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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Eating 1 Meal A Day For Weight Loss — What You Need To Know
Eating just one meal a day (often called OMAD — One Meal A Day) is an extreme form of intermittent fasting that some people try for weight loss. While it can create a significant calorie deficit, it carries health risks including nutritional deficiencies, muscle loss, and low energy. The NHS recommends safer, more sustainable approaches to weight loss alongside lifestyle changes. For eligible adults in the UK, prescription weight management medications are available that may help achieve weight loss without extreme dietary restriction.
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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.
Prescription Weight Loss Options Available In The UK
If you're struggling with weight management, prescription weight loss medications are now available in the UK for eligible adults. These are NHS-recognised treatments that work alongside dietary changes rather than requiring extreme eating patterns.
Three medications are currently licensed for weight management in the UK:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist administered once weekly
- Wegovy (semaglutide) — a GLP-1 receptor agonist injected once weekly
- Saxenda (liraglutide) — a GLP-1 receptor agonist injected once daily
In clinical trials, these medications helped participants lose between 14–21% of their body weight on average. You may be eligible if your BMI is 30 or above, or 27 or above with a weight-related health condition such as type 2 diabetes, high blood pressure, or sleep apnoea. Use our free GLP-1 weight loss calculator above to explore potential outcomes at different doses, and our BMI calculator to check your current BMI status.
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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.
NHS Access Versus Private Prescriptions In The UK
NHS access to prescription weight loss medication is available through specialist tier 3 weight management services. You'll need a GP referral, and availability varies significantly by region — some areas have waiting lists of several months. Your GP can advise you on local services.
Private access is available through UK-licensed prescribers following an online clinical assessment, without needing NHS referral. Costs typically range from £129–£320 per month depending on the medication and dose.
Rather than attempting extreme diets like one meal a day, talk to your GP about whether prescription weight loss treatment might suit you. They can assess your health, discuss eligibility, and explore both NHS and private options. Sustainable weight management works best when supported properly.
- 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.
Is eating one meal a day safe for weight loss?
Eating one meal a day (OMAD) can cause nutritional deficiencies, muscle loss, extreme hunger, fatigue, and metabolic slowdown. The NHS recommends losing weight at 0.5–1 kg per week through balanced nutrition and activity, not extreme restriction. Safer alternatives like prescription medication are available for eligible adults.
How much weight can you lose eating one meal a day?
Initial gradual weight management is often water and muscle loss, not fat loss. Long-term outcomes are usually poor because OMAD is unsustainable and leads to rebound weight gain. Evidence-based approaches like prescribed GLP-1 medication alongside lifestyle changes produce more sustainable results.
What's a healthier alternative to one meal a day for weight loss?
The NHS recommends a balanced, reduced-calorie diet (around 500 kcal deficit daily for 0.5 kg weekly loss), regular physical activity, and adequate sleep. Prescription weight loss medications like Mounjaro or Wegovy may help eligible adults; ask your GP if you qualify.
Can I get weight loss medication on the NHS in the UK?
Yes. Tirzepatide (Mounjaro) and semaglutide (Wegovy) are now approved by NICE for NHS use through specialist weight management services. Access requires a GP referral to tier 3 services. Availability varies by region; your GP can advise on local provision and waiting times.
What does the GLP-1 medication do that makes it work for weight loss?
GLP-1 medications like Wegovy activate a natural gut hormone pathway that reduces appetite, helps you feel fuller after smaller meals, and slows digestion. This supports sustainable weight loss alongside dietary changes, without requiring extreme eating patterns like OMAD.
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.