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The Body Mass Index Fallacy

BMI does not account for certain metabolic disorders.

Key points

  • The body mass index (BMI) can be misleading when diagnosing metabolic health.
  • Subcutaneous fat is more visible but significantly less dangerous than visceral fat.
  • Genetic factors, age, and gender can affect the subcutaneous vs. visceral fat ratio.
Vitalii Vodolazskyi/Shutterstock
Source: Vitalii Vodolazskyi/Shutterstock

By Mac E. Lancaster, BS, and Ran D. Anbar, MD

The measurement we primarily use to determine if someone is obese, overweight, or metabolically healthy is called the body mass index (BMI). It can be calculated based on weight and height (Centers for Disease Control and Prevention).

Doctors and schools use the BMI to assess if someone is healthy because it’s quick, easy to measure, and easy to categorize. The BMI ranges from underweight (< 18.5) to healthy weight (18.5-24.9), overweight (25.0-29.9), and obese (more than 30.0). Because there is an abundance of BMI data available, this measure is frequently used in articles about metabolic health.

It is critical to note that obesity, especially involving visceral fat in the abdominal area, increases the risk of cancer, cardiovascular disease, and metabolic disorders like insulin resistance and type 2 diabetes (T2D) (Engin, 2017). The problem is that BMI fails to address adequately certain types of metabolic situations including,

  • People who may have a low BMI but have disproportionately high levels of visceral fat are also known as thin outside, fat inside (TOFI) (Wu et al., 2020).
  • Roughly 30% of patients with a very high BMI (>30) have a healthy metabolism, with functional insulin sensitivity and relatively low visceral fat levels (Engin, 2017).

Although BMI can help doctors make quick assessments, it is a flawed system of measurement because it overgeneralizes and is misleading for atypical cases or specific aspects of obesity that are related to metabolic disorders. (Denis & Hamilton, 2013).

For example, an individual with a BMI of 35 would be diagnosed on paper as obese. However, if you add that they are a bodybuilder with thick bones and only 8% body fat, it becomes apparent that this person is metabolically healthy.

Thus, BMI does not account for visceral fat and genetics, which are key factors contributing to metabolic disorders. Let's examine these two markers of health further to empower you with a better understanding of metabolism.

Visceral vs. Subcutaneous Fat

There are two types of body fat: visceral and subcutaneous. They have different locations, purposes, and health implications. BMI does not distinguish these types of fat.

  • Subcutaneous fat is the main type of fat that you can visually see. It is found directly beneath the skin and is “jiggly” when you pinch it.
  • Visceral fat is deposited deep within the abdominal cavity and pads internal organs.

While neither type of fat is healthy in excess, visceral fat poses a significantly greater health risk (Xu et al., 2022).

Visceral fat grows when cells enlarge or become hypertrophic (Horwitz & Birk, 2023). Hypertrophic fat cells are less responsive to insulin, have a reduced capacity to store fat, and are associated with releasing inflammatory molecules (Horwitz & Birk, 2023). As a result, excess visceral fat is stored in areas not normally involved in fat storage, including skeletal muscles, the liver, and the pancreas (Horwitz & Birk, 2023).

Visceral fat is linked to a higher risk of heart disease, high blood pressure, T2D, and several types of cancer, independent of BMI (Małodobra-Mazur et al., 2020; Horwitz & Birk, 2023).

Conversely, subcutaneous fat cells are more likely to stay small and grow by multiplying via hyperplasia, making them less metabolically damaging than visceral fat (Małodobra-Mazur et al., 2020). Subcutaneous fat is necessary for padding muscles and bones, controlling consistent body temperatures, and storing excess energy as a usable source during hunger, fasting, or diseases.

As an endocrine organ, subcutaneous fat secretes hormones that reduce your risk of cancer, stabilize your weight and blood pressure, bolster your immune system, increase your insulin sensitivity, and reduce inflammation (Coelho et al., 2013). Appetite regulation is also heavily influenced by some hormones produced by subcutaneous fat (Miller, 2017).

Sumo wrestlers represent edge cases with extremely high BMIs and healthy metabolisms, with normal blood glucose and relatively low visceral fat levels (Denis & Hamilton, 2013). They can prolong a healthy metabolic state because most of their fat is subcutaneous, and they maintain intense physical training (Denis & Hamilton, 2013). However, when these athletes stop their regular exercise regimen, they are at immediate risk of developing metabolic disorders.

Genetics and Weight-Related Illnesses

Another factor BMI cannot account for is genetic variation. Compared to Westerners of the same BMI, South and East Asian people (Mittal, 2019) have a smaller body but are characterized as thin on the outside, fat on the inside (TOFI), with a higher average waist/hip circumference ratio (Leow, 2017).

Chinese people are more prone to visceral fat production and developing T2D (Wu et al., 2020). A recent study found that Asian people of Indian subcontinent descent living in Europe are two to four times more likely to develop T2D and are 40% more at risk of heart disease (Roberts et al., 2023). Another study found that even South Asian newborns had higher blood glucose levels and insulin, pointing toward TOFI characteristics (Karamali et al., 2015).

Another genetic factor is linked to differences in fat composition in males versus females. During and post-puberty, total body fat increases for females and males (Mittal, 2019). Females tend to accumulate more subcutaneous fat around the hips and thighs, while males store more visceral fat in the abdominal region (Mittal, 2019). Notably, pre-menopausal females show higher subcutaneous fat levels, while post-menopausal females show a higher ratio of visceral fat (Mittal, 2019).


BMI is an easy way to measure a patient’s health on the surface level. However, it excludes variables that make its reliability as a sole determining factor of health misleading. Because everyone's metabolism is different, learning about the factors and measurements associated with metabolism—and there are many more than the few mentioned above—is an important first step toward empowering you to take control of your health.

Mac Lancaster obtained his undergraduate degree in Cognitive and Behavioral Neuroscience at UC San Diego.


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