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 Wegovy — Foods and Dietary Guidance
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections licensed in the UK. One key difference between these medications is how they work: Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. This means they may affect appetite and digestion slightly differently — and the foods that work best with each can vary. This guide explains what to eat and avoid with both medications, so you can make informed dietary choices alongside whichever treatment your GP or prescriber recommends.
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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.
How Mounjaro and Wegovy Affect What You Can Eat
Both medications slow gastric emptying — the rate at which food moves through your stomach — which means you'll feel fuller faster and for longer. This naturally leads to smaller portion sizes.
With Mounjaro's dual mechanism (GIP + GLP-1), some patients report a more pronounced reduction in appetite and food cravings, meaning certain foods feel less appealing. With Wegovy's GLP-1-only mechanism, appetite suppression is still significant but may feel slightly different individually.
- Nausea and indigestion are common early side effects with both — particularly in weeks 1–4 of each dose increase. You may naturally avoid certain foods during this phase.
- Clinical trials (SURMOUNT for Mounjaro, STEP for Wegovy) showed both medications work best when paired with a reduced-calorie diet and physical activity — not through food restriction alone.
- Individual tolerance varies — what causes nausea for one person may be fine for another. Your prescriber can advise on personalised dietary adjustments.
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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.
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Best Foods to Eat With Both Medications
Regardless of whether you're taking Mounjaro or Wegovy, prioritise protein-rich, nutrient-dense foods that won't cause digestive upset:
- Lean proteins: chicken, turkey, white fish, eggs, Greek yoghurt — easier to digest than fatty meats
- Low-fibre carbs initially: white rice, white bread, pasta — switch to wholemeal as your tolerance improves
- Cooked vegetables: carrots, spinach, broccoli (soft), sweet potato — easier to digest than raw
- Healthy fats in small amounts: olive oil, avocado, nuts — but start cautiously as these can trigger nausea
Avoid high-fat, greasy, and heavily processed foods initially. Stay hydrated and eat slowly — both improve tolerance with either medication.
- 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 mean I have to avoid certain foods completely?
No. Mounjaro doesn't prohibit any foods, but nausea and reduced appetite may make fatty, spicy, or rich foods feel unappealing naturally. Most people find their tolerance improves within 4–8 weeks. Your GP can advise on personalised dietary guidance based on your specific side effects.
Can I eat the same foods on Mounjaro and Wegovy?
Yes, broadly. Both medications work through reduced appetite and slower digestion, so the same general principles apply: lean proteins, cooked vegetables, and whole grains work well. Individual tolerance may vary slightly due to the different mechanisms, but food choices are similar.
Will Mounjaro or Wegovy work without changing my diet?
Both medications are prescription-only treatments designed to be used alongside a reduced-calorie diet and increased physical activity — not instead of them. Clinical trials (SURMOUNT and STEP) showed best results when medication was paired with lifestyle changes. Your prescriber will discuss realistic dietary expectations.
Is it normal to feel nauseous with certain foods on these injections?
Yes, very common. Nausea is the most frequently reported side effect in the first 4 weeks of Mounjaro or Wegovy, particularly with fatty or rich foods. Most people adapt over time. If nausea is severe or persistent, contact your prescriber — dose adjustment or timing of meals can help.
Can I use the MyWeightCheck BMI calculator to track if my new diet is working?
Yes. Calculate your BMI now using the free BMI calculator on this page, then track it alongside your weight using our free progress tracker to see if your dietary changes and medication are supporting sustainable results. Monitor progress every 4–8 weeks.
Ready to take control of your weight loss journey?
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