Weight-loss surgery options: sleeve vs bypass, side by side

There isn’t one “weight-loss surgery” — see the real trade-off between the sleeve and the bypass, and the five questions that decide it for you.

Dr HB Lo

Integrative GP · Weight-loss surgery: sleeve vs bypass — decision prep

General information to help you prepare. Not medical advice and not an emergency service. It does not tell you whether to have surgery or which operation to choose. In an emergency call 000.

Your input

The thing worth knowing first

There isn’t one “weight-loss surgery”. The two operations that make up about 9 in 10 done in Australia trade off against each other — and the bigger one isn’t automatically the right one for you.

Sources: ANZMOSS — IFSO/ASMBS guidelines Bariatric Surgery Registry (Monash)

Felt at a glance

The two operations, side by side

Both are real options. This is a trade-off, not a ranking — there is no “best” operation, only the one that fits your health and what matters to you.
Trade-off	Gastric sleeve (sleeve gastrectomy)	Gastric bypass (Roux-en-Y)
What it does	Removes about 75–80% of the stomach, leaving a narrow tube. Nothing is re-routed.	Makes a small stomach pouch and re-routes the small bowel past part of the gut.
Typical weight loss (first ~1–2 yrs)	Around 50–60% of excess weight; ~25–29% of total body weight in real-world AU data. BSR	Generally more — around 65–80% of excess weight in comparative studies. comparison lit.
The operation	Simpler, one join, usually shorter.	Bigger operation, more joins, more complex.
Diabetes	Strong improvement; many come off medication. BSR	Often stronger diabetes effect.
Reflux / heartburn	Can start or worsen reflux.	Usually improves reflux.
Lifelong vitamins & monitoring	Yes — needed for life.	Yes — and a higher chance of vitamin/iron deficiency long-term.
Reversible?	No (stomach removed).	Not easily, but technically re-routable.

Bands and newer procedures exist too — these two are just the most common in Australia. Your surgeon can walk you through the others.

Numbers from: Brown et al. 2025, ANZ J Surg (BSR real-world) Monash BSR report multicentre sleeve-vs-bypass comparison

Before any operation: do you qualify?

Surgery is generally considered at BMI over 35, and from BMI 30–34.9 when type 2 diabetes or other metabolic disease isn’t controlled by other means. Thresholds are lower for people of Asian background (clinical obesity from BMI ~25, surgery considered from ~27.5). ANZMOSS / IFSO-ASMBS

This is the number your surgeon will start from — not a yes or no. It doesn’t tell you whether you qualify, and it isn’t a diagnosis.

The five questions that decide it — take these to your surgeon

Which operation fits my health and goals — and why? “Given my weight, my diabetes and my reflux, which operation would you talk through with me first, and what makes you lean that way?”
What weight loss is realistic for someone like me — in real numbers? “With your patients, what range of weight loss is realistic for me at one and two years — and how much usually comes back?”
What are the risks — the early ones and the lifelong ones? “What’s my chance of a serious complication, what’s the risk to life, and what vitamins and check-ups will I need forever?”
What are my non-surgery options, and how do they compare? “Could medication and lifestyle treatment get me a similar result — and what would we try first if I wanted to?”
What does life after this operation actually ask of me? “Day to day, what changes for good — eating, follow-up, supplements — and what support is there to help me stick with it?”

The credibility check

The honest part.

Surgery is a tool, not a cure — and it isn’t free of harm. It works best alongside lifelong eating, activity and follow-up changes, and weight can come back without them. In Australia the risk of dying within 90 days of surgery is very low — around 1 in 2,900 Bariatric Surgery Registry — but roughly 1 in 10 people have a complication, and you’ll need vitamins and check-ups for life. Some people do as well, or better, with medical and lifestyle treatment. The right answer is the one that fits your health and what matters to you — that’s a conversation, not a calculator.

Take the card with you

Email yourself this comparison to take to your GP and surgeon — one clean page, with the questions to ask.

A printable: the sleeve-vs-bypass trade-offs, your BMI context, and the five questions that decide it — formatted to hand over.

Sent — check your inbox. Here’s your comparison again so you can screenshot it now.

This is the general map. The full weight-loss surgery decision kit walks your exact situation — your BMI, your diabetes, your reflux — through every question, with the real numbers filled in, plus what life after surgery actually asks of you. See the weight & metabolic decisions hub, the BRAN question generator for this operation, and your baseline diabetes and heart risk numbers.

General information to help you prepare. Not medical advice, and not an emergency service. It does not tell you whether to have surgery or which operation to choose — that’s a decision for you, your GP and your surgeon. In an emergency call 000.