Maybe you’ve heard this before. If you haven’t, we’ll say it again: BMI is a flawed, unscientific, inaccurate, and racist tool. It doesn’t actually help us predict health, disease risk, or surgical outcomes. But despite growing awareness of its flaws, it is still used, and it is often used to deny or delay healthcare. This article will discuss the limits of using BMI in surgical evaluations, provide some tools for talking to surgeons who are willing to discuss their BMI restrictions and list some resources for learning more. Yep, we’re getting nerdy again, this time about BMI.
Aside: fat is not a bad word (and Hunter Shackelford is a wealth of fat, queer, and Black wisdom!) We use “fat” as a descriptor, not a value judgment. (We’ll include more resources on fat activism, being a fat patient, and general fat badassery at the end of this article.)
BMI and Gender Affirming Surgery
In a US study on patients seeking gender affirming surgery, one-quarter of participants were told to lower their BMI and come back later at their initial surgical consult. (1 Endocrine Practice)
This is bs.
- BMI doesn’t predict surgical outcomes.
- Delaying care for weight loss may cause more harm than good!
- Prescribing weight loss may cause more harm than good!
- There are other measures that can more accurately predict surgical outcomes.
Hang with us while we go into depth ahead!
One: BMI and Surgical Outcomes
A higher BMI has been associated with a higher risk of unwanted surgical complications. But BMI might not be the root cause for those complications, although it is used as a stand-in for risks that may or may not be present. Heart, lung, and blood vessel health are very important for surgical outcomes, as is airway health.
The things that may make a surgery more or less likely to be successful, and the things that may make a patient more or less likely to heal well after surgery are complex.
- If surgery is to halt or correct a disease process, the specifics of how the disease impacts the body
- Factors specific to the person, that might be changeable:
- Interventions available: smoking, alcohol intake, substance use, body composition, diabetes, hypertension, coronary artery disease, atrial fibrillation, cerebrovascular disease, anemia, malnutrition/nutrition, and mental health issues.
- Can’t change: age, genetics, family history, chronic obstructive pulmonary disease, history of stroke or myocardial infarction (heart attack,) congestive heart failure, or chronic kidney disease.
- Risks related to healthcare resources: the surgeon’s skill and knowledge, the anesthesiologist’s skill and knowledge, the facility and available equipment, and the procedures and processes in place at the surgical center to prevent injuries, accidents, and infections. This includes post-operative care quality.
- Systemic risks: racism, weight bias, transphobia, ageism, ableism, and other factors that contribute to minority stress.
- And random things we can’t easily predict. (2 StatPearls)
Interventions at the patient level can help lower surgical risk: there are tools to help patients with risk factors such as diabetes, high blood pressure, high cholesterol, and anemia (and other diseases) manage their conditions so they are in the best health possible for surgery. There are supports to help patients stop smoking and lower or stop alcohol use. And we have a lot of knowledge about optimizing nutrition and body reserves prior to surgery.
Note: being underweight before surgery is a risk factor, too!
You can read up on some of the general ways to optimize health before surgery here.
(We gotta mention: Minority stress plays a huge role in optimizing health before surgery. So many of the risk factors that have interventions are tied to systemic factors rooted in oppression like walkable cities, food deserts, available produce and leisure time scarcity, pollution, and navigating daily stressors.)
The thing is, all of these conditions can and do happen to people at every point on the BMI scale. Having a higher BMI doesn’t mean that a patient has any of these risk factors.
Risks Related to Healthcare Resources That Have Interventions:
There are body-composition factors related to weight that do impact surgical risk:
- Larger bodies may take longer to work on in surgery. Longer surgeries have a higher risk of complications.
- Anesthesia risks increase with weight.
- Higher BMI has been associated with a higher risk for blood clots (the actual risk relationship might be related to cardiovascular health, body size, body composition, or other factors rather than BMI: it’s probably more complicated that just plain BMI). (3 Plastic and Aesthetic Research)
HOWEVER, we also know that experienced surgeons tend to have lower complication rates.
Surgeons who are experienced in working with larger patients have skills that protect the patient. These are valuable and transferable skills.
Surgical equipment: There is surgical equipment designed for fat patients. There are hospitals and surgical centers that invest in this equipment: bariatric surgical centers prove that surgery on fat patients can be planned and equipped for (and have high safety ratings!)
Centers of Excellence: Surgeons, hospitals, and surgical centers are graded for safety and outcomes. And you can ask them about their grades.
- Hospitals are accredited by the Joint Commission.
