Bariatric and weight loss glossary
Half of a consultation can slip by when one unfamiliar word goes past and you do not stop to ask. This is the list of terms you are likely to hear, each in a sentence or two, with a link to the page that explains it properly.
Book a free consultationMedically reviewed by David G. Davtyan, MD, FACS, FICS, FASMBS · Last reviewed September 24, 2026
How to use this glossary
Terms are listed A to Z in the sections below. Each has a short, plain definition, the authoritative source it was checked against where the point is not self-evident, and a link to the page on this site that explains it in full.
Some procedures and medications are defined here because you will meet the words, not because they are offered by this practice or right for you. Which options fit your situation is decided in consultation. For an overview of how the options differ, see compare your weight loss options; for the questions patients ask most, the weight loss surgery FAQs.
One habit helps more than memorizing anything: when a word you do not know comes up in a visit, ask there and then.
Terms A–B
A
- Adjustable gastric band (Lap-Band)
An inflatable silicone band placed around the top of the stomach, creating a small pouch with an adjustable opening. It is tightened or loosened through a port under the skin; no stomach is removed. MedlinePlus, NIDDK
- Adjustment (fill)
Adding or removing fluid through the port to make an adjustable band snugger or looser, in the office, based on how you are eating and losing weight. MedlinePlus
- Allurion balloon
A swallowable intragastric balloon, formerly Elipse, that later empties and passes naturally, so it needs no endoscopy. FDA-approved in 2026. FDA
- Anastomosis
A surgical connection between two parts of the digestive tract, such as between a bypass pouch and the small intestine. ASMBS
- Anemia
Too few healthy red blood cells, causing tiredness or breathlessness. After surgery it is usually linked to low iron, B12 or folate. NIDDK, ASMBS nutrition guideline
B
- Band erosion
An adjustable band gradually wearing into the stomach wall. It is managed by the surgical team, generally by removing the band. NIDDK
- Band slippage
An adjustable band moving out of position. New heartburn, vomiting or trouble swallowing with a band is a reason to call your surgeon. NIDDK
- Bariatric surgery
Surgery on the stomach, the intestine or both to treat obesity. Current guidelines say "metabolic and bariatric surgery," because these operations also affect blood sugar and other metabolic conditions. ASMBS/IFSO 2022
- Benefits verification
The check a practice makes with your insurer on whether your plan covers bariatric care, what it requires first, and your share.
- Biliopancreatic diversion with duodenal switch (BPD/DS)
A sleeve-shaped stomach whose outlet is joined to a much lower part of the small intestine, bypassing most of it. It affects nutrient absorption more than a sleeve or standard bypass and needs closer lifelong monitoring. ASMBS, NIDDK
- Body contouring
Plastic surgery to remove loose skin and reshape the abdomen, arms, thighs or breasts after major weight loss, generally once weight is stable.
- Body mass index (BMI)
Weight in kilograms divided by height in meters squared. A screening number, not a diagnosis: it does not separate fat from muscle. Guidelines, device labels and insurers use it, not always with the same cutoffs. CDC
Terms C–D
C
- Calcium and vitamin D
Bone-health supplements taken after surgery. MedlinePlus bypass guidance specifies calcium citrate; your team will say which form and how much. MedlinePlus, ASMBS nutrition guideline
- Candidate
Someone for whom a procedure is clinically appropriate. The 2022 ASMBS/IFSO indications recommend surgery at BMI 35 or more and consideration at 30 to 34.9 with metabolic disease, lower in Asian populations. Insurers may use different criteria. ASMBS/IFSO 2022
- Class I, II and III obesity
Adult BMI categories: class I is 30 to 34.9, class II 35 to 39.9, class III 40 or higher. "Class III" or "severe obesity" now replaces the older "morbid obesity." MedlinePlus
- Comorbidity
A condition that occurs alongside obesity and is often worsened by it, such as type 2 diabetes, high blood pressure or sleep apnea. It matters for candidacy and insurance review.
