GLP-1s, Muscle & Metabolic Health

In the 2010s I saw a shift. And I loved it. Teenage girls were in the gym lifting weights. As a physio, teen patients were asking me how they could get strong. And slowly more and more people were talking about the importance of strength and muscle in menopause and old age.

We shifted out of the era of the ultra-thin fashion model. Extreme thinness wasn’t held up as the only beauty standard that mattered.

Women were getting stronger. Owning their space. And you could see it in how they moved.

And then Ozempic happened. To be fair, drugs like this have been around for decades (more below), but they seemed to explode into the mainstream overnight. And suddenly “ballet fit” was a thing. Thinness as a sign of status.

It slowly crept into my practice. Patients disclosing after several sessions that they’ve been on GLP-1s for 4 months. The goal? Weight loss.

And then the Super Bowl LX final on 8 February 2026. And an ad for the telehealth platform Ro featuring Serena Williams talking about using GLP-1s to lose 34lbs of weight.

And I…felt like I’d been punched in the gut. I watched a woman who had dominated the tennis world, and I couldn’t help feeling that the message being celebrated was that losing weight somehow made her more worthy.

Yes, skinny is having a moment again.

And as a healthcare professional I’m disappointed. And frustrated! Because metabolic health really matters. GLP-1 agonists are important medications. But right now so many people see them as simply a way to lose weight.

But have they stopped to ask why they want to lose weight? Or even if it will be beneficial for their health?

For many people living with diabetes or severe obesity, these medications are genuinely transformative. This isn’t an argument against GLP-1 agonists. It’s an argument for using them in a way that protects long-term health.

I don’t think the GLP-1 conversation should be about weight or size at all. I think it should be about health.

This is a theory-heavy post. I think it is helpful to understand all this! But if you’re just here for the practical bit…the top tips I give my physiotherapy patients are at the end of the post. No hard feelings if you jump straight there. I’ve included references and further reading resources at the bottom too.

Metabolism, weight, and body-composition

Glucose, insulin, and muscle mass

Metabolism is complex and individual. It’s impacted by internal factors like hormones and gut health, and lifestyle factors like stress, movement, and dietary variety. But absolutely central to metabolism is energy and fuel.

We consume food which our body burns to create energy for life and movement. And the most basic unit that our bodies’ use to generate energy is glucose.

We eat a meal, food is broken down and released into the blood as glucose. This transports the glucose throughout the body to where the fuel is needed. But for the body to function well, blood glucose should sit within a certain range. As blood glucose level starts to rise, the body releases the hormone insulin, that binds to cell receptors and prompts glucose transporters to move to the cell surface, clearing sugar from the bloodstream. And the glucose is processed to be stored as an energy reserve for later.

Most of us remember this from high school biology. But one thing we probably weren’t told is that repeated, large swings in glucose and insulin levels are not great for our body over the long-term.

On the most basic level, repeated exposure to high insulin levels can make cells less responsive to insulin’s signal. The pancreas compensates by producing even more insulin (your base blood levels go up), but eventually this becomes less effective. This is called insulin resistance and is one of the key drivers of type 2 diabetes. Hormonal and metabolic changes in perimenopause or postmenopause can bring higher rates of insulin resistance.

It is also a key driver of cardiovascular disease. Over time, insulin resistance together with chronically elevated glucose and insulin levels contributes to systemic inflammation, changes in cholesterol levels (particularly increases in LDL cholesterol), hypertension, hardening of blood-vessel walls, and fatty liver disease.

Tip: Interestingly, when blood glucose goes up, contracting muscle can also prompt muscle to absorb glucose, independently of insulin. Contracting muscle almost acts as a sponge that absorbs excess glucose, meaning you have fewer glucose and insulin spikes. This mechanism works especially well if you move after a meal – going for a walk, or even moving around the kitchen and washing dishes!

The overall efficiency of your body in burning glucose as fuel also factors in to metabolism. Regular exercise helps to boost the efficiency of the system, promotes insulin sensitivity, and over time can build more lean muscle. Muscle is important in metabolism – it is metabolically active, contributing to overall energy expenditure, while also improving glucose handling and insulin sensitivity.

Here are some blood tests and medical measures that you might want to discuss with your doctor or healthcare provider to better understand the health of your metabolism and glucose systems:

Full lipogram
Fasting blood glucose
Haemoglobin A1c
Fasting insulin (not routine, but ask if it will be useful)
Inflammatory markers
Blood pressure
Waist circumference (importance explained in the next section)

If these all look good, pause to consider if treatment with a GLP-1 is necessary.

