What is the optimal BMI for older adults? The answer may be different from what the standard adult BMI chart suggests.
In Episode 20 of The Geriatric Dietitian Podcast, we’re continuing our five-part series on BMI in older adults and taking a closer look at what research shows about BMI and all-cause mortality after age 65.
I use the word optimal intentionally. A certain BMI does not automatically make someone healthy or unhealthy. BMI is only one measurement, and it has plenty of limitations.
For this discussion, we’re looking specifically at the BMI ranges associated with the lowest rates of mortality in older adults.
What Does the Research Say About BMI in Older Adults?
The standard adult BMI chart classifies:
- Below 18.5 as underweight
- 18.5 to 24.9 as normal weight
- 25 to 29.9 as overweight
- 30 or higher as obese
But those standard categories do not necessarily reflect the BMI ranges associated with the lowest mortality in adults over age 65.
One of the major studies discussed in this episode was a meta-analysis that included 32 studies and nearly 200,000 older adults, with an average follow-up of about 12 years. Researchers found a U-shaped relationship between BMI and all-cause mortality.
The lowest rates of mortality were seen around a BMI of 27 to 27.9.
According to the standard adult BMI chart, that would fall within the “overweight” category. Yet among these older adults, this was where researchers found the lowest rates of all-cause mortality.
Why Lower BMI Is Not Always Better After 65
The research also showed that mortality did not immediately increase when BMI crossed into the traditional obese category.
Older adults were still doing well around a BMI of 30.9, and even around a BMI of 33 there was not a significant increase in mortality. A significant increase appeared when BMI reached the upper 30s.
On the other side of the curve, mortality increased sooner as BMI decreased. A BMI around 24 was still associated with good outcomes, but when BMI dropped to 20 or below, mortality increased by 28%.
Researchers specifically recommended monitoring older adults with a BMI below 23 so that causes of weight loss could be identified and addressed quickly.
This is one reason unintended weight loss is such an important concern in older adults. Lower is not automatically better. Weight loss can also contribute to muscle loss, and muscle is important for strength, function, and maintaining independence.
What Is the Optimal BMI for Older Adults?
Additional research discussed in this episode also supports the idea that older adults should be assessed differently.
A 2020 review of 71 studies found that older adults in the traditional overweight category often had lower mortality than those in the standard normal BMI category.
Another study published in 2022 looked at BMI along with measures such as strength, mobility, nutrition status, balance, and activities of daily living. The poorest outcomes were seen among older adults with a BMI below 25 and above 35.
For practical purposes, I use approximately 23 to 30 as the BMI range associated with the lowest rates of mortality in adults over age 65. But this is not about creating another rigid BMI rule. BMI is still only one number. We need to look at the whole person.
Muscle, Function, and Individualized Care Matter
Imagine an older adult with a BMI of 27. The standard BMI chart categorizes them as overweight, so they are automatically told to lose weight. They lose weight, but some of that weight is muscle. Older adults already have less muscle than younger adults, and that muscle is important for strength, nutrition, function, and independence.
That is why we do not want to chase a number on a BMI chart at the expense of the bigger picture. Care should also be individualized.
If someone has had a lower BMI throughout their life, their weight has remained stable, and nothing else has changed, that is very different from an older adult who is unintentionally losing weight.
The research gives us important information, but it does not replace individualized care.
In This Episode, You’ll Learn
- What research shows about the optimal BMI for older adults
- Why standard adult BMI categories may not apply the same way after age 65
- Why the lowest mortality was seen around a BMI of 27 to 27.9 in a large meta-analysis
- Why low BMI and unintended weight loss can be concerning
- Why maintaining muscle and function matters
- Why BMI should always be considered in the context of the individual
Learn More About BMI in Older Adults
Want to dive deeper into BMI, aging, mortality, muscle loss, and nutrition?
Read: BMI in the Elderly: What You Need to Know
Download my free Healthy Aging Nutrition Guide:
https://thegeriatricdietitian.myflodesk.com/
This is Part 2 of my five-part podcast series on BMI in older adults.
In the next episode, we’re talking about sarcopenia in older adults and why muscle matters more than weight.