On September 25, 2025, I attended a Canadian Nutrient Society/ASPEN webinar featuring Dr. Carla Prado, Dr. Manpreet Mundi, and Dr. Stuart Phillips, focusing on obesity, weight loss, and muscle preservation. Here’s a summary of the key takeaways, especially relevant for healthcare professionals, dietitians, and patients considering GLP-1 receptor agonists or other weight loss interventions.
Why Muscle Mass Matters
Muscle is more than just strength—it plays a critical role in:
- Structural support: mobility, balance, and posture
- Metabolic function: glucose uptake, energy expenditure, amino acid storage
- Immune function: production of myokines and glutamine
Sarcopenic obesity—having low muscle mass and high body adiposity —is associated with increased mortality and comorbidities. Preserving muscle during weight loss is therefore a key goal.
Weight Loss Interventions and Muscle Impact
Regardless of the method (low kcal diets, medications or surgery) weight loss comes from a variety of tissues (adipose, muscle and bones). As I tell my patients, my of us don’t mind losing fat tissues, but we all want to keep our muscles and bones.
So how much fat-free mass is lost based on the different weight loss interventions?
- GLP1s: 25–39% (Muscle loss is mostly due to caloric deficit, not the medication itself).
- Low-calorie diets: 14–23%
- Bariatric surgery: ~21%
About 60% of fat-free mass is muscle. The other 40% is made up of bone, organs and water.
Weight Cycling Concerns
- 50% of patients discontinue GLP-1 therapy after 1 year.
- Weight regain often leads to repeated cycles of loss and regain, which may increase risk of sarcopenia.
This wasn’t addressed in the webinar – but I did wonder if this statement was specific to GLP1s or all weight loss interventions. In my experience, most adults have done at least some weight cycling through their life.
Nutrition Considerations with GLP-1 Therapy
- Low appetite can lead to missed meals and inadequate nutrient intake.
- Micronutrients, fiber, protein, and fluid intake may be insufficient.
- Combining protein-rich foods with exercise helps preserve muscle mass.
- Both animal and plant proteins are effective, though plant proteins may require higher volume if appetite is suppressed.
For more about nutrition considerations and GLP1 therapy – check out my previous blog series here.
The Role of Exercise
- Physical activity: any movement by skeletal muscles requiring energy
- Exercise: planned, structured, and intentional activity to improve fitness
Benefits of exercise during weight loss:
- Maintains lean muscle mass
- Reduces visceral fat
- Improves bone health and metabolism
- Enhances insulin sensitivity and glucose uptake
- Lowers cardiovascular risk
Best approach for muscle preservation:
- GLP-1 therapy + resistance + aerobic exercise + protein intake
- Aerobic exercise alone helps lower-limb muscles, but resistance training is key for full-body preservation.
Body Composition and Muscle Outcomes
- On average, 25% of weight lost with GLP-1 therapy is lean mass, similar to diet or bariatric surgery.
- Muscle can be preserved with exercise and nutrient-dense protein intake.
- High-protein diets, especially combined with resistance exercise, optimize lean mass retention.
Another side note: how high-protein diets might impact kidney health wasn’t addressed in this webinar (more about why that might matter here). They also didn’t provide a specific protein target.
Other Benefits of GLP-1 Therapy
Beyond weight loss, GLP-1 agonists can improve:
- Cardiovascular health: reduced events, heart failure risk, and mortality
- Renal outcomes: reduced ESRD, slower eGFR decline, lower UACR
- Liver health: decreased MASH and fibrosis
- Obstructive sleep apnea: improvement with tirzepatide
Side effects:
- Primarily GI-related (intended outcome), often improve with continued therapy
- Risk of pancreatitis in patients with history; titration rates can reduce side effects
Key Takeaways
- Muscle preservation is critical during weight loss, especially for patients with obesity or sarcopenic obesity.
- GLP-1 therapies result in fat loss and fat-free mass loss, similar to diet or bariatric surgery.
- Exercise + protein intake is the most effective strategy to maintain muscle.
- Plant-based and animal proteins are both effective, but portion sizes may need adjustment if appetite is low.
- Long-term adherence to GLP-1 therapy and lifestyle support is important to prevent weight regain and muscle loss.
Conclusion
Preserving muscle during weight loss is essential not only for strength and mobility but also for metabolic health and long-term outcomes. Combining GLP-1 therapy with resistance and aerobic exercise and adequate protein intake appears to be the optimal approach for maintaining muscle while reducing fat. Clinicians and patients should prioritize strategies that maintain muscle mass alongside weight reduction to improve overall health outcomes.
