What you’re REALLY losing on GLP-1s · Mind and Body Solutions

What you’re REALLY losing on GLP-1s

One in eight American adults (almost 6% of all American adults, about 15 million people) has tried a GLP-1.

I can see why.

You inject yourself once a week. You lose weight. Your life gets easier.

What they do, mechanistically, is mimic an incretin hormone (GLP-1) that your gut releases when you eat.

This suppresses appetite, slows gastric emptying, and increases insulin response. You lose weight because you don’t feel like eating.

But nothing in life is that simple. When people lose weight on a GLP-1, roughly 25-40% of what they lose isn't fat…

It's lean mass. Muscle, bone, and organ tissue.

The STEP 1 trial of semaglutide (the trial that led to the drug's approval for weight loss) showed that lean mass accounted for about 45% of total weight loss.

SURMOUNT-1 with tirzepatide put it closer to 25-35%. Liraglutide (the earlier-generation GLP-1) ran as high as 60% in some studies.

Some GLP-1 defenders say that every weight-loss method causes some lean tissue loss. Diet, exercise, bariatric surgery, all of them.

True. But there are two things wrong with that defense.

First, GLP-1s cause a higher proportion of lean tissue lost than most other methods, especially when users don’t do resistance training or eat enough protein (most aren't since the drugs suppress appetite).

Second (and this is the thing nobody's talking about), losing that much lean tissue while trying to fix metabolic dysfunction accelerates the underlying problem.

Here's why…

Muscle is the most metabolically active tissue in your body. It burns calories at rest and absorbs glucose. It's where insulin sensitivity lives.

Lose 5-7 kg of lean mass (what semaglutide users averaged in STEP 1), and your resting metabolic rate drops. This hampers your ability to burn glucose. Insulin sensitivity worsens.

Less muscle also means less exercise capacity. You lift less, walk less, and push less in the gym, burning fewer calories with exercise and stagnating in your fitness goals.

And then there’s bone loss.

A 52-week semaglutide trial showed a 2.6% drop in hip bone mineral density and a 2.1% drop in lumbar spine bone mineral density versus placebo. A 146,000-patient analysis presented at the American Academy of Orthopedic Surgeons in 2026 showed a 30% increase in osteoporosis risk with GLP-1s and a doubling of osteomalacia rates, a bone-softening disease.

Picture the demographic most affected: Women aged 50-64. The single highest GLP-1 user group is also the demographic most vulnerable to osteoporosis.

Once you understand why this happens, you’ll see it isn't unique to GLP-1s.

This is why the rebound happens.

In the STEP 1 extension trial, semaglutide users lost an average of 17.3% of their body weight after 68 weeks on the drug. Then the drug was stopped.

They regained ⅔ of what they'd lost within a year of stopping. About 18% regained ALL weight, or more. Cardiometabolic improvements (blood pressure, blood sugar, lipids) reverted toward baseline (Wilding et al., 2022).

STEP 4 showed the same pattern. SURMOUNT extensions showed similar trajectories.

Fat returns. Lean mass does not exist without the factors that build it (protein + resistance training). Most don't do that. They end up weighing the same (or more) than they did at the start, with worse body composition. Less muscle, weaker bones, and a higher fat percentage.

We put 15 million people on these. Why aren't doctors saying any of this?

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What you’re REALLY losing on GLP-1s