- Compounded medication
A drug mixed by a pharmacy rather than an FDA-approved product. The FDA does not review compounded drugs for safety, effectiveness or quality before sale. FDA
- Conversion
A revision that changes one procedure into another, such as a band or sleeve converted to a gastric bypass.
D
- Deductible, copay and coinsurance
What you pay yourself: the deductible before the plan starts paying, a copay as a fixed amount per service, coinsurance as a percentage of the cost. HealthCare.gov
- Deep vein thrombosis (DVT)
A blood clot in a leg vein, which can travel to the lungs. It is why walking soon after surgery, compression and preventive medication are used. NIDDK
- Deficiency
A shortage of a vitamin or mineral, usually found on blood tests before symptoms. Many people have at least one before surgery, so testing starts beforehand. ASMBS nutrition guideline
- Dehydration
Too little fluid. It is a common early concern because the stomach holds little at once, so fluids are sipped through the day, apart from meals. MedlinePlus
- Diet stages
The planned return to eating after surgery: liquids, then puréed, then soft, then regular food, each held as long as your surgeon specifies. MedlinePlus
- Dumping syndrome
Nausea, diarrhea, or feeling light-headed or tired after a meal, caused by the stomach emptying too fast. Early dumping starts within 30 minutes of eating; late dumping 1 to 3 hours after. NIDDK
- Duodenum
The first part of the small intestine, just past the pylorus. Much iron and calcium is absorbed here, so both need attention after a bypass routes food past it.
Terms E–G
E
- Endoscopic sleeve gastroplasty (ESG)
A procedure done through an endoscope in which stitches placed inside the stomach reduce its size. There are no incisions and nothing is removed. The practice calls it the Accordion Procedure. FDA
- Endoscopy
A look inside the esophagus, stomach and duodenum with a thin, flexible camera passed through the mouth. It is also how balloons are placed and ESG is performed.
- Excess skin
Loose skin left after large weight loss. It can cause rashes and discomfort as well as affect appearance; see body contouring.
- Excess weight loss (%EWL)
Weight lost as a share of "excess" weight, usually weight above a BMI of 25. It reads higher than %TWL for the same result, so check which a figure uses. Hatoum & Kaplan 2013
- Exclusion
A plan clause saying a service is not covered at all. That is a different problem from a denial for missing paperwork.
F
- Fatty liver disease (MASLD)
Fat buildup in the liver linked to obesity and type 2 diabetes, now called metabolic dysfunction-associated steatotic liver disease. Older pages say NAFLD.
- Ferritin
A protein that stores iron. A ferritin blood test shows how much iron the body has in reserve. MedlinePlus
- Follow-up
Scheduled visits to check weight, nutrition and blood tests, and to adjust a band. Bariatric follow-up is lifelong. ASMBS nutrition guideline
- Formulary
The list of prescription drugs a plan covers, also called a drug list. It decides whether a weight loss medication is covered and can change from year to year. HealthCare.gov
- Fundus
The upper, dome-shaped part of the stomach, removed in a sleeve gastrectomy. Much of the hunger hormone ghrelin is made here.
G
- Gallstones
Hard deposits in the gallbladder. Rapid weight loss makes them more likely. NIDDK
- Gastric bypass (Roux-en-Y, RYGB)
The top of the stomach is stapled into a small pouch joined to the small intestine further down, so food skips most of the stomach and the first part of the intestine, in a Y shape. ASMBS, MedlinePlus
- Gastric plication
A laparoscopic operation that folds the stomach inward and stitches it to reduce its volume, without removing stomach or rerouting the intestine.
