The BMI measurement was created in 1800s by a Belgian mathematician, Adolphe Quetelet, and by the late 1900s, it has been adopted globally as an easy way for people to work out if they are over or underweight. The method of calculating one’s BMI is awfully simple. All you need is your weight and height to come up with a number corresponding to one of the four groups: underweight, healthy, overweight or obese. Healthcare officials have used BMI (body mass index) for decades, however, BMI has received criticism over the years. It has been criticized by oversimplifying the meaning of being healthy. Many scientific organizations claim that BMI as a measurement is outdated, inaccurate, and shouldn’t be used in medical and fitness settings.
This article tells you if BMI is an accurate predictor of health, when to use BMI, and a list of alternatives.
What is BMI?
BMI or body mass index was developed by Adolphe Quetelet as a quick way to estimate the degree of obesity in a given population.
The BMI scale is based on a mathematical formula that determines whether a person is of a “healthy” weight by dividing their weight in kilograms by their height in meters squared (1Trusted Source):
- BMI = weight (kg) / height (m2)
Lazy to do the math? Try searching up BMI calculators online like Delivery Rank.
Once BMI you get the BMI value, compare it to this chart.
| BMI range | Classification | Risk of poor health |
|---|---|---|
| Less than 18.5 | Underweight | High |
| 18.5–24.9 | Normal weight | Low |
| 25.0–29.9 | Overweight | Low to moderate |
| 30.0–34.9 | Obese class I (moderately obese) | High |
| 35.0–39.9 | Obese class II (severely obese) | Very high |
| Greater than 40 | Obese class III (extremely obese) | Extremely high |
Ideally, you would want to score a BMI between 18.5 to 24.9 as it means a lesser risk of poor health and diseases. According to the calculation, healthcare providers may suggest dietary and lifestyle changes if one doesn’t fall under the “normal weight” categories.
Why Use BMI?
BMI is simple to calculate, inexpensive and noninvasive surrogate measure of body fat. With proper equipment, individuals can keep track of their BMI with reasonable accuracy. Besides that, BMI allows public health professionals to make comparisons of individuals in a population across time, regions, and other subgroups.
Is it the most accurate measurement of health? No! Even Quetelet himself stated that BMI was an easy way to provide an overview of the health of the general population and is not accurate at determining an individual’s health. Despite these concerns of accuracy, healthcare professionals still use it as it is generally a good determinant of an individual’s health.
There is multiple studies supporting the theory that people in the “underweight” and “obese” category have increased risk of developing chronic diseases. Hence, healthcare professionals continue to utilize BMI as an easy determination of a person’s risk. However, it is acknowledged that BMI is generally not the most accurate way of determining one’s health and it should not be the only diagnostic tool used. Good nutrition and sufficient exercise is necessary to be healthy. Read our article on the benefits of good nutrition. Want to exercise more? Try walking. Read our article on the benefits of walking.
Supporting research from Healthline:
- A study showed that those in the “obese” category had a 20% risk of death from all causes of heart disease compared to those in the “normal” category.
- A study showed that those in the “underweight”, “severely obese” and “extremely obese” categories had premature deaths compared to those in the “normal” category.
- A 2017 retrospective study of 103,218 deaths found that those who had a BMI of 30.0 or greater (“obese”) had 1.5–2.7 times greater risk of death after a 30-year follow-up
- Other studies have shown that a BMI greater than 30.0 begins to significantly increase your risk of chronic health issues, such as type 2 diabetes, heart disease, breathing difficulties, kidney disease, non-alcoholic fatty liver disease, and mobility issues
- 5–10% reduction in a person’s BMI has been associated with decreased rates of metabolic syndrome, heart disease, and type 2 diabetes
Downsides of BMI
Factors such as age, sex, ethnicity, and muscle mass can influence the relationship between BMI and body fat. The primary clinical limitation of BMI is that it is unable to distinguish between excess fat, muscle, or bone mass. It also cannot distinguish where the fat is accumulated in an individual.
All weight is equal
BMI is a measure of excess weight, not fat. It is important to factor in one’s bone mass, muscle and fat to determine if they’re healthy. On average, older adults tend to have more body fat than younger adults for an equivalent BMI. Furthermore, women generally have greater amounts of total body fat than men with an equivalent BMI. Although 1kg of fat is the same as 1kg of muscle, muscle is denser and takes up less space. As a result, athletes may have a high BMI as a result of increased muscle mass but still be very lean and healthy.
