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Professional Refresher: Use of BMI in Elderly Patients
Most health organizations now recommend the use of body mass index (BMI) to assess
health status. Is BMI useful in the elderly population?
BMI is a formula for determining obesity. It is calculated by dividing a person’s weight in
kilograms (kg) by the square of the person’s height in meters. Standards classify a BMI of
18.5 kg as underweight, 25-29.9 kg as overweight, 30-39.9 kg as obese, and over 40 kg
as morbidly obese. A healthy BMI for adults is considered between 18.5-24.9 kg.
Individuals are considered unhealthy it they have a BMI of < 18.5 or > 25.
BMI has limitations in all populations. BMI cannot distinguish between lean body mass
and fat mass because it is based on weight, not percentage of body fat. As a result,
some very muscular people are unnecessarily placed in the “unhealthy” category. Some
experts believe that BMI has limited usefulness for measuring individual nutritional
status but serves a purpose for population studies.
BMI has limitations for defining health in the elderly. Federal standards for ideal weight
(BMI of 18.5-< 25) may be too restrictive for older adults. Recent evidence indicates that
a BMI between 25 and 30 may be protective against mortality in older adults,
particularly those in long-term care environments. One reason may be that persons with
higher BMIs are at less risk for hip fractures with falls and therefore at less risk for
surgical and post-operative complications.
Most experts suggest using a higher BMI threshold for underweight elderly individuals,
compared to what is used for the general population. International Dietetics and
Nutrition Terminology defines underweight in persons > 65 years of age as having a BMI
of < 23.
Other limitations of using BMI to assess nutritional status in the elderly include practical
issues. BMI is calculated based on weight and height. It is difficult to obtain accurate
measures of weight and height in many elderly persons, especially those who are
bedbound. As a result, BMI calculations sometimes are incorrect, particularly if height
and/or weight are self-reported rather than measured.
Implications for dietetics practitioners
BMI does not provide the same clues to health status in the elderly population as it does
in younger people. Dietitians should use care in using BMI as a measure of nutritional
status. A BMI of < 23 classifies an older adult (older than age 65) as underweight and
may require nutrition intervention. Health risks associated with a BMI of 18.5-25 in
younger populations may not apply for those older than age 65.
References and recommended readings
Academy of Nutrition and Dietetics. Pocket Guide for International Dietetics and
Nutrition Terminology Reference Manual: Standardized Language for the Nutrition Care
Process. 4th ed. Chicago, IL: Academy of Nutrition and Dietetics; 2013.
Chernoff R. Geriatric Nutrition: The Health Professionals Handbook. 4th ed. Burlington
MA: Jones and Bartlett Learning; 2014.
Cook Z, Kirk S, Lawrenson S, Sandford S. Use of BMI in the assessment of undernutrition
in older subjects: reflecting on practice. Proc Nutr Soc. 2005;64:313-317.
Famularo P. Desirable body weigh tin the older adult: what does the current research
indicate? Connections. Dietetics in Health Care Communities Dietetic Practice Group of
the Academy of Nutrition and Dietetics. 2014;40(1).
Mahan LK, Escott-Stump S, Raymond JL. Krause’s Food and the Nutrition Care Process.
13th ed. St. Louis MO: Elsevier Saunders; 2012.
MedlinePlus Medical Encyclopedia. Body mass index.
http://www.nlm.nih.gov/medlineplus/ency/article/007196.htm. Accessed June 29,
2015.
Contributed and updated by Nutrition411 staff
Review Date: 5/26/15