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
Fasting Diet for Weight Loss — What Works?
Fasting diets are one approach to weight loss that involves eating within specific time windows or reducing calorie intake on certain days. In the UK, intermittent fasting has gained popularity as a weight management strategy, though the NHS emphasises that sustainable weight loss requires a calorie deficit alongside increased physical activity. This guide explains how fasting works, what evidence shows, and how it fits within a broader weight loss approach. Individual results vary significantly, and your GP can advise whether fasting is appropriate for your personal health.
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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 Diets Work for Weight Loss
Fasting diets create a calorie deficit by restricting when or how much you eat. The most common method in the UK is 16:8 intermittent fasting—eating within an 8-hour window and fasting for 16 hours. Another popular approach is the 5:2 diet, where you eat normally five days weekly and restrict calories to around 500–600 kcal on two non-consecutive days.
The mechanism is straightforward: fewer eating windows typically means fewer calories consumed overall. However, evidence shows that intermittent fasting is not inherently superior to standard calorie restriction for weight loss. A calorie deficit of approximately 500 kcal per day typically results in losing around 0.5 kg weekly—the NHS recommended safe rate.
- 16:8 method: eat between noon and 8 PM, fast overnight and morning
- 5:2 diet: eat normally five days, restrict to 500–600 kcal twice weekly
- Eat-stop-eat: complete 24-hour fasts once or twice weekly
- Calorie deficit remains the key factor in weight loss
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.
Fasting and Weight Management — NHS Context
The NHS recognises intermittent fasting as one valid approach to weight management in the UK, though it emphasises that the best diet is one you can sustain long-term. Fasting works for some people because it simplifies eating rules, but it is not a clinically supported solution—you still need a calorie deficit.
If you find fasting makes you overeat during eating windows or causes fatigue, other approaches may suit you better. For prescription weight loss support, your GP can refer you to specialist weight loss medication NHS services, or you can access prescription weight loss through private assessment. Calculate your current BMI weight loss targets using our free BMI calculator above, and use our free progress tracker to monitor your weight loss journey regardless of which method you choose.
- 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 intermittent fasting work better than normal calorie restriction?
Evidence suggests both methods produce similar weight loss when calories are equal. The advantage of fasting is psychological—some people find it easier to follow eating windows than counting calories. However, if fasting makes you binge eat or feel unwell, standard calorie reduction may work better for you personally.
Can I drink tea or coffee during a fasting window?
Yes. Black tea, black coffee, and water are fine during fasting windows as they contain minimal calories. Avoid adding milk, sugar, or cream. Some people find that herbal tea helps them feel fuller during fasting periods without breaking the fast.
What should I eat during my eating window to lose weight?
Eat a balanced diet with protein, vegetables, whole grains, and healthy fats. Fasting doesn't mean you can eat unlimited calories during your eating window—you still need a deficit for weight loss. The NHS recommends whole foods over processed options to support overall health.
Is fasting safe for everyone?
Fasting is not suitable for pregnant or breastfeeding women, children, people with a history of eating disorders, or those with certain medical conditions. Always consult your GP before starting any fasting regimen, especially if you take prescription medication or have diabetes.
How does fasting compare to GLP-1 weight loss medication?
Fasting is a dietary approach that relies on calorie restriction, whilst GLP-1 weight loss injections work by reducing appetite and hunger signals. Both can support weight loss, but they operate differently. Fasting is free and available immediately, whilst prescription weight loss requires clinical assessment. Both work best combined with healthy eating and physical activity.
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.