Bariatric Surgery


Mr Ahmed R. Ahmed

What we do

The prevalence of obesity is rising rapidly. Currently, one quarter of UK adults are obese (BMI greater than 30kg/m2) and if trends continue, by 2050, obesity and its devastating health consequences will affect over 50% the population. Obesity is a leading cause of preventable death worldwide and is associated with a range of health problems including type 2 diabetes, cardiovascular disease, cancer and poor outcome COVID-19. The resulting costs to the NHS and the wider economy are estimated to at £49.9 billion per year (or 3% of GDP).

Currently, multidisciplinary diet and lifestyle programmes (known as Tier 3), which are costly to deliver, produce only modest weight loss of 3-5%, and often fail to result in long-term weight-loss maintenance. Bariatric surgery (now also referred to as metabolic surgery or Tier 4) is highly effective achieving 25-35% weight loss, is well maintained and results in resolution of many obesity-related co-morbidities. While it is cost effective (recommended by NICE and previously HTAs), provision remains low due to its high upfront cost and societal stigma against obesity. About 3.6m people in England are eligible for weight- loss surgery, but the latest figures show that just 6,627 people (0.2% of those eligible) had this surgery in 2017-18.

Therefore, there is a clear and urgent need for efficacious alternatives to tier 3 lifestyle measures as well as the requirement for interventions that are cheaper and safer than tier 4 surgical treatments and which offer sustained weight loss of >5% for those with a BMI >35kg/m2.

Why it is important

The aim of our research is to provide the best available evidence about the clinical efficacy and mechanism of action of lifestyle modification, pharmacotherapy, medical devices and bariatric/metabolic surgery. By understanding these mechanisms we can optimise their efficacy, safety and cost-effectiveness. We are also investigating predictors of clinical response to these treatments in order to personalise them to the patient’s specific characteristics.

As an internationally recognised centre for weight loss (metabolic) surgery, and as a clinical program in a world-renowned hospital (Imperial College Healthcare NHS Trust) and medical school (Imperial College London), we have a responsibility to lead on and participate in cutting-edge cross-disciplinary research in obesity and bariatric surgery.

How it can benefit patients

The results of our collegiate, cutting-edge research output improves treatment for patients undergoing bariatric surgery for morbid obesity and its related health conditions and in addition, will trail-blaze  the introduction of new and innovative treatments. 

Summary of current research

Bariatric/metabolic surgery

  • Mechanisms of action through state-of-the-art deep phenotyping. This includes dynamic metabolic studies, eating behaviour, gut hormone, bile acid, microbiota and omics, and functional neuroimaging.
  • Modification of surgical procedures to improve clinical outcomes
  • Prediction of diabetes remission
  • Male and female fertility, pregnancy, mental health, kidney and liver disease outcomes after surgery
  • Improvement of perioperative anaesthetic care

Development of novel non-surgical treatments for obesity 

  • Pharmacotherapy (commercial and investigator-led) e.g. GLP-1 receptor agonists, gut hormone combinations, oral encapsulated gut hormones.
  • Endoscopic treatments e.g. Duodenal Mucosal Resurfacing, Duodeno-jejunal bypass liner.
  • Interventional Radiology treatments e.g. left gastric artery embolization (EMBIO) 

Additional information

PhD students

  • Khalefah Malallah
  • Julia Kenkre
  • Yasmin Tabbakh
  • Ms Shahd Alabdulkader, “Comparison of the effects of the one-anastomosis gastric bypass to the Roux-en-Y gastric bypass on eating behaviour”. 
  • Ms Alhanouf Al Alsheikh, “Comparison of the effects of the vertical sleeve gastrectomy to the Roux-en-Y gastric bypass on eating behaviour”. 
  • Dr Vasha Kaur, “Metabolic effects of duodenal resurfacing on insulin resistant women with polycystic ovarian syndrome”. 
  • Dr Anna Kamocka: “Glucose metabolism in obese patients with type 2 diabetes mellitus undergoing standard vs. long limb Roux-en-Y-gastric bypass”. 
  • Dr Madhawi Aldhwayan, “Effects of the EndoBarrier on eating behaviour in obese type 2 diabetes patients”. 
  • Dr Ghalia Abdeen, “Changes in eating behaviour and meal patterns following Vertical Sleeve Gastrectomy”. 

