Losing weight isn’t just about watching the scale drop, because what you lose matters. The recent buzz around GLP-1 agonist medications (like semaglutide, known by brand names such as Ozempic® or Wegovy®) highlights a revolutionary approach to weight management. These drugs can trigger dramatic weight reduction by curbing appetite and slowing digestion. But as people celebrate shedding pounds with GLP-1, an important question arises: how is this weight loss affecting the body’s fat and muscle composition? And how can tools like a DEXA body fat scan play a role in tracking and optimizing these changes? In this article, we’ll explore the science of GLP-1 weight loss, its impact on body composition, and why measuring progress with a DEXA scan is so beneficial for anyone aiming to lose fat while preserving muscle.

What Is GLP-1 and How Does It Cause Weight Loss?

GLP-1 stands for glucagon-like peptide-1, a hormone our bodies naturally release in the gut in response to eating. It has multiple effects: it signals the pancreas to produce more insulin and, importantly for weight loss, it acts on the brain to suppress appetite and increase feelings of fullness. GLP-1 agonist medications mimic this hormone, dialing down hunger and helping people eat less. When combined with healthy diet and exercise habits, GLP-1 medications can lead to significant weight loss. Clinical trials of semaglutide showed striking results: over about 16 months, half of the participants lost 15% of their body weight, and nearly one-third lost 20% of their weight using the drug.

It’s no surprise that GLP-1 medications have surged in popularity as weight loss aids. They represent a new era of treating obesity as a chronic condition with medication, rather than relying solely on willpower. However, no weight loss method is a magic wand. While GLP-1 can dramatically cut weight, it’s important to understand what that weight loss is made of. Are those lost pounds coming mostly from body fat, or are we also losing a significant amount of muscle along the way? This is where GLP-1 and body composition become important to examine. To maintain long-term health, we want to ensure we’re losing fat while preserving as much lean muscle as possible.

Weight Loss and Muscle Loss: A Universal Challenge

Whether you lose weight through cutting calories, exercising more, taking GLP-1 medications, or any other method, one fact remains: whenever the number on the scale drops, you aren’t just losing fat. Some proportion of that weight loss will come from lean body mass, which includes muscle, water, and even a bit of bone. Weight loss and muscle loss often go hand-in-hand. This isn’t a quirk of GLP-1 alone, but a general rule of weight loss. Virtually all weight loss approaches universally induce the loss of lean body mass, even when you’re focusing on losing fat. Typically, when someone diets without specific strategies to protect muscle, about 1/4 of each pound lost tends to be from lean tissue and 3/4 from fat. This is sometimes called the “quarter rule” of weight loss.

Why does this happen? When you consume fewer calories than you burn, your body needs to tap into energy stores to make up the difference. Fat is a great energy reserve, but your body can’t convert fat into glucose to fuel the brain. Muscle, on the other hand, contains protein, which can be broken down into amino acids and then converted to glucose. Especially on a low-calorie or low-protein diet, the body will break down some muscle tissue to provide nutrients to the brain and other organs. A calorie deficit signals not just fat burning but also a bit of muscle catabolism. Our evolutionary biology has primed us to survive famine by using both fat and muscle for energy.

The result is that losing weight can, unfortunately, mean losing strength and metabolism-boosting muscle mass along with fat. This is a key reason doctors and dietitians harp on combining resistance exercise and high protein intake with any weight loss plan to try to minimize that muscle loss. The stakes are high. Muscle is not just for bodybuilders. It’s a metabolically active tissue that helps you burn calories at rest, stabilizes your joints and bones, and is vital for overall functional health. Losing too much muscle during weight loss can lead to fatigue, a slowdown in metabolism, and even an increased risk of injury or frailty. So, while seeing the scale number drop is exciting, we need to look under the hood at body composition to ensure the quality of the weight loss is good, which means losing fat and gaining muscle, or at least preserving muscle, to the greatest extent possible.

GLP-1 and Body Composition: Fat vs. Muscle Loss

The good news is that weight loss achieved with GLP-1 medications tends to come predominantly from body fat, including reductions in dangerous visceral fat. Patients on semaglutide, for instance, appear to lose a higher proportion of fat relative to muscle, which means their body fat percentage drops significantly.

