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 Food To Avoid When Taking Mounjaro
When taking Mounjaro (tirzepatide), certain foods can trigger or worsen the most common side effects — nausea, diarrhoea, constipation, and stomach pain. While Mounjaro works by reducing appetite, what you eat matters just as much as how much you eat. This NHS-aligned guide explains which foods to limit or avoid during your treatment, helping you manage side effects and stay comfortable whilst losing weight. Your prescriber should provide guidance, but understanding trigger foods puts you in control.
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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.
Foods and Food Groups To Limit or Avoid
High-fat and fried foods are among the most problematic on Mounjaro. These slow stomach emptying further and can trigger nausea, abdominal pain, and diarrhoea. Avoid: fried chicken, chips, takeaway meals, pastries, creamy sauces, and full-fat dairy products. Very spicy foods may worsen nausea and stomach discomfort — limit chilli, curry, and heavily seasoned dishes initially, then reintroduce slowly as tolerated. Sugary and processed foods offer little nutritional value and may cause cramping or digestive distress. These include sweets, biscuits, sugary drinks, and processed snacks. Alcohol — especially on an empty stomach — can amplify nausea and dehydration. Drinking alcohol with Mounjaro is not prohibited but should be minimal and always with food. Large meals are more likely to cause discomfort than portion size itself; eat smaller, frequent meals instead. Foods high in insoluble fibre (wholegrains, beans, raw vegetables) can worsen diarrhoea initially — introduce these gradually as your digestion settles.
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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 Diet and Staying Comfortable
Focus on easily digestible, lean protein sources: grilled chicken, fish, eggs, and Greek yoghurt support satiety without triggering nausea. Hydration is critical — drink water consistently throughout the day to prevent dehydration from diarrhoea and to support appetite control. Mounjaro can reduce thirst signals, so you may need to drink more than you think. Ginger tea, peppermint tea, and plain biscuits can help settle nausea when it occurs. Keep a food diary during your first weeks on Mounjaro — noting which foods trigger symptoms helps you identify your personal triggers. Side effects often improve after the first few weeks as your body adjusts; foods that cause problems initially may become tolerable later. Always discuss persistent side effects with your GP or prescriber, as dose adjustments or modifications to your diet plan may help.
- 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 on Mounjaro?
Not immediately. Most people experience reduced appetite and nausea, particularly in the first 4 weeks. You'll naturally eat less, which is the medication's intended effect. Focus on nutrient-dense, easily digestible foods initially. As side effects settle (typically weeks 4–8), you can gradually expand your diet, avoiding known triggers.
Is it safe to eat fatty foods occasionally on Mounjaro?
Occasional small amounts are usually tolerable, but large fatty meals often trigger nausea, stomach pain, and diarrhoea. High-fat foods also slow stomach emptying, which Mounjaro already slows. Start with small portions, observe your symptoms, and adjust based on personal tolerance.
Should I avoid carbohydrates on Mounjaro?
No, not entirely. Complex carbohydrates (oats, sweet potato, brown rice) are fine and support steady energy. Refined or sugary carbs (white bread, biscuits, sugary drinks) offer little nutrition and may cause stomach discomfort. Balance carbs with protein and healthy fats for best tolerance.
What if I'm constipated on Mounjaro — should I avoid fibre?
Constipation and diarrhoea both occur on Mounjaro, often alternating. If constipated, gradually increase soluble fibre (oats, porridge, psyllium) and water intake. Avoid insoluble fibre (raw veg, wholegrain) initially as it can worsen diarrhoea. Your GP can recommend laxatives if needed.
Does food affect how well Mounjaro works?
Mounjaro's appetite-suppressing effects work regardless of food choice — the medication itself reduces hunger signals. However, eating nutrient-dense, lower-fat foods prevents nausea and discomfort, making it easier to stick with your reduced-calorie diet plan and supporting sustainable weight loss alongside your injection.
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.