Wednesday, July 21, 2010

Skinny Does Not Equal Healthy

Conventional wisdom holds that being overweight or obese is unhealthy and raises your risk of disease and death.  We are all aware of the body weight and BMI trends of Americans the over the last two decades.  As a result weight loss is highly sought after by millions and encouraged by the government and the medical community. Concurrently, the diet and weight-loss industry has grown to a multi-billion dollar industry.  But is having a low BMI really healthier?     

It was thought that the relationship between BMI and mortality is a U-shaped, with the lowest risk with BMI between 21-25.  However, when you get into the research, it shows a different relationship.  Recently, it was found that a  higher BMI improved survival rate in hospitalized heart failure patients.  That is the more you weigh for your height, the more likely you are to survive.  Obviously, the issue can be confounded by the fact that sicker patients weigh less, therefore are more likely to die.  But, other studies have shown a similar relationship, like this study that showed BMI is inversely related to mortality in elderly after adjustment for waist circumference (see chart below).

Body mass index does have its limitations (doesn't differentiate between lean mass and muscle mass), but still holds a fairly good relationship for the American population.  More direct  measures of muscle mass and strength show a similar relationship.  This study showed that a low thigh circumference seems to be associated with an increased risk of developing heart disease or premature death.  Finally, weakness and poor function is related to hospitalization in elderly in this study. 

As we get older, it appears that muscle mass and muscular strength are more important than having a low BMI to decrease your risk of death and increase longevity.  This fact is rarely mentioned.  So often, a low BMI and weight loss are  stressed. We are penalized by health insurance companies for having a high BMI, while sarcopenia (the age-related loss of muscle mass) and muscular weakness are never even considered.  We need to promote and focus our interventions on increasing muscle mass and strength as we age.

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