- GERD (reflux)
Stomach acid repeatedly flowing back into the esophagus. Existing reflux matters when choosing a procedure, because it can worsen after a sleeve. Kodilinye et al. 2025
- Ghrelin
A hunger hormone made mainly in the stomach. Bariatric operations change hunger hormones, part of how they work beyond size. ASMBS
- GLP-1 receptor agonist
A medication that mimics the gut hormone GLP-1 and acts on brain areas that regulate appetite. Semaglutide and liraglutide are examples; tirzepatide also acts on GIP. NIDDK
- GLP-1s before surgery
October 2024 multisociety guidance, co-written with ASMBS, says most patients can continue a GLP-1 before elective surgery, decided case by case on the risk of slow stomach emptying. Multisociety guidance 2024
- Good faith estimate
A written estimate of expected charges that a provider must usually give you if you are not using insurance and request one or schedule care in advance. CMS
Terms H–L
H
- Hemoglobin A1c
A blood test showing your average blood sugar over the past three months, not just today. It is used to diagnose and monitor diabetes. MedlinePlus
- Hiatal hernia
Part of the stomach pushing up through the diaphragm opening that the esophagus passes through. It is often linked with reflux and may be repaired during a bariatric operation.
I
- Internal hernia
Intestine slipping through a gap in its supporting tissue created by a bypass. Abdominal pain after a bypass, even if it comes and goes, should be reported. Kodilinye et al. 2025
- Intragastric balloon
A temporary balloon that takes up space in the stomach so you feel full sooner. Depending on the device it is placed by endoscope or swallowed, and it must come out when its label specifies. FDA
- Iron
A mineral needed for red blood cells. ASMBS guidelines recommend checking iron before surgery as well as after. ASMBS nutrition guideline
L
- Laparoscopy
Surgery through several small incisions using a camera and long, thin instruments. Sleeve, bypass and band operations are usually done this way; endoscopic procedures need no incisions. MedlinePlus
- Leak
Fluid escaping from a staple line or connection that has not sealed. Fever, a racing heart or worsening pain after surgery need an immediate call. NIDDK, Kodilinye et al. 2025
- Liquid calories
Calories in drinks such as juice, soda, alcohol and sweetened coffee. They pass through a small stomach without restriction, so they are a common, easily missed source of regain.
Terms M–O
M
- Maintenance
The phase after active weight loss, when the goal is keeping weight stable through habits, follow-up and support.
- Malabsorption
Absorbing fewer calories and nutrients because food bypasses part of the small intestine, as after a gastric bypass or duodenal switch. MedlinePlus
- Marginal ulcer
An ulcer at or near the join between a bypass pouch and the intestine. Smoking and NSAIDs are major risk factors, so bypass patients are asked to avoid both. Salame et al. 2023
- MBSAQIP accreditation
The joint national accreditation program of the American College of Surgeons and ASMBS. Accredited centers meet standards for resources and practice and report outcomes to a national registry. American College of Surgeons, ASMBS
- Medical necessity
The standard insurers apply: care needed to diagnose or treat a condition that meets accepted standards of medicine. Each plan sets its own bariatric criteria. HealthCare.gov
- Muscle loss (lean mass)
Part of any rapid weight loss is muscle, not fat. Enough protein and strength exercise help limit it.
N
- Network (in-network, out-of-network)
The providers and facilities your plan has contracted with. Whether your surgeon and hospital are in network changes what you pay. HealthCare.gov
- NSAIDs
Anti-inflammatory painkillers such as ibuprofen and naproxen. They raise the risk of marginal ulcers after a bypass; ask before taking any painkiller. Salame et al. 2023
O
- Obesity
A chronic disease of excess body fat that raises the risk of many other conditions. In adults it is usually screened for as a BMI of 30 or more. MedlinePlus
- Obstructive sleep apnea
Repeated pauses in breathing during sleep as the airway narrows or closes, strongly linked to obesity. It affects anesthesia planning.
- One-anastomosis gastric bypass (OAGB, mini bypass)
A bypass variation with a long, narrow stomach pouch joined to a loop of small intestine by a single anastomosis, where a Roux-en-Y bypass uses two. Abu-Abeid et al. 2024
- Orbera balloon
An FDA-approved, saltwater-filled intragastric balloon placed and later removed through an endoscope. FDA
Terms P–R
P
- Plateau
A stretch when weight stops falling although you are following your plan. It is expected and not, by itself, a sign a procedure has failed.
