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A bombshell new clinical trial, published in June 2025
Lancet D&E, that gives us hard data on how the most exciting peptide in the world (Retatrutide) actually changes your body
composition. Let's breakdown what the study found, how it
compares to the other “big name” weight loss drugs to defend every last ounce of lean muscle, not just lose weight.
The Study
First, let’s get into the design.
The research team ran a gold-standard, double-blind, randomized controlled trial, including a DEXA substudy piggy backing off
the major retatrutide phase 2 trial for type 2 diabetes.
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Participants: Adults with type 2 diabetes and overweight or obesity.
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Intervention: They received weekly injections of retatrutide (at various doses, with 8 mg being the key “sweet spot”) and were
tracked for 36 weeks.
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What makes this study so critical is that they used DEXA scans to measure exactly
how much of the weight lost was fat, and how much was muscle.
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If you’ve ever dieted hard and watched your
muscles deflate, you know this is the million-dollar question in the world of weight loss.
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The control group included people on dulaglutide (a
GLP-1–only drug) and a placebo, so we could see how retatrutide really stacks up.
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The Results
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So, what did they find?
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At 36 weeks, participants taking 8 mg of retatrutide lost,
on average, a staggering 26.1% of their total fat mass (via DEXA).
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This was pure fat.
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And remember, these people are changing NOTHING about their
daily lives (other than just eating less because of the effects of the drug).
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The lean mass (“muscle”) loss was
approximately 20–40% of the total weight lost, meaning that a solid 60–80% of the weight loss was actual fat, not lean tissue.
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For comparison, the control group (on dulaglutide or
placebo) lost just a fraction of that.
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Placebo lost approximately –4.5% of their fat mass, while
dulaglutide lost about –2.6%.
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Retatrutide produced the largest absolute fat
loss ever recorded in an obesity/diabetes drug trial.
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And it did so with about the same lean mass preservation as
the “best” current drugs.
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Fat vs Muscle
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Every time you lose weight, even with the “miracle” GLP-1 drugs, some of it is going to be muscle, not just fat.
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The proportion matters.
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Losing too much muscle can tank your metabolism, weaken
your strength, and set you up for a rebound.
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Lose mostly fat, and you preserve your engine for the long
run.
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This 2025 DEXA study shows that the ratio of fat-to-muscle
loss is basically the same as you’d get with tirzepatide or semaglutide, but you
get way more total fat loss.
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In other words, retatrutide supercharges the process
without making the muscle loss any worse.
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This is a game-changer, especially for anyone who wants to
look, feel, and perform at their best.
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