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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Meal Replacements for Weight Loss: What Works?
Meal replacements are convenience foods designed to replace one or more daily meals whilst maintaining a reduced calorie intake. In the UK, they're commonly used as part of structured weight management plans and evidence suggests they can help support weight loss when combined with lifestyle changes. However, their effectiveness depends on how they fit into your overall weight management strategy. Our free BMI calculator can help you understand your current weight status, whilst our GLP-1 weight loss calculator shows how different approaches — including meal replacements alongside prescription options — might help you reach your goals.
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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.
How Meal Replacements Support Weight Loss
Meal replacements work by creating a calorie deficit — the foundation of any weight management uk programme. By replacing a standard meal (typically 600–800 kcal) with a prepared shake, bar, or soup (usually 200–400 kcal), you consume fewer calories without having to plan or prepare meals. The NHS recognises calorie control as essential for weight loss, recommending a deficit of approximately 500 kcal per day for sustainable loss of around 0.5 kg per week.
Common UK meal replacement brands include Slim-Fast, Herbalife, and Cambridge Diet — these are available over-the-counter and require no prescription. Some are fortified with vitamins and minerals to help maintain nutrition during dieting. However, research shows meal replacements work best when they're part of a structured approach that also includes:
- Behaviour change and habit formation
- Increased physical activity
- Learning sustainable eating patterns for long-term weight maintenance
For individuals seeking additional support, prescription weight loss medication such as GLP-1 injections (Wegovy or Mounjaro) may be recommended by a GP or specialist weight management service. These work through different mechanisms — suppressing appetite and supporting fuller feelings — and can be used alongside dietary approaches including meal replacements.
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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.
Meal Replacements vs Prescription Weight Loss Options
Meal replacements offer convenience and immediate calorie control but rely entirely on your ability to stick to the plan. Prescription weight loss medication like Wegovy (semaglutide) works differently — it's a once-weekly GLP-1 injection that helps reduce appetite and food cravings. Clinical trials showed participants on Wegovy at the maximum dose lost an average of around 15% of their body weight, though results vary.
Neither approach is "better" — they suit different people. Meal replacements need no prescription and are immediately available. Prescription options require clinical assessment and a GP referral (NHS) or private consultation, but provide pharmacological support that may make sustained weight loss easier. Many people combine both: using meal replacements for convenience whilst also addressing appetite regulation through medication. Your GP can help you decide which approach — or combination — suits your health situation and weight loss goals.
- 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.
Do meal replacements really work for weight loss?
Yes, when used consistently. By reducing calories, they support weight loss. However, studies show that stopping meal replacements often leads to weight regain unless eating habits have changed. They work best as part of a broader weight management uk plan including behaviour change and physical activity.
Are meal replacements safe to use long-term?
Short-term use (8–12 weeks) is generally safe for most adults. Long-term exclusive use isn't recommended because whole foods provide nutrients and fibre that shakes and bars cannot fully replicate. The NHS suggests meal replacements should be temporary tools, not permanent solutions.
Can I combine meal replacements with prescription weight loss medication?
Yes, many people use both together. Meal replacements provide structured calorie control whilst prescription options like GLP-1 weight loss injections reduce appetite. Your prescriber can advise whether combining both suits your situation. Use our GLP-1 weight loss calculator to explore this option.
How much weight can I lose with meal replacements?
Results vary significantly. With a typical meal replacement approach (replacing 1–2 meals daily alongside healthy meals), many people lose 0.5–1 kg per week initially. However, the rate slows over time. Individual factors including age, activity level, and starting weight all affect outcomes.
Are meal replacements better than just eating fewer calories myself?
Not necessarily better, but often easier. Meal replacements remove decision-making and portion guesswork. For some people, this structure helps maintain a calorie deficit. Others find self-planning sustainable. Both approaches work — choose whichever you can sustain. Try our weight converter and BMI calculator to track your progress.
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.