- Surgical centers are also accredited by the AAAHC.
- Surgeon accreditation is with the American College of Surgeons. They should also be accredited by their Board of Medical Specialties.
Pre-and post-operative care is important in managing risk, especially for complications like surgical site infections. The whole care team has a role.
A study of complications in aesthetic surgeries in cis populations (these are usually gender affirming procedures, too!) found an increased risk of complications in obese patients. However, only two of the listed complications had a statistically significant risk increase: deep vein thrombosis and pulmonary embolism. Both of these risks can be managed with medications, an emphasis on getting moving again after surgery, and appropriate compression gear/devices. (4 Asthet Surg J) Infection risk is also greatly reduced by safety procedures at all levels of care from the specialized techs who sterilize equipment to the people who clean operating rooms to the nurses who manage injections, scheduled meds, and dressing changes.
BMI and Gender Affirming Surgeries: The Research
There hasn’t been a lot of research looking at BMI and outcomes specifically for gender affirming surgeries, but there has been some. The authors all agree that strict limits on BMI that prevent people from obtaining gender affirming surgery do not make sense.
There isn’t evidence that gender affirming surgery on fat people is inherently riskier.
- Top-flattening surgery: there might be more risk of infection, bruising, and wound dehiscence (the wound edges don’t heal) for people with higher BMIs of 30+.
- A 2020 study of 97 patients showed NO DIFFERENCE in minor and major complication rates between individuals with BMI <30 and those with BMI >=30. (5 JPRAS)
- Another 2020 study of 145 patients found an increase in infections occurring in patients with BMIs =>40+ compared to patients with BMIs <30. (6 Aesthetic)
- A study of 153 patients obtaining drain-free mastectomy surgery between 2015 and 2018 had an overall low rate of complications but noted that infections (7 total) only occurred in patients with BMIs >30. Wound dehiscence (the incision edges split instead of healing together) occurred in three of those infections. This study was not a study about BMI or weight and did not control for other factors, so conclusions about BMI as a risk factor cannot be made. (7 ANNALS)
- Top Surgery – all types
- A study looking at 1865 patients obtaining chest-flattening surgeries and 1466 patients obtaining breast augmentation surgeries found that BMI => 35 was associated with higher complication risk, BUT
- NO difference in readmission or reoperation rates for differing BMIs in people getting breast augmentation.
- NO difference in reoperation rates for differing BMIs in people getting chest-flattening surgery. (8 Plastic and Reconstructive Surgery)
- Phalloplasty: The type of phalloplasty may affect risk:
- One study found no relationship between BMI and increased complications
- One study noted total flap loss (and later successful surgery!) in a patient who was classified as a heavy smoker with a BMI of 44.1. Smoking may be more important than BMI as a risk factor.
- A study found higher BMI and fewer complications among patients choosing anterolateral thigh flap phalloplasty.
- A study found a trend towards higher complication rates among patients choosing radial forearm flap phalloplasty with BMIs higher than 25 (but not statistically significant, so it could be chance.) (9 AMA J Ethics)
- One study identified 101 patients, 26.5% of which had BMIs => 30. NO correlation between higher BMI and surgery complications was found in penile inversion vulvovaginoplasties. (5)
- A study of 330 patients undergoing penile inversion vulvovaginoplasty found no correlation between BMI and complication rates. (10 J Urology)
- Another study of 475 patients undergoing penile inversion vulvovaginoplasty found a correlation between diabetes and post-operative infection but none between body weight and infection. (11 Plast Reconstr Surg)
A patient-centered approach to assessing gender affirming surgery eligibility with respect to BMI would utilize reliable predictors of surgical outcomes specific to each gender affirming surgery, include measures of body composition and body fat distribution rather than BMI alone.Patient-Centered Approaches to Using BMI to Evaluate Gender-Affirming Surgery Eligibility, AMA Journal of Ethics
Two: How Prescribing Weight Loss Can Make Things Worse
Weight stigma in health care is a whole thing. If you are fat, you’ve experienced it. You may have experienced it as a thin person. There is a growing body of evidence that tells us that:
- Most of the reasons why people are fat are not under personal control. It isn’t about willpower.
- There are no quick ways to lose weight.
- Almost everyone who loses weight will gain it back.
