What Is Body Mass Index & Why It’s Important For Plastic Surgery

Reviewed by Prof. Fuat Yuksel.

Body mass index or BMI is a measure that was developed almost 2 centuries ago by mathematician, astronomer, and statistician – Adolphe Quetelet to define the average man. Since then, it has found other applications, including screening candidates for plastic surgery, who usually ask what is body mass index and how it affects them? Let’s find out.

What is Body Mass Index?

Body mass index is a value that determines whether or not your weight is healthy (neither low nor high). It takes your weight and height into consideration relative to your age.

Keep in mind it’s not a direct measure of body fat in an individual, but it does provide a rough estimate of it. That’s why it’s an indicator of diseases that can arise as a result of being overweight or obese. These include heart disease, osteoarthritis, diabetes, cancer, sleep apnea, and gallstones, among others.

When finding the answer to what is body mass index, it’s important to keep in mind that BMI has certain limitations. The most significant is its inability to differentiate between muscle mass, bone and fat.

This means that a healthy person can have a high BMI because of their muscle mass, which is common among athletes. Moreover, sarcopenia, a kind of muscle mass loss that results from ageing, can make a person seem healthy, even if they have abnormal amounts of fat in the body. That’s why it’s better to find a BMI calculator by age. 

Other than that, the amount of fat in the body can vary depending on the gender and ethnicity of individuals. So, more accurate BMI calculators take gender, ethnicity, age, and activity levels into consideration before calculating the final value, even if they’re not always necessary.

Despite all this, you shouldn’t rely on this alone to determine whether or not you’re healthy. For that, you need to get examined by your doctor.

Measuring Waist Circumference in Addition to BMI

As body mass index does not measure fat directly or accurately, waist circumference is used in addition. It determines the amount of visceral fat in the body (the dangerous type of fat surrounding the organs, linked to type 2 diabetes and cardiovascular diseases).

To measure it, you have to put the tape measure in the area between the lowest rib and the top of the hip bone. Of course, it is different for men and women. According to WebMD, the normal waist circumference for men is 40 inches and less than 35 inches for women.

It’s possible that when evaluating your suitability for the cosmetic procedure, the doctor also measures your waist circumference. So, you should know about this in addition to what is body mass index.

BMI Calculator & Interpreting Results

To calculate the BMI, you have to divide your weight (in kg) by the square of your height (in meters). So, say your weight is 60 kg, and your height is 1.6 meters, your BMI will be 23.4 kg/m2. 

You can use the body mass index calculator by NHS ((BMI calculator female and male is the same) to calculate your own value. However, you need to know how to interpret the results. For men and women above the age of 20, it’s as follows:

  • Less than 18.5 – you’re underweight, which means that you need to gain weight to have a normal BMI.
  • Between 18.5 and 24.9 – you’re at a healthy weight.
  • Between 25 and 29.9 – you’re overweight and need to lose some weight to achieve a healthy BMI.
  • Over 30 – you’re obese and need to lose significant weight in order to fall in the healthy range.

You can also use the body mass index chart by the National Heart, Lung, and Blood Institute (NHLBI). It has height (in inches) in a column on the left side of the chart and weight (in pounds) across it. You have to cross the two values to find out whether you fall in the normal, overweight, obese, or extreme obesity category.

Knowing what is body mass index and its different values will help you understand how it affects plastic surgery. 

How Does BMI Affect Plastic Surgery? 

The purpose of asking patients for their BMI value is to ensure their safety during plastic surgery. That’s because research shows that the risk of complications increases with the increase in the BMI value of the patient undergoing plastic surgery.

According to a review published in the Aesthetic Surgery Journal in 2021, obese patients experience more complications when getting cosmetic procedures compared to normal-weight patients. They were also more likely to get reoperated. 

One study published in the World Journal of Plastic Surgery even estimated that the complication rate in obese abdominoplasty (tummy tuck) patients might be as high as 80%. It’s important to know what is body mass index as the following complications can arise in plastic surgery patients with a BMI above 30. 

