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 Diet Plans for Weight Loss in the UK
Losing weight successfully involves finding an approach that works for your lifestyle and health needs. In the UK, effective weight management combines dietary changes, increased physical activity, and — for eligible adults — prescription weight loss medication. This guide covers the most evidence-based diet plans available to UK residents, alongside prescription options that may support your weight loss journey. Understanding your BMI and individual health circumstances is the first step toward choosing the right plan for you.
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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.
Evidence-Based Diet Plans and Prescription Weight Management
The most effective diet plans for weight loss share one common feature: they create a sustainable calorie deficit. The NHS recommends losing weight at a rate of 0.5 to 1 kg per week for long-term success.
- Mediterranean diet: Strong evidence for sustainable weight loss and cardiovascular health. Emphasises whole grains, vegetables, olive oil, and lean proteins.
- Low-carbohydrate diets: Effective short-term weight loss, though long-term outcomes are similar to standard calorie restriction.
- Intermittent fasting (16:8 or 5:2): Emerging evidence supports modest weight loss when combined with overall calorie deficit.
- Prescription weight loss medication: For eligible adults, GLP-1 weight loss injections like Mounjaro (tirzepatide) and Wegovy (semaglutide) are NHS-approved and available privately. Clinical trials show average weight loss of 15–21% body weight alongside dietary changes. Saxenda (liraglutide) is also available as a daily injection option. All prescription options require a clinical assessment and work best combined with lifestyle changes, not as a replacement for them.
Use our free BMI calculator to assess your current weight category and determine if you might be eligible for prescription support.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
NHS Access vs Private Weight Loss Options
In the UK, adults with a BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions, may be eligible for prescription weight loss treatment. The NHS pathway involves referral to a specialist tier 3 weight management service through your GP — though availability varies significantly by region and waiting times can be lengthy.
Private access to prescription weight loss medication is available through registered online prescribers following a clinical assessment, without requiring an NHS referral. Either route requires evaluation by a licensed prescriber who will assess your medical history and suitability. Start by speaking with your GP about your weight management goals — they can advise on both NHS and private options available to you, and help determine if medication is appropriate. Our GLP-1 weight loss calculator can help you estimate potential outcomes if you're considering prescription support.
- 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 best diet plan for weight loss?
The best diet plan is one you can sustain long-term. Mediterranean, low-carbohydrate, and intermittent fasting approaches all have evidence supporting weight loss when combined with a calorie deficit of around 500 kcal per day (approximately 0.5 kg loss weekly). Consider your lifestyle, food preferences, and health conditions when choosing. Your GP or a registered dietitian can provide personalised advice.
Can I get prescription weight loss medication on the NHS in the UK?
Yes, if you're eligible. Adults with BMI ≥30 or BMI 27–29.9 with weight-related conditions may access prescription weight loss injections through NHS specialist weight management services. Referral comes from your GP. Availability and waiting times vary significantly by region. Ask your GP about referral options in your area.
What is the fastest safe rate of weight loss?
The NHS recommends losing 0.5–1 kg per week for sustainable, healthy weight loss that preserves muscle mass. This typically requires a calorie deficit of around 500 kcal daily. Faster weight loss is possible with medical supervision but increases risks of nutrient deficiency and muscle loss. Crash diets are not recommended.
How do GLP-1 injections like Mounjaro and Wegovy work for weight loss?
GLP-1 medications mimic natural gut hormones that signal fullness to your brain, reduce appetite, and slow digestion. Clinical trials show average weight loss of 15–21% body weight over 68–72 weeks when combined with reduced-calorie diet and increased activity. Individual results vary significantly. Both require prescription and clinical assessment.
Should I combine diet changes with prescription weight loss medication?
Yes. Prescription weight loss medications work best alongside sustainable dietary changes and increased physical activity — not as a replacement for lifestyle changes. Your prescriber will discuss this as part of clinical assessment. The combination approach typically produces better long-term results than either approach alone.
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.