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
How Gut Microbes Influence Weight Loss
Your gut microbiome — the trillions of bacteria living in your digestive system — plays a surprisingly important role in weight management and metabolism. Recent research suggests that the composition of your gut bacteria can influence how efficiently your body processes food, regulates appetite, and stores fat. Understanding this connection helps explain why weight loss approaches that support healthy gut function may be more effective. If you're exploring weight management in the UK, whether through lifestyle changes or prescription medications like GLP-1 injections, knowing how your gut works can help you make informed decisions about your 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 Your Gut Microbiome Affects Weight
Your gut microbiome contains around 100 trillion microorganisms that influence your digestive health and metabolism. A healthy, diverse microbiome helps regulate blood sugar, reduces inflammation, and supports the production of short-chain fatty acids that signal satiety to your brain. Conversely, an imbalanced microbiome (dysbiosis) is associated with obesity, insulin resistance, and increased calorie absorption from food.
Research shows that people with obesity often have lower microbial diversity and different bacterial ratios compared to people at a healthy weight. The bacteria Firmicutes and Bacteroidetes are key players — an imbalance between these two groups is linked to weight gain. Additionally, certain bacteria produce metabolites that reduce appetite and support weight loss, while others may promote fat storage. This is why supporting gut health through diet, fibre intake, and physical activity is considered part of effective weight management in the UK.
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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.
Gut Health and GLP-1 Weight Loss Medications
GLP-1 receptor agonist medications like Wegovy (semaglutide) work partly through the gut. These prescription weight loss injections slow gastric emptying — meaning food stays in your stomach longer — which sends prolonged fullness signals to your brain. This mechanism supports reduced calorie intake and sustainable weight loss. Alongside this, a healthier gut environment created by better dietary choices during weight loss may further improve the medication's effectiveness.
Our GLP-1 weight loss calculator can help you estimate potential results at different doses. For personalised advice about prescription weight loss medication and how it might work with your individual gut health, your GP or a licensed prescriber can assess whether treatment is suitable for you following a clinical assessment. Use our free BMI calculator to check your current status and understand whether weight management support may be beneficial.
Supporting Your Gut Health During Weight LossPractical steps to support gut health while managing weight:
- Increase fibre intake: Aim for 30g daily through vegetables, fruits, legumes, and whole grains — fibre feeds beneficial bacteria
- Eat fermented foods: Yoghurt, kefir, sauerkraut, and kimchi contain probiotics that support microbial diversity
- Stay hydrated: Adequate water supports digestion and nutrient absorption
- Reduce ultra-processed foods: These often kill beneficial bacteria and promote dysbiosis
- Manage stress: Chronic stress damages gut bacteria — try meditation, exercise, or relaxation techniques
Track your weight loss progress using our free progress tracker as you make these changes. Remember, sustainable weight loss typically occurs at 0.5–1 kg per week when combining lifestyle changes with increased physical activity.
- 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.
Can probiotics alone help me lose weight?
Probiotics may support digestive health and overall wellness, but they are not a weight loss solution on their own. Weight loss requires a calorie deficit through diet and physical activity. Probiotics work best as part of a comprehensive approach that includes a balanced diet high in fibre and regular exercise. If you're considering prescription weight loss medication, discuss probiotics with your GP or prescriber.
Does improving gut health help GLP-1 medications work better?
There is emerging research suggesting that a healthier gut environment may optimise the effectiveness of GLP-1 medications like Wegovy. Since these medications alter digestion and appetite signals partly through the gut, supporting your microbiome through diet and lifestyle may be beneficial. However, individual results vary, and the primary mechanism of GLP-1 weight loss remains appetite reduction.
What foods are best for a healthy gut microbiome?
Focus on high-fibre foods including vegetables, fruits, legumes, and whole grains; fermented foods like yoghurt and kefir; and foods rich in polyphenols such as berries, nuts, and green tea. Limit ultra-processed foods, excess sugar, and alcohol, which can harm beneficial bacteria. Consistency matters more than perfection — aim for gradual, sustainable dietary changes.
How long does it take to improve gut health?
Positive changes to your microbiome can begin within days to weeks of dietary improvements, though significant shifts typically take 4–8 weeks of consistent healthy eating. Gut health is an ongoing process rather than a destination, so think of it as part of your long-term health and weight management strategy.
Should I take probiotic supplements or eat fermented foods?
Fermented foods are generally preferred because they contain live bacteria plus additional nutrients and fibre. Probiotic supplements can be useful but quality varies and they are not regulated as strictly as medications in the UK. Start with fermented foods, stay hydrated, and increase fibre intake. Your GP can advise on supplements if needed.
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.