Body mass index measures body fat based on height and weight that applies to both adult men and women.
A person’s BMI can be determined by dividing their weight in kilograms by the square of their height in meters (kg/m2). The WHO considers a person with a BMI less than 18.5 or above 25 to be underweight or overweight, respectively; someone with 18.5-24.9 to be healthy; and 25- 29.9 to be obese.
What is Body Mass Index
Body Mass Index (BMI) is defined as the weight divided by the squared height in meters (kg/m2).
The Centers for Disease Control and Prevention states that BMI is used as an indicator of obesity because it is a simple and inexpensive screening method for body fat.
BMI is not a diagnostic tool since many other factors could contribute to weight gain or loss in an individual.
Body mass index is correlated with total body fat content in men and women, but the relationship is stronger in women. Some studies have found that this correlation between BMI and body fat percentage varies among ethnic groups. The average BMI for White American women aged 18-29 was 22.9±2.3; for Black American women, it was 28.7±4.1, and for Mexican American women, it was 26 +/- 3. Among men, the average BMI for non-Hispanic white males aged 18-29 years old was 24 +/- 4; for non-Hispanic black males, it was 25 +/- 4, and for Mexican American males,s it was 28 +/- 9.
For both men and women, BMI is correlated with percent body fat at different ages. Among children aged 5-11 years old, the correlation coefficient between BMI and percent body fat ranged from r=0.42 to 0.64 for boys and r=0.44 to 0.67 for girls depending on age group; among adolescents aged 12-19 years old, these correlations ranged from r=0.45 to 0.69 in boys and from r=0.48 to 0.78 in girls; among adults aged 20+ years old, these correlations ranged from r=0.38 to 0 .61 in men and from r=0.49 to 0.79 in women.
Evidence suggests that the relationship between BMI, fat mass, and fat-free mass does not differ between men and women until menopause, indicating that menopause affects female body composition independently of BMI or other factors such as age or physical activity level. Among postmenopausal women aged 50+, studies have found that higher BMI was associated with larger waist circumferences, lower hip circumference, more central adiposity (as measured by waist-to-hip ratio), lower muscle mass (as measured by bioelectrical impedance) than among similarly aged premenopausal women who had never used hormone replacement therapy; additionally, mail carriers women using hormone replacement therapy appeared to have greater muscle mass than those who were not using hormone replacement therapy.
BMI is correlated with waist circumference in adults; however, the relationship between BMI and waist circumference is stronger in men than women. This may be due to differences in body composition between genders or sex-specific effects of adipose tissue distribution on glucose metabolism. Among children aged 3–10 years old, the correlation coefficient for BMI and waist circumference was 0.57 in boys and 0.40 in girls; among adolescents aged 12–17 years old, these correlations ranged from r=0.60 to 0.71 depending on age group and gender; for adults overall (aged 20+), the correlation ranged from r=0.58 to r=062 .
How the Medical Community uses Body mass indext
The U.S. Preventive Services Task Force (USPSTF) recommends screening for obesity in all adults at risk for cardiovascular disease (e.g., overweight or obese), rather than simply using BMI, since this may better identify persons who are at risk of developing cardiovascular disease because they have excess body fat (e.g., due to metabolic syndrome) that is not completely accounted for by their weight; there is insufficient evidence to recommend routine screening with waist circumference in primary care settings .
It recommends measuring patients’ waist circumference once at baseline, noting that measurement should occur during normal breathing while the patient is standing and the measurement should be taken at the level of the iliac crest; furthermore, one study showed greater accuracy in waist circumference measurement when the specially trained technician did it than by the patient him/herself .
The USPSTF also recommends measuring blood pressure, fasting plasma glucose. Lipid levels, assessing diet, calculating BMI for patients aged ≥20 years old, calculating waist-to-hip ratio in men aged 40–45 years who are at increased cardiovascular risk (e.g., overweight or obese), assessing physical activity level (moderate-intensity aerobic activity for at least 150 minutes per week of vigorous-intensity aerobic activity for at least 75 minutes per week).
The American Cancer Society (ACS) advises that adults maintain a healthy weight throughout life; this may be particularly important for preventing cancer since obesity has been associated with several types of cancer , and it recommends eating a healthy diet and exercising regularly .
It recommends measuring waist circumference once at baseline for adults (aged ≥18 years), noting that measurement should occur during normal breathing while the patient is standing and the measurement should be taken at the level of the iliac crest; furthermore, one study showed greater accuracy in waist circumference measurement when the specially trained technician did it than by the patient him/herself . The ACS also recommends assessing dietary intake using tools such as 24-hour dietary recall or food frequency questionnaire, calculating BMI, and calculating other obesity-related measures such as waist-to-hip ratio.
According to published results from “The State of Obstructive Lung Disease: A Cross-sectional Survey” conducted in 2009, the diagnosis of obesity is based on BMI despite growing evidence that does not favor it because of its limitations in identifying patients at risk for respiratory problems.
The British Thoracic Society recommends that lung function tests are carried out as follows: spirometry, which assesses degree of airflow obstruction by measuring the volume and flow rate of air exhaled by a person after full exhalation; pulse oximetry, which measures arterial oxygen saturation; chest X-ray, to assess overall lung disease burden. It also recommends recording forced expiratory volume in 1 second (FEV1) % predicted and dividing this figure by height in meters squared to provide FEV1/Ht2 ratio. However, it notes that these equations require further research to determine their clinical usefulness.
