On a GLP-1? The Number on the Scale Isn't Telling You What You're Actually Losing
You step on the scale, the number's dropping, and it feels like winning. But weight loss on a GLP-1 isn't one thing it's fat loss and muscle loss happening at the same time, and for a lot of women, more of the second than they'd choose if anyone told them it was optional.
The mechanism, and why protein goes first
GLP-1 medications work by suppressing appetite that's the entire point, and it's why they're so effective. But appetite suppression doesn't ration food evenly. When intake drops, protein is usually the first thing to go, because it takes more effort to source, cook and chew than the carbohydrate-heavy, low-effort foods that survive a low-appetite day.
That matters because protein is the one macronutrient your muscle depends on to maintain itself. Take it away while you're in a calorie deficit, and your body doesn't just burn fat it starts breaking down muscle tissue too.
The data most people aren't shown
This isn't a fringe concern. A 2024 systematic review and network meta-analysis of GLP-1 receptor agonists found lean mass loss made up roughly a quarter of total weight lost across the trials analysed.¹ Other trial data on semaglutide specifically has put that figure as high as 40%² ³, and a 2025 case-series review in the sports medicine literature described a range of 26–40% of weight lost as lean tissue across recent trials.⁴ Put simply: for every 4kg lost, somewhere between 1kg and 1.6kg of that can be muscle, not fat and the proportion varies person to person depending on diet, training and the specific medication used.
Why this lands harder for women
Women start the process with a disadvantage: lower baseline muscle mass than men, and an accelerated rate of muscle loss around and after the menopause transition. A 2025 joint clinical advisory from the American College of Lifestyle Medicine, American Society for Nutrition, Obesity Medicine Association and The Obesity Society specifically named perimenopausal and menopausal status, alongside lower testosterone and low physical activity, as factors that raise the risk of muscle loss on these medications.⁵
Muscle isn't just about strength or appearance. It's what protects your resting metabolic rate, supports bone density, and determines how your body holds weight once you eventually reduce or come off the medication. Lose too much of it, and you're not just smaller you're more metabolically fragile than when you started.
The fix isn't complicated, it's just non-negotiable
The clinical literature on this is consistent, and it comes down to three things:
- Anchor a daily protein target. Expert consensus and narrative reviews on GLP-1 nutrition converge on roughly 1.2–1.6g of protein per kilogram of body weight per day during active weight loss, spread across meals rather than back-loaded into one sitting.⁶ ⁷ ⁸ On a low-appetite day, small, frequent, protein-first eating will get you closer to target than trying to force down a large meal.
- Resistance train at least twice a week. The medication creates the calorie deficit; resistance training is what tells your body which tissue to keep. Multiple reviews now list structured resistance training, alongside adequate protein, as the best-established strategy for preserving lean mass on GLP-1 therapy.⁴ ⁹
- Watch the quiet micronutrient gaps. When overall intake falls, it's not just protein that slips but iron, B12, and other micronutrients commonly monitored in GLP-1 care can fall alongside it, particularly in patients eating significantly less than before.¹⁰ A 2026 narrative review on medical nutrition in the GLP-1 era recommends a structured lab panel including vitamin D, B12, iron studies, folate, zinc and thiamine in higher-risk patients as part of ongoing monitoring.¹⁰ This is where a well-formulated supplement earns its place: filling documented gaps, not replacing food.
What just changed: GLP-1s now come as a tablet
In June 2026, the MHRA approved the UK's first oral GLP-1 tablet for weight management a once-daily semaglutide tablet (Wegovy), the same active ingredient as the injectable version, licensed for adults with a BMI of 30 or above, or 27–30 with a weight-related comorbidity.¹¹ Dosing starts at 1.5mg and titrates up to 4mg, 9mg and 25mg, with at least a month at each level.¹¹
The detail worth knowing if you're considering it: the tablet has to be taken on an empty stomach after at least 8 hours of fasting, with only a small sip of water, and no food, drink or other oral medication for at least 30 minutes afterwards as absorption depends on it.¹¹ That means your morning coffee, your supplements and your breakfast all need re-sequencing around the tablet, not the other way round.
Pill or pen, the fundamentals don't change. The medication still creates the appetite suppression. Protein, resistance training and micronutrient coverage are still what decide whether the weight you lose is mostly fat, or a meaningful chunk of muscle you'll wish you'd kept.
Want to know how much protein you actually need? Try out personalised protein calculator for women.
Written by: Dr Jo Mennie | Co-Founder & Women's Health Medical & Research Doctor
