Metabolic bariatric surgery – what do GPs need to know?

GP with special interest in obesity Dr Stephanie de Giorgio provides an overview of metabolic bariatric surgery and what key post-operative care GPs must be aware of

While the new obesity management medications are being discussed widely, there are still patients choosing to undergo metabolic bariatric surgery (MBS) for the management of their obesity.

MBS remains the most effective treatment for obesity that we have, in the long term.¹ This is absolutely the right choice for some patients, particularly those with Type 2 diabetes, and although the post-operative management and monitoring of patients who have had these procedures isn’t part of core GP contracted work, it is important that we know what our patients may have had done, and what they may need.

What kind of surgery may the patient have had?

There are two categories of surgery.

1. Restrictive, which includes gastric balloons and gastric bands. These simply make the available space for food in the stomach less, and can be a useful tool but do not fundamentally change the physiology of the patient.

2. Restrictive and malabsorptive. The most common procedures are a gastric bypass (Roux en Y gastric bypass, RYGB), sleeve gastrectomy (SG), one anastomosis (mini) gastric bypass (OAGB) and a duodenal switch. These surgeries cause a space restriction but more importantly, they alter the gut-brain hormone axis, causing appetite reduction and long-term changes to physiology, including the gut microbiome, enabling weight loss.²

What is the normal follow-up plan for patients?

All patients who have had surgery in the NHS or privately in the UK, should get 2 years of follow-up by the surgical team as per the NICE guidance.² After this, they are reliant upon GP care.

Patients who have opted to have surgery abroad for financial reasons, are often left without any follow-up and are likely to come and ask you for help.

This post-op care doesn’t have to be provided as it isn’t part of the GP contract, but you may choose to do so because it isn’t onerous and the patient has taken a pro-active decision for their health and may well take up less time due to resolution of long-term chronic conditions.

GPs may alternatively choose to direct patients to the care of a private GP if they feel unable to provide the care themselves. However in this case it would be sensible to contact the LMC or MDO for advice on your responsibilities, as some patients may not be able or willing to afford private care.

What monitoring and care does a patient need after surgery?

There are three areas that need addressing, ideally in an annual review:

1. Blood monitoring for nutrient deficiencies.
2. Changes to medications due to absorption issues.
3. Chronic health conditions that may improve/worsen including psychological illness/wellbeing.

1. Blood monitoring and supplementation

Blood tests

Patients undergoing surgery will need bloods at 6 months post operatively and then annually. (They may need these at 3 months if clinical concerns.)

This should initially be covered by the bariatric team; people who have had surgery abroad are unlikely to have anyone to provide this.

Patients with sleeve gastrectomy, gastric bypass or OAGB need the following annual blood tests:

• FBC.
• Ca.
• LFT.
• ECR.
• Vitamin B12 and folate.
• Ferritin.
• HbA1C.
• Lipids.
• Vitamin D.
• Zinc.
• Cu.
• Selenium.

Those with a gastric band need the above except Zinc, Cu, Selenium unless symptomatic. See the British Obesity and Metabolic Specialist Society (BOMSS) hub for more details on symptoms.⁴

Supplementation

The correct supplements for patients to take for SG, RYGB, OAGB are:

• Forceval vitamin or 2 x Centrum
• AdcalD3
• Ferrous sulphate in line with blood results
• IM vitamin B12 3/12 (even if levels are normal/high on blood tests).
• For borderline Zinc and Copper deficiencies, try prescribing 2 Forceval per day and redo bloods in 3/12. Ensure patient was not acutely unwell when bloods taken which can lower zinc levels. If remain low, then refer to dietitians.

Those with a gastric band just need a multivitamin.

For more information, please see the BOMSS nutritional guidance for GPs.  

2. Medication management

Immediately post-operatively, patients may not be able to swallow tablets, and may need liquid preparations of their medications or empty capsules or crush meds. A pharmacist should be able to advise. If there is no alternative, then consider the risk versus benefit of them being without their medication versus stressing the suture line. By about 6-8 weeks they should be able to go back to normal formulations. However, enteric coated capsules may not be absorbed as well as before the operation.

After this period, it is important to consider dose changes for medications such as antihypertensive, Type 2 diabetes and thyroid medications as bodyweight changes and monitoring accordingly.

Patients with Type 2 diabetes may rapidly drop their blood sugars post-operatively, going into remission within days. Therefore their medications may need to be reduced or stopped very soon post operatively.

SGLT-2 inhibitors must be stopped 48 hours prior to any pre-operative diet or surgery and they should not be given to patients who have had MBS due to the risk of ketoacidosis.

Contraception is one area that is vital to consider. For patients who have had restrictive and malabsorptive surgery, oral contraception, including emergency contraception (EC) may no longer be absorbed properly. Therefore patients must be switched to a non-oral form of contraception and warned that the only EC option for them is the insertion of a copper IUD.