How, if at all, does weight factor in?

Glucose that isn’t needed for energy when you eat is converted into (primarily) glycogen or fat to be stored for use later. These are stored in different places in your body and serve as either easy access reserves or long-term reserves. Both are necessary and healthy. But let’s be real here. The conversation around GLP-1s is often about weight. So let’s look at fat and weight a little more closely.

We need fat for temperature regulation, nerve and brain health, hormonal production and health, bone marrow, and healthy cell membranes, among other functions.

Within research and healthcare circles, there are honest debate and disagreement about what, if any, a ‘healthy’ body fat percentage or BMI is. It is largely accepted that men typically have a slightly lower healthy body fat percentage range than women. And we know that fertility and hormonal health is impacted if a woman’s body fat percentage is too low for her unique body (but this varies a lot between people). We also know that morbid obesity puts strain on heart, lungs, and musculoskeletal system. But what about the vast range of sizes and weights in between?

Interestingly, what seems far more important than amount of body fat alone, is overall lifestyle and the distribution of body fat.

That seems like a big claim. But a person who is active, has balanced stress levels, and eats a healthy diet that doesn’t cause wild swings in blood sugar will often have good overall health metrics (blood pressure, cholesterol, inflammatory markers, etc) regardless of overall percentage of body fat.

The converse is also true. If you have a poor lifestyle, live on chocolate cake and Netflix, are lonely and stressed, you could have a BMI below 18 and still be ‘skinny-fat’ – having health metrics that show poor metabolic health that people often assume is related to overweight and obesity.

Poor lifestyle, and sometimes hormonal imbalance and genetics, can also contribute to visceral fat (fat that wraps around your internal organs). The whole-body changes in menopause can cause changes in weight distribution, including increased visceral fat. Visceral fat is often linked with insulin resistance, heart disease, inflammation, liver damage, and certain cancers. A simple, low cost check for visceral fat is waist circumference.

Basically, lifestyle trumps scale.

Weight loss in musculoskeletal health

As a physio, I rarely if ever counsel my patients to lose weight. Because, from what I’ve seen, it often does more psychological harm than physical good….and the existing evidence isn’t granular enough to back it up.

Why do I say the evidence for losing weight to improve pain is poor? If someone has pain and changes their lifestyle, the pain often responds, even if they haven’t lost weight. Within the medical community weight loss is often spoken about as an important factor in managing knee arthritis (and even certain knee injuries). People cite studies to support it. But none of these studies effectively differentiate between weight loss and the lifestyle changes that were made to achieve the weight loss.

Yes, there is an impact of joint strain. Our joints can carry multiples of body-weight of strain in certain activities. You can make a case that weight-loss can reduce some of that strain. But practically, with many musculoskeletal conditions, improving strength, movement confidence, and overall health can reduce pain regardless of whether significant weight loss occurs.

What do I suggest to my patients instead of promoting weight loss? I’d rather discuss everything that I’m writing about here. I’ll say it all day: lifestyle and function trumps the number on the scale.

Lifestyle and function trumps the number on the scale.

Calorie deficit and RED-S

There is one other aspect of weight management that is important to look at. Calorie restriction.

When people are trying to lose weight, the general recommendation is to be in ‘calorie deficit’ – less intake of energy than what you use or burn. But here you need to be extra careful. Our bodies need fuel to function. We use energy for breathing, digesting, pumping our heart, repairing, healing, growing new cells…

If you restrict too much, especially in combination with an active lifestyle, you can end up with a condition called RED-S (relative energy deficiency in sport). RED-S impacts every major system in your body, including cardiovascular and hormonal. But many people miss the fact that RED-S can impact them even if they aren’t elite athletes. Simply stated, you need to fuel your body adequately to live an active lifestyle. Otherwise your health pays the cost.

Diet restriction is also closely linked to stress fractures, low bone density, and osteopenia. Much more about bone health coming up next week, so we’re not double tapping on this here today.

Ok. That was a long framework. But a really important one! Let’s move on to look at GLP-1s.

What are GLP-1s?

