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
Does Fasting Help With Weight Loss?
Fasting can support weight loss when it creates a calorie deficit, but it's not a clinically supported solution on its own. Whether intermittent fasting, time-restricted eating, or longer fasts, the key mechanism for weight loss remains the same: consuming fewer calories than your body burns. The NHS emphasises that sustainable weight management combines dietary changes with increased physical activity. Many people find fasting helpful for weight loss uk strategies, whilst others struggle with hunger or adherence. This guide explains how fasting works, what the evidence shows, and how it compares to other evidence-based approaches.
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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 Fasting Creates Weight Loss
Fasting works for weight loss by creating a calorie deficit — your body uses stored energy (fat) when you consume fewer calories than you burn. The NHS recommends losing weight at a rate of 0.5 to 1 kg per week for sustainable results, which typically requires a deficit of around 500 kcal per day.
Common fasting approaches include:
- 16:8 intermittent fasting: eating within an 8-hour window, fasting for 16 hours
- 5:2 diet: eating normally 5 days per week, restricting to 500–600 kcal on 2 non-consecutive days
- Eat-Stop-Eat: 24-hour complete fasts once or twice per week
- Time-restricted eating: limiting eating to specific hours, such as 12pm–8pm
The evidence shows that fasting creates weight loss primarily through calorie reduction, not through any special metabolic effect. When calories are equal, fasting produces similar results to traditional calorie restriction. Some people find fasting easier to follow because they have fewer eating windows to monitor.
Clinically BackedWeight Loss
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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.
Fasting vs Other Weight Loss Methods
Fasting is one approach to weight loss, but it's not necessarily superior to other methods. NHS weight management guidance emphasises that sustainable weight loss involves both dietary changes and increased physical activity — whatever eating pattern you choose.
For nhs weight loss support, your GP can recommend tier 1–4 services depending on your needs. For some people, prescription weight loss medication may be appropriate alongside lifestyle changes. Evidence suggests that even a 5% reduction in body weight can have meaningful health benefits including improved blood pressure, better blood sugar control, and reduced joint pain.
The best weight loss approach is one you can sustain long-term. Check your personal BMI and healthy weight range using our free BMI calculator above, then discuss with your GP which weight management strategy suits your circumstances.
- 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.
Does fasting speed up your metabolism?
No. Fasting does not increase your metabolic rate. Weight loss from fasting occurs because you consume fewer calories overall. Your body's metabolic rate may actually decrease slightly during extended fasts as a conservation response, but this is temporary and minimal.
How much weight can you lose with intermittent fasting?
Weight loss depends on your overall calorie deficit, not the fasting pattern itself. With a 500 kcal daily deficit, you might expect to lose approximately 0.5 kg per week. Individual results vary based on starting weight, diet quality, exercise, and metabolism.
Is fasting safe for everyone?
Fasting is not suitable for everyone. Avoid fasting if you're pregnant, breastfeeding, have a history of eating disorders, are taking certain medications like diabetes drugs, or have specific health conditions. Always consult your GP before starting any fasting regimen.
Can you lose weight without fasting?
Yes, absolutely. Traditional calorie restriction, balanced diets like Mediterranean eating, increased physical activity, and in some cases prescription weight loss medication all produce weight loss without fasting. Choose an approach you can sustain long-term.
Does fasting work better than prescription weight loss medication?
They're different approaches. Fasting creates weight loss through calorie reduction. GLP-1 weight loss medications support weight management by reducing appetite and helping you feel fuller, often alongside dietary changes. Your GP can advise which approach is appropriate for your circumstances.
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.