What is the normal Body Mass Index (BMI) for adults?

From the Guidelines

The normal Body Mass Index (BMI) for adults is between 18.5 to 24.9 kg/m2.

BMI Categories

• Underweight: < 18.5 kg/m2
• Normal weight: 18.5 to 24.9 kg/m2
• Overweight: 25.0 to 29.9 kg/m2
• Obese: >= 30 kg/m2 as defined by the World Health Organization (WHO) 1. It is essential to note that BMI is not an ideal marker of obesity as it cannot differentiate between higher weights due to increased adiposity versus muscularity and cannot identify visceral adiposity, which has negative metabolic effects 1. Additionally, population-specific BMI cutoffs may be lower for Asian populations 1. The use of BMI as a screening tool has been recommended in the initial clinical assessment of obesity, despite its limitations in assessing adiposity in clinical practice, particularly among adults with a BMI of 30 kg/m2 or higher 1.

From the Research

Normal Body Mass Index (BMI) for Adults

The normal BMI for adults is generally considered to be between 18.5 and 24.9 kg/m2 2.

• A BMI of 18.5-24.9 is typically classified as normal weight
• A BMI of 25-29.9 is classified as overweight
• A BMI of 30 or higher is classified as obese

BMI Categories

The World Health Organization (WHO) defines the following BMI categories:

• Underweight: BMI < 18.5
• Normal weight: BMI = 18.5-24.9
• Overweight: BMI = 25-29.9
• Obese: BMI ≥ 30 However, some studies suggest that the relationship between BMI and mortality is more complex, and that the optimal BMI range may vary depending on age and other factors 3, 4.

BMI and Mortality

Research has shown that there is a J-shaped relationship between BMI and all-cause mortality, with the lowest mortality risk typically observed in the normal weight range (BMI 20.0-24.9) 2.

• A BMI below 20.0 or above 30.0 is associated with increased mortality risk
• The relationship between BMI and mortality may be influenced by factors such as age, sex, and smoking status
• Some studies have found that overweight or obese individuals may not have a significantly increased mortality risk compared to those with a normal BMI, particularly in older adults 3, 4.

Limitations of BMI

It is essential to note that BMI has several limitations as a measure of health, including:

• It does not account for muscle mass or body composition
• It may not accurately reflect health risks for certain populations, such as athletes or older adults
• It is a simplistic measure that does not capture the complexity of human health 5, 6.