Written by Dr. Simone Pirita

The results can be impressive. Many people lose 10 to 20% of their body weight over the course of treatment, with some experiencing even greater reductions depending on the medication, dosage, and duration of therapy.

With weight loss occurring more easily than before, it is understandable that many people begin to wonder whether exercise is still necessary. If the number on the scale is going down, why spend time strength training or fitting in regular walks?

The answer is that weight loss is only one part of the picture.

Exercise remains one of the most important factors in protecting your health while taking a GLP-1 medication. It helps preserve muscle mass, supports metabolism, improves cardiovascular fitness, strengthens bones, reduces inflammation, and increases the likelihood that your weight loss is primarily coming from body fat rather than lean tissue.

In other words, GLP-1 medications work best when paired with movement, not replacing it.

Weight Loss Does Not Mean Fat Loss

One of the biggest misconceptions about weight loss is that every pound lost comes from body fat.

In reality, weight loss is made up of a combination of fat, water, glycogen, and lean body mass. Lean body mass includes skeletal muscle, connective tissue, organs, and other metabolically active tissues. While some loss of lean tissue is expected during any weight loss journey, preserving as much muscle as possible is important for both short-term health and long-term success.

Research suggests that approximately 25 to 40% of the weight lost while taking GLP-1 medications may come from lean body mass. While lean body mass includes more than just skeletal muscle, including water, connective tissue, and organs, studies indicate that a substantial portion of this loss is true muscle tissue. The exact amount varies depending on factors such as age, sex, baseline muscle mass, the rate and magnitude of weight loss, protein intake, and physical activity levels. In the absence of structured resistance training and adequate protein intake, modeling data suggest that skeletal muscle may account for approximately 10 to 15% of total weight loss in females and 20 to 25% in males. Given the critical role of muscle in metabolic health, physical function, insulin sensitivity, and long-term weight maintenance, preserving lean mass should be considered a central goal of any GLP-1 treatment plan, not an afterthought.

Now this is not unique to GLP-1 medications. Weight loss through calorie restriction alone also results in some muscle loss. However, because GLP-1 medications substantially reduce appetite, people often eat much less overall, making it easier to unintentionally consume too little protein and too few calories to adequately support muscle maintenance. One study found that less than 10% of patients on GLP-1 therapy met recommended protein intake levels, with average daily protein consumption as low as 33 grams, far below what is needed to preserve muscle.

Without strategies to preserve lean tissue, weight loss can come at the expense of strength and physical function.

Why Muscle Matters More Than You Think

Many people associate muscle with athletic performance or appearance, but muscle is essential for overall health.

Skeletal muscle plays a central role in blood sugar regulation by storing and using glucose, making it one of the body’s largest sites of insulin-sensitive tissue. It also supports balance, mobility, joint stability, and the ability to perform everyday tasks independently.

Muscle is metabolically active tissue, meaning it requires energy to maintain. Although it is not the primary determinant of metabolism, preserving lean muscle during weight loss helps support a healthier metabolic rate than losing muscle alongside fat.

Maintaining muscle also becomes increasingly important with age. Adults naturally lose muscle mass over time, and significant losses during weight reduction may increase the risk of weakness, falls, and reduced physical function later in life. Losing 6 kg of lean mass in under a year, as has been observed in clinical trials of GLP-1 medications, is comparable to a decade or more of normal age-related muscle decline compressed into months.

The most effective way to preserve muscle during weight loss is through resistance training. Studies on calorie restriction show that resistance training can reduce lean body mass loss by 50 to 95%. While direct evidence in GLP-1 populations is still emerging, early data are consistent with this benefit.

Whether you use free weights, resistance bands, machines, or bodyweight exercises, challenging your muscles encourages your body to retain lean tissue even while in a calorie deficit. Research consistently shows that combining resistance training with adequate protein intake helps people lose a greater proportion of fat while preserving more muscle.

You do not need to spend hours in the gym. Two to three full-body strength sessions each week can provide meaningful benefits, particularly when exercises target all major muscle groups.

GLP-1 Medications Don’t Improve Fitness on Their Own

This may be the most surprising finding in the research: despite all their metabolic benefits (lower blood sugar, reduced cardiovascular risk, decreased inflammation), GLP-1 medications alone have not been shown to improve cardiorespiratory fitness, which is your body’s ability to use oxygen during exercise.

Cardiorespiratory fitness is one of the strongest independent predictors of how long you will live. It is more predictive of mortality than cholesterol, blood pressure, or even smoking status. And it is the one thing these powerful medications cannot give you. Only exercise can.

