Mounjaro and Nutrition: how to maximise results

1. What are GLP-1 medicines?

GLP-1 receptor agonists — and, in the case of Mounjaro® (tirzepatide), dual GIP/GLP-1 receptor agonists — are prescription-only medicines that mimic gut hormones involved in regulating appetite and blood glucose. In practice, they slow gastric emptying, increase satiety and reduce “food noise” — the constant urge to eat.

The best known in Portugal:

• Mounjaro® (tirzepatide) — weekly injection
• Wegovy® (semaglutide, weight-management dose) — weekly injection
• Ozempic® (semaglutide, indicated for type 2 diabetes) — weekly injection
• Saxenda® (liraglutide) — daily injection

2. Benefits — and what the medicine does not do

Clinical trials show significant average weight loss, improved glycaemic control and cardiometabolic benefits. For many people who have struggled against hunger for years, it is the first time that eating stops being a constant battle.

But there are three things the medicine does not do:

1. It does not choose what you eat. Less appetite with poor nutrition means deficits in protein, iron, calcium and vitamins — felt as fatigue, hair loss and weakness.
2. It does not protect muscle. Without a strategy, a substantial part of the weight lost is lean mass.
3. It does not create habits. When treatment ends, what remains is what you built during the process — or the lack of it.

3. Side effects: dietary management

The most common adverse effects are digestive — nausea, reflux, bloating, constipation — especially when the dose is increased. Many of them can be managed through diet:

Nausea and bloating

• Small, frequent meals instead of 2–3 large ones
• Avoid fried food, very fatty meals and heavy sauces — they slow gastric emptying even further
• Eat slowly and stop at the first sign of fullness (it comes sooner than you are used to)
• Drink between meals, not during them, so as not to take up stomach volume

Reflux

• Do not lie down for 2–3 hours after eating
• Have a lighter, earlier dinner

Constipation

• Increase fibre gradually (vegetables, fruit with the skin on, oats, well-tolerated pulses)
• Water throughout the day — eating a smaller volume of food also reduces the water “hidden” in food
• Daily movement, even if it is just walking

4. Protein: the number one priority

With a reduced appetite, the natural tendency is to eat “whatever you fancy and whatever fits” — and protein is almost always the first thing to disappear from the plate. It is the most costly mistake of the treatment.

The practical reference I use in consultations for most adults in active weight loss on GLP-1 is 1.5 to 2 g of protein per kg of body weight per day (adjusted individually in consultation, especially if there is kidney disease — in which case the value is set with your doctor).

How to get there with little appetite

• Always start the meal with the protein — if fullness arrives halfway through, the essentials are already covered
• Spread it over 3–4 moments in the day: 25–40 g per meal goes further than a single dose
• Dense, easy sources: eggs, fish, chicken, Greek yoghurt/skyr, fresh cheese, pulses, tofu
• When solids are difficult: shakes with yoghurt or milk + fruit, or a protein supplement recommended in consultation

5. How to preserve muscle mass

In rapid weight loss without a strategy, up to 25–40% of the weight lost can be lean mass. Losing muscle means losing the tissue that uses the most energy at rest — in other words, it prepares the ground for regaining the weight when treatment ends, with a worse body composition than at the start.

The protection formula has three components, and none of them is optional:

1. Enough protein (previous section) — the building material
2. Strength training 2–3x a week — the stimulus that tells the body “this tissue is needed”
3. Monitoring body composition — without measuring lean mass vs. fat mass, nobody knows what is really being lost. Home scales are not enough.

This is why nutritional support during GLP-1 treatment is not an “extra”: it is what distinguishes losing weight from losing fat.

6. Practical eating strategies

• Quality first: with less volume, every meal has to be nutritionally dense — protein + vegetables + wholegrain carbohydrates in small portions
• Do not skip meals “because you are not hungry”: reduced appetite does not eliminate nutritional needs; plan 3–4 mini-meals at set times
• Hydration as a habit, not as thirst: thirst also decreases with treatment — set a daily target (≈30–35 ml/kg) and spread it out
• Alcohol with caution: calories without nutrition, poorer digestive tolerance and a higher risk of hypoglycaemia in people with diabetes on medication
• Micronutrients monitored: iron, B12, calcium and vitamin D deserve attention in consultation; supplement only with good reason, not from a catalogue

7. Physical exercise during treatment

Strength training is protein’s inseparable partner in preserving muscle. General recommendations (to be adapted to your condition and with medical approval where applicable):

• Strength 2–3x/week — machines, free weights, resistance bands or bodyweight; progressive intensity is what counts
• A daily walk or other light-to-moderate cardio for cardiovascular health and bowel regularity
• Training after a meal with protein improves tolerance (training on an empty stomach with a suppressed appetite increases the risk of dizziness)

8. Maintenance after the medication is stopped

It is the topic nobody talks about at the start and that decides everything at the end. When the medication ends (your doctor’s decision), appetite returns gradually — and discontinuation studies show that much of the weight is regained by those who built nothing else during treatment.

People who maintain their results generally have three things in place:

1. Preserved muscle mass — a metabolism that keeps working in your favour
2. Habits practised during treatment — meal structure, protein first, managing emotional hunger learned while biological hunger was silenced
3. A planned transition — gradual adjustment of the eating plan in the months when the medication is stopped, with close monitoring, instead of an abrupt return to “before”

GLP-1 treatment is a unique window of opportunity: months in which hunger does not get in the way of building habits. Using it only to “eat less” is wasting it.

Disclaimer: this content is for educational purposes only and does not replace individual medical or nutritional advice. The dietitian does not prescribe, adjust or recommend medicines: any decision about Mounjaro®, Wegovy®, Ozempic®, Saxenda® or any other treatment (starting, dose, stopping or managing adverse effects) is the sole responsibility of the prescribing doctor. Nutritional support complements — never replaces — medical treatment. The brands mentioned are the property of their respective owners; they are mentioned for information only and this does not constitute advertising of medicines. Results vary from person to person.