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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Serving Sizes For Weight Loss — What You Need To Know
Getting serving sizes right is one of the most effective ways to achieve sustainable weight loss in the UK. Portion control directly affects your calorie intake, which is the foundation of any successful weight management plan. Whether you're managing your weight naturally through diet and exercise, or exploring prescription weight loss options, understanding proper serving sizes helps you make consistent progress. The NHS recommends a calorie deficit of around 500 kcal per day for steady weight loss of approximately 0.5 kg per week. This guide covers practical portion control strategies and evidence-based serving size recommendations to support your weight management journey.
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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.
Understanding Portion Control And Calorie Intake
Serving size refers to a standard amount of food, whilst portion size is the amount you actually eat. These are often different — portions are typically larger than recommended servings. The key to weight loss is aligning your portions with sensible servings to create a calorie deficit.
A calorie deficit of around 500 kcal per day results in losing approximately 0.5 kg per week — the NHS-recommended safe rate. This means if your maintenance calorie requirement is 2,000 kcal daily, aiming for 1,500 kcal creates the deficit needed for steady loss. However, portion control alone isn't the whole picture. Combining smaller portions with increased physical activity, balanced nutrition, and consistent tracking amplifies results.
Use our free weight loss calculator to estimate how calorie deficit and portion control may affect your progress over time. Our BMI calculator also helps you set a realistic healthy weight target based on your height, which can guide your overall calorie and portion goals.
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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.
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Practical Serving Size Guidelines For Common Foods
The NHS and British Nutrition Foundation provide simple visual guides for portion sizes. A palm-sized portion of protein (meat, fish, legumes) is approximately 100–120g. A fist-sized portion of carbohydrates (rice, pasta, bread) is roughly 40–50g dry weight. Two handfuls of vegetables represent a generous serving. One thumb-sized portion of fat (butter, oil) is about 10–15g.
Meal planning using these visual guides makes portion control intuitive without constant calorie counting. Weigh foods initially to understand portion sizes visually, then you can estimate more easily. Drink water before meals — thirst is often mistaken for hunger. Eat slowly, use smaller plates, and avoid eating directly from packaging. Track your portions using our free progress tracker alongside weight measurements to see how portion control correlates with your results.
- 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.
What's the difference between a serving size and a portion size?
A serving size is a standardised amount set by nutritional guidelines (e.g. 100g of meat). A portion is what you actually eat, which is often larger. Understanding this distinction helps you realign portions to recommended servings for weight management and calorie control.
How do I know if my portions are too large?
Use the hand-size visual guide: palm for protein, fist for grains, two handfuls for vegetables, thumb for fats. Weigh your usual portions for a few days to compare against NHS guidelines. You can also calculate your target daily calories and track portions to stay within your deficit.
Can serving size control alone lead to weight loss without exercise?
Yes, weight loss occurs through calorie deficit. However, the NHS recommends combining portion control with increased physical activity for sustainable results, better cardiovascular health, and to preserve muscle mass during weight loss. Even modest activity (150 minutes weekly) significantly improves outcomes.
Are serving sizes the same for everyone?
No. Serving size recommendations vary by age, sex, height, weight, and activity level. Your GP or a registered dietitian can provide personalised serving size targets based on your individual calorie needs and health goals, especially if you have medical conditions affecting nutrition.
How do serving sizes relate to prescription weight loss medication?
Prescription weight loss medications like GLP-1 injections (Mounjaro, Wegovy) work alongside portion control, not instead of it. These medications may reduce appetite and help you naturally eat smaller portions, but serving size awareness and sustained dietary changes remain essential for long-term weight management success.
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.