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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Weight Loss Meal Replacements — What Works in the UK
Meal replacement shakes, soups, and sachets are popular UK weight loss tools that replace one or more daily meals with a lower-calorie alternative. They can support weight management by making calorie counting easier and providing structured nutrition. However, they work best alongside lifestyle changes rather than as a standalone solution. Understanding how meal replacements fit into a broader NHS weight loss approach—including diet, activity, and sometimes prescription options—helps you choose the right strategy for sustainable results.
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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 through calorie deficit. A typical meal replacement shake contains 150–250 kcal, compared to an average meal of 600–800 kcal, creating a significant daily deficit. The NHS recommends a deficit of around 500 kcal per day for sustainable loss of approximately 0.5 kg per week. Meal replacements also help by:
- Reducing decision fatigue around food choices
- Providing consistent macro and micronutrient balance
- Offering portion control without measuring
- Supporting appetite control through structured meal timing
Popular UK options include Slimfast, Herbalife, Cambridge Diet, and supermarket own-brand shakes. Most include protein and fibre to help you feel fuller. Use our free BMI calculator to understand your starting point, then consider meal replacements as part of a wider weight management UK plan rather than a structured approach.
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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.
Meal Replacements vs Prescription Weight Loss Options
While meal replacements address calorie intake, prescription weight loss medications like GLP-1 injections work differently—they help regulate appetite itself. For adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions, a GP may refer you to NHS weight loss services or private prescribing for options like Wegovy (semaglutide) or Mounjaro (tirzepatide).
Clinical trials show these medications may help reduce appetite and support feeling fuller after smaller portions, often resulting in greater average weight loss than meal replacements alone. The best approach often combines elements: structured eating (including meal replacements), increased physical activity, and—where clinically appropriate—prescription medication. Track your progress with our free progress tracker as you test what works for you.
- 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.
Are meal replacement shakes effective for weight loss?
Yes, meal replacements can support weight loss by creating a calorie deficit, which is essential for losing weight. They work best when combined with healthy eating habits on non-replacement days and regular physical activity. Individual results vary—some people lose weight consistently, while others plateau if they don't combine replacements with broader lifestyle changes.
Can I use meal replacements on the NHS?
Meal replacements are not NHS-prescribed products, but they are widely available in UK supermarkets and pharmacies. The NHS supports calorie-deficit approaches and may recommend structured dietary approaches through weight management services. Your GP can advise whether meal replacements fit your personal weight loss plan alongside other strategies.
How long can I use meal replacement shakes safely?
Most UK products are designed for short to medium-term use (8–12 weeks) alongside one or two regular meals daily. Very low-calorie liquid diets (under 800 kcal/day) should only be followed under medical supervision. For sustained weight loss beyond a few months, transitioning to regular balanced meals with smaller portions is recommended to avoid nutrient deficiencies and support long-term habits.
Do meal replacements work better than prescription weight loss injections?
Meal replacements and prescription medications work differently. Meal replacements reduce calorie intake; GLP-1 medications help regulate appetite. Clinical trials of Wegovy (semaglutide) show participants lost an average of around 15% of body weight—often more than meal replacements alone. For best results, many people combine diet control (including meal replacements if helpful) with prescription medication if eligible and prescribed by their GP.
Should I use meal replacements if I'm eligible for Mounjaro or Wegovy?
Not necessarily either/or. If prescribed a GLP-1 medication, you'll still need to eat regular, nutritious meals—the medication helps regulate appetite, not replace eating. Some people find meal replacements helpful for structure during the first few weeks of medication, while others move straight to regular balanced meals. Always discuss your approach with your prescriber or GP for personalised guidance.
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.