Maintaining lean muscle during weight loss is just as important as shedding excess fat. Recently, powerful GLP-1 agonist medications have surged in popularity as effective treatments for obesity. These drugs help people lose a significant amount of weight, but muscle retention during weight loss is a critical concern that often gets overlooked. Patients on GLP-1 medications may be losing muscle along with fat, potentially leading to frailty despite a lower weight. In this article, we’ll explore how GLP-1 and muscle loss are connected, why preserving muscle is vital, and practical strategies to ensure you lose fat and not valuable muscle.

Understanding GLP-1 Weight Loss Medications

GLP-1 receptor agonists are a class of medications originally developed to treat type 2 diabetes, but they also induce substantial weight loss. They work by mimicking a gut hormone (GLP-1) that reduces appetite, slows stomach emptying, and improves blood sugar control. These drugs have been repurposed or explicitly formulated for obesity treatment. So, what is the best GLP-1 for weight loss?

• Semaglutide (Wegovy®, Ozempic®) – A once-weekly GLP-1 agonist injection. Clinical trials of semaglutide 2.4 mg (Wegovy) showed an average weight reduction of around 15% of body weight over ~68 weeks. This was a game-changer in obesity treatment, far exceeding older drugs in effectiveness.

• Liraglutide (Saxenda®) – A once-daily GLP-1 agonist injection. Liraglutide (3 mg dose for weight loss) produces more modest weight loss and was one of the first GLP-1 drugs approved for obesity.

• Tirzepatide (Mounjaro®) – A once-weekly dual GLP-1 agonist and GIP agonist. Tirzepatide is highly effective for weight loss, with trials showing unprecedented results. It’s currently approved for diabetes but expected to be approved for obesity as well.

Each medication’s effectiveness can vary, but head-to-head data suggest that tirzepatide may be the most effective GLP-1 for weight loss to date. A 72-week trial in adults with obesity found an average of 20.2% change in body weight with tirzepatide versus 13.7% with semaglutide. This makes tirzepatide arguably the frontrunner in terms of sheer weight reduction. Of course, the best GLP-1 agonist for weight loss for any individual also depends on personal factors, such as tolerance, medical history, and access. All of these medications can help shed pounds. The key is ensuring those pounds come predominantly from fat, not muscle.

Why Preserving Muscle Matters During Weight Loss

Weight loss isn’t just about watching the scale go down. It’s about improving body composition and health. Lean muscle mass is metabolically active tissue that plays a crucial role in strength, mobility, and even maintaining a healthy metabolism. If you lose too much muscle while dieting, you may end up weaker, have a slower metabolic rate, and be more prone to weight regain. Preserving lean mass is especially important for older adults to prevent frailty and maintain functional ability. The goal is muscle retention during weight loss, so that as you get lighter, you become a healthier and stronger version of yourself, not just a more petite frame of your old self.

However, weight loss often does include some muscle loss. In a typical diet, about 20–30% of weight lost can come from lean tissue. With the very effective GLP-1 drugs, the changes can be dramatic, and researchers have noted the need to monitor body composition. In obesity trials of GLP-1 agonists, participants lost a significant portion of muscle along with fat. In some cases, 10% or more of their muscle mass is lost in about a year, an amount of muscle loss that could equate to roughly 20 years of normal age-related decline. This degree of muscle reduction is not trivial: losing 10% of your muscle might mean weaker strength, lower stamina, and even a decrease in basal metabolic rate. Such findings emphasize why we must pay close attention to tirzepatide and muscle loss. If we ignore muscle, a person could reach their target weight yet end up with a higher body-fat percentage than expected, or with new issues like fatigue or frailty.

GLP-1 and Body Composition: Fat vs. Lean Weight Loss

How do GLP-1 weight loss drugs affect your body composition? In terms of GLP-1 effects on body composition, studies show that the majority of weight lost on these medications is fat, but a notable portion is lean mass. It’s not as simple as “all the weight lost is fat.” It’s important to remember that “lean mass” includes more than just muscle. It also includes water, organ tissue, and bone. Early in weight loss, a drop in glycogen and water can register as lean mass loss. Over a more extended period, though, changes in lean mass do reflect changes in muscle and other tissues. When we observe a 5–7 kg loss of lean mass in a patient, some of that is likely actual muscle tissue that we want to preserve. This is why researchers and clinicians emphasize the importance of monitoring body composition. Experts have called on drug manufacturers and the FDA to include body composition outcomes in trials, not just total weight loss. The good news is that the effects of GLP-1 on body composition primarily focus on fat loss.

