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's the Best Diet to Use With Mounjaro?
There isn't a single "best diet" with Mounjaro — what works depends on your individual health, preferences, and how your body responds to the medication. Mounjaro (tirzepatide) is a prescription-only weight management injection that works most effectively when combined with a reduced-calorie diet and increased physical activity. The NHS emphasises that weight loss medications are a tool to support lifestyle changes, not a replacement for them. This guide explains how diet works alongside Mounjaro, compares it with Wegovy, and helps you understand what a prescriber will look for when assessing your suitability.
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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.
Mounjaro vs Wegovy — How Diet Strategy Differs
Both Mounjaro and Wegovy are prescription-only weight loss injections, but they work differently — which may affect your dietary approach. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways. In the SURMOUNT-1 clinical trial, participants on Mounjaro lost an average of 15–20.9% of their body weight at 72 weeks, alongside a reduced-calorie diet and exercise. Wegovy (semaglutide) is a GLP-1 agonist only, and STEP-1 trial data showed approximately 14.9% average body weight loss at 68 weeks under the same conditions.
- Mounjaro's dual mechanism may reduce appetite and cravings more intensely for some people
- Wegovy's single mechanism is also highly effective, with a longer track record in the UK market
- Both medications slow gastric emptying, which means smaller portions feel more satisfying
- Neither medication "burns fat" on its own — calorie deficit remains essential
- Trial results are averages — individual outcomes vary significantly
The "best diet" with either medication is one you can sustain long-term alongside the medication's appetite-suppressing effects.
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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.
Diet Principles That Work With Mounjaro
Rather than following a restrictive fad diet, evidence suggests sustainable approaches work best with Mounjaro. Most people find that reduced portion sizes feel natural because the medication helps with satiety, so you don't need to drastically cut calories yourself. A balanced approach including protein, vegetables, healthy fats, and complex carbohydrates supports muscle retention during weight loss.
- Protein intake (1.2–1.6g per kg body weight) helps preserve muscle mass whilst losing fat
- Staying hydrated and eating slowly allows the medication's fullness signals to register
- Managing nausea (a common early side effect) by eating smaller, bland meals initially
- Avoiding high-sugar or high-fat foods, which may worsen gastrointestinal side effects
Use our free BMI calculator and GLP-1 weight loss calculator to understand your starting point and projected outcomes. Your prescriber and a registered dietitian can personalise this further based on your health conditions and preferences.
- 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.
Does Mounjaro work without changing your diet?
No. Clinical trials showed weight loss only when Mounjaro was combined with a reduced-calorie diet and increased physical activity. The medication supports appetite control, but you must still create a calorie deficit. A prescriber will discuss dietary expectations before starting treatment.
Is Mounjaro better than Wegovy for weight loss?
Both are effective prescription medications with strong clinical trial data. Mounjaro showed slightly higher average weight loss (15–20.9%) compared to Wegovy (14.9%) in separate trials, but individual results vary. Your prescriber will assess which is more suitable based on your health profile, not on superiority claims.
What is tirzepatide and how does it differ from semaglutide?
Tirzepatide (Mounjaro's active ingredient) is a dual GIP and GLP-1 receptor agonist. Semaglutide (Wegovy) is a GLP-1 agonist only. The dual mechanism of tirzepatide may offer different appetite control patterns, but both require clinical assessment and prescription in the UK.
Can I get Mounjaro on the NHS in the UK?
NICE has approved tirzepatide for NHS specialist weight management services, but access varies significantly by region and availability. Many areas have long waiting lists. Private access is available through GPhC-registered online pharmacies following a clinical assessment with a licensed UK prescriber.
What if I have Mounjaro side effects — can I change my diet to help?
Yes. Nausea and digestive issues are common, especially in the first weeks. Small, bland meals, adequate hydration, and avoiding greasy foods can help. If side effects persist, speak to your prescriber — dose adjustment or changing medication may be appropriate.
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.