GLP-1 (glucagon-like peptide-1) is a natural hormone produced in your small intestine after you eat. It regulates blood sugar, signals fullness to the brain, and slows digestion. Medications that mimic this hormone (called GLP-1 agonists) are used to treat Type 2 diabetes and obesity.

These drugs have been used in the management of diabetes for about 20 years. Which means that the class of medications isn’t brand new, but we are still learning about the long term effects and uses of them.

Here’s a little more info…

Natural GLP-1 lowers blood sugar by stimulating the pancreas to produce insulin in response to rising blood levels after a meal. It blocks the secretion of glucagon, so lowers the amount of sugar released by your liver. It slows the emptying of your stomach, which slows how quickly glucose is absorbed into your blood. And it is involved in satiety, the feeling of fullness, by acting on the areas in your brain that processes this.

GLP-1 agonists are either administered as sub-cutaneous injections, or can be taken as oral medication. The frequency of injectable medications varies between drugs, being administered from twice a day, daily, or weekly. Common drugs and well-known brands include semaglutide (Ozempic) and tirzepatide (Mounjaro, a dual action GLP-1/GIP).

These medications work on the biological drivers of blood sugar (stabilising blood sugar) and satiety, which can lead to reduced appetite and weight loss. Because the action is within the system itself, the effect usually only lasts while the drug is taken. They are typically prescribed over the long-term, and are only one part of the medical management plan. Lifestyle and diet is still very important.

Blood glucose is the marker we measure most often, but insulin sensitivity is one of the underlying physiological processes we’re trying to improve. GLP-1 agonists improve glucose regulation directly and can improve insulin sensitivity indirectly (through weight loss, reduced liver fat, and better metabolic function), but they don’t simply “fix” insulin resistance on their own. That’s where lifestyle is important. With all of the pieces in place, fasting insulin level may start to drop over time – which is the treatment effect that is hoped for.

Menopause: GLP-1s are increasingly being prescribed in menopause. Menopause involves a big shift in metabolism driven by hormonal changes. And with it come increased risks of cardiovascular disease. Track your health. And if you are concerned about your markers, discuss this with your gynae or endocrinologist. I’d suggest asking what they would recommend for your exact circumstances, and how menopause hormone replacement therapy (m-HRT) can possibly be used in conjunction with a GLP-1 to promote health.

GLP-1 agonists and obesity

The rise of treatment of obesity as a recognized, standalone medical condition is relatively new (recognised from 1997 by WHO and 2013 by AMA) and very complex. It involves medication, psychology, and lifestyle.

That said, obesity is not yet well understood from a health perspective. Classification and diagnosis are important for us to better study and understand the relationship between adiposity, environment, and health. It’s a tricky and complex issue because it’s closely linked to how people feel about themselves and engage with the world. And we do need to understand it better.

It’s helpful to remember that you have ‘pre-clinical obesity’ and ‘clinical obesity’, a stand-alone illness with demonstrated organ damage. Clinical obesity clearly needs treatment and support. And lifestyle change benefits both.

The cultural rise of GLP-1 agonist use for weight loss is impacting the narrative significantly. I’m not convinced that a diagnosis of obesity, in isolation, automatically means treatment should focus on weight loss. According to the evidence currently available, the size of a body is not a reliable proxy for the health of that body.

Your weight loss choices are entirely your own and shaped by many factors, health being just one of them. If your goal is weight loss for its own sake, that is your choice. And I’d still encourage you to take a moment to consider the why behind your goal before you start a new treatment plan.

Interesting fact: some people experience ‘food noise’, a term for constant awareness of food around them. The cake on the table ‘talking’ to them. People on GLP-1s often say that their food noise goes away or is very reduced. This on its own can be life changing.

Here’s the picture in a nutshell:

Although GLP-1 agonists improve blood sugar regulation and promote satiety, they don’t

reverse poor diet
automatically restore metabolic health
replace lifestyle

There is still great benefit in regular movement, adequate nutrition, sleep, and resistance training. These medications are one tool, not the whole treatment.

Work closely with your prescribing physician to monitor your response, manage side effects, and to titrate to the correct dose for your unique body. I’d also suggest working with a dietician, at least initially – I explain why below.

If you’re on a GLP-1, what should you prioritise?

This bit here is the reason I’m writing this post. And while it might feel like a tiny footnote after lots of theory, it’s important.

