GLP-1 Medications: What Happens When You’re On One

This post isn’t about whether you should take a GLP-1 medication, or my personal opinion on them. I’ll save that for another day.

What I want to talk about here is what happens once you start taking one.

Most people lose a significant amount of weight on these drugs. That sounds like good news—and in many ways, it is. But when I say “weight,” that doesn’t just mean fat. It also includes muscle and lean body mass.

Losing fat is good. Losing muscle is not.

Muscle is where a lot of the good happens in your body. It’s your largest reservoir for glucose. It gives you strength and stability as you age, helping you avoid injuries. And it’s one of the biggest predictors of longevity and quality of life. So when muscle mass goes down, so does your ability to stay strong, metabolically healthy, and independent.

How GLP-1s Reduce Appetite & Why That Matters for Macros

These medications work by suppressing your hunger, slowing gastric emptying, increasing feelings of fullness, and reducing the “food noise” in your brain (all good things in many respects). (Nature)

But that lower hunger can make it harder to eat enough total food—even more so enough of the right stuff like protein and fiber. When your appetite is reduced, you might naturally eat smaller meals, skip snacks, or avoid foods that fill you up but are more voluminous or fibrous. That’s where muscle loss risk increases if you’re not intentional.

That’s one of the reasons we created Andy’s Way. It’s a small, convenient amount of food designed to help you hit those aggressive protein targets and your daily fiber goals, without overwhelming your appetite.

How Much Muscle Loss Happens & How to Prevent It

  • Studies show that with GLP-1 receptor agonist (GLP-1 RA) therapy for obesity, up to 40% of total weight loss can come from fat-free mass (which includes muscle, water, organs, etc.). (PubMed)

  • In some cases, lean body mass loss ranges from 15-40% of the total weight lost, especially without protective measures. (PubMed)

What helps preserve muscle (and minimize loss of lean body mass) while on GLP-1s:

  1. Resistance training (strength work) → tell your muscles to stay. (PubMed)

  2. High protein intake → enough to support muscle repair and rebuild, especially since appetite is lowered. Some studies suggest more protein can significantly protect older adults and women on GLP-1s. (Endocrine Society)

  3. Consistent exercise + nutrition right from the start → not waiting until muscle loss becomes obvious. (Mass General Advances)

 


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