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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Intermittent Fasting for Weight Loss — What Works in the UK
Intermittent fasting (IF) is an eating pattern that cycles between fasting and eating windows. Rather than focusing on what you eat, it restricts when you eat. Evidence suggests intermittent fasting can support weight management in the UK, particularly when combined with a reduced-calorie diet and increased physical activity. However, it works best as part of a broader lifestyle approach, not as a standalone solution. This guide explains the common fasting schedules, how they work, and how to assess whether intermittent fasting suits your health goals.
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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.
Common Intermittent Fasting Schedules
Several intermittent fasting protocols are popular in the UK. The 16:8 method (also called time-restricted eating) involves fasting for 16 hours and eating within an 8-hour window — for example, eating between noon and 8 PM. The 5:2 diet involves eating normally five days per week and restricting calories to 500–600 kcal on two non-consecutive days. The Eat-Stop-Eat method uses full 24-hour fasts once or twice weekly. The Alternate-Day Fasting (ADF) alternates between fasting days and regular eating days.
- 16:8 is easiest to maintain long-term and fits most UK work schedules
- 5:2 is flexible and requires less strict daily adherence
- Full-day fasting methods are more challenging but may produce faster results
- The best method is one you can sustain consistently
All of these approaches create a calorie deficit when paired with balanced eating during non-fasting periods. Research shows that intermittent fasting results in similar weight loss to traditional calorie restriction — the advantage is the simplicity of timing rather than counting every meal.
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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
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Intermittent Fasting and Weight Management in the UK
For weight management in the UK, intermittent fasting works because it typically reduces overall calorie intake without requiring strict meal-by-meal tracking. During eating windows, it's important to maintain a balanced diet with adequate protein, fibre, and nutrients. The NHS recommends losing weight at a sustainable rate of 0.5 to 1 kg per week — intermittent fasting can support this when combined with regular physical activity.
If you have type 2 diabetes, take blood pressure medication, or have other health conditions, speak to your GP before starting intermittent fasting. You can use our free BMI calculator to check your current weight status and track your progress with our free progress tracker as you implement dietary changes. Intermittent fasting is not suitable during pregnancy or for people with a history of eating disorders.
- 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 better than traditional calorie restriction for weight loss?
Clinical evidence suggests intermittent fasting produces similar weight loss results to standard calorie restriction. The advantage is simplicity — timing your meals rather than counting calories at every meal. Individual results vary; some people find it easier to maintain than traditional dieting, while others prefer structured meal planning. The best approach is whichever one you can sustain consistently.
Can I combine intermittent fasting with prescription weight loss medication?
Prescription weight loss medications like GLP-1 injections (Wegovy, Mounjaro) work alongside dietary changes, not instead of them. Intermittent fasting can be combined with these medications, but you should discuss your eating pattern with the prescriber during your clinical assessment. They will advise whether your chosen fasting schedule is appropriate for your individual health profile.
How quickly will I lose weight with intermittent fasting?
Weight loss depends on your total calorie intake, activity level, and metabolism — not just eating schedule. The NHS recommends aiming for 0.5–1 kg per week for sustainable loss. Some people see faster initial results due to water loss; longer-term results reflect genuine fat loss. Progress varies significantly between individuals; use our free progress tracker to monitor your personal results.
Is intermittent fasting safe if I have diabetes or take medications?
If you have type 2 diabetes, take blood pressure medication, or have other chronic conditions, consult your GP before starting intermittent fasting. Fasting periods can affect medication timing and blood sugar control. Your GP can advise whether intermittent fasting is appropriate and whether medication adjustments are needed during eating windows.
What should I eat during my eating window to support weight loss?
Focus on whole foods: lean proteins, vegetables, whole grains, and healthy fats. Avoid high-calorie processed foods and sugary drinks. Adequate protein intake (20–30g per meal) helps preserve muscle during weight loss and keeps you feeling fuller longer. Hydration is important — drink water throughout fasting periods. The key is maintaining a calorie deficit while eating nutritious, balanced meals.
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.