Collaborative Clinical trials

  • The Jon Moulton Charity Trust, Roux-en-Y gastric bypass with standard vs. long alimentary limb for type 2 diabetes mellitus. The Long Limb-2 double blinded RCT2020-2023 
  • EMBIO trial – Left gastric artery embolisation (LGAE) for weight loss in patients with BMI 35-50 kg/m2.  [NIHR EME – Ref: 17/11/49 -  £1,200,000 
  • REINFORCED RELOAD trial – MEDTRONIC.  NIHR Portfolio Study ID: 19066.  £61,388.59  (2015-2016) [Mr Ahmed - Awarded Leading Commercial Principal Investigators 2016 by NIHR for conducting this study] 
  • Gastric Bypass, adjustable gastric Banding or Sleeve gastrectomy surgery to treat severe and complex obesity: a multi-centre randomised controlled trial (The By-Band-Sleeve Study) - NIHR HTA (ref: 09/127/53).  £3,939,934   (2012-2020) 
  • A randomized controlled trial of a duodenal sleeve bypass device (Endobarrier) compared with standard medical therapy for the management of obese subjects with type 2 diabetes (Co-I) – NIHR EME  (Ref:12/10/04) Total grant £1,500,000  (2014-2018) 
  • Are the metabolic and weight loss effects of Roux-en-Y bypass surgery mediated by gut hormones? (Co-I) - MRC Experimental Medicine Challenge Grant programme (Ref: MR/K02115X/1).  Total grant £2,500,000  (2013-2018)  
  • Are gut hormone changes why the long-limb gastric bypass is more effective than the standard-limb gastric bypass in improving type 2 diabetes mellitus? (Co-I) -  NIHR EME (Ref: 13/121/07).  Total grant £885,529.46   (2015-2018) 


1: Behary P, Tharakan G, Alexiadou K, Johnson N, Wewer Albrechtsen NJ, Kenkre J, Cuenco J, Hope D, Anyiam O, Choudhury S, Alessimii H, Poddar A, Minnion J, Doyle C, Frost G, Le Roux C, Purkayastha S, Moorthy K, Dhillo W, Holst JJ, Ahmed AR, Prevost AT, Bloom SR, Tan TM. Combined GLP-1, Oxyntomodulin, and Peptide YY Improves Body Weight and Glycemia in Obesity and Prediabetes/Type 2 Diabetes: A Randomized, Single-Blinded, Placebo-Controlled Study. Diabetes Care. 2019 Aug;42(8):1446-1453. doi: 10.2337/dc19-0449. Epub 2019 Jun 8. PMID: 31177183. 

2: Miras AD, Pérez-Pevida B, Aldhwayan M, Kamocka A, McGlone ER, Al-Najim W, Chahal H, Batterham RL, McGowan B, Khan O, Greener V, Ahmed AR, Petrie A, Scholtz S, Bloom SR, Tan TM. Adjunctive liraglutide treatment in patients with persistent or recurrent type 2 diabetes after metabolic surgery (GRAVITAS): a randomised, double-blind, placebo-controlled trial. Lancet Diabetes Endocrinol. 2019 Jul;7(7):549-559. doi: 10.1016/S2213-8587(19)30157-3. Epub 2019 Jun 4. PMID: 31174993. 

3: Kamocka A, McGlone ER, Pérez-Pevida B, Moorthy K, Hakky S, Tsironis C, Chahal H, Miras AD, Tan T, Purkayastha S, Ahmed AR. Candy cane revision after Roux-en-Y gastric bypass. Surg Endosc. 2020 May;34(5):2076-2081. doi: 10.1007/s00464-019-06988-4. Epub 2019 Aug 8. PMID: 31392513; PMCID: PMC7113192. 

4: Alexiadou K, Cuenco J, Howard J, Wewer Albrechtsen NJ, Ilesanmi I, Kamocka A, Tharakan G, Behary P, Bech PR, Ahmed AR, Purkayastha S, Wheller R, Fleuret M, Holst JJ, Bloom SR, Khoo B, Tan TM. Proglucagon peptide secretion profiles in type 2 diabetes before and after bariatric surgery: 1-year prospective study. BMJ Open Diabetes Res Care. 2020 Mar;8(1):e001076. doi: 10.1136/bmjdrc-2019-001076. PMID: 32209584; PMCID: PMC7103850. 

5: Hameed S, Salem V, Tan TM, Collins A, Shah K, Scholtz S, Ahmed AR, Chahal H. Beyond Weight Loss: Establishing a Postbariatric Surgery Patient Support Group- What Do Patients Want? J Obes. 2018 Feb 14;2018:8419120. doi: 10.1155/2018/8419120. PMID: 29666701; PMCID: PMC5832182. 

6: Miras AD, Kamocka A, Pérez-Pevida B, Purkayastha S, Moorthy K, Patel A, Chahal H, Frost G, Bassett P, Castagnetto-Gissey L, Coppin L, Jackson N, Umpleby AM, Bloom SR, Tan T, Ahmed AR, Rubino F. The Effect of Standard Versus Longer Intestinal Bypass on GLP-1 Regulation and Glucose Metabolism in Patients With Type 2 Diabetes Undergoing Roux-en-Y Gastric Bypass: The Long-Limb Study. Diabetes Care. 2020 Nov 6:dc200762. doi: 10.2337/dc20-0762. Epub ahead of print. PMID: 33158945. 

7: Miras AD, Ravindra S, Humphreys A, Lascaratos G, Quartey KNK, Ahmed AR, Cousins J, Moorthy K, Purkayastha S, Hakky S, Tan T, Chahal HS. Metabolic Changes and Diabetes Microvascular Complications 5 Years After Obesity Surgery. Obes Surg. 2019 Dec;29(12):3907-3911. doi: 10.1007/s11695-019-04095-w. PMID: 31372874. 

