What is BMI (Body Mass Index) and What Does it Mean?

What is BMI (Body Mass Index) and What Does it Mean

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Body Mass Index, or BMI, is a number that is calculated based on your height and your weight. It is a measure of obesity. There are dozens of BMI calculators that you can easily find on the internet. When you plug in your height and your weight, you get a number that characterizes your degree of obesity.


Less than 18.5 = underweight

18.5 – 24.9 = normal

25 – 29.9 = overweight

30 – 34.9 = obese

over 35 = extremely obese


BMI is extremely important when evaluating someone for an elective procedure, like cosmetic surgery. This is because the level of obesity is related to the risk for surgical complications. The data shows that people with a BMI above 30 are at increased risk for having a complication during or after surgery.  These complications may include a negative reaction to anesthesia, breathing problems, heart attack, stroke, and blood clots. These can be serious and even fatal.  Additionally, we know that people with BMI over 30 are at increased risk for healing problems. This means that incisions may be slower to heal, there can be infections, and an overall poorer cosmetic result. This is extremely important with procedures requiring long incisions such as tummy tucks and breast reductions.

Based on this date, Board Certified Plastic Surgeons are likely to decline to perform surgery on you if your Body Mass Index is above 30. This makes sense, since we certainly would never want to place you at risk, especially for an elective cosmetic procedure. Of course, if you needed life-saving surgery, the surgeon will perform the procedure no matter what your BMI is, but plastic surgery is different and we try to to keep all the risks at the lowest possible level.

The criticism with Body Mass Index calculations is that it is imprecise and doesn’t always accurately reflect someone’s obesity or surgical risk level. This is definitely true.  A simple calculation using your height and weight does not take everything into consideration. BMI does not consider things like bone mass, muscle mass, or fat distribution. Men tend to have a higher BMI and this doesn’t necessarily mean that they are more obese. A muscular man may have minimal fat but a very high BMI. For example, NBA superstar Shaquille O’Neal stands 7’1” tall and 324 pounds. This makes his BMI 31.5 and in the obese range, but no one would consider this elite athlete to be too obese for surgery.  Also, patients who have lost a lot of weight will usually still carry significant excess skin. A person who has successfully lost 100 pounds and has no fat left on their body, may be carrying 20+ pounds of extra skin. Using a simple BMI calculator, they may have a BMI over 30 only because of the extra skin they are carrying around.  There is no Board Certified Plastic Surgeon that would deny skin removal surgery in this case, even though the BMI is above the accepted limit of 30. Also, the location of the excess fat is very important, and not considered in the BMI calculations. Excess fat in the extremities, like thighs and legs, carries less surgical risk than excess weight in the abdomen. This is because central obesity (fat in the abdomen) is more dangerous than peripheral obesity (fat is the arms and legs).  An apple shape is more dangerous than a pear shape. These are some of the things that must be considered when analyzing someone’s BMI and whether they are a safe surgical candidate.  Therefore, BMI is a guide and needs to be used together with other things like a surgeon’s experience and physical evaluation of the patient.  

In my practice, I absolutely use Body Mass Index to help me decide if I am going to operate on a patient. When someone calls to schedule a consultation, we always ask for a current height and weight, allowing us to calculate their BMI.  I will allow people to be seen in consultation if their BMI is below 32. I will then evaluate them in person and decide if it is safe to perform elective cosmetic surgery the way they are. I may tell the person that they need to lose a few more pounds, in order to get their BMI below 30, before I will agree to operate on them.

So, BMI is definitely something you should be aware of, since Board Certified Plastic Surgeons care about it.  You should google a BMI calculator and plug in your numbers.  This will help you be most prepared for your consultation and give you an idea whether or not you will be required to lose weight prior to your surgery. Your goal should be to have your BMI below 30 and as close to normal as you can.

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