- The cycle of weight loss and weight gain may be more harmful to overall health than never losing weight in the first place. (13 Nutrition J, 14 Sage)
We must consider the ethics of recommending that patients pursue medical or surgical interventions for weight loss before undergoing gender affirming surgery without evidence that weight loss will significantly affect surgical outcomes as well as long-term outcomes in cases in which patients lose weight preoperatively and then experience postoperative weight regain.Should BMI Help Determine Gender-Affirming Surgery Candidacy? AMA Journal of Ethics.
For trans folk, all of this can be more complicated:
- It’s already hard to get gender affirming care, and even harder to access gender affirming surgery.
- We have societal factors that may make weight gain more likely and weight loss less likely in our communities compared to other communities. We talk about some social determinants of health in our blog on the benefits of cardiovascular exercise for LGBTQ people.
- Lack of accessible nutrition
- Lack of safe ways and places to exercise
- Minority stress and its impacts on mental and cardiovascular health
- We have higher rates of eating disorders
- For Black and trans folks of color, racism also plays a part in weight bias.
- Weight can be protective and keep us safer.
- Weight can be a positive part of our identities.
And most importantly: GENDER AFFIRMING CARE SAVES LIVES.
Requiring an individual to lose weight before agreeing to surgery ignores that refusing treatment may be more harmful and risky to overall health and well-being than proceeding with surgery.
Losing weight safely or sustainably is difficult and often not achievable for most patients recommended to pursue weight loss. It can even be harmful for some individuals to attempt any weight changes, especially those with an active or previous eating disorder, which is characteristic of a large portion of trans individuals. Additionally, permanent weight loss attempts often result in cycles of weight loss and regain, which are ineffective and have their own health risks.Should BMI Help Determine Gender-Affirming Surgery Candidacy? AMA Journal of Ethics.
Three: Informed Consent, Shared-Decision Making
Surgeons do have an ethical duty to assess and discuss the risks of specific surgeries with specific individuals in their care.
Surgeons also have tools to help them predict and discuss surgical risks. (2)
Several of these risk calculators are available for you to try at home, although it may help to know some medical terminology and the results of some lab tests when you fill them out.
American College of Surgeons National Surgical Quality Improvement Program Based Model (ACS NSQIP)
This calculator predicts the risk of the following complications in the 30 days after surgery:
- Cardiac arrest or myocardial infarction (heart attack)
- Surgical site infection
- Urinary tract infection
- Venous Thromboembolism (VTE)
- Renal failure (kidney failure)
- Return to OR
- Discharge to a nursing or rehab facility
It does include BMI as one of the 19 input factors.
Things To Know Before Using This Calculator
The calculator requires a CPT code for the surgical procedure. We keep a list of CPT codes for gender affirming surgeries on our gender affirming surgery page – see the link to our surgeon referral database. You can enter a procedure name to pull up a list of CPT codes, but it looks like not many gender affirming surgeries are in the calculator. We were able to run a calculation using “hysterectomy.”
ASA Class – this is an anesthesiology risk classification. (15 StatPearls)
Persons with BMI <30 with no other risk factors would be ASA Class 1.
Persons with BMI 30 – 40 and no other risk factors would be ASA Class 2.
Persons with BMI >40 or a lower BMI and poorly controlled hypertension or diabetes would be ASA Class 3.
50 year old individual, ASA Class 2 – mild systemic disease, BMI >40, surgery: total abdominal hysterectomy.
The risk of three potential complications are elevated compared to “average” and five are lower. Most of the differences are minimal. This isn’t a full picture of surgical risk, but it can illustrate that BMI alone doesn’t make a big difference in the overall risk of complications.
Higher risk of:
- Risk of any complication was calculated at 10% compared to an average risk of 8.4%.
- Surgical site infection: 7.0% compared to 4.3% average risk.
- Venous Thromboembolism: 1.0% risk compared to 0.7% average risk.
- Return to OR: 2.0% risk compared to 1.8% average risk.
The Physiological and Operative Severity Score for Enumeration of Mortality and Morbidity (POSSUM)
Note: this calculator uses 12 different patient-related measurements and 6 procedure-related predictors to estimate outcomes.
This calculator DOES NOT use BMI. You can TRY THIS AT HOME but you’ll need some specific blood work information to more accurately predict risk, and it may be helpful to do this calculator with your surgeon and discuss the results together.
What it does:
The P-POSSUM calculator generates a predicted mortality (chance of death) risk, a physiological score (an estimate of how healthy the patient is overall; lower is less risk), and an operative severity score (lower is a less risky operation.)
CAUTION: this calculator is known to overestimate risk in otherwise lower-risk individuals and is meant to be done at the time of surgery.
