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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