Plant protein and GLP-1 GI side effects

Gastrointestinal side effects are the main reason people reduce or stop semaglutide and other GLP-1 receptor agonists. A small pilot study published in June 2026 in Current Developments in Nutrition asked whether a plant-based high-protein shake could help participants manage those symptoms while also keeping protein intake adequate^[1].

What the study did

Withrow and colleagues enrolled 20 adults with a BMI above 27 kg/m² who had been on GLP-1 receptor agonist therapy for at least four weeks. Thirteen were on Ozempic and seven were on Wegovy. Participants consumed one to two servings of a plant-based protein shake daily for seven days. The trial was single-arm and open-label^[1]. There was no control group, which is a significant design limitation this article returns to below.

The primary outcome was self-reported gastrointestinal symptom severity, measured at baseline, two hours after the first serving, and at end of week. Secondary outcomes included daily protein and fibre intake, assessed through three-day dietary recall at the start and end of the intervention, and acceptability of the shake rated on standard likability scales.

What the results showed

All 20 participants completed the seven days without dropout. Acute GI symptoms, particularly abdominal bloating and constipation, improved significantly two hours after consuming the first shake (P less than 0.05)^[1]. Participants averaged 1.7 servings per day and reported significant increases in protein and fibre intake by the end of the week. The shakes were rated favourably on acceptability scales.

The protein intake finding matters in a specific way. A 2025 commentary in Obesity Pillars, drawing on the 42nd International Symposium on Diabetes and Nutrition, noted that GLP-1 therapy patients should target more than 1.2 g of protein per kilogram of body weight daily to help preserve lean mass during weight loss^[2]. Patients on GLP-1 agonists often eat less overall, which means protein intake can fall below that threshold. The Withrow pilot suggests a palatable, plant-based format may support intake in that population.

Why GI symptoms are a practical problem

A 2024 JAMA review of obesity medications reported that nausea affected 28% to 44% of patients on GLP-1 agonists, diarrhoea 21% to 30%, and constipation 11% to 24%^[3]. Those rates span liraglutide, semaglutide, and tirzepatide at their approved obesity doses. For most patients, symptoms are dose-dependent and front-loaded during titration, but for a meaningful minority they persist. Discontinuation rates in the STEP and SURMOUNT trial programmes attributed to adverse events ran from roughly 5% to 12% on higher doses.

Nutritional quality during GLP-1 therapy is a related concern. Reduced appetite and nausea change which foods feel tolerable. High-fat or dense foods become less appealing; high-protein foods, which tend to slow gastric emptying further, can worsen symptoms for some users. A formulation specifically designed to sit comfortably on a suppressed appetite, while also delivering protein and fibre, addresses a real gap in practical guidance.

The limitations

Seven days. Twenty participants. No comparator arm. The Withrow study is a proof-of-concept pilot, not evidence of benefit in the clinical sense. The P less than 0.05 symptom improvement at two hours tells you the participants felt better shortly after drinking the shake; it does not tell you whether plant-based formulation was necessary, whether any protein shake would have produced the same result, or whether the effect holds past a week^[1]. Open-label design means reporting bias cannot be ruled out. The study also did not adjust for GLP-1 dose or duration of therapy.

The study was also conducted in people already tolerating their GLP-1 medication, not in people who had just started or who had stopped because of symptoms. Generalising to either of those groups requires caution. A randomised design with a standard protein shake as the comparator arm would go a long way toward clarifying whether the plant-based composition matters or whether the benefit is simply from eating a palatable, protein-rich food.

What this means for readers

Nothing in this study should be read as a recommendation to add a specific product to any treatment plan. That conversation belongs with a prescribing clinician or dietitian who knows the individual case. What the pilot does is add to a growing body of practical literature on how to manage the nutritional side of GLP-1 therapy. For readers tracking the research on nutrition and semaglutide, the broader picture on side-effect management, protein targets, and what the STEP trials showed on body composition is covered on the semaglutide peptide page.

Larger, controlled trials with longer follow-up are needed before plant-based protein formulations can be integrated into formal clinical guidance on GLP-1 side-effect management. The Withrow pilot gives investigators a signal and a protocol to build on.