About David Gans
Gastric bypass patient · Vitamin researcher · Founder of BypassVitamins.com
Lost 231 lbs after Roux-en-Y gastric bypass in January 2024
My story
I had Roux-en-Y gastric bypass in January 2024. I walked into the operating room at the heaviest point of my life and walked out into a new set of rules that nobody had really explained to me. Drink slowly. Protein first. Chew everything twice. And take your vitamins, every day, for the rest of your life, or your labs will crash.
I took the rules seriously. In the 15 months after surgery I lost 231 lbs. That is the number every bariatric patient wants to know, so I put it up front: 231 pounds, across roughly a year and a half of strict protein targets, walking, and a boring supplement routine. No miracle, just the post-op protocol done the way the ASMBS guidelines say to do it.
The vitamin part was the one that surprised me. I assumed, like most people, that any bariatric multivitamin would do. I thought the label read bariatric and that meant it was built for me. It is not. A lot of the formulas sold online are designed for gastric sleeve patients, who only need 18mg of iron. Roux-en-Y bypass patients need 45mg or more, because the surgery reroutes food past the duodenum where most iron is absorbed. Taking a sleeve formula after bypass is one of the most common mistakes I see in the bariatric groups I am in, and nobody gets warned about it clearly enough.
So I started comparing. I pulled the label data on every bariatric multivitamin I could find, checked the price per day, and built a spreadsheet. Then I got annoyed at my own spreadsheet, and I built this site.
Why BypassVitamins.com exists
There are a lot of bariatric vitamin sites online. Most of them are either run by a single brand that is ranking its own products, or they are SEO-driven affiliate sites that list every product in existence without filtering for surgery type. Neither of those is useful to the patient who walks out of a post-op appointment and needs to buy something in the next 48 hours.
BypassVitamins.com is built around one question: what is the cheapest ASMBS-compliant multivitamin for a gastric bypass patient this week? Everything else on the site is there to support that answer. The comparison table. The iron and B12 guides. The FAQ that explains why calcium citrate is different from carbonate after bypass. All of it exists so a patient can make a confident choice in a few minutes instead of falling into a research rabbit hole.
I am not a doctor. I am not a registered dietitian. I am a patient who reads the ASMBS guidance, reads the product labels, and ranks what I find by a simple number. I write in first person because that is the honest frame for this work. If you have a specific health question, your surgeon and your bariatric dietitian are the right people to talk to. The job of this site is to narrow the field before that appointment, not to replace it.
The site is part of the Dutch Goose network of bariatric comparison sites, which also includes SleeveVitamins.com for gastric sleeve patients and BestBariatricMultivitamins.com for cross-procedure comparisons. Each site is tuned to a different patient population and different ASMBS thresholds.
How I rank products
Four rules, in this order. Nothing else changes the ranking.
Start with ASMBS guidance
Every product is checked against the American Society for Metabolic and Bariatric Surgery 2016 integrated health nutritional guidelines for Roux-en-Y gastric bypass. That document is the clinical baseline. If a formula does not hit 45mg of elemental iron and 1,000mcg of B12, it does not belong on this site for bypass patients.
Rank by price per day
The only sort order that matters to a patient who takes a vitamin for life is price per day. I calculate this from the listed Amazon price divided across the full servings per container. I use 3-month (90-day) supply pricing where available because that is the cheapest way most bariatric vitamins are sold.
Read the label, not the marketing
Iron content is the number one thing patients get wrong after bypass. The amount that matters is elemental iron, not the amount of the iron compound. Most bypass formulas use ferrous fumarate or bisglycinate and list elemental iron on the back. I only count that number. Claims like bariatric formula or bypass ready mean nothing by themselves.
Update weekly
Prices change. Amazon listings churn. I re-check every product on the list every Sunday. When a product is discontinued or reformulated, it gets updated or removed. You can see the last-updated date at the bottom of each comparison page.
How this site makes money
BypassVitamins.com is reader-supported. When you click an Amazon link on this site and buy the product, Amazon pays a small referral fee at no extra cost to you. That is the only way the site is funded. I do not take sponsorship money from supplement brands, and no brand pays to be listed or to be ranked higher.
The Amazon Associate relationship is disclosed on every comparison page and inside the site footer. The FTC requires it, and more importantly, you deserve to know. If the affiliate model ever creates a conflict with honest product ranking, my rule is simple: the ranking wins. If the cheapest ASMBS-compliant formula is not in the Amazon program, it still gets listed first. The goal is to help bypass patients not overpay for the wrong vitamin, not to maximize commission.
Questions, corrections, or product suggestions?
If a price looks wrong, a product should be added, or you just want to say hello, I read everything.
contact@bypassvitamins.comOr head to the comparison to see the current rankings.
Compare all 15 bypass vitamins →