How to Preserve Muscle on GLP-1 Therapy

The answer comes down to two main factors: exercise and nutrition. These lifestyle components are crucial for anyone losing weight, and they remain so when you’re on a medication that’s suppressing your appetite.

1. Prioritize Resistance Training: To signal your body to keep (or even build) muscle, you need to use those muscles. Strength training is the most direct way to stimulate muscle fibers. When you challenge your muscles, you give your body a reason to hold onto them. Aim for at least 2–3 sessions of resistance exercise per week covering all major muscle groups. If you’re new to it, start with bodyweight exercises or light weights and gradually increase intensity. The key is consistency. Studies show that incorporating regular strength training can significantly improve muscle retention during caloric restriction. The only way to prevent muscle loss somewhat while losing weight is to combine exercise with a higher-protein diet. Don’t rely solely on the medication to do the work. You have to “use it or lose it” when it comes to muscle. Consider adding some aerobic exercise as well, as it’s great for overall health, but resistance exercise is king for muscle preservation.

2. Eat Enough Protein: GLP-1 drugs often blunt your appetite, which can be a double-edged sword. It helps you eat less, but it might also make it harder to get all the nutrients you need. Protein is the most critical macronutrient for muscle maintenance. Ensure you’re consuming sufficient protein each day, spread across your meals. Good sources include lean meats, poultry, fish, eggs, low-fat dairy, legumes, tofu, and protein supplements if needed. Exactly how much protein one needs can vary, but a standard guideline during weight loss is about 1.2–1.5 grams of protein per kilogram of body weight per day. For example, a 90 kg person might aim for roughly 110–135 grams of protein daily when trying to preserve muscle. Adequate protein provides the building blocks your muscles require to repair and maintain themselves, especially when you’re eating at a calorie deficit. Don’t forget overall nutrition and calories. Extremely aggressive calorie cuts can force the body to break down muscle for energy. With GLP-1 drugs, you may naturally eat much less, so make sure the calories you do eat are rich in protein and micronutrients. Hydration is also important, since dehydration can affect muscle performance and measurements.

3. Monitor Strength and Functional Performance: One practical way to measure if you’re preserving muscle is to track your strength or performance in everyday activities. Are you able to lift the same weights or even make progress in the gym? Is getting up from a chair, climbing stairs, or carrying groceries feeling easier, or at least not harder, as you lose weight? Ideally, you want to lose weight and gain health, not lose your ability to stay active. Some doctors measure grip strength or walking speed in patients as rough indicators of muscle function. These should remain steady or improve as fat is lost. If you notice significant drops in strength or energy, it’s a sign you may need to adjust your regimen.

4. Avoid Crash Dieting Mentality: While the GLP-1 medication will help control your appetite, it’s still possible to under-eat protein or under-use your muscles if you’re not careful. Avoid the trap of thinking the drug alone will magically sculpt you. A speedy rate of weight loss or very low intake can cause disproportionate muscle loss. It might be tempting to eat as little as possible, but remember that the goal is sustainable fat loss. Losing weight more gradually and deliberately will yield a better outcome than simply focusing on how quickly the scale can drop.

By following these steps, you can effectively create a scenario akin to a GLP-1 for body recomposition. Many individuals on GLP-1 therapy who incorporate weight training and sufficient protein intake find that they not only lose substantial fat but also maintain or even increase their lean mass.

Tracking Your Body Composition with DEXA Scans

The best way to track muscle loss is to use body composition measurements. One gold-standard method is a DEXA scan. A DEXA body composition scan (DEXA stands for Dual-Energy X-ray Absorptiometry) is essentially a specialized body fat scan that can distinguish between bone, lean tissue, and fat tissue across your entire body. In a quick, non-invasive procedure, you get a detailed report of your body fat percentage, lean mass, and even visceral fat levels. A DEXA scan is a fast and highly accurate way to measure body composition, providing detailed insights into your body fat percentage and lean muscle mass in just minutes. This means you can literally see how much fat you’ve lost and whether your muscle mass is staying steady.

