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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Best Intermittent Fasting For Weight Loss
Intermittent fasting (IF) is an eating pattern that cycles between periods of eating and fasting, and evidence suggests it can support weight loss when combined with a calorie deficit. Unlike traditional dieting, IF focuses on *when* you eat rather than *what* you eat. In the UK, several IF methods are popular, including 16:8 (fasting for 16 hours, eating within an 8-hour window), the 5:2 diet (eating normally five days, restricting calories two days), and OMAD (one meal a day). While IF can be effective for weight management in the UK, results vary significantly between individuals, and it works best alongside lifestyle changes like increased physical activity.
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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.
Popular Intermittent Fasting Methods In The UK
16:8 (Time-Restricted Eating): Fast for 16 hours, eat within an 8-hour window (e.g., noon to 8 PM). This is the most popular IF method in the UK and suits people with regular daily routines. Research suggests it may help reduce overall calorie intake naturally.
5:2 Diet: Eat normally five days per week, restrict calories to 500–600 kcal on two non-consecutive days. This approach is flexible and easier to sustain for some people, though calorie days require discipline.
Eat-Stop-Eat: Complete 24-hour fasts once or twice weekly. More challenging than other methods and not suitable for everyone.
OMAD (One Meal A Day): Eat only once daily within a 1-hour window. Very restrictive and not recommended without medical guidance, particularly for those with diabetes or on medication.
The NHS supports intermittent fasting as a potential weight loss approach but emphasises that it works best when combined with a healthy diet and regular physical activity.
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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.
Does Intermittent Fasting Work Better Than Other Methods?
Studies comparing intermittent fasting to continuous calorie restriction show similar weight loss results when total calorie intake is equal. The key advantage of IF is that some people find it easier to follow because they don't count calories daily—they simply avoid eating during fasting windows. However, individual results vary significantly.
For weight management in the UK, the most important factor is choosing an approach you can sustain long-term. Intermittent fasting is not inherently superior to other methods; it's simply an alternative structure that suits some people better than others. If you struggle with IF, traditional calorie deficit eating, Mediterranean diet approaches, or prescription weight loss support may be more suitable. Use our free BMI calculator to assess your starting point, and our weight loss calculator to explore different weight management options including GLP-1 medication alternatives if appropriate.
- 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.
Is intermittent fasting safe for everyone in the UK?
Intermittent fasting is not suitable for everyone. Avoid IF if you are pregnant, breastfeeding, have a history of eating disorders, take certain medications, have type 1 diabetes, or are under 18. If you have type 2 diabetes, take medication, or have other health conditions, consult your GP before starting IF to ensure it's safe for you.
How much weight can you lose with intermittent fasting?
Weight loss depends on total calorie intake, not fasting method alone. The NHS recommends losing 0.5–1 kg per week as a sustainable rate. With a 500 kcal daily deficit through IF, you might lose approximately 0.5 kg weekly. Individual results vary based on starting weight, metabolism, diet quality, and activity level.
Does intermittent fasting boost metabolism?
Intermittent fasting does not significantly boost metabolism beyond the effects of calorie restriction. Some studies suggest short-term metabolic changes, but long-term metabolic rate remains similar to standard dieting. Weight loss occurs because total calorie intake is reduced, not because fasting "speeds up" metabolism.
What should you eat during intermittent fasting eating windows?
During eating windows, focus on nutritious whole foods: lean proteins, vegetables, whole grains, legumes, and healthy fats. Avoid using eating windows as an excuse to consume high-calorie junk food—the quality of what you eat still matters for health and sustainable weight loss.
Can intermittent fasting be combined with prescription weight loss medication?
Combining IF with prescription weight loss medication like Mounjaro or Wegovy requires medical guidance. Some medications slow gastric emptying, which may interact with extended fasting. Always inform your GP or prescriber if you're considering IF while taking any weight loss medication or other prescriptions.
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.