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
Free tracker included with every download this week
What Should You Eat When Taking Mounjaro?
If you're on Mounjaro (tirzepatide), diet remains one of the most important factors in achieving weight loss. While the medication helps reduce appetite and food cravings, what you choose to eat still matters significantly. This guide explains how to structure your diet alongside Mounjaro treatment in the UK, including NHS recommendations, managing side effects, and making practical food choices that support your weight loss goals. Use our GLP-1 weight loss calculator to project potential outcomes when combining dietary changes with Mounjaro therapy.
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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 on Mounjaro — Key Principles
Mounjaro (tirzepatide) works best when combined with a reduced-calorie diet and increased physical activity. The medication may help you feel fuller on smaller portions, but you still need to create a calorie deficit to lose weight. NHS guidance suggests aiming for a sustainable loss of 0.5–1 kg per week, which typically requires a deficit of around 500 kcal per day.
During your dose titration period (increasing from 2.5 mg to your maintenance dose), you may experience nausea, vomiting, or constipation. Eating smaller, more frequent meals can help. Focus on:
- Lean proteins (chicken, fish, eggs, lentils) — help preserve muscle during weight loss
- Non-starchy vegetables (broccoli, spinach, peppers) — high in nutrients, low in calories
- Whole grains in moderation — support stable blood sugar
- Healthy fats (olive oil, avocado, nuts) — support satiety and nutrient absorption
Avoid sugary foods, fizzy drinks, and high-fat processed foods — these can trigger side effects and undermine weight loss.
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.
Managing Side Effects Through Diet
Mounjaro side effects like nausea and constipation are often diet-related. Eat slowly and chew thoroughly — rushing can worsen nausea. Stay hydrated with water and sugar-free drinks; dehydration worsens constipation. If you experience stomach pain or severe nausea, contact your GP immediately, as this may indicate a more serious condition.
Many people find that eating soft, easily digestible foods during the first few weeks helps. Gradually reintroduce normal foods as your body adjusts. If constipation persists, your GP may recommend increasing fibre intake or suggest a mild laxative. Track your progress and side effects using our free progress tracker — this helps you identify which foods work best for your body on Mounjaro.
- 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.
Can I eat normally while on Mounjaro?
You can eat most foods, but portions will naturally be smaller due to increased fullness signals. Focus on nutrient-dense foods rather than high-calorie processed options. The medication suppresses appetite, making it easier to eat less, but you still need to make healthy choices for optimal weight loss and nutrition.
Should I follow a specific diet plan with Mounjaro?
NHS guidance recommends a balanced, reduced-calorie diet alongside Mounjaro. You don't need a specific branded diet — focus on lean proteins, vegetables, whole grains, and healthy fats. Your GP or a dietitian can provide personalised advice based on your health conditions and preferences.
Will Mounjaro work without changing my diet?
Mounjaro is less effective without dietary change. The medication is approved specifically for use alongside a reduced-calorie diet and increased physical activity. Clinical trials showed weight loss results when patients combined Mounjaro with these lifestyle changes — diet remains essential.
What if I have nausea when eating on Mounjaro?
Eat smaller meals more frequently, chew slowly, and avoid greasy or heavy foods. Stay hydrated with water. If nausea is severe or persistent, contact your GP — it may indicate an adjustment issue or require a dose review. Most people find nausea improves within 1–2 weeks as their body adjusts.
How long should I follow this diet after stopping Mounjaro?
If you stop Mounjaro, the appetite-suppressing effects typically wear off within days to weeks. Continue with healthy eating habits learned during treatment to maintain weight loss. Your GP can advise on transitioning off the medication and maintaining your progress.
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.