BMI (Body Mass Index) is an internationally recognized indicator for assessing the degree of obesity and health risks in the human body. It is calculated by dividing weight (in kilograms) by the square of height (in meters). BMI is mainly used for:

• Quickly assess the nutritional status of the population
• Identify weight related health risks
• Monitor the trend of weight changes
• As a reference for developing health intervention measures

According to the standards of the World Health Organization (WHO), BMI is classified as follows:

• < 18.5：Being underweight
• 18.5 - 24.9：normal weight
• 25.0 - 29.9：overweight
• 30.0 - 34.9：Obesity level I
• 35.0 - 39.9：Obesity Level II
• ≥ 40.0：Obesity level III (severe obesity)

Please note that these standards may be adjusted according to the characteristics of local populations in different countries and regions.

Although BMI is a useful population screening tool, it also has its limitations:

• Cannot distinguish the ratio of fat and muscle
• Not considering fat distribution (abdominal fat vs hip fat)
• May not be applicable to certain specific populations (such as pregnant women, breastfeeding women, children, elderly people, athletes)
• Not considering differences in bone density

Therefore, clinical evaluation should be combined with other indicators such as waist circumference, body fat percentage, blood pressure, blood glucose, etc.

Measure height:

• Wearing lightweight clothing and standing barefoot
• Back, hips, legs, and heels tightly against the wall
• Keep your head level and keep your eyes looking straight ahead
• Read with a straight ruler or height measuring instrument

Measure weight:

• Use a calibrated weight scale
• Measure at the same time every day (e.g. on an empty stomach in the morning, after defecation)
• Wearing similar lightweight clothing
• Barefoot or wearing the same lightweight shoes

BMI is associated with various health risks:

• Being underweight：Malnutrition, weakened immunity, increased risk of osteoporosis
• normal weight：Lowest health risk
• overweight：Increased risk of cardiovascular disease, diabetes and hypertension
• obesity：The risks of cardiovascular disease, diabetes, hypertension, some cancers, sleep apnea syndrome, etc. are significantly increased

These risks are also influenced by other factors such as family history, lifestyle, fat distribution, etc.

The assessment of BMI in children is different from that in adults, and age and gender factors need to be considered:

• The BMI value of children varies with age and cannot be directly used according to adult standards
• Usually, BMI percentile curve is used for evaluation
• < 5th percentile: underweight
• 5-85th percentile: normal weight
• 85-95 percentile: Overweight
• > 95th percentile: Obesity

The assessment of BMI in children should be carried out by professional medical personnel, combined with comprehensive judgment of growth and development curves。