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
Free tracker included with every download this week
Low Calorie Weight Loss — What You Need to Know
Low calorie weight loss involves eating significantly fewer calories than your body normally requires — typically between 800 and 1,200 calories per day. This approach can produce faster results than standard calorie restriction, but the NHS recommends it only under medical supervision due to potential risks like nutrient deficiency and muscle loss. Understanding how low calorie diets work, who they suit, and what support is available in the UK will help you make informed decisions about weight management.
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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 Low Calorie Diets Work and NHS Guidance
Low calorie diets (LCDs) create a substantial energy deficit, forcing your body to use stored fat for fuel. The standard recommendation in the UK for safe, sustainable weight loss is losing 0.5 to 1 kg per week — achieved through a moderate deficit of around 500 calories daily. Low calorie approaches aim for faster loss (1–1.5 kg weekly or more) but require careful planning.
The NHS categorises weight loss diets as:
- Moderate calorie restriction: 1,500–1,800 kcal/day for women, 1,900–2,200 kcal/day for men — safe for self-directed weight loss
- Low calorie diet (LCD): 800–1,200 kcal/day — requires GP supervision and typically lasts 8–12 weeks
- Very low calorie diet (VLCD): under 800 kcal/day — only under specialist medical care, usually with meal replacement products
Calculate your baseline energy needs using our free BMI calculator, then discuss a personalised deficit with your GP before starting any structured low calorie approach.
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.
Medical Support and When Low Calorie Diets Are Appropriate
Low calorie diets are most effective when combined with medical supervision, lifestyle changes, and psychological support. Your GP may recommend an LCD as part of NHS weight management services, especially if you have obesity-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea.
For some patients, prescription weight loss medication — such as GLP-1 injections — may be recommended alongside dietary changes. These work by reducing hunger and appetite, making it easier to maintain a moderate calorie deficit naturally, rather than enforcing severe restriction. Our GLP-1 weight loss calculator can help you understand how medication and lifestyle combine for weight loss. Always consult your GP before starting any new diet or weight loss plan.
Track your progress consistently using our free progress tracker — logging weight, measurements, and how you feel helps identify what works for your body. Remember that low calorie diets require adequate protein (to preserve muscle), plenty of vegetables for nutrients and satiety, and consistent hydration. gradual weight management can sometimes cause hair loss, fatigue, or gallstones — reasons why medical oversight matters. If you experience severe fatigue, dizziness, or unusual symptoms on a low calorie diet, stop and contact your GP immediately.
- 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's the difference between a low calorie diet and a very low calorie diet?
A low calorie diet (LCD) is 800–1,200 kcal/day and can be followed under GP supervision for 8–12 weeks. A very low calorie diet (VLCD) is under 800 kcal/day and only under specialist care, usually with meal replacement products. VLCDs produce faster weight loss but carry higher risks of nutrient deficiency and muscle loss.
Is a low calorie diet safe to do on my own?
No — the NHS recommends low calorie diets only under medical supervision. Moderate calorie restriction (1,500–1,900 kcal/day depending on your sex) is safer for self-directed weight loss. Always speak to your GP before significantly restricting calories, especially if you take medication or have existing health conditions.
How much weight can you lose on a low calorie diet per week?
On an 800–1,200 kcal/day diet, loss is typically 1–1.5 kg per week, though it varies by individual metabolism, starting weight, and activity level. The NHS recommends a sustainable rate of 0.5–1 kg weekly. Faster loss increases risks of nutrient deficiency, muscle loss, and gallstones.
Can prescription weight loss medication replace a low calorie diet?
Prescription medications like GLP-1 injections are designed to work alongside dietary changes, not replace them. They reduce hunger and appetite cravings, making it easier to maintain a moderate calorie deficit naturally. A GP assesses whether medication is suitable for you based on your BMI and health conditions.
What should I eat on a low calorie diet?
Focus on high-protein foods (lean meat, fish, eggs), plenty of vegetables for volume and nutrients, and whole grains in moderation. Avoid sugary drinks, processed foods, and oils. Meal planning with a dietitian (available through NHS weight management services) helps ensure you get adequate nutrients within your calorie target.
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.