- Polycystic ovary syndrome (PCOS)
A hormonal condition affecting ovulation, closely linked to obesity and insulin resistance. Weight loss can change fertility, so pregnancy timing is discussed before surgery.
- Port (access port)
A small reservoir under the skin of the abdomen, connected to an adjustable band by tubing. Fluid is added or removed through it with a fine needle. MedlinePlus
- Pouch
The small upper part of the stomach that receives food after a gastric bypass, or above an adjustable band. It fills quickly, so a few bites can feel like a meal. ASMBS, MedlinePlus
- Pre-operative diet
A lower-calorie, often mostly liquid diet before surgery, commonly used to shrink the liver. Your surgeon sets its length and content.
Your insurer’s decision, before a procedure, that it is medically necessary; also called preauthorization or precertification. It does not by itself guarantee payment. HealthCare.gov
- Protein
The nutrient given priority after surgery, for healing and to protect muscle while weight comes off. Eat it first; shakes help while capacity is small. MedlinePlus
- Psychological evaluation
An assessment of eating patterns, support and readiness by a mental health professional, often required by insurers. It is preparation, not a character test.
- Pylorus
The muscular valve at the lower end of the stomach that controls how fast food empties into the duodenum. A sleeve keeps it.
R
- Restrictive procedure
One that works mainly by limiting how much the stomach holds, such as the band, balloon and ESG. Bypass procedures add malabsorption.
- Revision
A later operation or procedure that corrects, adjusts or replaces an earlier bariatric procedure, for example because of a complication, reflux or weight regain.
- Roux limb
In a Roux-en-Y bypass, the length of small intestine joined to the new pouch, which food travels down. It meets the limb carrying digestive juices further down, forming the Y. ASMBS
Terms S–Z
S
- SADI-S
Single-anastomosis duodeno-ileal bypass with sleeve gastrectomy: a sleeve joined to a loop of intestine several feet from its end, with one bowel connection. A simpler relative of the duodenal switch. ASMBS
- Semaglutide
A GLP-1 receptor agonist: the active ingredient of Wegovy (chronic weight management) and Ozempic (type 2 diabetes). NIDDK
- Sleep study (polysomnography)
An overnight test, at home or in a lab, that records breathing and oxygen during sleep to check for sleep apnea.
- Sleeve gastrectomy (gastric sleeve)
Removal of about 80 percent of the stomach, leaving a banana-shaped tube closed with staples. It limits how much you eat and changes hunger hormones; the intestine is not rerouted. ASMBS, NIDDK
- Staple line
The row of surgical staples sealing the stomach where it was divided or partly removed. Early liquid diet stages help protect it while it heals. MedlinePlus
- Stoma
The opening between the pouch and the rest of the stomach in an adjustable band; adjustments change its size. Also used for the outlet of a bypass pouch.
- Stretching (of the stomach)
The stomach removed in a sleeve does not grow back, but the remaining stomach or pouch can stretch somewhat with repeated overeating.
- Stricture
A narrowing of the new stomach or of a connection to the intestine, making solid food hard to swallow. It is usually diagnosed, and often treated, through an endoscope. NIDDK, Kodilinye et al. 2025
- Supplements
Vitamins and minerals taken for life after surgery. ASMBS guidelines recommend B12, calcium and thiamine for all patients, with more depending on the procedure. ASMBS nutrition guideline
T
- Thiamine (vitamin B1)
A B vitamin needed by the nerves and brain. Deficiency is a particular risk with repeated vomiting after any procedure, so persistent vomiting should never be waited out. ASMBS nutrition guideline
- Tirzepatide
A medication that mimics two gut hormones, GIP and GLP-1. It is the active ingredient of Zepbound (weight management) and Mounjaro (type 2 diabetes). NIDDK
- Total body weight loss (%TWL)
Weight lost as a percentage of starting weight. It is less influenced by starting BMI than %EWL, so it compares results more fairly. Hatoum & Kaplan 2013
- Type 2 diabetes
A chronic condition of high blood sugar from poor insulin response. It is one of the metabolic diseases the 2022 ASMBS/IFSO indications weigh at a BMI of 30 to 34.9. ASMBS/IFSO 2022
V
- Vitamin B12
A vitamin for nerves and red blood cells. ASMBS recommends B12 supplements for everyone after surgery and routine checks after a bypass, sleeve or duodenal switch. ASMBS nutrition guideline
W
- Weight regain
The return of some lost weight after a procedure. It is common, has several causes, is treatable, and is not a personal failure.
