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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One Meal A Day Weight Loss Results in 30 Days
One meal a day (OMAD) is an extreme fasting approach that significantly restricts eating to a single daily window. While gradual weight management is possible in the first 30 days, the results are often unsustainable and can pose serious health risks. In the UK, if you're looking for sustainable weight management backed by clinical evidence, prescription options like Mounjaro and Wegovy are available through NHS weight loss services or private assessment. This guide explains what OMAD results typically look like, the risks involved, and evidence-based prescription weight management alternatives available to eligible UK adults.
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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.
OMAD Results in 30 Days — What the Evidence Shows
One meal a day can produce rapid initial weight loss in the first 30 days, typically ranging from 2–5 kg (4–11 lbs), though individual results vary significantly. This early loss is largely water weight and glycogen depletion rather than sustained fat loss.
- Week 1–2: Rapid loss of 1–1.5 kg due to glycogen depletion and reduced water retention
- Week 3–4: Loss typically slows to 0.5–1 kg per week as the body adapts
- Metabolic adaptation: OMAD can trigger metabolic slowdown, making continued weight loss harder after the initial period
However, OMAD carries significant health risks including nutrient deficiencies, muscle loss, disrupted hormones, and gallstone formation. It is not recommended by the NHS or major health organisations for sustainable weight management in the UK. If you're considering gradual weight management, speaking with your GP about evidence-based prescription weight management options is safer and more effective.
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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.
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Prescription Weight Management Options Available in the UK
For eligible UK adults seeking sustainable weight management backed by clinical evidence, prescription GLP-1 medications are available through NHS specialist services or private assessment. Mounjaro (tirzepatide) and Wegovy (semaglutide) are the two main options — both licensed for weight management and showing realistic, sustained weight loss results without the risks of extreme fasting.
- Mounjaro: Clinical trials showed average weight loss of 15–21% body weight over 72 weeks
- Wegovy: Clinical evidence supports average weight loss of approximately 15% body weight
- Eligibility: Adults with BMI ≥30, or BMI ≥27 with weight-related health conditions
- NHS access: Referral through GP to tier 3 specialist weight management services (waiting times vary by region)
- Private access: Available through UK-licensed prescribers following online clinical assessment
Try our free GLP-1 weight loss calculator to see projected realistic results with prescription weight management options, alongside a reduced-calorie diet and increased physical activity.
- 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 you support gradual weight management safely with one meal a day?
Extremely rapid loss of 10kg in 30 days would require a severe calorie deficit and is unsafe. The NHS recommends losing 0.5–1kg per week for sustainable results. OMAD may produce 2–5kg loss initially (mostly water weight), but comes with risks including muscle loss, nutrient deficiency, and metabolic damage. Prescription weight management with medication is evidence-based and safer.
What happens to your metabolism after 30 days of OMAD?
After the initial 30-day period, OMAD often triggers metabolic adaptation — your body becomes more efficient at conserving energy, making continued weight loss harder. Muscle loss is also common, which further slows metabolism. This is why extreme restriction is unsustainable. Balanced approaches with moderate calorie deficit and prescription support work better long-term.
Is one meal a day safe for 30 days?
One meal a day is not recommended by the NHS or health professionals for 30 days or longer. Risks include nutrient deficiencies, hormonal disruption, gallstone formation, muscle loss, and disordered eating patterns. If you're interested in rapid yet safer weight loss, speak with your GP about prescription weight management options available in the UK.
What are realistic 30-day weight loss results with UK prescription medication?
With Mounjaro or Wegovy at starting doses, realistic 30-day results are typically 1.5–3kg alongside a reduced-calorie diet and exercise. These medications work more gradually than OMAD but produce sustainable results. Clinical trials showed average weight loss of 15–21% over several months, not days. Use our free GLP-1 weight loss calculator to estimate potential results.
Can my GP prescribe weight loss injections on the NHS?
GPs can refer you to specialist tier 3 weight management services where Mounjaro and Wegovy may be prescribed. However, NHS availability and waiting times vary by region. Private prescription is also available through UK-licensed online services following clinical assessment. Ask your GP about both NHS and private pathways in your area.
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.