According to a study published in 2011, no agreement exists between self-reported and measured BMI values among U.S. adults ages 65 years and older from two nationally representative health surveys, which contradicts the validity of self-reported height and weight data for classifying older adults by BMI categories.
The American Gastroenterological Association (AGA) recommends that clinicians measure waist circumference in men with a body mass index of 25–34.9 kg/m² who have additional risk factors for cardiovascular disease, women with a body mass index ≥25 kg/m² or ≥23 kg/m² if they are aged >45 years or postmenopausal, people with a family history of early-onset heart disease, people with elevated blood triglyceride level or low high-density lipoprotein cholesterol level.
People who are American Indian or Alaska Native, African American, Asian American or Pacific Islander American, Hispanic/Latino, or Middle Eastern; it also recommends that clinicians assess abdominal fat distribution in men with a waist circumference ≥102 cm (40 inches) and women with a waist circumference ≥88 cm (35 inches) by measuring the skinfold thickness at the iliac crest using a Harpenden caliper.
The Canadian Task Force on Preventive Health Care published recommendations for preventive health care in 2003 which advises clinicians to assess body weight history, including recent changes for patients aged < 20 years old and those who are overweight should be screened for obesity, it also suggests assessing whether other family members are obese if the patient is younger than 20 years old.
The Endocrine Society published clinical practice guidelines in 2009 which recommends measuring waist circumference for adults aged ≥18 years who have body mass index (BMI) ≥25 kg/m² to aid in assessment of cardiovascular risk, noting that Asians have higher abdominal fat content at lower BMI levels compared with their Caucasian counterparts.
It also recommends evaluating the waist-to-hip ratio via measurement of waist circumference and hip circumference.
In addition, the American Association of Clinical Endocrinologists(AACE) published a position statement on diagnosing and treating metabolic syndrome in 2003, which recommended assessing waist circumference to identify patients at high risk for cardiovascular disease; it also stated that waist circumference was more accurate than BMI in identifying people at risk for developing cardiovascular disease.
The International Diabetes Federation (IDF) published guidelines on management of diabetes in 2006 which recommends assessing central obesity by measuring waist circumference, noting that the prevalence of type 2 diabetes in most populations is positively associated with continuous distributions of serum insulin levels and inversely related to mean fasting levels of HDL cholesterol.
The National Heart, Lung, and Blood Institute(NHLBI), part of the National Institutes of Health (NIH), published Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report in 1998, which suggests measuring waist circumference if BMI >23 kg/m²; it notes that clinical judgment is important since the cut-off point for abdominal obesity should be lower in people with Asian ancestry.
The National Heart, Lung, and Blood Institute published Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report in 1998, which recommends measuring waist circumference if BMI >23 kg/m²; it notes that clinical judgment is important since the cut-off point for abdominal obesity should be lower in people with Asian ancestry.
Recommendations for determining optimal body weight are given by the Metropolitan Life Insurance Company (MLIC), which were updated as part of its 1983 “Standard Weight Tables.”
According to these standards: a man weighing 112 pounds (51.7 kilograms) and 5 feet 5 inches (1.65 meters) in height have an “ideal weight” of 132 pounds (60.2 kilograms).
The Public Health Service Expert Panel on the Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults published a guideline that suggests that clinicians measure waist circumference and BMI to determine risk for cardiovascular disease . The panel also discusses that abdominal obesity is assessed by measuring waist circumference since it provides a better indicator of health risks than BMI.
The US Department of Health and Human Services Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults recommend assessing overweight or obese patients using BMI or waist circumference alone or both; it notes that although vertical-band measurements may be useful when estimating fat distribution throughout the body, they are not reliable or valid for estimating visceral fat. The Surgeon General’s Call to Action to Prevent and Decrease Overweight and Obesity 2001 suggests measuring waist circumference in overweight patients (>25% over desirable weight) to evaluate the need for weight loss.
According to a 2005 review published in the International Journal of Obesity, BMI is an acceptable method for assessing overweight. Still, it should be complemented by waist circumference measurement since it provides a better indicator of cardiovascular risk factors such as high blood pressure, high cholesterol levels, and diabetes. In addition, the National Heart Foundation of Australia also recommends that both men and women with a waist circumference >102 cm (40 inches) have a further evaluation for cardiovascular disease risk factors.
The American Society of Bariatric Physicians (ASBP) practice parameters recommend using waist circumference to assess overweight and obese patients for health risks associated with obesity.
The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the US Department of Health and Human Services, published Clinical guidelines on identifying, evaluating, and treating overweight and obesity in adults: the evidence report. It suggests measuring waist circumference if BMI >25 kg/m²; it notes that although vertical-band measurements may be useful when estimating fat distribution throughout the body, they are not reliable or valid for estimating visceral fat.
According to a 2005 review published in the International Journal of Obesity, BMI is an acceptable method for assessing overweight. Still, it should be complemented by waist circumference measurement since it provides a better indicator of cardiovascular risk factors such as high blood pressure, high cholesterol levels, and diabetes.