There is more detailed information on medications in the BOMSS GP Hub.⁴  

3. Chronic health conditions and psychological wellbeing

Chronic conditions associated with obesity, such as Type 2 diabetes, hypertension, hyperlipidaemia may all resolve after surgery. As discussed above, Type 2 diabetes may go into remission only days after surgery.

For many patients, they feel more healthy and psychological distress caused by their negative inner weight bias will improve. Negative inner weight bias is the belief a person has that having obesity makes them a bad person, that their weight makes them unlovable, unworthy and inadequate and that they are to blame. It develops as a result of repeated experiences with external weight bias and stigma over time

But for some, there may be physical or emotional side effects that need discussing:⁵

Psychological

Psychological issues may include body dysmorphia, new addictive behaviours, anxiety, low mood, relationship difficulties or distress caused by excess skin. Refer for these as appropriate.

Physical issues

Common physical side effects can include heartburn or reflux and dysphagia or vomiting. A PPI may be helpful but these symptoms should be investigated if they persist. Abdominal pain may be a sign of gallstones which are very common after significant weight loss, with rates of between 10.4% to 52.8% within 6–12 months postoperatively.⁶

Dumping syndrome is caused by release of gut hormones and rapid entry of water into the gut.⁷ It is important to be aware:

• It can be early (40% patients with SG and RYGB) which is within 15 mins of a meal, where the symptoms are vasomotor and include palpitations, faintness, flushing, abdominal pain, diarrhoea, bloating and nausea.
• It can also be late, which affects about 25% of patients (with SG and RYGB) approx. 1-3 hours after eating and symptoms can be tremor, sweating, fatigue, confusion, hunger, weakness and syncope.
• Ensuring that meals are low glycaemic index and include protein, can help these symptoms. If not, refer to a bariatric dietitian or endocrinologist.

Problems with excess skin can be distressing, but surgery for this is almost never provided by the NHS. Therefore patients will have to access this treatment privately.

Weight regain post MBS

Because obesity is a life-long, chronic, relapsing remitting disease, it is normal for people who have had MBS to regain some weight.¹ This should not be seen as a failure of treatment, but part of the disease of obesity.⁸

Patients may need support through this time, and now that we have pharmacotherapeutic options for treatment, starting GLP-1 medications may enable them to lose some of the regained weight and manage their weight long term.^8,9

Recognising post-operative emergencies

Most post-operative emergencies will occur in the immediate days or weeks after the surgery, however, as some patients return from abroad only 48 hours after surgery, they may present to primary or urgent care with symptoms. For some patients who have surgery abroad, they do not know what operation they had and emergency referral is vital.

Symptoms that need to be urgently assessed in the early post-operative period:

• Abdominal pain.
• Wound infections.
• Fever and signs of sepsis.
• Continuous vomiting.
• Haematemesis/melaena.

After the initial post-operative phase, urgent problems may include:

• Abdominal pain due to gallstones, herniae, adhesions, ulceration.
• Dizziness/unconsciousness post-prandially.
• Confusion and neurological symptoms – thiamine/B12 deficiency.
• Severe heartburn/reflux/dysphagia.
• Haematemesis/melaena.

Summary

MBS is a safe and effective treatment for the life-long disease of obesity. Although weight loss medications have reduced the number of patients having the procedures at present, many patients still do, and it is important that we understand what our patients may have had and what after care they need.

Dr Stephanie de Giorgio is a GP with special interest in obesity and co-director of All About Obesity

References

1. Sjostrom L. Review of the key results from the Swedish Obese Subjects (SOS) trial – a prospective controlled intervention study of bariatric surgery. J Intern Med 2013 Mar;273(3):219-34
2. Cornejo-Pareja I et al. Metabolic and endocrine consequences of bariatric surgery. Front Endocrinol (Lausanne) 2019 Sep 19:10:626
3. NICE. Overweight and obesity management. [NG246] 2025
4. BOMSS GP Hub. Available at: https://bomss.org/gp-hub/
5. Shiau J, Biertho L. Canadian Adult Obesity Clinical Practice Guidelines. Bariatric surgery: Post-operative management. Available at: https://obesitycanada.ca/wp-content/uploads/2025/03/14-Canadian-Adult-Obesity-CPG-Bariatric-Surgery-PostOperativeMgmt.pdf
6. Chen S et al. (2025) Gallstones after bariatric surgery: mechanisms and prophylaxis. Front Surg 2025:12:1506780
7. Bettini S et al. Diet approach before and after bariatric surgery. Rev Endocr Metab Disord 2020 Sep;21(3):297-306
8. Lingvay I et al. Obesity in adults. Lancet 2024;404(10456):972-987
9. Gracia Pratama K et al. Glucagon-like peptide-1 receptor agonists for post-bariatric surgery weight regain and insufficient weight loss: A systematic review. Obes Med 2024;46:100533