Is BMI an Accurate Predictor of Health?

What is BMI?

“BMI” stands for “body mass index。”BMI是由比利时数学家兰伯特·阿道夫·雅克·奎特勒特（Lambert Adolphe Jacques Quetelet）于1832年开发的（ 1 ).

He developed the BMI scale to quickly estimate the degree of overweight and obesity in a given population to help governments decide where to allocate health and financial resources ( 1 ).

有趣的是，Quetelet表示，BMI在研究单个人方面没有用，而是对人口总体健康的快照。然而，它被广泛用于衡量个人的健康（ 1 ).

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 ( 1 ):

• BMI = weight (kg) / height (m²)

或者,可以计算体重指数除以weight in pounds by height in inches squared and multiplying by 703:

• bmi =（重量（lbs） /高度（在²)) x 703

You can also use an online BMI calculator, such as the one provided by the National Institutes of Health .

Once BMI is calculated, it’s then compared to the BMI scale to determine whether you fall within the “normal” weight range ( 2 ):

According to this calculation, a healthcare professional may suggest health and lifestyle changes if you don’t fall within the “normal” weight category.

Some countries have adopted this BMI scale to better represent the size and stature of their populations. For example, Asian men and women have been shown to be at a higher risk of heart disease at a lower BMI, compared with non-Asians ( 3 ).

Though this can give the healthcare professional a snapshot of a person’s health based on a person’s weight, it doesn’t consider other factors, such as age, sex, race, genetics, fat mass, muscle mass, and bone density.

概括

Body mass index (BMI) is a calculation that estimates a person’s body fat using their height and weight. A BMI of 18.5–24.9 is considered “normal” weight with a low risk of poor health, while anything above or below may indicate a higher risk of poor health.

Is it a good indicator of health?

Despite concerns that BMI doesn’t accurately identify whether a person is healthy, most studies show that a person’s risk of chronic disease and premature death does increase with a BMI lower than 18.5 (“underweight”) or of 30.0 or greater (“obese”) ( 4 , 5 ).

For example, a 2017 retrospective study of 103,218 deaths found that the people 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 ( 4 ).

Another study of 16,868 people showed that those in the “obese” BMI category had a 20% increased risk of death from all causes and heart disease, compared with those in the “normal” BMI category ( 6 ).

The researchers also found that those who were in the “underweight” category and the “severely obese” or “extremely obese” categories died an average of 6.7 years and 3.7 years earlier, respectively, than those in the “normal” BMI category ( 6 ).

Other studies have shown that a BMI greater than 30.0 begins to significantly increase the risk of chronic health issues such astype 2 diabetes，心脏病，呼吸困难，肾脏疾病，非酒精性脂肪肝病和流动性问题（ 7 , 8 , 9 , 10 , 11 , 12 , 13 ).

此外，一个人的BMI降低了5-10％，与降低的率有关metabolic syndrome, heart disease, and type 2 diabetes ( 14 , 15 , 16 , 17 ).

由于大多数研究表明肥胖者的慢性疾病风险增加，因此许多卫生专业人员可以将BMI用作一个人的风险的一般快照。不过，它不应该是唯一使用的诊断工具（ 18 , 19 ).

概括

尽管BMI因其过度简化健康而受到批评，但大多数研究都支持其估计一个人患慢性病风险的能力，尤其是一个人患有早期死亡和代谢综合征的风险。

Downsides of BMI

Despite research associating a low (below 18.5) and high (30 or greater) BMI with increased health risks, there are numerous flaws with its use.

Doesn’t consider other factors of health

BMI only answers “yes” or “no” regarding whether a person is of “normal” weight, without any context of their age, sex, genetics, lifestyle, medical history, or other factors.

Relying only on BMI may miss other important measurements of health, such as cholesterol, blood sugar, heart rate, blood pressure, and inflammation levels, and overestimate or underestimate a person’s true health.

What’s more, despite men’s and women’s varying body compositions — with men having more muscle mass and less fat mass than women — BMI uses the same calculation for both groups ( 20 ).

Plus, as a person ages, their body fat mass naturally increases and muscle mass naturally declines. Numerous studies have shown that a higher BMI of 23.0–29.9 in older adults can be protective against early death and disease ( 21 , 22 ).

Finally, simply using BMI to determine a person’s health ignores other aspects of health, includingmental well-beingand complicated sociological factors such as income, access to affordable and nutritious food, food skills and knowledge, and living environment.

Assumes all weight is equal

虽然1磅或公斤的肌肉重量与1磅或公斤脂肪相同，但muscle is denserand takes up less space. As a result, a person who is very lean but has high muscle mass may be heavier on the scale.

For example, a 200-pound (97-kg) person who is 5 feet 9 inches (175 cm) tall has a BMI of 29.5, which classifies them as “overweight.”

However, two people of the same height and weight could look completely different. One may be a bodybuilder with high muscle mass, while the other may have higher fat mass.

If only BMI is considered, this could easily misclassify a person as “overweight” or “obese” despite their low fat mass. Therefore, it’s important to consider a person’s muscle, fat, and bone mass in addition to their weight ( 23 , 24 , 25 ).

不考虑脂肪分配

Though a greater BMI is linked to poorer health outcomes, the location of fat on the body may make a bigger difference.

Those with fat stored around their stomach area, known as android or apple-shaped body types, have a greater risk of chronic disease than those with fat stored in their hips, buttocks, and thighs, known as gynoid or pear-shaped身体类型( 26 , 27 , 28 , 29 ).

For example, in a review of 72 studies that included data from more than 2.5 million people, researchers found that those with apple-shaped fat distribution had a significantly higher all-cause mortality risk, while those with pear-shaped fat distribution had a lower risk ( 30 ).