In a randomized trial of 195 adults with obesity, participants who combined a GLP-1 medication with a structured exercise program saw their cardiorespiratory fitness improve by 4.8 mL/kg/min, a clinically meaningful gain. Those on the medication alone? No significant improvement in fitness at all.

Exercise also promotes fat oxidation (especially visceral fat, the dangerous fat around your organs), increases mitochondrial function, improves insulin sensitivity, and raises your resting metabolic rate. These are benefits that complement and amplify what GLP-1 medications do, creating a synergy that neither approach achieves alone.

Exercise Protects Your Bones

Rapid weight loss, whether from medication, surgery, or extreme dieting, can decrease bone mineral density and increase fracture risk.

Research has shown that GLP-1 therapy alone significantly decreased bone mineral density at the hip and spine. But when exercise was added to the medication, bone density was fully preserved at all sites, even though the combination group lost more total weight. Exercise-containing groups also showed slight increases in forearm bone density, a non-weight-bearing site, suggesting that exercise benefits bone health through mechanisms beyond just mechanical loading.

This finding is particularly important for women approaching or past menopause, who are already at elevated risk for osteoporosis.

Building Habits That Last

GLP-1 medications can be highly effective while they are being taken, but long-term success depends on more than medication alone.

When people stop GLP-1 medications, studies show that up to two-thirds of the lost weight can be regained within a year. But here is the critical detail: the weight that comes back is predominantly fat, not muscle. This means each cycle of losing and regaining can leave you with progressively less muscle and more fat, a worse body composition than where you started, and a potentially increased risk of sarcopenia.

Developing sustainable habits such as regular exercise, adequate protein intake, and balanced nutrition helps support muscle mass, cardiovascular fitness, and overall metabolic function regardless of whether someone continues medication long term. Retaining lean mass during treatment could also help blunt fat regain if medication is eventually discontinued.

Rather than viewing exercise as a way to burn calories, it is more helpful to think of it as an investment in strength, mobility, and lifelong health.

What Kind of Exercise Should You Do?

Based on current evidence and guidelines from major medical societies, the ideal exercise program while on a GLP-1 medication includes:

• Resistance (strength) training at least 2 to 3 times per week, targeting all major muscle groups. This is the single most important type of exercise for preserving muscle mass during weight loss. Think squats, lunges, push-ups, rows, and deadlifts, or machine-based equivalents.
• Aerobic exercise for at least 150 minutes per week at moderate intensity (brisk walking, cycling, swimming) or 75 minutes at vigorous intensity. This is what builds your cardiorespiratory fitness, the benefit the medication cannot provide.
• Gradual progression. Since some people experience fatigue or nausea with GLP-1 medications, start with modest goals and build up slowly. Consistency is far more important than perfection.

You do not need to exercise perfectly to experience these benefits. A few resistance training sessions each week, regular walks, or any activity you enjoy can make a meaningful difference.

Protein and Exercise Work Together

Resistance training is most effective when paired with adequate protein intake.

Because GLP-1 medications reduce appetite, some people unintentionally consume too little protein to support muscle maintenance. Current recommendations suggest consuming 1.6 to 2.4 grams of protein per kilogram of lean body weight daily during active weight loss. As a simpler benchmark, aiming for at least 80 to 120 grams of protein per day can help ensure adequate intake for most people.

Including a quality protein source at each meal can help provide the amino acids needed to repair and preserve muscle during weight loss. Prioritize protein-rich foods first at each meal, since reduced appetite may limit how much you eat overall. Good options include eggs, Greek yogurt, cottage cheese, fish, lean poultry, beans and legumes.

However, it is important to understand that protein alone, without resistance training, is not enough to prevent muscle loss. Excess dietary protein above what the body needs for muscle repair can actually be converted to fat. The combination of adequate protein and regular strength training is what makes the difference.

Protein needs vary based on age, body size, activity level, and medical history, so individualized guidance from your naturopathic doctor may be helpful.

Ready to Take a Whole-Person Approach to Weight Management?

GLP-1 medications have transformed obesity treatment and metabolic health care, helping many people achieve significant weight loss. However, the goal should not simply be to lose weight. It should be to improve body composition, preserve muscle, support metabolic health, and maintain long-term physical function.

If you are interested in a personalized, evidence-based approach to weight management or metabolic health, book a complimentary discovery call with Dr. Simone Pirita, ND. Together, you can discuss your health goals, review your medical history, and determine whether a comprehensive treatment plan is the right fit for you.