GLP-1 agonists help your body regulate blood sugar more effectively by enhancing its normal hormonal responses to eating. They can be remarkably effective medications, but they don’t replace the benefits of resistance exercise, good nutrition, adequate sleep and regular movement – all of which remain essential for long-term metabolic health.

But there are 2 areas within lifestyle management that many of my patients who are taking GLP-1 agonists aren’t addressing adequately: muscle loss and gut health.

Weight loss and muscle health

Muscle is important for health and quality of life. As you age, and particularly in menopause, if you’re not actively working at maintaining muscle mass you lose muscle, a process called sarcopenia where you lose lean muscle mass as you age. This can be as much as 3–8% per decade, and starts when you’re between 30 and 35-years old. This can be exacerbated by weight loss.

If you are losing weight without paying attention to how you eat and how you move, you will likely be losing significant muscle mass – during rapid weight loss or inadequate protein intake, a significant proportion of weight lost can come from lean muscle as well as fat.

Given what we know about fat and muscle, that doesn’t result in a body that is better equipped for metabolic health! There’s one more reason muscle matters – your bones depend on it. We’ll dive into that next week.

To maintain, or even gain, muscle mass as you age, you should be intentional about eating enough good quality protein, and you should be doing some form of resistance exercise that promotes muscle strength. This is especially true if you’re in menopause or taking a GLP-1 agonist.

Yes, I said resistance exercise 😉 Exercise that, done regularly, builds muscle strength and lean muscle mass. This doesn’t have to mean CrossFit! It can be bodyweight exercise. Climbing stairs carrying the groceries. Using exercise-bands, lifting weights, or even higher intensity Pilates or yoga. We’ll look at this in a little more depth later in the series when we unpack some of the fitness trends.

When it comes to eating enough protein, it doesn’t have to be big shifts. Many people simply struggle to eat enough protein because they feel full so quickly. Try to spread protein intake through the day – try to include it with every meal and snack, even in a small amount. And if your appetite is low, eat protein before simple carbs in your meal.

Because this is so important, I strongly recommend that any of my patients that are using GLP-1s see a dietician who can monitor their body composition to ensure that they aren’t losing lean muscle mass.

And don’t forget…muscle makes climbing the stairs easier now, and living an independent life, long into the future, more likely. It’s not just about metabolism!! At all. It’s a thriving and quality of life thing.

GLP-1s and Gut Health

The second aspect, gut health, is a little easier to miss. But also really important. Because GLP-1s slow stomach emptying, this means that food moves more slowly through your gut. Too slowly is not a good thing – it’s associated with increased risk of constipation, bloating, and general discomfort.

And this is compounded by the fact that if your appetite is down, you will likely reduce your fibre intake. Which means less bulk being moved through your gut, less insoluble fibre for your gut bugs to eat, and possibly reduced immunity and mood. None of which are things we want as a side effect!

To maintain healthy fibre levels, be intentional about eating plenty of vegetables, legumes, whole grains, and some fruit. And help your body to move that fibre through your gut by staying hydrated.

Some people may also experience nausea, reflux, and gastroparesis (more serious, less common) when they start to take GLP-1s. The side effects usually improve after a few weeks, but should be monitored by your prescribing physician.

Which means my top tips if you’re on a GLP-1 agonist are:

Eat enough protein
Include strength exercises in your workout
Be intentional about eating fibre
Drink lots of water
Consult a dietician to monitor muscle-mass and tailor a plan for your unique needs

Yes, weight loss is a loaded topic. I don’t have a single woman in my close circle who hasn’t been impacted by weight and body image on some level.

I don’t know Serena Williams’ medical history, and I know her Super Bowl ad mentioned metabolic markers too. Maybe her genetics predispose her to metabolic disease.

But in my book, strong and healthy trumps skinny every day of the week and Sunday.

I hope that this post has helped you to see weight from a slightly different viewpoint. I know it’s not going to undo decades of messages that you and I have internalised. But I hope it will help you to see how incredible your metabolism really is. And to be a little more gentle and accepting of yourself.

And finally. Listen to your body. Learn to trust it. Use tests to guide you and to make sure your health is on track. Pick nourishing food, and move often. Be and feel strong. Laugh with people you love. But first and foremost. Don’t punish your body and force it to fit into someone else’s mould of ‘good enough’. You’re already good enough simply because you were made enough. Live in a way that celebrates that.

🤍 Carmen

GLP-1s and Metabolic Health: Why I’m More Interested in Muscle Than Weight