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 Plan For Weight Loss
Intermittent fasting (IF) is an eating pattern that cycles between periods of eating and fasting, and it's one of several approaches people use for weight management in the UK. Evidence suggests IF can support weight loss when combined with a calorie deficit and healthy lifestyle choices. However, the "best" plan varies by individual — what works for one person may not suit another. This guide explores the most popular intermittent fasting methods, how they work, and how they fit within broader weight management strategies alongside other approaches like prescription weight loss medication or GLP-1 weight loss support.
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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
16:8 (Time-Restricted Eating): You eat within an 8-hour window and fast for 16 hours. For example, eating between noon and 8 PM. This is the most popular IF method and easiest to sustain long-term. Clinical evidence shows modest weight loss comparable to standard calorie restriction.
5:2 Diet: You eat normally five days per week and restrict calories to 500–600 kcal on two non-consecutive days. This method is flexible and allows normal eating patterns most days, making it sustainable for many people.
Eat-Stop-Eat: Complete 24-hour fasts once or twice weekly. Requires more discipline but can create a larger weekly calorie deficit. Not suitable for everyone, particularly those with a history of disordered eating.
Important context: Research shows IF results in weight loss primarily because it creates a calorie deficit—not because fasting itself is metabolically special. For weight management in the UK, the NHS emphasises that any sustainable eating pattern that creates a calorie deficit works, whether that's IF or regular calorie restriction.
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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.
Intermittent Fasting vs Other Weight Loss Approaches
Intermittent fasting works for some people because it naturally limits eating windows and may reduce overall calorie intake. However, it's not superior to other methods for everyone. Some people find fasting difficult and prefer consistent, smaller meals throughout the day.
For individuals struggling with weight loss through diet and lifestyle alone, prescription weight loss medications like GLP-1 injections (Wegovy or Mounjaro) may provide additional support. These work through different mechanisms—reducing appetite and supporting fuller feelings—and are used alongside dietary changes. NHS weight management pathways include structured diet support, physical activity guidance, and access to specialist services where prescription weight loss options may be considered. Calculate your BMI using the tool on this page to understand your current weight category, and speak with your GP about which weight management approach suits your individual health situation.
- 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.
Which intermittent fasting plan is best for weight loss?
There's no single "best" plan—the best approach is one you can sustain long-term. 16:8 (time-restricted eating) is most popular and easiest to maintain. 5:2 is flexible if you prefer eating normally most days. Eat-stop-eat creates larger deficits but requires more discipline. Weight loss depends on creating a calorie deficit, not the specific IF method. Consult your GP if you have medical conditions.
How much weight can I lose with intermittent fasting?
Weight loss varies significantly between individuals. Research shows IF produces weight loss of approximately 3–7% body weight over 8–24 weeks—similar to standard calorie restriction. Results depend on maintaining a calorie deficit, diet quality, physical activity, and adherence. Slower, sustainable loss (0.5–1 kg weekly) is recommended by the NHS for long-term success.
Is intermittent fasting safe for everyone?
IF isn't suitable for everyone. Avoid IF if you're pregnant, breastfeeding, have a history of disordered eating, take certain medications requiring food, or have specific medical conditions. People with type 2 diabetes on medication should discuss IF with their GP first. Always consult your GP before starting any new eating pattern, especially if you have health conditions.
Can I combine intermittent fasting with weight loss medication?
Intermittent fasting and prescription weight loss medications like GLP-1 injections work through different mechanisms and can theoretically be combined. However, GLP-1 medications naturally reduce appetite and food intake, so additional fasting may not be necessary. Any combination should be discussed with your prescriber or GP to ensure it's safe and appropriate for your individual situation.
How does intermittent fasting compare to the NHS weight loss approach?
The NHS emphasises sustainable calorie deficit through balanced diet and increased physical activity—the specific eating pattern (IF or regular meals) is less important than overall adherence. IF works for some people because it reduces eating opportunities, naturally lowering calories. If IF doesn't suit you, other methods like reducing portion sizes, tracking food, or using weight loss calculators work equally well for weight management.
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.