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
Mounjaro and Keto Diet — A UK Health Guide
Many people taking Mounjaro wonder whether combining the injection with a keto (ketogenic) diet might improve their results. The short answer is: it may be possible, but requires careful planning and GP guidance. Mounjaro (tirzepatide) works by activating GLP-1 and GIP receptors to reduce appetite, while keto is a very low-carbohydrate approach. Both can support weight loss, but combining them demands attention to nutrition, side effects, and individual health. This guide explains how they might work together and what to watch for.
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 is a dual GIP and GLP-1 receptor agonist that helps regulate appetite and blood sugar. A ketogenic diet typically involves consuming fewer than 50g carbohydrates daily, shifting the body toward using fat for energy (ketosis). Theoretically, both approaches support calorie deficit and fat utilisation—the core of weight loss.
However, several practical considerations apply:
- Slower gastric emptying: Mounjaro slows how quickly food leaves the stomach, which may intensify keto's appetite suppression—potentially useful, but can cause nausea or constipation if carbohydrate intake is too low.
- Medication absorption: Very low-carb intake might affect how some medications are absorbed. Mounjaro's KwikPen injection itself is not affected, but oral medications taken alongside may be.
- Nutrient intake: Keto diets can be nutritionally challenging; Mounjaro reduces appetite further, increasing the risk of under-eating key nutrients.
- Side effects overlap: Both approaches can cause nausea, constipation, or diarrhoea—combining them may intensify these effects.
Clinical trials for Mounjaro (SURMOUNT studies) used balanced, reduced-calorie diets—not specifically ketogenic approaches. Evidence for combining tirzepatide with keto is limited.
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.
What Your GP Should Know Before Combining Them
If you're considering keto alongside Mounjaro, discuss this with your GP or prescriber before starting. They need to monitor your progress closely because:
- Very restrictive diets can increase side effect severity and nutrient deficiency risk.
- Blood sugar changes may occur differently on keto than on a standard calorie-restricted diet—important if you have diabetes or prediabetes.
- Your Mounjaro dose titration (gradual increase) may need adjustment based on your chosen diet approach.
- Some people experience better adherence and fewer side effects on a moderate, balanced diet rather than very low-carb.
A safer approach for many is a reduced-calorie, balanced diet (including moderate carbs) alongside Mounjaro, as this is what clinical evidence supports. If you strongly prefer keto, work with your prescriber to ensure it's done safely with regular check-ins. Use our free GLP-1 weight loss calculator to estimate potential outcomes with Mounjaro at different doses on your chosen diet plan.
- 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 start a keto diet while taking Mounjaro?
You can discuss keto with your GP or prescriber, but clinical evidence for Mounjaro supports balanced, reduced-calorie diets rather than very low-carb approaches. If you proceed with keto, do so under medical supervision. Combining both may intensify side effects like nausea and constipation, so close monitoring is essential.
Will Mounjaro work better on keto than a normal diet?
Clinical trials for Mounjaro (tirzepatide) used balanced diets, not ketogenic diets. Average weight loss is approximately 15–21% of body weight with Mounjaro alone. Keto might not significantly improve results and may increase side effect severity. Individual outcomes vary—your prescriber can advise what's best for you.
Does keto affect how Mounjaro works?
Mounjaro's mechanism (GIP and GLP-1 receptor activation) isn't directly changed by diet composition. However, very low-carb intake combined with Mounjaro's appetite-suppressing effects may lead to inadequate calorie or nutrient intake. The slower gastric emptying caused by Mounjaro may also intensify keto's digestive side effects.
What should I eat while taking Mounjaro instead of keto?
The NHS recommends a balanced, reduced-calorie diet: lean proteins, plenty of vegetables, whole grains in moderation, and healthy fats. Aim for a calorie deficit of around 500 kcal per day for approximately 0.5kg weight loss weekly. This approach is evidence-based for Mounjaro and typically causes fewer side effects than very restrictive diets.
Can I combine Mounjaro with other low-carb diets like Atkins?
Most low-carb diets carry similar considerations as keto: increased side effect risk, nutrient deficiency potential, and limited clinical evidence alongside Mounjaro. A moderate approach—reducing refined carbs but including vegetables, whole grains, and balanced nutrition—is safer and better supported by evidence. Always discuss with your GP first.
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.