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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What Diet Works Best When Taking Mounjaro?
Mounjaro (tirzepatide) is a prescription-only weight management injection that reduces appetite and helps you feel fuller after eating smaller portions. But diet still matters — Mounjaro works best when combined with sensible eating habits and increased physical activity. This guide explains what to eat, what to avoid, and how to manage common digestive side effects whilst on Mounjaro treatment. Use our GLP-1 weight loss calculator to estimate your potential results alongside dietary changes.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
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.
Dietary Approach When Taking Mounjaro
Mounjaro works by mimicking GIP and GLP-1 hormones, which signal fullness to your brain and slow how quickly food leaves your stomach. This means portion sizes naturally decrease — many people report eating half their usual amount without hunger. Your diet should focus on nutrient-dense foods in smaller quantities rather than complete dietary overhaul.
The NHS recommends:
- Protein at every meal — chicken, fish, eggs, legumes, tofu (helps maintain muscle during weight loss)
- Whole grains in modest portions — brown rice, oats, wholemeal bread (easier to digest than white carbohydrates)
- Plenty of non-starchy vegetables — broccoli, spinach, peppers, courgettes (low calorie, high fibre)
- Healthy fats in small amounts — olive oil, avocado, nuts (satiating but calorie-dense)
- Adequate hydration — 6–8 glasses of water daily (especially important with Mounjaro)
A calorie deficit of around 500 kcal per day typically results in loss of approximately 0.5 kg per week. Mounjaro helps create this deficit by reducing hunger naturally.
Clinically BackedWeight Loss
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Foods to Avoid and Managing Side Effects
Whilst on Mounjaro, avoid high-fat, greasy, and heavily processed foods — these can worsen nausea, diarrhoea, and stomach discomfort, which are common side effects. Skip fried foods, pastries, fatty cuts of meat, and sugary snacks.
If you experience nausea or constipation — the most common digestive issues on Mounjaro — try:
- Eating smaller, more frequent meals rather than three large ones
- Ginger tea or ginger biscuits for nausea relief
- High-fibre foods gradually (sudden increases worsen digestive upset)
- Cooked vegetables rather than raw if digestion is sensitive
- Bland foods initially — toast, rice, plain chicken — until side effects settle
Most digestive side effects improve after the first 2–4 weeks as your body adjusts. Track your progress using our free progress tracker to monitor both weight and how your digestion responds to dietary changes.
- 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.
Do I need to follow a specific diet plan on Mounjaro?
No — Mounjaro works with any balanced, calorie-controlled diet. There is no mandatory "Mounjaro diet". The medication itself reduces appetite, making it easier to eat smaller portions of regular foods. Your GP or a dietitian can provide personalised guidance if you prefer structured support.
Can I eat normally on Mounjaro?
Yes, but portion sizes will likely be much smaller. Many people report that Mounjaro removes the desire to overeat — you naturally stop when satisfied. This means you can eat most foods you enjoy, just in significantly reduced quantities.
What if I feel nauseous when eating on Mounjaro?
Nausea is very common, especially in the first few weeks. Try eating smaller meals, avoiding high-fat foods, sipping ginger tea, and eating bland foods temporarily. If nausea is severe or persistent, contact your prescriber — a dose adjustment or anti-nausea medication may help.
How long does it take for appetite suppression to work?
Most people notice reduced appetite within days to a week of starting Mounjaro, though this varies. The effect becomes more pronounced at higher doses. You may feel full after eating just a few bites initially — this is normal and typically reduces as your body adjusts.
Is there a difference between Mounjaro and Wegovy for dietary needs?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist, whilst Wegovy (semaglutide) is a GLP-1 agonist only. Both reduce appetite similarly, so dietary guidance is comparable. Individual responses vary. Your prescriber can advise which is more suitable during your clinical assessment.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.