GLP-1s and the Gut: What Fitness Professionals Need to Know About GI Side Effects

GLP-1 medications like Ozempic, Wegovy, and Mounjaro are gaining attention for their role in supporting weight loss, improving blood sugar regulation, and curbing appetite. But while their popularity grows, so do questions—and legitimate concerns—about how these medications impact digestion.

As a Functional Medicine Nutritionist, I see firsthand how shifts in gut function ripple through the entire body. The gut is more than a digestive tube—it’s central to immune regulation, hormone balance, nutrient absorption, even emotional well-being. When digestive function is disrupted—whether through slowed motility, reduced appetite, or altered microbiome dynamics—energy, recovery, and resilience can all take a hit.

For fitness professionals working closely with clients on GLP-1s, understanding how these medications influence GI function is key. It helps you spot the early signs of distress, tailor support more effectively, and guide clients toward sustainable changes that work with the body, not against it.

Why GI Side Effects Matter

GLP-1s slow gastric emptying—that’s part of how they support weight loss and satiety (the feeling of fullness that tells you to stop eating.) But that same mechanism can also lead to a range of digestive symptoms, including:

• Nausea and vomiting
  Often experienced early on or during dose increases, these symptoms may cause clients to avoid food, compromise hydration, or skip workouts.

• Delayed gastric emptying (gastroparesis)
  For some people, stomach motility (the muscle contractions that move food through the digestive tract) slows significantly—leading to bloating, early fullness, indigestion, or in rare cases, severe vomiting.

• Bezoars
  Yes, it’s a real term. A bezoar is a solid mass of undigested material that can form in the stomach. While uncommon, they’ve been documented more frequently in those on GLP-1s due to slowed digestion—and can require medical intervention.

• Diarrhea or constipation
  These symptoms may interfere with nutrient absorption, hydration, and electrolyte balance—all of which impact physical performance and recovery.

What Fitness Professionals Should Watch For

You may be the first to notice when something’s not quite right—often before a client connects the dots themselves. Red flags to tune into include:

• A client consistently skipping meals or feeling “too full” to eat.

• Reports of early satiety, bloating, or unusual GI discomfort.

• Energy dips, muscle fatigue, or signs of under-recovery from workouts.

These issues often show up early in GLP-1 use, when side effects are strongest and dietary intake is rapidly changing. Over time, some clients adapt—while others continue to struggle with low appetite or inconsistent fueling, which can affect strength, stamina, or mood.

Because clients may not bring these concerns up on their own, gentle, open-ended questions can help surface important information. Try asking:

“How’s your digestion feeling lately?”
“Have your meals or snacks changed much since starting the medication?”
“Are you getting enough fuel to support your workouts and recovery?”

Your curiosity and care can help clients feel seen and supported—and allow you to guide them toward adjustments that preserve performance while honoring where they are.

How to Support Your Clients

As a fitness professional, you don’t need to be an expert in GLP-1 pharmacology—but you do play a critical role in helping clients navigate how these medications impact their body, energy, and progress.

✔ Prioritize protein and preserve muscle
You know this: loss of lean body mass is a risk during weight loss—no matter the method. GLP-1s can amplify that risk if clients aren’t eating enough or are avoiding strength training. Encourage consistent resistance work and adequate protein intake to support metabolism, mobility, and recovery.

Pro Tips: Keep in mind that slowed digestion can affect how protein is broken down and absorbed, especially during the early stages, so smaller, more frequent protein-rich meals may be easier to tolerate—especially early on. And yes—even if workouts may need to be shorter or gentler in the early stages.

✔ Recognize bio-individuality
No two bodies respond the same way. One client may feel energetic and empowered, while another battles nausea, GI discomfort, or emotional disorientation. While you don’t need to diagnose or treat the discomfort, you can observe, ask, and refer when needed. Track changes in energy, performance, or motivation with curiosity and care.

✔ Focus on what’s functional
If a client is struggling—physically or emotionally—after the introduction of GLP-1 medications, help them anchor in what is going well: consistent hydration, a post-workout walk, a meal they enjoyed and tolerated well. Functional wins build confidence, and confidence builds momentum. It’s not about perfection; it’s about progress that honors their body’s cues.

Functional Fitness Meets Functional Nutrition

You already understand the power of functional movement—training that supports everyday strength, flexibility, and real-life demands. In Functional Nutrition, we apply that same principle internally: helping the body’s systems—digestion, blood sugar regulation, inflammation, detoxification, hormone balance—work better through personalized lifestyle interventions.

It’s a natural partnership. When function is the focus, we move beyond aesthetics or quick fixes and into long-term resilience. That’s where your expertise meets mine—and where your clients can find lasting change.

Final Thought

GLP-1s are a tool—not a cure-all. They can offer powerful support, but they also place demands on the body—especially the gut. As a fitness professional, your awareness of these GI effects positions you as a more informed and compassionate ally.

And when it comes to digestion, one truth always holds: when the gut is off, the whole body feels it.

As I always say: We are not what we eat, but what our body can do with what we eat. That truth brings nutrition right back to digestion—and why it matters so much.

Stay curious. Stay connected. And keep supporting your clients with care.

—
Andrea Nakayama is a Functional Medicine Nutritionist and educator known for her work at the intersection of systems biology and clinical practice. Through her Functional Nutrition training and certification program, Full Body Systems, she and her team train thousands of coaches and clinicians to improve client outcomes by addressing the root causes of health challenges—particularly through the lens of digestion, inflammation, and personalized nutrition.

References:

• Zhu M, Liu Q, Zhu Q, et al. Gastrointestinal adverse events with GLP‑1 receptor agonists: Real‑world evidence from a cohort of 10,328 patients. Pharmaceutics. 2023;17(2):199.
  https://pubmed.ncbi.nlm.nih.gov/38399414/

• Preda CM, Burtea DE, Rusu OG, et al. Gastric bezoars associated with GLP‑1 receptor agonist therapy: A case series and review. Journal of Clinical Medicine. 2023;12(13):4184.
  https://pubmed.ncbi.nlm.nih.gov/36723995/

• Gofron KK, Wasilewski A, Małgorzewicz S. Effects of GLP‑1 analogues on the gut microbiota: A systematic review. Nutrients. 2025;17(8):1303. https://www.mdpi.com/2072-6643/17/8/1303