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
Keto and Mounjaro: Can You Combine Them?
Many people ask whether they can follow a ketogenic (keto) diet while taking Mounjaro (tirzepatide). The short answer is yes — but there are important considerations. Mounjaro is a prescription-only weight management injection that works alongside dietary changes, not instead of them. A keto diet is a low-carbohydrate eating approach. Both can theoretically work together, though your approach should be guided by your GP or prescriber. This guide explains how Mounjaro works, how keto diets function, and what you should consider before combining them.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
How Mounjaro and Keto Work Together
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — a once-weekly injection that may help regulate appetite and reduce food cravings by activating two natural hormone pathways. It works by slowing gastric emptying (how quickly food leaves your stomach) and signalling to your brain that you feel fuller after meals.
A ketogenic diet is a high-fat, moderate-protein, very low-carbohydrate eating plan that shifts your body into ketosis, where it burns fat for fuel instead of carbohydrates. This typically involves limiting carbs to under 50g per day.
In theory, Mounjaro and keto can complement each other — Mounjaro reduces appetite while keto provides a structured dietary framework. However, combining them means you're using two weight loss mechanisms simultaneously, which requires careful monitoring.
Clinical trials of Mounjaro showed average weight loss of 15–21% of body weight over 72 weeks, achieved alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Important Considerations and Safety Points
If you're considering combining a keto diet with Mounjaro, discuss this with your GP or the prescriber who manages your Mounjaro treatment. They need to know about any dietary changes because:
- Medication interactions: Keto can affect how your body processes medications, particularly if you're also taking diabetes medication or other prescriptions
- Side effects may intensify: Mounjaro commonly causes nausea, constipation, and reduced appetite — a restrictive keto diet might worsen these
- Nutritional balance: Both keto and Mounjaro require attention to ensure you're getting adequate nutrients, fibre, and hydration
- Blood sugar monitoring: If you have type 2 diabetes or prediabetes, combining both approaches affects your blood sugar levels and may require medication adjustments
Never start a keto diet without mentioning it to your prescriber. Your GP can advise whether it's safe for your individual health circumstances and monitor you appropriately.
- 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 follow a keto diet while taking Mounjaro?
Yes, you can combine them, but it requires your GP's approval first. Both approaches aim for weight loss, so combining them intensifies the effect — which needs medical oversight. Mounjaro can cause reduced appetite and digestive changes; keto is already restrictive. Discuss this combination with your prescriber before starting any new diet.
Will Mounjaro work better with a keto diet?
Evidence suggests Mounjaro works effectively alongside a standard reduced-calorie diet. Adding keto may increase weight loss initially, but long-term outcomes depend on what you can sustain. The most effective diet is one you can stick to long-term. Your prescriber can advise on the best dietary approach for your individual circumstances.
Are there side effects of combining keto and Mounjaro?
Mounjaro commonly causes nausea, constipation, and reduced appetite — all of which may be intensified by keto's restrictive nature. You might experience more digestive discomfort, fatigue, or nutrient deficiencies. This is why medical supervision is essential. Your GP can monitor you and adjust your approach if needed.
What's the difference between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist with average weight loss of 15–21%. Wegovy (semaglutide) is a GLP-1 agonist alone with average weight loss around 15%. Both are prescription-only and work alongside lifestyle changes. Your prescriber will determine which is suitable for you based on your health profile.
How do I track my progress with Mounjaro and diet changes?
Use our free GLP-1 weight loss calculator to estimate potential outcomes at different Mounjaro doses. Our BMI calculator helps you track how your weight relates to healthy ranges, and our free progress tracker lets you log weekly weight changes alongside dietary and exercise notes — all essential for discussing progress with your GP.
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.