Nutritionist Sarah Di Lorenzo: How to prevent muscle loss and hair loss while on Ozempic, Wegovy or Mounjaro

GLP‑1 receptor agonists, including semaglutide and tirzepatide (marketed as Ozempic, Wegovy and Mounjaro), have transformed the weight‑management landscape faster than almost any pharmaceutical intervention I’ve seen in my career.

The results for many people are genuinely remarkable.

But as a clinical nutritionist watching this unfold in real time, I want to talk honestly about two side effects that are not getting nearly enough attention: muscle loss and hair loss.

Both are largely preventable, and almost nobody is being told how.

GLP‑1 medications work primarily by suppressing appetite and slowing gastric emptying, and the result is a significant reduction in calorie intake.

The weight that comes off includes both fat and lean muscle mass, and the proportion of muscle lost is the part that concerns me most.

Clinical trial data suggest that roughly 20–40 per cent of total weight lost on these medications can be lean mass, depending on the study, the drug and how body composition is measured.

This is at least comparable to, and in some trials appears higher than, what is typically seen with calorie restriction alone, and in some cases higher than what occurs with bariatric surgery when adequate protein intake is maintained.

This matters enormously, and it is not just about appearance.

Muscle is the body’s largest site of glucose disposal, a primary driver of resting metabolic rate, and the tissue most directly responsible for physical strength and functional independence as we age.

Muscle is exactly what someone with a weight problem needs to preserve, yet these medications can increase the proportion of muscle lost if we do not actively protect it.

Losing muscle at this rate while losing weight sets up exactly the conditions for the weight regain and metabolic slowdown that so many people fear once the medication is stopped.

A body with less muscle simply burns fewer calories at rest, regardless of the number on the scale. When weight does come back on, it is, in most cases, predominantly fat.

Over years and repeated cycles, this pattern contributes to what is sometimes called osteosarcopenic obesity — higher fat mass sitting on lower bone and muscle mass.

The good news is that we know how to mitigate a lot of this.

Protein intake needs to increase, not decrease, while on these medications and yet the opposite often happens.

With appetite so significantly suppressed, hitting roughly 1.2 to 1.6 grams of protein per kilogram of body weight per day is challenging for many.

I tell every patient on a GLP‑1 medication the same thing: eat your protein first at every single meal. You may only have an appetite for a small amount of food, and that small amount needs to count.

Resistance exercise is equally non‑negotiable. It is the only intervention that directly signals the body to preserve muscle tissue even in a significant calorie deficit.

Several major manufacturers and prescribing bodies are now explicitly recommending resistance training and adequate protein alongside these medications, which reflects how seriously this concern is being taken in clinical practice.

Hair loss on GLP‑1s is a temporary but distressing shedding that typically appears three to six months after starting the medication and is being reported more frequently.

In most cases, what we are seeing is telogen effluvium — a type of diffuse, non‑scarring hair shedding where many hairs shift into the “resting” phase and fall out across the scalp at once, usually a few months after a significant physical or nutritional stress.

Telogen effluvium is a well‑recognised consequence of rapid weight loss and substantial calorie restriction.

The body effectively deprioritises hair follicle growth during a period it interprets as stress, pushing a larger proportion of follicles into the shedding phase simultaneously.

Current evidence suggests that, in many people using GLP‑1s, hair changes are driven largely by the rate of weight loss and nutritional factors, rather than a direct toxic effect of the drug on hair follicles themselves, though research is ongoing and a small drug‑specific contribution cannot be completely ruled out yet.

The key nutritional drivers are primarily inadequate protein and key micronutrient shortfalls.

Hair is almost entirely composed of keratin, a protein structure that cannot be built without sufficient amino acids, along with nutrients such as iron, zinc and biotin.

Deficiencies in these are common when overall food intake drops quickly.

Ferritin (the body’s iron store) is particularly worth checking, as iron deficiency is one of the most common and most overlooked contributors to hair shedding in any period of reduced intake or rapid weight loss.

The reassuring part is that telogen effluvium is usually self‑limited. Once the underlying stress and deficiencies are addressed, shedding tends to settle over several months and regrowth follows. But prevention is far better than waiting for thinning hair to appear and then trying to back‑track.

GLP‑1 medications are a genuine tool and for many people, a transformative one when they are used thoughtfully and for those who truly need them.

But they are not a substitute for nutrition and movement; they work best with these foundations, not instead of them.

Adequate protein at every meal, resistance exercise, and attention to key micronutrients are not optional extras for someone using these medications.

They are the difference between losing weight well and losing muscle, hair and metabolic resilience along with it.

Like many medications, GLP‑1s come with pros and cons. For those struggling with weight, some of the best long‑term outcomes still come from addressing the underlying drivers of weight gain — sleep, stress, food quality, movement, medications, hormones and then, if needed, layering medications on top of that, not the other way around.

Anyone starting a GLP‑1 medication should be having this conversation with their doctor and a clinical nutritionist or dietitian from day one, not as an afterthought once side effects appear.