However, this doesn’t mean muscle loss isn’t a concern on GLP-1. Remember, any substantial weight loss will take some lean mass with it, and GLP-1 is no exception. Because GLP-1 can lead to rapid and significant weight drops, in some cases, the amount of muscle lost can still be considerable if no countermeasures are taken. Clinical data show that lean body mass can account for up to 15–40% of the total weight lost when using GLP-1 therapies. For example, if someone loses 20 pounds on a GLP-1 medication, it’s possible that 3 to 8 of those pounds might be from lean tissue and the rest from fat. A range of 15–40% is quite broad, and where an individual falls in that range depends on factors like their diet, protein intake, exercise routine, age, and starting body composition. Someone who doesn’t exercise and eats very little protein while on a GLP-1 drug could lose a high proportion of muscle. On the other hand, a person who engages in resistance training and keeps their protein intake up might only have a small fraction of their weight loss come from muscle. GLP-1 weight loss monitoring is crucial. Patients and providers should track not just how much weight is lost, but what is being lost.

Personalized Care Adjustments Based on DEXA Results

One must know how healthcare providers might use DEXA scan data to tailor and optimize weight loss strategies and overall care plans for individuals on GLP-1 medications. A high-protein, nutrient-rich eating plan can be considered a diet for muscle gain and fat loss. When you consume ample protein, you give your body the amino acids it needs to repair and maintain muscle tissue, even in a calorie deficit. Protein also has a high thermic effect, and it promotes satiety, which can help when your appetite is suppressed on GLP-1. Additionally, adequate protein can help prevent excessive bone density loss during weight loss, which is another concern for some individuals.

When you challenge your muscles through exercise, you stimulate muscle protein synthesis and essentially tell your body, “Hey, I need this muscle tissue for daily activities, don’t use it as fuel!” Even doing full-body strength training 2–3 times per week can make a significant difference in preserving lean mass. People on GLP-1 might find it easier to incorporate exercise as they lose weight and feel lighter on their feet, but early on, some report fatigue or low energy intake that can make workouts challenging.

One more factor to consider is hydration and electrolyte balance. Sometimes what appears as lean mass loss on a scale or basic bio-impedance device is actually water fluctuation. Ensuring you stay well-hydrated and possibly supplementing electrolytes if you’re eating much less will help maintain proper fluid balance in muscle tissue. This isn’t a direct way to prevent muscle protein loss, but it can prevent misleading weight drops due to water loss and help keep your muscles functioning optimally.

Visceral Fat: The Hidden Risk (and Reward of GLP-1)

Not all fat is created equal. When we talk about losing fat for health, the type of fat that often matters most is visceral fat – the fat that accumulates deep in your abdomen around your internal organs (liver, pancreas, intestines, etc.). This “belly fat” is metabolically active and can secrete inflammatory hormones. High visceral fat is strongly linked to increased risks of heart disease, type 2 diabetes, and other metabolic problems. Reducing visceral fat can significantly improve health markers like blood pressure, blood sugar control, and cholesterol levels.

From a health perspective, this visceral fat loss is a huge win. For example, cutting visceral fat can reduce fatty liver issues, lower inflammation, and even potentially decrease the risk of certain cancers associated with obesity. However, how do you know you’re losing visceral fat? This isn’t something a regular scale or even a measuring tape can fully tell you. That’s where a visceral fat scan comes into play.

Preventing the 'Skinny Fat' Phenomenon

Losing weight on GLP-1 medications can sometimes result in a lower number on the scale but a persistently high body fat percentage, a condition often called being “skinny fat.” This happens when muscle mass is lost alongside fat, leaving the body leaner but still with excess fat relative to muscle. DEXA scans are invaluable for detecting this imbalance, as they provide a detailed breakdown of fat and lean tissue.

What Is a DEXA Body Composition Scan?

One gold-standard tool for this purpose is the DEXA body composition scan (DEXA stands for Dual-Energy X-ray Absorptiometry). Originally developed to measure bone density, DEXA technology has become a body mass scan that can quantitatively measure fat, lean tissue, and bone in different regions of your body.

Here’s How It Works

You lie down fully clothed on the DEXA machine table, and a scanning arm passes over your body. It sends two low-dose X-ray beams at different energy levels through your body. Different tissues absorb X-rays to different extents. Bone absorbs the most, fat and muscle absorb differently as well. By using two energy levels, the machine can distinguish between bone and soft tissue, and then, within soft tissue, it can differentiate fat vs. lean based on the absorption profiles. The scan is painless, quick, and the radiation exposure is extremely low.

What results do you get from a DEXA scan? You receive a detailed report of your body composition: your total body fat percentage, total fat mass in pounds (or kg), total lean mass, and bone mineral content. Even more useful, it provides a segmental analysis. Breaking down these metrics by body region. For instance, you can learn how much fat vs. muscle you have in your left arm versus your right arm, or how your leg composition compares to your torso. The DEXA also estimates visceral fat specifically by looking at the deeper abdominal area. In other words, it’s not just a fat-versus-muscle test, but a visceral fat scan as well, pinpointing the amount of fat surrounding your organs. All this information is invaluable to someone on a weight-loss or fitness journey. It’s like taking a flashlight and shining it inside your body to see exactly where things stand.

