Are you eating enough? Do you know about transferrin
What a routine blood test taught me about GLP-1 medications and protein
One of the things I love most about general practice is that I'm constantly learning.
Medicine is rarely static. Sometimes the biggest lessons don't come from textbooks or conferences. They come from patterns I notice in clinic.
This week I reviewed a patient who had lost around 15 kg on a GLP. They felt well, had good iron stores, and their blood tests were largely reassuring. But one result caught my attention.
Their transferrin was slightly low. At first glance, this can prompt thoughts about inflammation, liver disease, or other medical conditions. But everything else looked reassuring.
It made me stop and wonder.
Could this simply reflect reduced protein intake during significant weight loss?
GLP-1 medications work because we eat less
Medications such as Wegovy (semaglutide) and Mounjaro (tirzepatide) reduce appetite and help people feel fuller for longer.
That's exactly how they help with weight loss.
But eating less means we're not just reducing calories. We may also be eating less protein unless we're consciously prioritising it.
For many people, this isn't a problem. But over months of treatment, inadequate protein intake can contribute to:
- Loss of muscle mass (rather than just fat)
- Reduced strength
- Slower recovery from exercise
- Lower production of proteins made by the liver
- Potential changes in blood markers, including proteins such as transferrin
This particular result reminded me that our blood tests sometimes reflect nutrition just as much as disease.
Weight loss isn't the only goal
One of the biggest shifts in obesity medicine over the past few years has been recognising that not all weight loss is equal.
We don't simply want the number on the scales to go down. We want people to lose excess fat while preserving muscle, strength, bone health and metabolic health.
That means paying attention to:
- Protein intake
- Resistance exercise
- Sleep
- Ongoing nutritional review
These are every bit as important as the medication itself.
Are you eating enough protein?
Many people taking GLP-1 medications tell me:
" I'm just not hungry anymore."
That's wonderful if it helps reduce overeating. But it also means meals become much smaller, snacks disappear, and it's surprisingly easy to fall well short of your daily protein requirements.
If you're eating half as much as you used to, it's worth asking:
Am I still getting enough protein for my body?
I'm still learning too
I don't know for certain that this patient's slightly low transferrin was caused by reduced protein intake.
There are many potential causes, and blood tests always need to be interpreted in the context of the whole clinical picture.
But it reminded me of something important.
As more and more people use GLP-1 medications, we need to think beyond the scales.
We need to ask not only, "How much weight have you lost?" but also:
- How much muscle have you preserved?
- Are you eating enough protein?
- Are you maintaining strength?
- Are you protecting your bones for the future?
And how do we assess this?
Every patient teaches us something. This patient reminded me that successful weight loss isn't just about eating less.
It's about nourishing your body well while you lose weight. And even if one thinks they are 'eating enough' - sometimes we need to reassess.
What did I learn from this deep dive: I will now actively look for a decrease in transferrin to help guide my patients to ensure that they are eating enough.
