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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Ulcerative Colitis And Weight Loss — What You Need To Know
Living with ulcerative colitis can make weight management challenging. Inflammation, medication side effects, and dietary restrictions may all impact your ability to lose weight safely. If you're struggling with weight alongside inflammatory bowel disease (IBD), understanding how these conditions interact is essential before starting any weight loss programme. This guide explains the relationship between ulcerative colitis and weight loss, and how to approach weight management in the UK.
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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.
How Ulcerative Colitis Affects Weight Management
Ulcerative colitis affects weight loss in several ways. Active inflammation in the colon increases calorie expenditure and can cause unintended weight loss or make it difficult to gain weight. Medication effects — particularly corticosteroids — may increase appetite and cause weight gain, whilst other treatments can suppress appetite. Dietary restrictions vary by individual; during flare-ups, you may tolerate only low-fibre, bland foods, which limits nutritional variety.
Malabsorption is also common in ulcerative colitis — your bowel may not absorb nutrients efficiently, meaning you may need more calories to maintain a healthy weight. Psychological stress related to your condition can affect eating patterns. Before pursuing weight loss, discuss your specific situation with your GP or gastroenterologist, as losing weight too quickly or restricting calories inappropriately may trigger or worsen flare-ups. NHS weight management services are available and can provide support tailored to IBD.
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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.
Safe Weight Loss Strategies For Ulcerative Colitis
If your GP advises weight loss, work with a dietitian experienced in IBD to create a safe plan. Focus on nutrient-dense foods you tolerate well rather than aggressive calorie restriction. During remission, gradual weight loss of 0.5–1 kg per week is safer than rapid loss. Stay hydrated and monitor your symptoms closely; increased bowel symptoms may mean you need to adjust your approach.
Prescription weight loss medication — such as GLP-1 weight loss injections — require careful consideration with your medical team. These medications slow gastric emptying and affect gut function, which may interact unpredictably with ulcerative colitis. Never start weight loss injections without discussing your IBD diagnosis with your prescriber first. Use our free GLP-1 weight loss calculator to understand options, but always prioritise discussion with your gastroenterologist before proceeding.
When To Seek Professional SupportYou should speak to your GP or gastroenterologist before starting any weight loss programme if you have ulcerative colitis. They can advise whether now is the right time, given your current disease activity. Your NHS GP can refer you to tier 2 or tier 3 NHS weight management services, which are equipped to support people with complex medical conditions including IBD. If you're interested in exploring GLP-1 weight loss options, ensure your prescriber is aware of your ulcerative colitis diagnosis — this is essential information for clinical assessment.
Consider also consulting a specialist IBD dietitian through your gastroenterology service. They understand both weight loss and disease management, and can help you navigate nutrition safely. Track your weight and symptoms using our free progress tracker to identify patterns and share data with your healthcare team.
- 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 I take Wegovy or Mounjaro if I have ulcerative colitis?
Both Wegovy (semaglutide) and Mounjaro (tirzepatide) slow gastric emptying and affect gut function. These effects may interact with ulcerative colitis unpredictably. A prescriber must know about your IBD diagnosis before assessing suitability. Never start GLP-1 medication without discussing your ulcerative colitis with your medical team first. Your gastroenterologist may advise against it, or suggest timing it carefully.
Is it safe to lose weight while in a flare-up?
No. Active inflammation increases calorie needs and losing weight during a flare-up can worsen symptoms and delay recovery. Work with your team to achieve remission first, then discuss safe weight loss strategies. gradual weight management or calorie restriction during flare-ups may trigger more inflammation and should be avoided.
What does the NHS offer for weight loss with ulcerative colitis?
Your GP can refer you to NHS tier 2 or tier 3 weight management services. These services assess complex medical conditions, including IBD, and develop personalised plans. Some services can prescribe weight loss medication if appropriate, but your IBD status will inform their recommendation. Specialist IBD dietitians are also available through gastroenterology services.
How much weight should I aim to lose per week safely?
The NHS recommends 0.5–1 kg per week for sustainable, safe loss. With ulcerative colitis, losing at the slower end of this range (or even more slowly) is often safer. Faster loss increases the risk of triggering flare-ups or worsening symptoms. Always progress under medical supervision.
Can I use the BMI calculator if I have ulcerative colitis?
Yes, our free BMI calculator provides a useful health baseline. However, BMI has limitations and doesn't account for your individual circumstances with IBD. Use it for general information, but discuss your healthy weight range with your GP or dietitian, as they can advise on what's realistic given your condition.
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.