaglutide vs. tirzepatide) on outcome measures will be explored using an appropriate method (e.g., multiple linear regression or a related linear model, such as a linear mixed-effects model).