BUT this calculator can show how blood pressure and heart rate can affect surgical risk AND we know that lowering blood pressure and heart rate are achievable goals for many people.
What To Do About It All:
In a just world, we would have greater access to ally surgeons. That isn’t always the case. We’ll share some resources below, but we also want to state that we support all of our patients in accessing surgery and optimizing health. While we do not support BMI restrictions or generic weight loss requirements prior to surgery from a systemic approach, we do support patients who choose to lose weight to access surgery. We also support our patients who choose to advocate for surgery at their current size!
If weight loss to access surgery rather than finding a supportive surgeon or fighting an unsupportive surgeon is the best fit for our patients, we will discuss prescription options, including pioglitazone and Ozempic. Stay tuned for our next article: Pioglitazone, Ozempic, and Weight Cycling.
Identifying Ally Surgeons
Gathering this information is time-consuming, and individual surgeons may update their policies at any time, so we can’t guarantee that it is inclusive or up to date. None of this information is meant to be used as a recommendation of the surgeons themselves. This is an actively evolving conversation within the surgical community, as well.
We include BMI limit information in our surgery referral database.
If you are a surgeon who would like to be included in our surgery referral database, please contact us at email@example.com.
Community-sourced list of top surgery surgeons.
The University of Michigan and the University of Miami reportedly do not have BMI limits. (5)
Rachel Bluebond-Langner is active in the discussion around BMI limits and surgery risks, and is supportive of extensive informed consent.
The Crane Center for Transgender Surgery did their own literature search and concluded that “In a comprehensive review of the literature, we found limited evidence that suggests high BMI is associated with higher risk of complications.” (16)
Tools for interacting with a reluctant surgeon:
Have your referring prescriber intervene or, better yet, ask them to only refer you to ally surgeons.
Consider asking the surgeon to go through the above risk calculators with you using different weights to see an estimate of how much weight impacts your surgery risk. They may learn something!
Download our handout of Essential Readings on BMI and Gender Affirming Surgery to give to your surgeon (registration required.)
Historical Information, Further Readings About the BMI, and Fat Badassery:
What’s Wrong With the BMI
- The original data calculations were meant only to estimate the average weight and height of a population.
- It was NEVER meant to describe an individual’s body makeup or health
- The original data used French and Scottish (presumably) cis men: WHITE CIS MEN ONLY
The ideas behind calculating an average height and weight of a population were then used to create actuarial tables for insurance policy pricing.
- These tables were calculated using self-reported data from:
- Self-reported weight and height: MIGHT NOT EVEN BE ACCURATE
- Who were applying for life insurance coverage: RICH ENOUGH TO AFFORD INSURANCE. Did we mention WHITE?
- Designed for corporate profit: let’s charge fat people more!
- Each insurance company had their own sets of data.
- No adjusting for things that could affect weight like age, occupation, disability, etc.
These tables then got picked up by medical researchers looking for an easy way to describe bodies (as if!)
- The first studies used (presumably) cis men from the United States, Finland, Italy, Japan and South Africa. And then promptly discarded the data from the South African Bantu cis men.
- And they admitted that their tool for identifying obesity wasn’t very good.
- Obesity itself doesn’t indicate health.
We’ll recap. The BMI
- Is not meant to be used for individuals.
- Has very small diversity in the population data used. IT’S RACIST.
- Assumes that the average of the measurements of the population used are the ideal measurements.
- Doesn’t accurately identify body composition.
- Doesn’t actually identify or measure overall health.
Dr. Larmie also runs the #NoWeigh Campaign
Stay Checked-In With QueerDoc:
- Tyler G. Martinson, Shruti Ramachandran, Rebecca Lindner, Tamar Reisman, Joshua D. Safer, High Body Mass Index is A Significant Barrier to Gender-Confirmation Surgery for Transgender and Gender-Nonbinary Individuals, Endocrine Practice, Volume 26, Issue 1, 2020,Pages 6-15, ISSN 1530-891X, https://doi.org/10.4158/EP-2019-0345.
- Shaydakov ME, Tuma F. Operative Risk. [Updated 2023 May 2]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532240/
- Castle E, Blasdel G, Shakir NA, Zhao LC, Bluebond-Langner R. Weight stigma mitigating approaches to gender-affirming genital surgery. Plastic and Aesthetic Research. 2022; 9: 20. http://dx.doi.org/10.20517/2347-9264.2021.130
- Lucas Goldmann Bigarella, Ana Carolina Ballardin, Luísa Serafini Couto, Ana Carolina Porciuncula de Ávila, Vinícius Remus Ballotin 1, Anderson Ricardo Ingracio, Matheus Piccoli Martini. The Impact of Obesity on Plastic Surgery Outcomes: A Systematic Review and Meta-analysis Aesthet Surg J. 2022 Jun 20;42(7):795-807. doi: 10.1093/asj/sjab397.
