Why DEXA Scans Matter When Using GLP-1 Medications

GLP-1 medications can be an incredibly effective tool for weight management, but the number on the scales only tells you how much weight you have lost — not what you have lost.

This is where a DEXA body composition scan can be valuable. When losing weight, we want to see a reduction in body fat, while maintaining as much lean tissue as possible. DEXA allows us to look beyond total body weight and measure changes in fat mass, lean mass and visceral fat.

Why does this matter with GLP-1s?

GLP-1 medications can significantly reduce appetite and food intake. While this can help with fat loss, eating substantially less can also make it harder to meet your protein and overall nutritional requirements.

Some loss of lean mass can occur during weight loss, but remember that DEXA lean mass is not the same as muscle mass. Lean mass also includes water and other non-fat tissues.

Don't scan too soon

For some people, we recommend waiting approximately 2 weeks after starting a GLP-1 before having your baseline DEXA. The initial weight loss can partly reflect changes in fluid, glycogen and the amount of food in your digestive system, rather than just body fat. Because DEXA-measured lean tissue includes water, a reduction in hydration can appear as a reduction in lean mass on the scan. Having less food in the digestive tract can also influence the measurement. Everyone responds differently. Some people experience a noticeable initial drop in fluid and weight, while others don't.

What if the scales stop moving?

Many people starting a GLP-1 also decide to start exercising, particularly resistance training, at the same time. You may reach a point where the scales appear to stop moving — but that doesn't necessarily mean nothing is happening. You could be losing body fat while gaining lean tissue. Your body composition can therefore be improving even when your total body weight has barely changed. This is one of the reasons we don't want to judge progress using the scales alone.

What happens when you come off the medication?

Maintaining muscle throughout your weight-loss journey is important for more than just strength and physical function. Muscle is metabolically active tissue, so losing a significant amount of muscle can reduce your resting energy expenditure. If you then regain weight after stopping a medication, having less muscle and a lower energy expenditure can make it easier to regain body fat. This is why protecting muscle during weight loss matters, not just while you are taking the medication, but for what happens afterwards.

Look beyond the scales

Two people could both lose 10 kg, but their results could look very different on a DEXA. One may have lost mostly body fat while maintaining their lean mass. Another may have lost considerably more lean tissue.

Both weigh 10 kg less — but the outcomes aren't the same.

The goal isn't simply to become lighter. The goal is to lose excess body fat while protecting muscle, strength and long-term health. A DEXA gives us another piece of the puzzle — helping us understand not just how much weight you've lost, but what is changing underneath the scales.

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