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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Best Weight Loss Diet Plan for UK Adults
Finding the best weight loss diet plan means combining sustainable eating habits with support from your GP and, if eligible, prescription weight management options. The most effective approach combines dietary changes, increased physical activity, and professional guidance tailored to your individual health needs. Whether you're looking for diet-only strategies or considering weight management medication available through the NHS or private prescribing in the UK, this guide covers evidence-based options to help you achieve sustainable weight loss. Start by calculating your BMI using our free BMI calculator to understand your current weight status and eligibility for different support options.
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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.
UK-Licensed Prescription Weight Loss Options
For UK adults who meet clinical eligibility criteria, prescription weight loss medications offer evidence-based support alongside lifestyle changes. The main weight loss injections available in the UK include:
- Mounjaro (tirzepatide) — dual GIP and GLP-1 receptor agonist; clinical trials showed average weight loss of 15–21% over 72 weeks; once-weekly injection
- Wegovy (semaglutide) — GLP-1 receptor agonist; clinical evidence demonstrates approximately 15% average weight loss; once-weekly injection
- Saxenda (liraglutide) — GLP-1 receptor agonist; once-daily injection option for those preferring daily dosing
Eligibility typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. These are prescription-only medicines requiring clinical assessment before prescribing. Access through the NHS involves referral to specialist tier 3 weight management services, though availability varies significantly by region. Private prescribing is also available through UK-licensed prescribers following an online assessment. Our GLP-1 weight loss calculator can help estimate potential results at different doses when used alongside reduced-calorie diet and increased physical activity.
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.
NHS Tier Approach vs Private Access
The best weight loss diet plan approach in the UK depends on your preferences, timeline, and circumstances. Through the NHS weight loss pathway, you receive support from specialist multidisciplinary teams, but waiting lists in many areas can extend several months or longer. Private weight management through a UK-licensed prescriber offers faster access without NHS referral, though costs typically range from £129–£320 monthly depending on medication and dose. Both routes require you to commit to dietary changes and physical activity — medication supports but does not replace lifestyle modification. Start a conversation with your GP to discuss your weight management goals and eligibility. You can use our free weight converter to track weight changes between kg and stone, and our progress tracker to log your journey alongside any dietary or medication adjustments your healthcare team recommends.
- 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.
What is the most effective weight loss diet plan for UK adults?
Evidence supports a combination approach: sustainable calorie deficit (typically 500 kcal/day for 0.5 kg weekly loss), Mediterranean or low-carbohydrate diet frameworks, regular physical activity, and professional support. The NHS recommends losing no more than 0.5–1 kg per week. For eligible adults, prescription GLP-1 or dual GIP/GLP-1 medications provide evidence-based support alongside lifestyle changes, with clinical trials showing 15–21% average weight loss over several months.
Am I eligible for prescription weight loss medication on the NHS?
You may be eligible if your BMI is 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or cardiovascular disease. For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds may apply. Speak to your GP about referral to your local tier 3 specialist weight management service. Eligibility assessment is individualised.
What's the difference between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist; Wegovy (semaglutide) is a GLP-1-only agonist. Clinical trials show Mounjaro produced average weight loss of 15–21%, slightly higher than Wegovy's approximately 15%. Both are once-weekly injections. Efficacy varies individually. Your prescriber will advise which is more suitable based on your medical history and preferences.
How quickly will I lose weight on prescription weight loss medication?
Weight loss is gradual and individual. Clinical trials show meaningful results after 4–8 weeks, with weight loss typically plateauing around 12–16 weeks at a stable dose. Average results are 15–clinically studied weight loss over 12–18 months. Results depend on adherence to medication, dietary changes, and physical activity. Faster loss than 1–1.5 kg weekly is not recommended without medical supervision.
Can I get weight loss medication privately in the UK without NHS referral?
Yes. Private weight management through UK-licensed prescribers (following online clinical assessment) is available without NHS referral. This typically costs £129–£320 monthly depending on medication and dose. Prescribers assess eligibility using the same clinical criteria as the NHS. Medication is dispensed by GPhC-registered pharmacies. This route offers faster access but requires you to self-fund treatment.
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.