From the Guidelines
A person is considered underweight when their Body Mass Index (BMI) is below 18.5 kg/m². This classification is widely accepted by healthcare professionals as the threshold for identifying underweight status in adults, as stated in the study by 1. BMI is calculated by dividing a person's weight in kilograms by their height in meters squared (kg/m²). Being underweight can indicate potential health concerns including nutritional deficiencies, weakened immune function, hormonal imbalances, and decreased bone density. For those with a BMI below 18.5, it's advisable to consult with a healthcare provider who may recommend increasing caloric intake with nutrient-dense foods, addressing any underlying medical conditions, or working with a registered dietitian to develop a healthy weight gain plan.
Some key points to consider:
- The World Health Organization (WHO) classification for adults defines underweight as a BMI of less than 18.5 kg/m², as mentioned in the study by 1.
- Being underweight can have serious health consequences, including increased risk of infections, osteoporosis, and decreased immune function, as noted in the study by 1.
- BMI provides a useful screening tool, but it doesn't directly measure body fat or account for factors like muscle mass, bone density, or ethnic differences in body composition, so clinical judgment should accompany BMI assessment, as stated in the study by 1.
It's essential to approach weight management with a comprehensive plan that considers individual factors, such as overall health, lifestyle, and nutritional needs. By working with a healthcare provider, individuals can develop a personalized plan to achieve a healthy weight and improve their overall well-being.
From the Research
Definition of Low BMI
- A person is considered to be underweight when their Body Mass Index (BMI) is below 18.5 kg/m2 2.
- However, the definition of low BMI may vary depending on the population being studied and the specific health outcomes being considered.
Health Risks Associated with Low BMI
- A low BMI (less than 22 kg/m2) has been associated with an increased risk of fracture and all-cause mortality in older adults 3.
- In hospitalized adults, a low BMI has been linked to a higher risk of malnutrition and prolonged hospital stay 4.
- In elderly women, a low BMI has been associated with an increased risk of osteoporosis and fracture 5.
BMI Categories
- The World Health Organization (WHO) defines the following BMI categories:
- Underweight: BMI < 18.5 kg/m2
- Normal weight: BMI = 18.5-24.9 kg/m2
- Overweight: BMI = 25-29.9 kg/m2
- Obese: BMI ≥ 30 kg/m2 2
- However, these categories may not be applicable to all populations, and the risk of health problems may vary depending on the individual's age, sex, and other factors.
Relationship Between BMI and Health Outcomes
- The relationship between BMI and health outcomes is complex, and a low BMI may not always be associated with poor health outcomes 6.
- In some cases, a low BMI may be associated with a lower risk of certain health problems, such as myocardial infarction 6.
- However, a low BMI may also be associated with a higher risk of other health problems, such as osteoporosis and fracture 5.