Mounjaro (tirzepatide) has become increasingly familiar to Australians using medication to manage type 2 diabetes or support weight management.
For many people, one of its most noticeable effects is a significant reduction in appetite. You may feel full after only a small amount of food, think about food less often, or simply find that you are skipping meals because you are not hungry.
That may contribute to weight loss — but there is another important question worth asking:
Are you still eating enough to nourish your body?
Mounjaro changes more than your appetite
Mounjaro works on GIP and GLP-1 receptors and can reduce appetite and food intake. It also slows gastric emptying, particularly earlier in treatment.
For someone who previously struggled with hunger or appetite regulation, this can feel like a welcome change.
However, when your appetite becomes very small, your intake of protein, vitamins, minerals, fibre and fluid can fall along with your energy intake.
This matters because weight loss and good nutrition are not necessarily the same thing.
Can Mounjaro increase the risk of malnutrition?
Potentially, yes.
The Australian Product Information for Mounjaro includes a warning that malnutrition has been reported in people receiving tirzepatide, including severe cases. Nutritional consequences can include vitamin and mineral deficiencies, protein deficiency and low body weight.
This doesn't mean everyone taking Mounjaro will become malnourished.
It does mean that nutritional adequacy deserves attention — particularly when appetite suppression is substantial, weight is falling quickly, meals have become very small or gastrointestinal side effects are making eating difficult.
You can have a higher body weight and still be undernourished
This is an important point.
Malnutrition isn't determined simply by what somebody weighs.
A person can be living in a larger body and still have inadequate intake of protein, iron, calcium, vitamin B12 or other important nutrients.
When appetite is strongly suppressed, it becomes increasingly important to consider what is being eaten, not simply how little is being eaten.
What about muscle?
When we lose weight, we don't lose only body fat. Some lean tissue can also be lost.
This makes maintaining adequate protein intake and using your muscles particularly important during significant weight loss.
Preserving muscle becomes even more important as we get older because muscle contributes to strength, mobility, metabolic health, independence and our ability to carry out everyday activities.
If your weight is falling but you are also feeling increasingly weak, tired or physically less capable, that deserves attention.
Signs that your food intake may need reviewing
It may be worth having your nutrition assessed if you are taking Mounjaro and you:
• regularly skip meals because you aren't hungry
• struggle to finish even small meals
• are eating only once or twice a day
• have persistent nausea, vomiting, diarrhoea or constipation
• are losing weight very rapidly
• feel unusually tired or weak
• notice reduced strength or muscle
• are drinking very little
• are relying heavily on snack foods because meals feel too difficult
• have known low iron, vitamin B12, vitamin D or other nutritional deficiencies.
These symptoms can have many causes, so they shouldn't automatically be attributed to Mounjaro. Persistent symptoms should be discussed with your GP or prescribing clinician.
If you can only eat a little, make that little count
When appetite is limited, simply telling someone to “eat a healthy diet” isn't particularly helpful.
Instead, we can make smaller amounts of food work harder nutritionally.
Start with protein
Try to include a protein-rich food at each meal or eating occasion.
Depending on your individual needs, this might include:
Eggs, Greek yoghurt, cottage cheese, milk, fish, chicken, lean meat, tofu, tempeh, lentils or legumes.
If you're struggling to eat a full meal, eating the protein component first can sometimes help ensure it isn't left behind when you become full.
Don't forget iron
Iron intake can become inadequate when overall food intake drops, particularly if you were already at risk of iron deficiency.
Iron-containing foods include lean red meat, chicken, fish, eggs, legumes, tofu, iron-fortified cereals, nuts and seeds.
Plant sources of iron can be paired with a vitamin C-rich food — such as capsicum, kiwifruit, berries, citrus or tomato — to help improve absorption.
Protect your bones
Calcium and vitamin D remain important during weight loss.
Milk, yoghurt, cheese and calcium-fortified alternatives can provide calcium without requiring a large volume of food.
This is particularly important for people already at risk of osteopenia or osteoporosis.
Include fibre — but don't forget fluid
Constipation can occur while taking Mounjaro.
Fibre can help, but suddenly adding large amounts of fibre while eating and drinking very little isn't necessarily the answer.
Fruit, vegetables, wholegrains, legumes, nuts and seeds can all contribute fibre, but your intake needs to be considered alongside hydration and your individual gastrointestinal symptoms.
Small meals are still meals
You don't have to force yourself through a large dinner just because that's how you used to eat.
Three smaller meals plus one or two nourishing snacks may be much more manageable.
A small bowl of Greek yoghurt with fruit and nuts, an egg on wholegrain toast, soup enriched with lentils or chicken, or a smoothie containing milk or yoghurt can provide useful nutrition in a relatively small volume.
Don't chase the lowest possible number on the scales
Weight is only one measure of health.
How you feel, your strength, nutritional status, relationship with food, ability to exercise and your capacity to maintain the changes you are making matter too.
Mounjaro can be a useful tool for appropriately selected people, but the goal shouldn't be to eat as little as physically possible.
The goal is to lose weight, when clinically appropriate, while remaining adequately nourished and protecting your health.
A dietitian can help you work out whether you're eating enough
If you are taking Mounjaro or another GLP-1-based medication and aren't sure whether your diet is meeting your nutritional needs, an Accredited Practising Dietitian can assess what you're actually eating and identify areas that may need attention.
This may include looking at protein, iron, calcium, fibre and fluid intake, meal timing, gastrointestinal symptoms, weight changes and relevant blood results.
At The Cooroy Dietitian, I provide practical nutrition support for people in Cooroy, Noosa and across the Sunshine Coast.
The aim isn't to work against your medication or weight-loss goals.
It's to make sure that while your appetite may be smaller, your nutrition isn't forgotten.
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