Variously on this site, most recently here, I have reported on studies which show that being ‘overweight’ is associated with a reduced risk of death compared to having what would be generally taken to be a ‘normal’ or ‘healthy’ weight. The studies that show this association are based on the measurement known as the body mass index (weight in kg divided by the square of someone’s height in meters). The main problem with the BMI is that it tells us nothing about body composition. It is possible therefore for individuals to be fit, healthy and quite well-muscled, and to register supposedly elevated BMI values.
But recently a study has been published which suggests that the life-saving qualities of a raised BMI reading may not be down so much to muscle, but fat. The study, published on-line in the American Journal of Clinical Nutrition, looked at the relationship between a variety of body measurements and risk of death (mortality) as well as risk of illness (morbidity) in individuals aged 65 or more in a geriatric hospital in Paris, France .
Over time, the researchers discovered that having higher fat mass was associated with a reduced risk of mortality and morbidity.
For example, compared to the 30 per cent of people with the lowest fat masses, those with the highest 30 per cent of fat masses had a 70 per cent reduced risk of mortality, and a 75 per cent reduced risk of death or complications from their original illness.
There was, however, no significant association with other body measurements, including muscle mass, and mortality and morbidity.
This study suggests that bodily fat can be a bit of a lifesaver for elderly individuals. It has been suggested that fat provides a much-needed fuel reserve when individuals are struggling with a disease process that is ‘catabolic’ (i.e. body wasting) in nature.
The authors of this study also cite other studies which link, in the elderly population, lowered risk of mortality as body weight increases [2-4]. These studies, however used the BMI to assess weight, which as we know, tells us nothing about body composition. The interesting thing about this most recent study is that it suggests that it is increased body fatness that may confer benefit. More evidence is required to see if this turns out hold true for the elderly generally.
However, with the evidence as it stands, it seems that being ‘overweight’ from a BMI perspective is associated with reduced risk of death, and that in the elderly, being a bit chubby may confer health-related and survival advantages.
1. Bouillanne O, et al. Fat mass protects hospitalized elderly persons against morbidity and mortality. Am J Clin Nutr 29th July 2009 [epub before print publication]
2. Landi F, et al. Body mass index and mortality among hospitalized patients. Arch Intern Med 200;160:2641-4
3. Mattila K, et al. Body mass index and mortality in the elderly. Br Med J (Clin Res Ed) 1986;292:867-8
4. Grabowski DC, et al. High body mass index does not predict mortality in older people: analysis of the Longitudinal Study of Aging. J Am Geriatr Soc 2001;49:968-79