- Ives, Graham C. MD; Fein, Lydia A. MD, MPH†; Finch, Lindsey JD‡; Sluiter, Emily C. BS; Lane, Megan MD; Kuzon, William M. MD, PhD; Salgado, Christopher J. MD§. Evaluation of BMI as a Risk Factor for Complications following Gender-affirming Penile Inversion Vaginoplasty. Plastic and Reconstructive Surgery – Global Open 7(3):p e2097, March 2019. | DOI: 10.1097/GOX.0000000000002097
- Eric M Pittelkow, MD and others, Female-to-Male Gender-Confirming Drainless Mastectomy May Be Safe in Obese Males, Aesthetic Surgery Journal, Volume 40, Issue 3, March 2020, Pages NP85–NP93, https://doi.org/10.1093/asj/sjz335
- Gallagher, Sidhbh, Rahmani, Farrah, Russell, Arielle, Duquette, Stephen. A Drain-free Technique for Female-to-Male Gender Affirmation Chest Surgery Decreases Morbidity: Outcomes From 306 Consecutive Masculoplasties. Ann Plast Surg. 2019;83(1):15-21. doi:10.1097/SAP.0000000000001810.
- Zietowski, Maeson L. BS1; Bond, Stephanie M. MD2; Hanson, Summer E. MD, PhD2. 104. Evaluating the Impact of BMI on Postoperative Outcomes after Gender Affirming Surgery. Plastic and Reconstructive Surgery – Global Open 11(5S):p 65, May 2023. | DOI: 10.1097/01.GOX.0000938004.69148.dd
- Elijah Castle, Laura Kimberly, PhD, MSW, MBE, Gaines Blasdel, Augustus Parker, Rachel Bluebond-Langner, MD, and Lee C. Zhao, MD, MS Should BMI Help Determine Gender-Affirming Surgery Candidacy? AMA J Ethics. 2023;25(7):E496-506. doi: 10.1001/amajethics.2023.496.
- Thomas W. Gaither, Mohannad A. Awad, E. Charles Osterberg, Gregory P. Murphy, Angelita Romero, Marci L. Bowers, Benjamin N. Breyer, Postoperative Complications following Primary Penile Inversion Vaginoplasty among 330 Male-to-Female Transgender Patients, The Journal of Urology, Volume 199, Issue 3, 2018, Pages 760-765, ISSN 0022-5347, https://doi.org/10.1016/j.juro.2017.10.013.
- Buncamper ME, van der Sluis WB, van der Pas RSD, et al. Surgical outcome after penile inversion vaginoplasty: a retrospective study of 475 transgender women. Plast Reconstr Surg. 2016;138(5):999-1007.
- Whitney Riley Linsenmeyher, Sarah Garwood, Patient-Centered Approaches to Using BMI to Evaluate Gender-Affirming Surgery Eligibility, AMA J Ethics. 2023;25(6):E398-406. doi: 10.1001/amajethics.2023.398.
- Bacon, L., Aphramor, L. Weight Science: Evaluating the Evidence for a Paradigm Shift. Nutr J 10, 9 (2011). https://doi.org/10.1186/1475-2891-10-9
O’Hara, L., & Taylor, J. (2018). What’s Wrong With the ‘War on Obesity?’ A Narrative Review of the Weight-Centered Health Paradigm and Development of the 3C Framework to Build Critical Competency for a Paradigm Shift. SAGE Open, 8(2). https://doi.org/10.1177/2158244018772888
- Doyle DJ, Hendrix JM, Garmon EH. American Society of Anesthesiologists Classification. [Updated 2022 Dec 4]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441940/
- Erin Carter, Michael Safir, Ashley DeLeon, Curtis Crane, and Richard Santucci, IS A BMI CUTOFF FOR GENDER AFFIRMATION SURGERY SCIENTIFICALLY SUPPORTED?, The Journal of Urology CME, 1 May 2022, https://doi.org/10.1097/JU.0000000000002577.12 https://cranects.com/wp-content/uploads/sites/307/2022/06/BMI-Cutoff-Study.pdf
Protecting and Advancing Health Care for Transgender Adult Communities