A DEXA body composition analysis is a quick, safe imaging test that tells you exactly how much fat and muscle you have and where. It’s like getting a full report card on your body composition. If you’re serious about monitoring your progress in monitoring fat and muscle, DEXA is one of the best tools you can have in your arsenal.

How to Track Weight Loss Progress

Most people measure their weight-loss success by the scale or by how their clothes fit. While those are useful to a point, they don’t tell the full story. Let’s break down the benefits of using DEXA scans to track progress:

• See the Quality of Weight Loss: A regular scale simply gives one number: total weight. A DEXA scan, on the other hand, shows how much of that weight is fat, lean tissue, and bone. When you’re losing weight, you can use sequential DEXA scans to ensure that most of the weight you’re losing is fat. DEXA allows GLP-1 weight loss monitoring at a granular level – beyond just “X pounds lost,” it tells you “X pounds of fat lost, Y pounds of muscle lost/gained.”

• Track Regional Changes: Maybe you started doing strength training, and you wonder if you’re building muscle in your legs or arms while losing fat in your belly. A DEXA can answer that. It might show, for instance, that you gained a pound of lean mass in your legs while losing 3 pounds of fat from your abdominal region. This level of detail is incredibly motivating and can validate that your exercise routine is working even if your total weight hasn’t changed dramatically. You could be recomposing, losing fat and gaining muscle at the same time, which might make your scale weight plateau, but DEXA will reveal the positive changes happening underneath. Without a DEXA, many people might get discouraged by a static scale reading, not realizing they’ve traded 5 pounds of fat for 5 pounds of muscle.

• Objective Accountability: Scheduling periodic DEXA scans creates accountability beyond the scale. Knowing that you have an upcoming scan can motivate you to stick to your nutrition and exercise plan, because you’re excited to see the changes in your report. It’s common for folks to treat a DEXA scan as an objective check-in that keeps them honest. This can be both sobering and encouraging. If the results aren’t what you hoped, it’s a clear signal to reassess habits. If they’re great, it’s a confidence boost to continue.

• Avoiding Misleading Metrics: We’ve all heard of BMI (Body Mass Index) and how it can label a very muscular person as “overweight” because it doesn’t distinguish muscle from fat. Similarly, a weight scale can mislead when you’ve got changes in muscle or hydration. By using a DEXA scan scale approach, you avoid those pitfalls.

Explores recommendations for how often individuals on GLP-1 medications should undergo DEXA scans to monitor changes in body composition effectively. For individuals using GLP-1 medications, experts generally recommend undergoing a DEXA scan before starting treatment to establish a baseline for body composition. After initiation, follow-up scans are typically recommended every 3 to 6 months to monitor changes in fat and muscle mass. This interval allows for timely detection of unwanted muscle loss or other body composition shifts, enabling early adjustments to diet, exercise, or medication. In cases of rapid weight loss or specific health concerns, more frequent scans may be appropriate, based on your healthcare provider’s guidance.

DEXA scans are becoming more widely available and affordable. There are medical imaging centers, sports performance labs, and wellness clinics like BOD that offer DEXA body composition scans to the public. The cost can range from perhaps $50 to $150 per scan, and sometimes packages are available for multiple scans. Considering the wealth of information you get, many find it a worthy investment in their health tracking.

At the end of the day, it’s not just about weighing less. It’s about living more. With GLP-1 therapies helping to peel away unhealthy fat, and DEXA scan scale insights guiding you to preserve what’s precious, you have a powerful combination to ensure your weight loss is effective and empowering. Here’s to a healthier body and a smarter way to reach your goals!

Sources

• Mass General Advances in Motion – “Preserving Lean Body Mass in Patients Taking GLP-1 for Weight Loss” (June 6, 2025)

• American Diabetes Association – “New GLP-1 Therapies Enhance Quality of Weight Loss by Improving Muscle Preservation” (Press Release, June 23, 2025)

• UCLA Health – “Semaglutide for weight loss – what you need to know” (January 12, 2023)

• Sokary S., Bawadi H. – “Exploring beyond numeric weight loss: The metabolic effects of semaglutide”, Clinical Nutrition ESPEN 67:435-440 (2025)

• Iowa Radiology – “Should I Wait to Get Body Composition Analysis Until I’m Done with My Diet?” (Jan 17, 2025)