🏥 Roux-en-Y Gastric Bypass Metabolic Simulator

Baseline Gastrointestinal Anatomy

Normal stomach, duodenum, and jejunum form one continuous digestive path.

• ~1,200 mL: Normal stomach capacity (before any surgery)
• ~25 cm: Duodenum length (first small bowel segment)
• ~600 cm: Total small bowel length (roughly 20 feet)
• 1.0×: Baseline GLP-1 / PYY (reference secretion level)

The intact stomach reservoir

Full stomach stretches to hold a large meal comfortably.

Duodenum and nutrient mixing

Bile and pancreatic enzymes mix with food here first.

Distal small bowel and L-cells

Hormone-producing L-cells sit mostly far down the bowel.

Surgical Creation of the Gastric Pouch

A stapled-off pouch near the esophagus becomes the new small stomach.

• 15–30 mL: New pouch volume (adjustable illustrative range)
• ~95%: Volume reduction vs stomach (dramatic size decrease)
• ~6 cm: Staple line length (divides pouch from remnant)
• ~1,100 mL: Remnant stomach volume (left in place, unused)

Stapling and pouch formation

Staples divide a thumb-sized pouch from the rest.

The excluded stomach remnant

Remnant stays connected to blood supply, not to food.

Early restrictive effect

Small pouch limits meal volume almost immediately.

Intestinal Rerouting — the Roux Limb

Food now skips the stomach remnant and duodenum entirely.

• ~100–150 cm: Bypassed bowel length (duodenum plus proximal jejunum)
• ~15–20%: Small bowel bypassed (of total bowel length)
• ~100–150 cm: Roux (alimentary) limb length (pouch to jejunojejunostomy)
• 2 anastomoses: New connections created (gastrojejunal and jejunojejunal)

The alimentary limb pathway

Pouch connects directly down to mid-jejunum bowel.

The biliopancreatic limb

Bile and enzymes still flow from the bypassed segment.

The jejunojejunostomy junction

Both limbs merge downstream into one common channel.

The Hindgut Hormonal Shift

Undigested nutrients reach distal bowel early, flooding gut hormones.

• up to 5×: GLP-1 rise (within weeks of surgery)
• up to 3×: PYY rise (appetite-suppressing hormone)
• rapid: Insulin sensitivity change (measured in days)
• days: Glucose normalization timing (often before real weight loss)

The hindgut hypothesis

Early nutrient exposure to L-cells drives the hormone surge.

GLP-1 and glucose control

GLP-1 boosts insulin release and slows gastric emptying.

PYY and appetite suppression

PYY signals fullness, reducing overall food intake.

Weight Loss and Diabetes Remission

Sustained weight loss follows fast, often pre-emptive glucose normalization.

• ~60–70%: Excess weight loss at 1 yr (typical surgical outcome)
• ~60–80%: Type 2 diabetes remission (of eligible patients)
• within days: Remission often begins (before major weight change)
• 10+ years: Durability of outcomes (long-term follow-up data)

Weight loss trajectory

Weight decline continues steadily over months post-surgery.

Diabetes remission mechanism

Combined hormonal and caloric effects normalize blood sugar.

Long-term metabolic maintenance

Most patients sustain benefits for many years afterward.