What’s BMI?

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One of my RDNs posed this question recently related to BMI levels for older adults:

I’ve been seeing transfer notes from the hospital along with other nursing homes with diet/nutrition histories where RDNs are charting that BMIs of less than 23 is underweight. For example, 1 note documented a BMI of 21.3 was underweight”for age” for a man who was 92. State surveyors are also asking for a list of residents with BMI under 21 and wanting to see interventions on them. The MDS does not trigger for a low BMI until under 19. Do we need to adapt our practices?

The National Institute of Health classification of overweight and obesity by body mass index (BMI) is as follows:

Classification – Normal

Obesity Class – None

Classification – Overweight

BMI (kg/m2) – 25.0-29.9

Classification – Obesity

Obesity Class – I

BMI (kg/m2) – 30.0-34.9

Classification – Obesity

Obesity Class – II

Classification – Extreme Obesity

Obesity Class – III

BMI (kg/m2) – > 40

BMI is interpreted based on age, health history, usual body weight, and weight history.

Adults should be evaluated for signs of nutritional status and decline using body mass index (BMI) as one of several things. Data suggests that a higher BMI range may be protective in older adults and the standards for ideal weight (BMI of 18.5 to 25) may be overly restrictive in the elderly. A lower BMI might be considered detrimental to older adults because of association with declining nutrition status, possible pressure ulcers, infection and other complications. A BMI of 19 or less may indicate nutritional depletion, while a BMI of 30 or above indicates obesity.

In the literature, there is a lot of conversation about a BMI of 21-23 (rather than 18/19) as considered on the low side for older adults. At exactly the same time, there’s a whole lot of conversation about the”obesity paradox” saying a greater BMI might be protective against some diseases and death. There’s still a lot of controversy concerning the effectiveness of BMI for older adults, regardless of what is considered”too low” or”too high”.

To our knowledge, there are no firm recommendations from any source on BMI cutoffs for elderly adults. The MDS triggers a CAA if BMI is < 18.5, although as stated above a higher BMI can probably be considered too low for older adults.

In clinical practice, the BMI number is not as important as how it compares to an individual’s history. Monitoring changes over time is what is important.

If state surveyors question whether everybody with a low BMI needs an intervention, consider explaining that if a low BMI was normal with this person’s life history, then we wouldn’t try to fix it – although interventions might be put in place for other reasons (poor intake, weight loss, wounds, etc.). And for an older person with a high BMI of 35 who had been overweight their whole life, it is highly likely that lifestyle and habits are put and weight loss would probably not be necessary or successful in older age.

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