Problems with Anaesthesia 

According to the American Society of Anesthesiologists (ASA), sleep apnea is one of the most serious complications that can arise during the surgery of obese patients. It’s a condition where a person stops breathing while they’re unconscious, as happens when general anaesthesia is given in more invasive, major plastic surgery.

They are also at a greater risk of experiencing respiratory and cardiovascular problems while they’re being operated on. Moreover, the ASA states that the placement of a breathing tube and finding veins for delivering the medication is another problem. In addition, they take longer to regain consciousness, which can add time to the recovery. 

Infections & Slow Recovery

Many studies have shown that patients having a body mass index higher than 30 are at an increased risk of developing an infection after the surgery. Plus, the wound infection can lead to other problems like dehiscence (reopening of the wound) and bad scarring. This will also prolong the stay in the hospital, increasing costs.

There are different reasons why this happens. Obese individuals are more likely to have an impaired immune system, making them more vulnerable to infections. In addition to that, they suffer from other health problems like high blood pressure, cardiovascular and respiratory diseases, diabetes, and cancer; the effects of these diseases can prolong recovery after surgery.

Other Complications 

Other than the complications mentioned above, if your body mass index is above 30, you may also experience tissue necrosis. The risk of deep vein thrombosis or DVT (formation of a blood clot in a deep vein) is also high.

According to a study published in the Current Opinion in Hematology, the cause may be chronic inflammation and dysfunction of the process that prevents blood clots from forming (fibrinolysis). Since the surgical time also increases with these patients, that can act as another risk factor for DVT. 

Seroma and hematoma formation is another problem. Some patients also require follow-up treatments in clinics or hospitals. All these complications can impact the outcome of the aesthetic surgery, which can lower the overall satisfaction with the results. 

What’s the Ideal Body Mass Index for Plastic Surgery?

After understanding what is body mass index and its impact on patients, many people want to know the BMI value that they need to undergo plastic surgery. It needs to be less than 30. 

However, if you’ve had gastric sleeve surgery or lost significant weight by any other means and are left with excess hanging skin, the weight of it will increase the overall BMI value, even if you don’t have as much fat in the body.

Such instances can cause functional problems for the patient. It’s best to get evaluated by a surgeon to find out if you’re suitable for plastic surgery.

How To Lower BMI Before Surgery?

Fortunately, body mass index doesn’t always stay the same for an individual. You can change it. And while you’re doing it, keep in mind that you need to be close to your ideal body weight before the surgery so that it doesn’t fluctuate right after and affect the postsurgical outcome. You can do the following things in order to lose weight:


One of the best ways to lose weight is to exercise. Here, to have the surgery more quickly, do not try to exercise too much to achieve your weight goal more quickly as it can harm your body.

According to Medline, if you exercise too much and do not rest enough, you can end up underperforming while feeling tired, depressed, irritated, anxious, and demotivated. Additionally, you may suffer from sleep problems, sore muscles, and overuse injuries.

Healthy Diet

Proteins, fruits, vegetables, and drinking ample water can help you in your weight loss journey. You must avoid foods that contain a lot of bad cholesterol and sugar.

You can keep tabs on the number of calories that you’re consuming every day. Lastly, do not try any fad diets as they’re usually quite dangerous. You need to lose weight more sustainably.

Sleep Well

People who sleep less are more likely to be hungrier, craving foods high in calories, probably due to hormonal changes. In addition, if you’re not getting enough sleep, you’re less likely to be physically active due to tiredness. Therefore, make sure that you’re getting 8 hours of sleep. 


Plastic surgery patients often wonder what is body mass index since it can determine the suitability for their procedure.

It’s a measure of weight and height, and you can calculate it online to find out if your BMI is more or less than 30, which is the cutoff for plastic surgery.

The index has certain limitations, so it’s always better to get assessed by a doctor in a clinic or hospital to find out if you’re truly healthy or not.

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