During a full-body fat scan via DEXA, you lie on a table while a machine scans your body. The result is a report breaking down how many pounds (or kilograms) of fat mass and lean mass you have, and where. For example, you’ll see fat vs. muscle distribution in your arms, legs, trunk, etc., and often a calculation of visceral fat in the abdominal region. Visceral fat is the “deep” fat around your organs, and DEXA can estimate it. It performs a DEXA scan for visceral fat as part of the analysis. Tracking these metrics over time is incredibly useful. If you do a DEXA scan before starting GLP-1 therapy and then repeat it a few months into treatment, you can objectively tell how much fat you’ve lost and whether you’ve lost any lean mass. Ideally, you want to see your fat mass dropping while lean mass stays the same or even rises slightly. If the scan shows you’re losing significant lean mass, that’s a cue to intensify your muscle-preserving efforts. It takes the guesswork out of recomposition. You have numbers to guide you.

Other methods for measuring body composition include bioelectrical impedance scales and handheld devices. These can give rough estimates of body fat%, though their accuracy is lower than DEXA. Skinfold calipers and circumference measurements can also be used by professionals to estimate changes in fat vs. muscle. But DEXA remains a best-in-class tool for precision. It’s often used in research for this reason. Keep in mind, DEXA scans are not typically an everyday measurement, but even periodic scans can validate that your plan is working or warn you if adjustments are needed.

At BOD, for example, clients can get a comprehensive DEXA body composition analysis in about a 6-minute scan. Such a full-body fat scan provides a baseline and ongoing checkpoints for anyone on a weight loss journey. The detailed report doesn’t lie. You’ll see if your biceps have lost muscle or if that belly fat is shrinking. A service like BOD’s can even track subtle changes, helping you and your healthcare team make informed decisions. Using a DEXA scan for body fat and muscle tracking is empowering, as it shifts the focus from “What is my total weight today?” to “What is my fat weight and my muscle weight today?” This is precisely what we care about when using GLP-1 drugs for healthy weight loss.

Don’t hesitate to measure progress with tools beyond the bathroom scale. Seeing improvements in your fat-to-muscle ratio can be highly motivating. You might find that even if the scale slows down, your fat loss is continuing and your muscle percentage is increasing, which is a significant win. And if the data isn’t as good as hoped, you have an early warning to change course. Knowledge is power, and a DEXA scan provides very actionable knowledge about your body.

GLP-1 agonist medications have revolutionized weight loss, enabling many people to lose a substantial amount of body fat and improve their health. But it’s crucial to remember that weight loss quality matters just as much as quantity. Even the best GLP-1 agonist for weight loss won’t automatically yield a healthy outcome if you lose muscle indiscriminately. The ultimate goal is a better body composition and better overall fitness. By prioritizing lean muscle preservation through resistance exercise, adequate protein intake, and smart tracking, you can ensure that your transformation is truly positive. Think of it this way: you want to lose weight and gain health, not trade one set of problems for another.

Successful weight loss with GLP-1 drugs isn’t just about losing. It’s also about gaining. Gaining strength, gaining metabolic health, and gaining knowledge of your body. With the right approach, you can harness the powerful fat-loss effects of these medications for body recomposition, meaning a healthier fat-to-muscle ratio. You’ll look better, feel stronger, and set yourself up for long-term success. A healthier you is not defined by the scale alone, but by the quality of your weight loss. Lose the fat, keep the muscle, and you’ll truly transform your body for the better.

Sources

• news.harvard.edu Harvard Gazette – “Losing fat is good, but losing muscle isn’t”, March 18, 2024.

• drugs.com Drugs.com – Does Ozempic cause muscle loss and how to prevent it?, medically reviewed Aug 19, 2025.

• pubmed.ncbi.nlm.nih.gov Aronne et al., New England Journal of Medicine – Tirzepatide vs. Semaglutide for obesity, 2025.

• easo.org EASO (ECO 2023) – New analysis shows improved body composition with tirzepatide across age groups, May 21, 2023.

• scientificamerican.com Scientific American (The Conversation) – “Why You Don’t Just Lose Fat When You’re on a Diet”, by Adam Collins, Sept 22, 2022.

• health.ucdavis.edu UC Davis Health – “DXA Body Composition Analysis” (Sports Medicine program overview).