In fact, the authors highlighted that BMI doesn’t consider where fat is stored on the body, which can misclassify a person as being unhealthy or at risk of disease ( 30 ).

May lead to weight bias

It’s expected that a medical professional uses their best judgment, meaning they would take the BMI result and consider their patient as a unique individual.

However, some health professionals use only BMI to measure a person’s health before providing medical recommendations, which can lead toweight biasand poor quality healthcare ( 31 , 32 ).

Those with higher BMIs more often report that their doctors focus only on their BMI, even if their appointment is for an unrelated concern. Often, serious medical issues go unnoticed or are incorrectly seen as weight-related problems ( 31 ).

In fact, studies have shown that the higher a person’s BMI is, the less likely they are to attend regular health checkups due to fear of being judged, distrust of the healthcare professional, or a previous negative experience. This can lead to late diagnoses, treatment, and care ( 33 ).

May not be relevant for all populations

Despite the wide use of BMI among all adults, it may not accurately reflect the health of certain racial and ethnic populations.

例如，许多研究表明，与白人相比，亚洲血统在较低的BMI截止点上患慢性病的风险增加（ 34 , 35 , 36 ).

In fact, the World Health Organization developed Asian-Pacific BMI guidelines, which provide alternative BMI cut-off points ( 2 , 37 , 38 ):

大量的研究表明,这些替代cut-off points better identify health risk among Asian populations. Still, more research is needed to compare these cut-off points with multi-generation Asian Americans ( 39 , 40 , 41 ).

Also, Black people may be misclassified asoverweightdespite having lower fat mass and higher muscle mass. This may suggest that chronic disease risk occurs at a higher BMI cut-off point than in people of other races, especially among Black women ( 35 , 42 , 43 , 44 ).

In fact, one 2011 study found that Black women were considered metabolically healthy at cut-off points 3.0 kg/m²higher than people who are not Black, which further puts into question the usefulness of BMI for all racial and ethnic groups ( 45 ).

Finally, relying only on BMI ignores the cultural importance of body size to different groups. In some cultures, higher fat mass is viewed as healthier and more desirable. Healthcare professionals should consider what “health” means to each individual ( 46 , 47 , 48 ).

Considering that significant health decisions, such as surgical procedures and weight loss interventions, are based on BMI and weight, it’s important that all health professionals go beyond BMI to ensure they’re making patient-centered recommendations.

概括

BMI considers only a person’s weight and height as a measure of health, rather than the individual. Age, sex, race, body composition, medical history, and other factors may affect a person’s weight and health status.

更好的选择

Despite the many flaws of BMI, it’s still used as a primary assessment tool because it’s convenient, cost-effective, and accessible in all healthcare settings.

但是，有一些BMI的替代方案可能是一个人健康的更好指标 - 尽管每个人都有自己的一系列优势和缺点（ 49 , 50 , 51 , 52 ).

Waist circumference

Definition

较大的腰围 - 女性大于35英寸（85厘米）或男性40英寸（101.6厘米）的大于35英寸（85厘米） - 表明腹部地区的体内脂肪更大，这与慢性疾病的风险更高有关。

Benefits

它很容易测量，只需要尺寸的胶带。

Downsides

It doesn’t consider different body types (e.g., apple-shaped vs. pear-shaped) and builds (e.g., muscle and bone mass).

腰围比

Definition

Ahigh ratio(greater than 0.80 in women or greater than 0.95 in men) indicates higher fat stores in the stomach area and is linked to a greater risk of heart and chronic disease.

A low ratio (lower than or equal to 0.80 in women or lower than or equal to 0.95 in men) suggests higher hip fat storage, which is associated with better health.

Benefits

它很容易测量，仅需要测量胶带和计算器。

Downsides

It doesn’t consider different body types (e.g., apple-shaped vs. pear-shaped) and builds (e.g., muscle and bone mass).

Body fat percentage

Definition

Body fat percentageis the relative amount of body fat a person has.

Benefits

It distinguishes between fat mass and fat-free mass and is a more accurate representation of health risk than BMI.

Downsides

Convenient assessment tools (such as skinfold measurements, portable bioelectrical impedance analysis, and at-home scales) come with a high risk of error.

More accurate tools (such as dual-energy X-ray absorptiometry, underwater weighing, and BodPod) are expensive and inaccessible for many.

Lab tests

Definition

Lab testsare various blood and vital sign measurements that can indicate chronic disease risk (e.g., blood pressure, heart rate, cholesterol, blood glucose levels, inflammation).

Benefits

These tests provide a more detailed review of a person’s metabolic health and don’t rely only on body fat as a measurement of health.

Downsides

Most of the time, a single lab value is not sufficient to diagnose or indicate risk.

Regardless of the assessment tool used, it’s important for healthcare professionals to not rely on one test alone. For example, a healthcare professional may measure a person’s BMI and waist circumference, and if concern arises, a blood test may follow.

It’s important to treat each patient as an individual to determine what health means to them — physically, mentally, emotionally, and spiritually.

概括

Other body assessment tools can be used instead of BMI, such as waist circumference, body fat percentage, and blood tests. However, each comes with its own set of advantages and disadvantages.

The bottom line

体重指数（BMI）是一种极具争议性的健康评估工具，旨在估计一个人的体内脂肪和健康状况不佳的风险。

Research typically shows a greater risk of chronic disease as BMI increases above the “normal” range. Furthermore, a low BMI (below 18.5) is also linked to poor health outcomes.

That said, BMI fails to consider other aspects of health, such as age, sex, fat mass,muscle mass, race, genetics, and medical history. What’s more, using it as a sole predictor of health has been shown to increase weight bias and health inequities.

Though BMI can be useful as a starting point, it should not be the only measurement of your health.