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
Does Low Iron Affect Weight Loss?
Low iron levels can significantly impact your ability to lose weight effectively. Iron is essential for carrying oxygen around your body, producing energy, and supporting your metabolism. If your iron stores are depleted, you may experience fatigue, reduced exercise capacity, and a slower metabolic rate — all of which can make weight loss more difficult. Understanding this connection is important if you're struggling to see results despite following a healthy diet and exercise plan. If you suspect low iron may be affecting your weight management in the UK, it's worth discussing with your GP, who can arrange a blood test to check your iron levels.
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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 Low Iron Affects Your Metabolism and Weight Loss
Iron plays a critical role in creating haemoglobin, the protein that transports oxygen throughout your bloodstream. Without adequate iron, your cells cannot produce sufficient energy, which directly impacts your basal metabolic rate — the calories you burn at rest. This means your body may naturally burn fewer calories during the day, making a calorie deficit harder to achieve.
Low iron can also cause:
- Persistent fatigue — reducing motivation for physical activity and exercise
- Reduced exercise performance — less oxygen to muscles during workouts means you burn fewer calories during training
- Brain fog and poor concentration — making it harder to stick to healthy eating plans
- Weakened immune system — increasing illness risk and disrupting weight loss progress
If you're experiencing unexplained weight loss resistance despite maintaining a calorie deficit, low iron may be a contributing factor worth investigating with your GP.
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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.
Iron Deficiency Symptoms and When to Seek Help
Common signs of iron deficiency include unusual tiredness, shortness of breath, dizziness, pale skin, and cold hands and feet. These symptoms can make maintaining a structured weight management plan difficult. In the UK, your GP can perform a simple blood test to check your ferritin and haemoglobin levels.
If iron deficiency is confirmed, treatment typically involves iron supplements or dietary changes, and most people notice improvements in energy and exercise capacity within a few weeks. Once your iron levels normalise, you may find that weight loss becomes easier to achieve. This is why addressing underlying nutritional deficiencies is just as important as diet and exercise when pursuing sustainable weight management.
- 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 is the connection between iron and weight loss?
Iron transports oxygen to your cells, which fuels energy production and metabolism. Low iron reduces oxygen availability, slowing your metabolic rate and making weight loss harder. Fatigue from low iron also reduces physical activity, further impacting calorie burn.
How do I know if I have low iron?
Common signs include persistent tiredness, shortness of breath, dizziness, pale skin, and cold extremities. A blood test from your GP can measure ferritin and haemoglobin levels. If you suspect low iron, ask your GP for testing.
Can I lose weight while iron deficient?
Weight loss is more challenging with low iron because your metabolism slows and fatigue reduces exercise capacity. While modest loss may still occur, addressing the deficiency first often makes sustainable weight loss easier and faster.
How long does it take to fix low iron and see weight loss results?
Iron supplements typically take 4–12 weeks to rebuild iron stores, depending on severity. Most people notice improved energy within 2–4 weeks. Once iron normalises, weight loss may accelerate as metabolism and exercise capacity improve.
Should I take iron supplements while using prescription weight loss medication?
Always inform your GP of any supplements you're taking if prescribed weight loss medication like Wegovy or Mounjaro. GLP-1 medications can affect nutrient absorption, so your prescriber needs to know about iron supplementation to avoid interactions.
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.