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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Diet Plan for Weight Loss and Muscle Gain
Losing weight while building muscle is possible, but it requires a different approach to simple calorie restriction. The key is maintaining adequate protein intake, strength training, and a moderate calorie deficit — not an aggressive one. This guide explains how to structure a diet that supports both goals, including the role of NHS weight management, prescription options, and practical strategies for UK adults looking to transform their body composition.
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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 to Lose Weight While Building Muscle
The traditional approach to weight loss focuses solely on reducing calories, but building muscle requires a different strategy. Body recomposition — losing fat while gaining muscle — is most effective when you combine three elements: a moderate calorie deficit (300–500 kcal per day), adequate protein intake (around 1.6–2.2g per kg of body weight), and progressive strength training at least 3 times per week.
- Calorie deficit: Too aggressive (over 1000 kcal deficit) causes muscle loss alongside fat loss. A moderate deficit of 300–500 kcal per day allows fat loss whilst preserving lean tissue.
- Protein intake: High protein is critical for muscle repair and growth. Aim for protein at every meal — chicken, fish, eggs, yoghurt, legumes, and protein-rich foods.
- Strength training: Progressive resistance work signals your body to preserve and build muscle, even in a calorie deficit.
- Recovery: Sleep 7–9 hours per night and manage stress — both affect hormone levels and muscle recovery.
Rate of change: expect slow, sustainable progress. You may lose 0.5 kg of fat per week while gaining 0.5 kg of muscle, meaning the scale changes slowly but body composition improves significantly.
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.
Diet Composition and Meal Planning
A practical diet for weight loss and muscle gain typically includes 40% protein, 35% carbohydrates, and 25% fats, though individual needs vary. Carbohydrates fuel strength training, protein supports muscle growth, and fat maintains hormone balance. Use our free BMI calculator to assess your starting point, then calculate your daily calorie target: multiply your bodyweight (kg) by 22–24 to get a baseline maintenance estimate, then subtract 300–500 for a deficit.
Meal timing helps: eat protein and carbohydrates around your workouts, and distribute protein evenly across the day (30–40g per meal) rather than concentrated at one meal. Hydration, micronutrient density, and consistency matter more than perfection. Track intake using a food app for 2–4 weeks to learn portion sizes, then adjust based on progress — weight loss, energy levels, and strength gains.
- 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 lose weight and gain muscle at the same time?
Yes, especially if you're new to strength training or returning after a break. This is called body recomposition — losing fat whilst building muscle. It happens slower than pure weight loss or muscle gain alone, but the result is better body composition and strength. Adequate protein, moderate calorie deficit, and progressive resistance training are essential.
How much protein do I need for muscle gain while losing weight?
Aim for 1.6–2.2g of protein per kilogram of body weight per day. For an 80kg adult, that's roughly 128–176g daily. This supports muscle repair and growth during a calorie deficit. Spread protein across meals — 30–40g per meal is most effective for muscle protein synthesis.
Can prescription weight loss medication help with body recomposition?
GLP-1 weight loss medications like Wegovy may support fat loss by reducing appetite, but they don't build muscle. Combining prescription weight management with strength training and high protein intake could support body recomposition — but this should only be attempted under GP or prescriber guidance. Always discuss fitness goals with your prescriber.
How do I calculate my calorie deficit for weight loss and muscle gain?
Estimate daily maintenance calories (bodyweight in kg × 22–24), then subtract 300–500 kcal for a moderate deficit. Use our free BMI calculator and weight converter to track your starting point. Track actual food intake for 2–4 weeks, monitor progress, and adjust by 100–200 kcal if needed based on weight trends and strength.
How long does body recomposition take to see results?
Changes are slower than pure weight loss. You may see strength improvements within 4–6 weeks and visible body composition changes within 8–12 weeks. The scale may change slowly because muscle is denser than fat. Use progress photos, measurements, and strength metrics — not just scale weight — to track success. Our free progress tracker helps log these changes.
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.