The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Mounjaro and Protein: Your Complete UK Guide
When taking Mounjaro (tirzepatide), protein intake becomes increasingly important because the injection can reduce appetite and food intake. This means you need to be intentional about eating enough protein to preserve muscle mass during weight loss. This guide explains how to balance protein nutrition while using this prescription weight loss medication, and what your GP or prescriber can advise about your individual needs.
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What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Why Protein Matters on Mounjaro
When you're in a calorie deficit during weight loss, your body can break down muscle tissue for energy if protein intake is insufficient. Mounjaro works by reducing appetite and helping you feel fuller longer, which is how the dual GIP and GLP-1 agonist mechanism supports weight loss — but this reduced hunger can make it easy to under-eat protein without realising.
- Adequate protein helps preserve lean muscle mass during weight loss
- Muscle tissue burns more calories at rest than fat tissue, supporting long-term metabolism
- Protein also promotes satiety, which can actually complement Mounjaro's appetite-suppressing effects
- The NHS and clinical nutrition guidance recommend higher protein intake during calorie-restricted weight loss
A prescriber or registered dietitian can assess your individual protein needs based on your activity level, current muscle mass, and weight loss goals. Our free GLP-1 weight loss calculator can help you project potential weight loss outcomes, but personalised nutritional guidance should always come from a healthcare professional.
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Recommended Protein Intake on Mounjaro
General guidance for weight loss: Aim for 1.6–2.2 grams of protein per kilogram of body weight daily, or roughly 25–35 grams per meal if distributed across three meals. For example, at 80 kg body weight, you'd target 128–176 grams of protein daily.
If you're exercising during your weight loss journey, higher protein intake (closer to 2.2 g/kg) may help preserve muscle and support recovery. Good UK protein sources include chicken, fish, eggs, Greek yoghurt, cottage cheese, beans, lentils, and tofu. Because Mounjaro reduces appetite, prioritise protein-rich foods early in meals to ensure you meet your daily target even if you're eating less overall. Your GP or a registered dietitian can give you personalised advice for your specific situation.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Will Mounjaro cause muscle loss if I don't eat enough protein?
Weight loss naturally involves some muscle loss, but adequate protein intake — typically 1.6–2.2 g/kg of body weight daily — helps minimise this. Mounjaro reduces appetite, making it crucial to be intentional about hitting protein targets. Combine this with resistance exercise and discuss individual needs with your GP or dietitian.
Can I use Mounjaro if I'm vegan or vegetarian?
Yes, but you'll need to carefully plan plant-based protein sources such as beans, lentils, tofu, tempeh, nuts, seeds, and quinoa to meet daily targets. Because Mounjaro reduces appetite, prioritising protein at each meal is essential. Discuss plant-based nutrition strategies with a registered dietitian alongside your prescriber.
How is Mounjaro prescribed in the UK?
Mounjaro (tirzepatide) is prescription-only and available through NHS specialist weight management services or private prescribers following a clinical assessment. Your prescriber will check your eligibility, review your medical history, and monitor you throughout the KwikPen dose titration schedule, starting at 2.5 mg and potentially increasing up to 15 mg weekly.
What's the difference between Mounjaro and Wegovy for protein needs?
Both Mounjaro (tirzepatide, dual GIP/GLP-1 agonist) and Wegovy (semaglutide, GLP-1 agonist only) reduce appetite similarly, so protein requirements are essentially the same. Both require intentional protein intake to preserve muscle during weight loss. Your prescriber can advise which medication suits you and discuss personalised nutrition alongside your treatment.
Should I take protein supplements on Mounjaro?
Protein supplements (shakes, powders) can help you meet targets if whole-food sources are difficult due to reduced appetite, but whole foods are preferred where possible. A registered dietitian can advise whether supplements suit your situation and which types are best. Always discuss any supplements with your prescriber, as some may interact with medications.
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