International Obesity Standards: Scientific Cognition and Health Guidelines

The global obesity rate is on the rise. Scientific and unified international obesity standards have become a key basis for public health prevention and control and personal health management. At present, the judgment system formulated by the World Health Organization (WHO) is the international core standard. This system takes Body Mass Index (BMI) as the core and conducts comprehensive judgment in combination with age, gender, ethnic differences and auxiliary indicators, providing a unified reference framework for global obesity prevention and control.

I. Core Indicator: BMI and International Universal Standards

The calculation formula of Body Mass Index (BMI) is weight (kg) divided by the square of height (m), i.e., kg/m². Due to its simple calculation, it can effectively reflect the correlation between weight and height in the population, and is applicable to adult men and women of all ages. It was officially adopted as the core indicator for obesity judgment by WHO in 1995.

According to the adult standards released by WHO in 1998, BMI values are divided into five grades, clarifying the differences in health risks:

• BMI < 18.5: Underweight, low risk of obesity-related diseases but increased probability of other health problems;
• 18.5 ≤ BMI < 24.9: Normal Weight, moderate health risk;
• 25.0 ≤ BMI < 29.9: Overweight, increased risk of chronic diseases;
• 30.0 ≤ BMI < 34.9: Obesity Grade Ⅰ, moderate disease risk;
• 35.0 ≤ BMI < 39.9: Obesity Grade Ⅱ, high disease risk;
• BMI ≥ 40: Obesity Grade Ⅲ, extremely high disease risk.

This standard has provided a unified benchmark for global obesity epidemiological research and public health policy formulation, ensuring the comparability of data in different regions.

Ⅱ. Special Groups: Judgment Standards for Children and Adolescents

Children and adolescents are in the growth and development stage, and their body composition changes significantly with age, so adult standards cannot be applied. WHO has formulated a differentiated system by age groups:

1. Children Aged 0-5

Based on the WHO “Child Growth Standards” in 2006, Weight-for-Height is taken as the core indicator and judged by gender: Overweight ≥ 2 standard deviations, Obesity ≥ 3 standard deviations, which can avoid judgment deviations caused by rapid growth and development.

2. Adolescents Aged 5-19

The BMI-for-Age indicator is adopted to formulate standards in combination with gender: Overweight is higher than the growth reference median + 1 standard deviation, and Obesity is higher than the median + 2 standard deviations, which can accurately reflect the obesity status of adolescents.

Ⅲ. Auxiliary Indicators: Supplementary Value of Waist Circumference and Body Fat Percentage

BMI cannot distinguish the ratio of muscle to fat, nor can it reflect fat distribution. Therefore, WHO takes waist circumference and body fat percentage as auxiliary indicators to improve the accuracy of judgment.

1. Waist Circumference: Evaluation of Central Obesity

Waist circumference directly reflects abdominal fat accumulation and is closely related to chronic diseases. The international universal standard is male ≥ 90 cm and female ≥ 80 cm. It should be measured while standing naturally and breathing calmly, encircling the navel horizontally.

2. Body Fat Percentage: Accurately Reflecting Fat Level

Body fat percentage is the percentage of fat weight in total weight. The WHO standard is male ≥ 25% and female ≥ 35%. The normal reference range for adult males is 6%～14%, and for females is 10%～14%. Exceeding this range indicates fat abnormality. Measurement can be carried out through professional methods such as Bioelectrical Impedance Analysis (BIA), and the results of household body fat scales can be used as a reference.

Ⅳ. Regional Adaptation: Standard Adjustments for Different Races

The universal WHO standards are based on Western population data, while people in the Asia-Pacific region have slimmer body types, with higher body fat percentage and earlier manifestation of disease risks at the same BMI. In 1999, the International Obesity Task Force (IOTF) proposed Asian standards: Normal 18.5～22.9, Overweight 23.0～24.9, Obesity ≥ 25.0.

China formulated the “Adult Weight Judgment” standard based on local data, defining adult BMI ≥ 28.0 as obesity. The central obesity standard is male waist circumference ≥ 90 cm and female ≥ 85 cm, improving the pertinence of prevention and control.

Ⅴ. Rational Cognition: Limitations of the Standards

Although international obesity standards have important reference value, they have limitations:

• BMI cannot distinguish muscle from fat; muscular people may be misjudged as overweight, and “hidden obesity” patients may be misjudged as normal;
• Special groups such as pregnant women and the elderly are not applicable to conventional standards. For example, the appropriate BMI for the elderly over 80 is 22.0～26.9;
• Standards are only for risk screening reference. Individual health needs comprehensive evaluation combining diet, exercise, heredity and other factors.

Ⅵ. Summary: Value and Application of the Standards

International obesity standards have constructed a scientific judgment system with BMI as the core, playing a significant role in population screening and policy formulation. It is necessary to rationally view the values in personal health management and avoid absolute interpretation.

Future standards will be continuously optimized with in-depth research, and individuals establishing healthy eating and exercise habits and maintaining the balance of body composition are far more important than simply pursuing BMI compliance.