8: Hameed S, Salem V, Alessimii H, Scholtz S, Dar O, Miras AD, Meeran K, Bloom SR, Ahmed AR, Purkayastha S, Chahal H, Tan T. Imperial Satiety Protocol: A new non-surgical weight-loss programme, delivered in a health care setting, produces improved clinical outcomes for people with obesity. Diabetes Obes Metab. 2021 Jan;23(1):270-275. doi: 10.1111/dom.14207. Epub 2020 Oct 15. PMID: 32991078. 

9: Ilesanmi I, Tharakan G, Alexiadou K, Behary P, Alessimii H, Bovill-Taylor C, Kenkre J, Choudhury S, Doyle C, Purkayastha S, Miras A, Tsironis C, Chahal H, Bloom SR, Oliver NS, Ahmed AR, Khoo B, Tan TM. Roux-en-Y Gastric Bypass Increases Glycemic Variability and Time in Hypoglycemia in Patients With Obesity and Prediabetes or Type 2 Diabetes: A Prospective Cohort Study. Diabetes Care. 2020 Dec 17:dc201609. doi: 10.2337/dc20-1609. Epub ahead of print. PMID: 33334806. 

10: Tharakan G, Behary P, Wewer Albrechtsen NJ, Chahal H, Kenkre J, Miras AD, Ahmed AR, Holst JJ, Bloom SR, Tan T. Roles of increased glycaemic variability, GLP-1 and glucagon in hypoglycaemia after Roux-en-Y gastric bypass. Eur J Endocrinol. 2017 Dec; 177(6):455-464. doi: 10.1530/EJE-17-0446. Epub 2017 Aug 30. PMID: 28855269; PMCID: PMC5642268. 

11: Tharakan G, Scott R, Szepietowski O, Miras AD, Blakemore AI, Purkayastha S, Ahmed A, Chahal H, Tan T. Limitations of the DiaRem Score in Predicting Remission of Diabetes Following Roux-En-Y Gastric Bypass (RYGB) in an ethnically Diverse Population from a Single Institution in the UK. Obes Surg. 2017 Mar; 27(3):782-786. doi: 10.1007/s11695-016-2368-9. PMID: 27613192; PMCID: PMC5306254. 

12: Miras AD, Kamocka A, Pérez-Pevida B, Purkayastha S, Moorthy K, Patel A, Chahal H, Frost G, Bassett P, Castagnetto-Gissey L, Coppin L, Jackson N, Umpleby AM, Bloom SR, Tan T, Ahmed AR, Rubino F. The Effect of Standard Versus Longer Intestinal Bypass on GLP-1 Regulation and Glucose Metabolism in Patients With Type 2 Diabetes Undergoing Roux-en-Y Gastric Bypass: The Long-Limb Study. Diabetes Care. 2020 Nov 6 

13: Miras AD, Pérez-Pevida B, Aldhwayan M, Kamocka A, McGlone ER, Al-Najim W, Chahal H, Batterham RL, McGowan B, Khan O, Greener V, Ahmed AR, Petrie A, Scholtz S, Bloom SR, Tan TM. Adjunctive liraglutide treatment in patients with persistent or recurrent type 2 diabetes after metabolic surgery (GRAVITAS): a randomised, double-blind, placebo-controlled trial. Lancet Diabetes Endocrinol. 2019 Jul;7(7):549-559. 

14: Glaysher MA, Mohanaruban A, Prechtl CG, Goldstone AP, Miras AD, Lord J, Chhina N, Falaschetti E, Johnson NA, Al-Najim W, Smith C, Li JV, Patel M, Ahmed AR, Moore M, Poulter N, Bloom S, Darzi A, Le Roux C, Byrne JP, Teare JP. A randomised controlled trial of a duodenal-jejunal bypass sleeve device (EndoBarrier) compared with standard medical therapy for the management of obese  subjects with type 2 diabetes mellitus. BMJ Open. 2017 Nov 15;7(11). 

15: Miras AD, le Roux CW. Metabolic Surgery in a Pill. Cell Metab. 2017 May 2;25(5):985-987.  

16: Miras AD, Chuah LL, Khalil N, Nicotra A, Vusirikala A, Baqai N, Graham C, Ravindra S, Lascaratos G, Oliver N, le Roux CW. Type 2 diabetes mellitus and microvascular complications 1 year after Roux-en-Y gastric bypass: a case-control study. Diabetologia. 2015 Apr 18.  

17: Scholtz S, Miras AD, Chhina N, Prechtl CG, Sleeth ML, Daud NM, Ismail NA, Durighel G, Ahmed AR, Olbers T, Vincent RP, Alaghband-Zadeh J, Ghatei MA, Waldman AD, Frost GS, Bell JD, le Roux CW, Goldstone AP. Obese patients after gastric bypass surgery have lower brain-hedonic responses to food than after gastric banding. Gut. 2014  

18: Miras AD, Chuah LL, Lascaratos G, Faruq S, Mohite AA,  Shah PR, Gill M, Jackson SN, Johnston DG, Olbers T, le Roux CW. Bariatric surgery does not exacerbate and may be beneficial for the microvascular complications of type 2 diabetes mellitus. Diabetes Care, 2012 Dec; 35(12): e81 

Our researchers