The muscle tax: are weight loss drugs making you weaker?

Before GLP-1 medications such as Wegovy and Mounjaro arrived, losing weight was often viewed as a simple equation: eat less, move more and watch the kilos disappear. But as the popularity of the drugs has soared, a more nuanced conversation has emerged. The number on the scales tells only part of the story. What really matters is what you're losing.

For active men and women alike, that's become an increasingly important distinction. Muscle isn't just something that fills out a T-shirt or powers a PB in the gym. It's one of the body's most metabolically active tissues, helping regulate blood sugar, maintain strength and mobility, support healthy ageing and determine how many calories we burn at rest. Lose too much of it, and the benefits of weight loss can come at an unexpected cost.

Some reports, such as those published in the medical journal The Lancet, have suggested that as much as 40 per cent of the weight lost on GLP-1 medications may come from lean tissue.

While that doesn't necessarily mean half your weight loss is muscle – lean mass also includes water and other tissues – it has sparked an important question. Can you lose fat without paying a ‘muscle tax’?

According to functional nutrition practitioner and certified menopause specialist Cindi Stickle, the answer is yes – but only if people understand that GLP-1 medications don't replace good nutrition or exercise. "The biggest mistake I see is that women assume eating less automatically equals better results," she says. "GLP-1 medications reduce appetite, but they don't reduce the body's need for nutrients."

Although Stickle specialises in supporting women through perimenopause, many of the challenges she sees apply equally to active people using GLP-1 medications. The drugs make it easier to eat less, but they don't reduce the body's need to recover from training, repair damaged muscle or maintain lean tissue. In fact, that's where many people unintentionally come unstuck.

Appetite isn't the same as nutrition

One of the defining features of GLP-1 medications is appetite suppression. For many people, that's precisely why they work so well. Hunger is reduced, portion sizes naturally shrink and maintaining a calorie deficit suddenly feels achievable. The problem, says Stickle, is that appetite and nutritional requirements are two very different things.

"Many women end up eating only one or two small meals a day and struggle to meet even half of their daily protein needs," she explains. "When protein intake drops and total calories become too low, the body doesn't just use stored fat for fuel. It can also break down muscle tissue."

She regularly sees clients skipping meals because they simply don't feel hungry, relying on convenience foods because they're easier to tolerate, or avoiding protein-rich foods altogether because meat, eggs or dairy are often the hardest foods to eat when appetite is suppressed.

Those habits may accelerate weight loss, but they also increase the risk that some of the weight disappearing isn't body fat at all. The consequences can appear surprisingly quickly.

"Energy levels can begin to decline anywhere from a few days to a few weeks after consistently under-fuelling," says Stickle. "Muscle loss develops more gradually but can begin surprisingly early during weight loss if protein intake and resistance training aren't prioritised."

In short, successful fat loss requires more than simply eating less. "The body still needs enough protein and nutrition to preserve lean muscle."

Is muscle loss inevitable?

Stories about muscle loss have prompted concern among people considering GLP-1 medications, but Stickle believes much of the discussion misses an important point. "I don't believe muscle loss is an inevitable consequence of taking GLP-1 medications," she says. "Some loss of lean mass commonly occurs during any significant weight loss, but how much muscle someone loses is heavily influenced by lifestyle."

In other words, the medication isn't solely responsible. Instead, it's the behaviours that often accompany treatment that determine whether the body hangs on to muscle or sacrifices it.

"The women who tend to preserve the most muscle are the ones who prioritise adequate protein, perform regular resistance training, stay hydrated and avoid chronic under-fuelling," she says. That's an important distinction because it shifts the focus away from blaming the medication itself. "The reduced appetite it creates often leads people to unintentionally eat too little, especially too little protein, and many aren't strength training consistently," Stickle explains.

For women in perimenopause, the challenge is even greater because declining oestrogen naturally accelerates age-related muscle loss. But the underlying lesson extends well beyond menopause. "Whether someone is an athlete or simply exercises regularly, reduced appetite doesn't reduce recovery needs," she says. "They still need enough protein, enough total calories and progressive resistance training to support performance, recovery and preserve lean tissue."

For cyclists, runners and regular gym-goers, that may mean paying even closer attention to nutrition than before starting treatment. Training creates the stimulus that tells the body to retain muscle; protein provides the raw materials to repair it. Remove either, and the body has less reason – or ability – to maintain lean tissue while weight is falling. As Stickle puts it: "GLP-1 medications are powerful tools, but nutrition and exercise determine whether the weight lost is primarily fat or includes a significant amount of muscle."

How to beat the muscle tax

Muscle loss isn't inevitable and while GLP-1 medications create the conditions in which it can happen, experts agree that a combination of smart nutrition and resistance exercise can dramatically shift the balance towards fat loss instead.

For Jemma Cooke, specialist nurse and nursing director at Weight Medics, there are three non-negotiables. "My priorities are protein, strength training and avoiding extreme calorie restriction," she says. "Patients who follow those three principles tend to see much better changes in body composition rather than 'just' a lower number on the scales."

Her recommendation is for people using GLP-1 medications to aim for around 1.2-1.6g of protein per kilogram of body weight each day, spread across meals rather than consumed in one sitting. Just as importantly, strength training should remain part of the weekly routine, even if body weight is falling rapidly.

"Twice-weekly strength training at minimum, focusing on large compound movements for the legs, back and upper body, provides the stimulus your body needs to retain muscle," she says. Crash dieting on top of appetite-suppressing medication is where problems often begin.

"People think eating as little as possible will maximise results, but an aggressive calorie deficit increases the risk of losing lean tissue alongside fat." Cooke is also keen to move people away from judging success purely by the scales.

"The scale is a very blunt tool," she says. "It doesn't tell you whether you're losing fat or muscle, nor does it capture the real changes happening in your body." Instead, she encourages patients to monitor waist measurements alongside simple performance markers such as press-up numbers, grip strength or how much weight they can squat. Even paying attention to everyday function can provide useful feedback.

"Can you climb stairs without getting winded? Are you stronger than you were last month? That's real progress." Likewise, rapid weight loss accompanied by persistent fatigue, declining gym performance or finding everyday tasks unexpectedly difficult should all raise concerns.

"If someone's losing weight rapidly but also reporting disproportionate fatigue or weakness, or they're struggling with their usual training loads, that's telling me they might be losing muscle alongside fat," says Cooke. "That's the point to review protein intake, exercise and, in some cases, even slow the rate of weight loss."

As GLP-1 medications become an increasingly common part of obesity treatment, both Cooke and Stickle believe the conversation needs to evolve beyond simply prescribing injections and celebrating kilograms lost.

"I think every patient starting these medications should receive clear guidance from day one," says Cooke. "That means talking about protein targets, giving them strength-training basics and teaching them to monitor how their body actually functions rather than fixating on the scale."

Ultimately, the real measure of success isn't simply becoming lighter. It's losing fat while preserving the muscle that supports strength, performance and long-term health.

Rob Kemp is co-author of BURNING UP, FROZEN OUT: What Every Man Needs to Know About the Menopause (But No One Told You)  (Sheldon Press, £16.99).

source https://www.bbcgoodfood.com/health/weight-loss/the-muscle-tax-are-weight-loss-drugs-making-you-weaker