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
How Mounjaro Affects Your Meals and Eating
Mounjaro (tirzepatide) is a prescription-only once-weekly injection that works by activating two natural hormone pathways (GIP and GLP-1) to help regulate appetite and support feeling fuller after smaller meals. Many people taking Mounjaro notice significant changes in how they eat, including reduced appetite, altered food preferences, and smaller portion sizes. Understanding what to expect with meals can help you manage the adjustment period more effectively and support sustainable weight management alongside dietary changes and increased physical activity.
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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 Mounjaro Changes Eating and Meal Size
Mounjaro works by signalling to your brain that you're full, which typically results in naturally eating less without feeling deprived. Most people on Mounjaro report:
- Reduced appetite and food cravings throughout the day
- Feeling fuller after smaller meal portions
- Less interest in snacking between meals
- Changed food preferences — some foods become less appealing
- A slower pace of eating without conscious effort
The appetite suppression usually becomes noticeable within the first 1–2 weeks and often increases as your dose increases from the starting dose of 2.5 mg up to the maximum 15 mg. This is why a reduced-calorie diet works well alongside Mounjaro — you're naturally eating less, making a calorie deficit easier to maintain. Clinical trials showed that participants on Mounjaro at maximum dose lost an average of approximately 21% of their body weight, though individual results vary considerably.
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.
Common Meal-Related Side Effects and Management
Nausea is the most commonly reported side effect of Mounjaro and often affects eating habits. It typically occurs when starting or increasing your dose and usually improves within a few days to a week as your body adjusts. Managing nausea: eat smaller, more frequent meals; avoid fatty or rich foods; stay hydrated; eat slowly; and take ginger or peppermint tea if tolerated. Some people experience constipation or diarrhoea — both can affect appetite and meal enjoyment. If nausea persists beyond a week or severely impacts your ability to eat nutritious meals, contact your prescriber. Severe or worsening stomach pain requires urgent medical attention. Track your progress using our free progress tracker to monitor how your eating and weight change over time.
- 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.
Will Mounjaro stop me from eating enough?
No. Mounjaro reduces appetite, but you should still eat enough nutritious meals to meet your energy and nutrient needs. If you're struggling to eat adequate food, feel unwell, or notice signs of malnutrition, speak to your GP or prescriber immediately.
What should I eat when taking Mounjaro?
Focus on protein-rich foods, vegetables, whole grains, and adequate hydration. Avoid very fatty, greasy, or sugary foods — these may trigger nausea and are less satisfying anyway. Smaller, balanced meals work better than large meals. Your prescriber or a dietitian can give personalised nutrition advice.
Does Mounjaro affect meal timing?
Not directly, but many people naturally eat fewer meals per day because they feel full longer. Some skip breakfast or lunch without hunger. There's no required meal timing — eat when hungry. Your body signals appetite differently, so listen to your hunger cues.
How long does nausea from Mounjaro last?
Nausea typically peaks in the first few days after starting or increasing a dose and improves within 3–7 days as your body adjusts. Most people adapt well. Eating smaller meals, staying hydrated, and avoiding rich foods helps. If nausea persists beyond a week, contact your prescriber.
Can I use a weight loss calculator to predict results with Mounjaro?
Yes. Our free GLP-1 weight loss calculator can help you estimate potential weight loss based on your starting weight and dose, though individual results vary. Clinical trials showed Mounjaro at 15 mg (maximum dose) helped participants lose approximately 21% of body weight on average alongside reduced-calorie diet and physical activity.
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.