In Aged Care we often see BMI (Body Mass Index) used as a quick health check. However, BMI alone can be misleading in older adults.
Research shows the “healthy” BMI range for older adults is higher compared with younger people.
The lowest risk of death in older adults is at a BMI 24–30.9 kg/m². Research comparing several studies including approx. 200,000 Australians aged ≥65 found that being overweight did not increase mortality risk, but BMIs below 23 or above ~33 did.
Therefore, the recommended BMI range for older adults is 24-30.9kg/m2
As we age, our bodies lose muscle (sarcopenia) and gain fat even if weight is stable.
Two seniors can have the same BMI but very different body compositions. BMI doesn’t distinguish fat from muscle, so it often underestimates risk.
Studies have repeatedly shown “BMI alone is not a sufficient indicator of healthy body composition” in older adults.
For example, one analysis found many older people with “normal” BMI had high body fat and low muscle, and vice versa.
In fact, BMI often misses malnutrition in the elderly: one study concluded that many malnourished older adults still had a high BMI.
Instead of using a person’s appearance or BMI to assess their health, use validated screening tools to assess a residents malnutrition risk.
Several validated malnutrition screening questionnaires exist e.g. the Malnutrition Screening Tool (MST) or Mini Nutritional Assessment Short form (MNA-SF).
These screening tools look at weight change, appetite, intake and other factors. For example, the MST asks about recent weight/appetite loss and is easy to use.
Tools like these identify “at risk” residents far better than BMI alone. Standard 5.5.5 of the strengthened aged care standards specify all residents must be screened using a validated malnutrition screening tool.
Residents deemed “malnourished” or “at risk of malnutrition” using these screening tools should be referred to an Accredited Practising Dietitian.
It is important to watch changes in weight, not just the number. A big warning sign is unintentional weight loss.
Guidelines note that a loss of ≥5% body weight (in 3–6 months) correlates with malnutrition and poor prognosis.
This means even an “overweight” resident who drops 5%+ of their weight should be evaluated by an Accredited Practising Dietitian (APD).
Weight loss in older adults is often muscle mass loss, which they cannot afford. It should NOT be brushed off with “they can afford to lose a little weight” – in older adults, that attitude can cost muscle, independence and even life.
In short: any significant weight loss in aged-care residents (especially >5%) is a signal to assess nutrition, regardless of their BMI.
A common belief is that overweight older adults can “afford” to lose weight. Evidence says otherwise.
Older adults lose muscle more quickly than younger people, so even moderate weight loss can weaken them.
Research shows us that overweight adults had no higher mortality risk – and in fact being slightly heavier might be protective.
Bottom line: don’t encourage needless dieting in aged care residents. Instead, focus on balanced meals and muscle-strengthening nutrition.
It’s critical to remember that every older person, at any weight or BMI, can be at risk of malnutrition.
Recent data show about 40% of older Australians are malnourished or at high risk, and many live with chronic diseases, isolation or eating difficulties.
A high BMI or “healthy weight” stamp doesn’t guarantee optimal nutrition.
For instance, one study found that among older people with a BMI in the healthy weight range 70% had muscle loss, osteoporosis or excess fat – in other words, hidden nutritional problems.
That’s why we say: don’t assume “they look well.” Watch for subtle signs (weakness, poor wound healing, repeated falls) and use screening.
All adults – thin, above their healthy weight range or in-between – need good nutrition.
In aged care, our goal is well-being, not just numbers on a chart.
By looking beyond BMI/weight and focusing on the whole person – weight trends, muscle strength, appetite and diet – we can catch malnutrition early and keep our residents strong.
When in doubt, refer to an Accredited Practising Dietitian for guidance on nutrition assessment and support.
