Where did the Body Mass Index (BMI) come from?
The World Health Organisation (WHO) uses Body Mass Index (BMI) to determine whether a person is of a healthy weight for their height. WHO has decided that a BMI of 18.5 – 24.9kg/m2 for younger adults has the lowest health risks (1). This range has been based primarily on studies in younger adults, where risks of diabetes, cardiovascular disease, certain cancers, and mortality associated with increased body weight have been well documented.
However, recent studies have started to show that people who are older than 65 years of age (which is mostly our residents in aged care facilities) may have different BMI ranges to reflect mortality and morbidity risk. Recent meta-analysis of 32 cohort studies (2) (level II and III, n=197940) of community-dwelling elderly people aged ≥65 years found a U-shaped association between all-cause mortality, with mortality risk lowest at BMI 24 – 31 kg/m2.
Leading Nutrition Recommendations for BMI
With the new and strong emerging evidence, Leading Nutrition are welcoming a change to our current recommendations. The new BMI classifications for people aged 65 years and older are below:
|23 – 30.9||Healthy Weight|
Leading Nutrition (along with other healthcare organisations such as Queensland Health) will no longer be using the old healthy weight BMI range of 22 – 27. You will see this transition come into effect in March 2018 with updates in our dietetic assessments and Aged Care Weight Tracker service. You may still see some cross over within the aged care industry, but we expect it will eventually change to BMI 23 – 30.9. It’s certainly our aged care experience that the morbidity and mortality risks are much higher at the lower BMI.
How is BMI calculated?
BMI = weight (kilograms) / height (metres) x height (metres)
For example if you have a resident with a height of 1.65m and weight of 65kg. You would calculate: 65/1.65 x 1.65 = 23.9. This gives us a BMI of 23.9kg/m2, classifying this resident as borderline healthy weight.
What does this mean for aged care facilities?
You won’t have to make any changes to your current care for residents or referrals to your dietitian. It will just be good to note that those residents who may have been considered as “overweight” may now be within their “healthy weight ranges”. Remember that in aged care we are all focused on minimising malnutrition at all weights and it is the changes in weight that may indicate changes in healthy status for residents.
Keep in mind…
Please remember there are limitations in using BMI.
• You can’t tell between fat, muscle or fluid mass so using BMI may not be accurate. For the elderly, muscle mass is much lower in comparison to fat mass, and many have medical conditions that can increase fluid mass as well.
• BMI calculations rely on the height measurement to be accurate, and loss of height occurs in the elderly.
• Does not take into account presence of sarcopenia or malnutrition (loss of muscle and function).
Despite these limitations, BMI continues to be the most commonly used measure of weight status across the spectrum of health care settings. Therefore, we just have to remember to use the appropriate BMI ranges for residents over 65 years of age. If you are unsure about how to use BMI or what to do with the results, your specialist aged care dietitian can assist you with this.
Contact Leading Nutrition below or on 1300 722 712 for more information on this change. If you would like to know more about our Aged Care Weight Tracker, please click the button below or contact us.
1. World Health Organisation (2013) Obesity and Oveweight. Available from: http://www.who.int/mediacentre/factsheets/fs311/en/
2. Winter JE et al. (2014) BMI and all-cause mortality in older adults: a meta-analysis. Am J Clin Nutr, doi:10.3945/ajcn.113.068122.
3. Zeanandin G, Molato O, Le Duff F, Gue´rin O, He´buterne X, Schneider SM. Impact of restrictive diets on the risk of undernutrition in a freeliving elderly population. Clin Nutr 2012;31:69–73.