Apr 9, 2020
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Using the Body Mass Index (BMI)

BMI is an abbreviation used for body mass index and it is calculated from a person’s height and weight. The Centers for Disease Control and Prevention (CDC) use BMI to define terms like overweight and obese. Someone who is underweight would have a BMI below 18.5; Normal weight is considered 18.5 to 24.9; Overweight would be 25.0 to 29.9; Obese would be classified as 30.0 and above and 40 and above is considered morbid obesity. People with very low BMI’s or very high BMI’s tend to have more health issues than those at normal BMI. It is important to be aware though that a person can have a normal BMI but still be at risk for certain health issues if they are not taking proper care of themselves as far as exercise, proper eating, etc.

Using the BMI does have some limitations in certain age and population groups. BMI will not distinguish between lean body mass and fat mass because it is based on weight, not percentage of body fat. This means that some very muscular people could be considered to have an “unhealthy” BMI even though they are very healthy.


A dietitian needs to be cautious when using it with the elderly. The BMI doesn’t always provide the same indication of health status for an older adult as it does with a younger person. It may sometimes be difficult to get accurate measures of weight and height in the elderly, therefore leading to inaccurate results. Some experts believe that the range 18.5-25 may be too restrictive for an elderly person. Perhaps the range of 25-30 may be more reasonable especially those in a long term care setting. The thought is that a higher BMI may make an elderly person at less risk for hip fractures from a fall and less risk for complications after a surgical procedure.


BMI is just one indicator of the health status of a patient/resident but there are other factors that should be taken into consideration. The dietitian is an expert as far as nutritional assessment and should be consulted for professional recommendations.