Why Supplements Are Non-Negotiable
Before surgery, your stomach absorbed nutrients across a large surface area. After gastric sleeve, roughly 80 percent of that capacity is gone. Even if your diet is good, your body can no longer extract enough of certain vitamins and minerals from food alone. The result, without supplementation, is deficiency – and the consequences of deficiency after bariatric surgery are serious: anaemia, nerve damage, bone density loss, hair loss, and profound fatigue that can take months to reverse.
This is not something that happens to careless patients. It can happen to anyone who is not supplementing consistently. We know this from personal experience. Around month eleven, both of us hit a wall – fatigue that sleep did not fix, brain fog, cold intolerance, and a general deterioration that took blood tests to diagnose and several months of consistent supplementation to correct. We had been taking supplements, but not reliably enough, and the gap showed up in our bloodwork.
The lesson: supplements after gastric sleeve are a permanent part of life, not a post-op phase you eventually graduate from.
What We Take Every Day
Our routine has been refined over two years based on our blood results and guidance from our clinical team. The core of it is a bariatric-specific multivitamin – not a standard supermarket multivitamin, but one formulated for post-bariatric absorption, with higher doses of the nutrients most at risk after sleeve surgery.
On top of the multivitamin, we take the following separately because they either require higher doses than a standard multi provides, or because they need to be taken at specific times for proper absorption.
Vitamin D3 with K2: the sleeve does not directly affect vitamin D absorption, but deficiency is extremely common in the UK regardless, and the combination with K2 supports calcium routing to bones rather than soft tissue. We take this year-round, with a higher dose through autumn and winter.
Vitamin B12: the stomach produces a protein called intrinsic factor that is needed to absorb B12 from food. After surgery, less stomach means less intrinsic factor. Sublingual B12 (dissolved under the tongue) or a B12 spray bypasses the need for intrinsic factor and absorbs directly into the bloodstream – we use these rather than standard tablets.
Iron: particularly important for Kirsten, whose Crohn’s disease creates additional absorption challenges. Low iron is one of the more common deficiencies after bariatric surgery, especially in women. Iron should be taken separately from calcium – they compete for absorption.
Calcium citrate: calcium carbonate (the most common form) requires stomach acid to be absorbed, which is reduced after surgery. Calcium citrate absorbs without needing stomach acid and is the recommended form for bariatric patients. The daily dose should be split across the day, typically 500mg at a time, rather than taken all at once.
Omega-3: supports cardiovascular health, inflammation, and brain function. Not specific to bariatric surgery but worth including given the reduced food variety in the first year.
Blood Tests: The Only Way to Know
Feeling fine is not a reliable indicator of your nutrient levels. Deficiencies can build slowly over months before symptoms appear – and by the time you notice the fatigue, the hair loss, or the muscle weakness, you may already have a significant deficit to correct.
We get full bariatric blood panels at least every six months. This covers iron, ferritin, B12, folate, vitamin D, calcium, full blood count, thyroid, and a range of other markers. The results tell us whether what we are taking is working, and whether anything needs adjusting.
If your GP practice does not routinely offer bariatric blood monitoring, it is worth asking specifically for a post-bariatric panel. BOMSS guidelines set out what should be tested and at what intervals – your bariatric team can provide a monitoring schedule.
Staying Consistent
The biggest challenge with supplements is not finding the right ones – it is taking them every day without fail. Supplements in a drawer get forgotten. A busy week becomes a month of inconsistency. Travel disrupts routines.
What has worked for us: keeping everything visible on the kitchen counter, not stored away. Taking them at the same time each day, attached to an existing habit (for us, morning coffee). When travelling, packing a week’s supply into a day-of-week pill organiser so there is no guesswork. If you miss a day, take it when you remember rather than skipping entirely.
Consistency over perfection. One missed day every few weeks is not a problem. A gradual slide into rarely taking them is how deficiencies develop.
Sources
BOMSS (British Obesity and Metabolic Surgery Society) – Guidelines on perioperative and postoperative biochemical monitoring and micronutrient replacement for patients undergoing bariatric surgery
Parrott J et al. – American Society for Metabolic and Bariatric Surgery Integrated Health Nutritional Guidelines for the Surgical Weight Loss Patient 2016 Update (Surgery for Obesity and Related Diseases, 2017)
NHS – Vitamins and minerals overview (nhs.uk)
Mechanick JI et al. – Clinical Practice Guidelines for jthe Perioperative Nutrition, Metabolic, and Nonsurgical Support of Patients Undergoing Bariatric Procedures – 2019 Update (Surgery for Obesity and Related Diseases, 2020)
About this content
This blog is written by James and Kirsten, a couple from the UK who had gastric sleeve surgery together in March 2024.
We started this blog because we couldn't find any sources of content that details before surgery, the surgery and then life post surgery - so we decided to write one ourselves.
Everything on this site is based on our own experience and the research we have done along the way. It is not medical advice. Gastric sleeve surgery is a serious procedure and every patient's journey is different. Please always consult your own bariatric team or GP before making any decisions about your health or treatment.
Some posts on this site may contain featured or sponsored content, or affiliate links. Where this is the case, it will always be clearly stated at the top of the article. Our opinions are always our own.
Publish Date: 30 December 2025 | Last Reviewed: 7 June 2026 | Next Planned Review: 7 December 2027