Scientific assessment of obesity: Application standards of body mass index (BMI) and waist circumference in health management

Using the Body Mass Index (BMI) to measure body fat percentage is closer to the true extent of obesity than using weight alone. While taller people tend to weigh more than shorter people, this doesn't necessarily mean they have a higher body fat percentage. BMI is less affected by height when measuring obesity. In practice, there's a clear correlation between BMI and body fat percentage for most people; that is, a higher BMI generally indicates a greater percentage of body fat. Therefore, BMI is a relatively good indicator of the degree of obesity.

However, this method also has its limitations. For example, tall, muscular athletes may have BMI values ​​exceeding the normal range, and this excess BMI is due to muscle mass rather than excessive body fat. As people age, the proportion of fat tissue in their body weight gradually increases; therefore, for the same BMI, older adults will have a higher body fat percentage than younger people. Thus, BMI may underestimate the degree of obesity in older adults.

waistline

Waist circumference refers to the length of the waist circumference. It is currently recognized as the simplest and most practical indicator for measuring the degree of fat accumulation in the abdomen (central obesity). As mentioned above, numerous studies have shown that abdominal fat accumulation is a significant cause of various metabolic diseases. Even with a normal BMI, a waist circumference exceeding the threshold significantly increases the risk of obesity-related chronic diseases. Using both waist circumference and BMI together can better estimate the relationship with the risk of various related diseases.

(II) Classification of Obesity

Based on BMI or waist circumference, the degree of obesity can be divided into several levels. This classification is artificially set based on the relationship between different BMI or waist circumference and the body fat content they represent and the risk of disease. 1. Classification based on BMI. (1) The World Health Organization (WHO) classifies overweight and obesity based on the distribution of BMI values ​​in the normal Western population and their relationship with the incidence and mortality of cardiovascular diseases. BMI < 18.5 is classified as underweight, BMI between 18.5 and 24.9 is classified as normal, BMI between 25.0 and 29.9 is classified as overweight, and BMI ≥ 30.0 is classified as obese.

(2) Given that Asians have a higher body fat percentage than Westerners with the same BMI, the WHO standards are not applicable to Asian residents. The WHO Obesity Expert Advisory Group recommends that countries collect epidemiological and disease risk data on obesity among their residents to determine the BMI classification criteria for their populations. my country has conducted several large-scale surveys on the relationship between BMI and the incidence of related diseases. In 2000, under the organization and leadership of the China Obesity Working Group of the International Life Sciences Institute China Office, data from 13 large-scale epidemiological surveys conducted in my country since the 1990s, totaling approximately 240,000 adults, were analyzed.

Data analysis examined the relationship between BMI and the prevalence of related diseases, proposing threshold values ​​for judging overweight and obesity in Chinese adults. A BMI < 18.5 is considered underweight and may indicate other health problems; a BMI between 18.5 and 23.9 is considered normal weight; between 24.0 and 27.9 is overweight; and a BMI ≥ 28.0 is considered obese. The analysis showed that individuals with a BMI ≥ 24.0 have a 2.5 times higher prevalence of hypertension and a 2.0 times higher prevalence of type 2 diabetes compared to those with a BMI below 24. For most people, their height and weight are likely more of a concern.

2. According to waist circumference classification

Waist circumference reflects the extent of abdominal fat accumulation. Based on the relationship between waist circumference and the risk of related diseases, the China Obesity Working Group proposed minimum waist circumference values: no more than 85 cm (2 feet 6 inches) for men and no more than 80 cm (2 feet 4 inches) for women. Those who reach or exceed these limits have a 2.3 times higher prevalence of hypertension and a 2.0 to 2.5 times higher prevalence of type 2 diabetes compared to those with normal waist circumference. In 2006, the Disease Control Department of the Ministry of Health of my country published these BMI and waist circumference limits in the "Guidelines for the Prevention and Control of Overweight and Obesity in Chinese Adults."

Different countries and organizations have varying definitions of waist circumference cut-off points for central obesity in adults. Currently, in my country, the clinical application generally adopts a waist circumference of no more than 85 cm for women and no more than 90 cm for men. The subject stands with feet 25-30 cm apart, distributing weight evenly across both legs. A measuring tape is used to measure the length around the abdomen horizontally, from the midpoint between the upper edge of the iliac crest and the lower edge of the 12th rib. The tape is held firmly against the skin without compressing soft tissue, and the reading is accurate to 0.1 cm. Measurements are taken at the end of a normal expiration.