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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Diet With Mounjaro: NHS Guidance for UK Adults
Mounjaro (tirzepatide) works best alongside a reduced-calorie diet and increased physical activity — it's not a replacement for lifestyle changes. In the UK, Mounjaro is prescribed through NHS specialist tier 3 weight management services or private prescribing following clinical assessment. This guide explains how diet fits into Mounjaro treatment, what the NHS expects, and how to support your weight loss safely whilst taking this prescription injection.
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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.
How Diet Works With Mounjaro on the NHS
Mounjaro is a dual GIP and GLP-1 receptor agonist — it helps reduce appetite and supports feeling fuller after smaller meals. This makes it easier to maintain a reduced-calorie diet, but the medication does not work alone. The NHS expects patients to combine Mounjaro with dietary changes to achieve weight loss.
- Calorie deficit: You'll need to consume fewer calories than you burn. The NHS recommends a deficit of around 500 kcal per day, which typically results in loss of approximately 0.5 to 1 kg per week.
- Food choices: Focus on whole foods — lean proteins, vegetables, whole grains, and healthy fats. Mounjaro may reduce appetite for all foods, including nutritious ones, so portion control becomes easier but nutrient density matters more.
- Dose titration: Mounjaro is gradually increased over weeks (starting at 2.5 mg, escalating to 15 mg maximum). During dose titration, side effects like nausea may make eating difficult — this is temporary and usually improves within days.
- Nausea management: In clinical trials, nausea was very common early on. Eating smaller meals, staying hydrated, and avoiding greasy or spicy foods can help. If severe nausea persists beyond a week, contact your prescriber.
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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
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NHS Eligibility and Dietary Expectations
In the UK, Mounjaro access through the NHS is via specialist tier 3 weight management services. You'll typically be assessed by a multidisciplinary team including dietitians. The NHS expects patients to demonstrate commitment to dietary and lifestyle change — Mounjaro is prescribed alongside, not instead of, a structured diet and exercise plan.
You may be offered NHS dietary support, including appointments with a registered dietitian who can create a personalised eating plan. Private prescribing routes (through online clinics) provide Mounjaro without requiring NHS referral, but you're still responsible for maintaining a healthy diet and monitoring your own nutrition. Use our GLP-1 weight loss calculator to estimate potential weight loss at different doses when combined with dietary changes, and track your progress with our free progress tracker to monitor both weight and dietary habits.
- 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 lose weight on Mounjaro without changing my diet?
No. Mounjaro reduces appetite but does not clinically studied weight loss alone. The NHS and clinical trials (SURMOUNT-1) show that weight loss occurs when Mounjaro is combined with a reduced-calorie diet and increased physical activity. Without dietary changes, weight loss is unlikely.
What should I eat in the first week of Mounjaro?
In the first week (starting at 2.5 mg), focus on small, frequent meals. Nausea is common, so avoid greasy, spicy, or heavy foods. Eat bland, easy-to-digest foods like crackers, toast, soup, eggs, and lean chicken. Stay hydrated. Most people find nausea improves within a few days as their body adjusts.
How much can I expect to lose with Mounjaro and diet combined?
In the SURMOUNT-1 clinical trial, participants using Mounjaro at 15 mg alongside a reduced-calorie diet and exercise lost an average of approximately 21% of their body weight over 72 weeks. Individual results vary significantly based on diet adherence, baseline weight, and other factors.
Will my GP help me with diet planning on Mounjaro?
If prescribed through NHS tier 3 services, you'll have access to dietitian support as part of the specialist multidisciplinary team. If obtaining Mounjaro privately, you may need to arrange dietary support separately (private dietitian or NHS GP referral to tier 2 weight management services).
Can I use Mounjaro with intermittent fasting or very low-calorie diets?
Very low-calorie diets (under 800 kcal per day) should only be used under medical supervision, especially with Mounjaro — the combination can increase risks of nutrient deficiency, gallstones, and muscle loss. Intermittent fasting (like 16:8) may work for some people, but discuss it with your prescriber first to ensure it's safe for you.
Ready to take control of your weight loss journey?
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