Glosario — en español
El glosario en español es una página propia, escrita para pacientes hispanohablantes. Estas páginas explican en español varios de los términos de arriba:
- Glosario bariátrico en español
- Bypass gástrico en Y de Roux: qué se hace, paso a paso
- Síndrome de dumping después del bypass
- Hierro, B12 y calcio: las carencias que se vigilan de por vida
- Ajustes de la banda gástrica: qué son y su importancia
- Qué es un centro acreditado MBSAQIP y por qué importa
- Todo el contenido en español
Where Dr. Davtyan sees patients
Spanish is spoken at all four offices. The first consultation with Dr. Davtyan is free and commits you to nothing.
A word you still want explained?
Bring it to your consultation. Asking what something means is a normal part of the visit, and the first consultation is free and commits you to nothing.
Sources
- ASMBS — Bariatric Surgery Procedures
- NIDDK — Types of Weight-loss Surgery
- NIDDK — Weight-loss Surgery Side Effects
- NIDDK — Definition & Facts for Dumping Syndrome
- NIDDK — Prescription Medications to Treat Overweight & Obesity
- MedlinePlus — Gastric bypass surgery
- MedlinePlus — Laparoscopic gastric banding
- MedlinePlus — Vertical sleeve gastrectomy
- MedlinePlus — Your diet after gastric bypass surgery
- MedlinePlus — Health risks of obesity
- CDC — About Body Mass Index (BMI)
- FDA — Weight-Loss and Weight-Management Devices
- FDA — Medical Devices for Weight Loss: What to Know
- FDA — Summary of Safety and Effectiveness Data, Allurion Gastric Balloon System
- FDA — FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss
- Eisenberg D, et al. 2022 ASMBS/IFSO Indications for Metabolic and Bariatric Surgery. Obes Surg
- Kindel TL, et al. Multi-society guidance on GLP-1 receptor agonists in the perioperative period. Surg Endosc 2024
- Parrott J, et al. ASMBS Nutritional Guidelines 2016 Update: Micronutrients. SOARD 2017
- Hatoum IJ, Kaplan LM. Advantages of percent weight loss for reporting weight loss after gastric bypass. Obesity 2013
- Salame M, et al. Marginal Ulcers after Roux-en-Y Gastric Bypass. J Clin Med 2023
- Kodilinye SM, et al. Complications of Metabolic and Bariatric Surgery. Gastroenterol Hepatol 2025
- Abu-Abeid A, et al. Technical Considerations in One Anastomosis Gastric Bypass. Obes Surg 2024
- American College of Surgeons — MBSAQIP
- ASMBS — MBSAQIP
- HealthCare.gov Glossary — Preauthorization
- HealthCare.gov Glossary — Medically necessary
- HealthCare.gov Glossary — Deductible
- HealthCare.gov Glossary — Network
- HealthCare.gov Glossary — Formulary
- CMS — Good faith estimates
- MedlinePlus — A1C test
- MedlinePlus — Ferritin blood test
This glossary gives general definitions of terms used in bariatric and weight loss care. It is not medical advice, it does not describe what any individual should expect, and including a procedure or medication here does not mean it is right for you or that the practice offers it. Follow the instructions of your own care team.