Differing BMI among different populations
Research shows that BMI may not be standardized across all racial and ethnic populations. Numerous studies shown that people of Asian descent have an increased risk of developing chronic diseases at lower BMI points. The World Health Organization (WHO) has developed Asian-Pacific BMI guidelines which provide alternative BMI points for Asians.
| BMI range | Classification |
|---|---|
| Less than 18.5 kg/m2 | Underweight |
| 18.5–22.9 kg/m2 | Normal weight |
| 23.0–24.9 kg/m2 | Overweight |
| Greater than 25.0 kg/m2 | Obese |
In contrast, black people have lower fat mass and higher muscle mass, and may be misclassified as overweight. Research suggests that chronic disease risks occur at a higher BMI point compared to other races. A study in 2011 found that Black women were considered metabolically healthy at cut off points at 3.0kg/m2 higher than those who are not Black, hence further questioning the applicability of standardized BMI among different races.
Weight bias
Medical professionals are expected to use BMI as a general guideline and use their judgement coupled with the BMI score to assess a patient. However, healthcare professionals who strictly follow BMI score when making an assessment can lead to weight bias and the patient not receiving the right treatment. There has been multiple complaints from patients with high BMI’s that doctors only focus on their BMI and as a result serious medical issues are left untreated. As a result, studies show that the higher the BMI, the less likely a patient will attend health check ups due to distrust in the system, leading to later diagnoses, treatment, and care.
Doesn’t consider fat distribution
Although a high BMI is linked to a higher risk of health issues, the location of fat may make a bigger difference. Those with fat stored around their stomach (apple shaped body type), have a greater risk of chronic disease than those with fat stored in their hips, buttocks and thighs (pear shaped body). Researchers reviewed 72 studies and found that those with apple shaped body type have significantly higher risks of developing chronic diseases compared to pear shaped body types.
What other measures of body fat are there?
Other methods to measure body fat include measuring skinfold thicknesses, bioelectrical impedance, underwater weighing, measuring waist circumference (sometimes divided by height) and dual energy x-ray absorption. These methods may be more accurate than measuring one’s BMI, however they can be expensive, intrusive, not widely available or difficult to standardize and as a result, some of these measures are considered to be inappropriate for routine clinical practice.
Conclusion
Body Mass Index (BMI) has several criticisms on its ability to accurately estimate a person’s body fat. It is unable to factor in aspects such as health, age, sex, fat mass, muscle mass, race, genetics and medical history. Furthermore, medical practitioners solely relying on BMI to make judgement on their patients is shone to increase weight bias. Despite its criticisms, it is an easy, noninvasive method that can generally alert medical professionals about chronic health issues in patients. Generally, people with BMI above or below the “normal” range has shown to show a greater risk of chronic diseases. Although there are more accurate body fat measures out there, they are generally more expensive, invasive and not widely available. BMI does not measure body fat directly, hence should not be the only diagnostic tool. Instead, BMI should be used as a means to track the weight status in populations and serve as a screening tool for medical practitioners to identify potential weight problems in individuals.
References:
“Body Mass Index – CDC.” https://www.cdc.gov/obesity/downloads/bmiforpactitioners.pdf. Accessed 3 May. 2021.
“Body Mass Index – CDC.” https://www.cdc.gov/obesity/downloads/bmiforpactitioners.pdf. Accessed 3 May. 2021.
“Why you should stop measuring your BMI to find out if you’re healthy ….” 18 Aug. 2017, https://www.independent.co.uk/life-style/health-and-families/bmi-stop-measuring-weight-height-health-measure-fitness-fat-a7894951.html. Accessed 3 May. 2021.
“BMI Flaws, History, and Other Ways to Measure … – Everyday Health.” 17 Mar. 2021, https://www.everydayhealth.com/diet-nutrition/bmi/bmi-flaws-history-other-ways-measure-body-weight/. Accessed 3 May. 2021.
“Is BMI an Accurate Way to Measure Body Fat? – Scientific American.” 22 Jun. 2019, https://www.scientificamerican.com/article/is-bmi-an-accurate-way-to-measure-body-fat/. Accessed 3 May. 2021.
“3 Reasons Why BMI Is Not an Accurate Measure of Health – Insider.” 21 Jan. 2021, https://www.insider.com/is-bmi-accurate. Accessed 3 May. 2021.
“Why BMI is inaccurate and misleading – Medical News Today.” 25 Aug. 2013, https://www.medicalnewstoday.com/articles/265215. Accessed 3 May. 2021.
“Is BMI an Accurate Predictor of Health? – Healthline.” 29 Oct. 2020, https://www.healthline.com/nutrition/is-bmi-accurate. Accessed 3 May. 2021.
“Why BMI is inaccurate and misleading – Medical News Today.” 25 Aug. 2013, https://www.medicalnewstoday.com/articles/265215. Accessed 3 May. 2021.