Friday Q&A: Weight and Longevity

Q: I've been following this discussion Being Slightly Heavy Aids Longevity  for a while & would like to hear your perspective (phew! Managed to NOT ask you to "weigh in"). I've read that the numbers are skewed because people who are very sick tend to be under weight, and then there is that group of people that become intentionally underweight because they believe it encourages longevity. Thoughts?

A: No causal relationship exists between body weights (BMI) and death. One cannot predict health and the risk of death from BMI alone as there are several confounding factors that need to be taken into consideration. No doubt, longevity (in terms of mortality rates) is lower among people with BMIs of less than 18 (underweight) or greater than 30 (overweight). Being overweight or underweight puts an individual at risk from several associated diseases. Both Western medicine and Ayurveda agree that too little fat (underweight) or excess fat (overweight) can trigger an entire gamut of health issues that in turn affects the quality of life. I do not see any purpose in having a long lifespan while suffering from diabetes, arthritis, infections, osteoporosis or other health issues. It is for this very reason that I advocate quality of life rather than life span extension. All of us are equally aware about ways to improve our quality of life. In addition, anything in moderation is good and that applies to weight issues as well.

—Ram (Professor Rammohan Rao, Buck Institute for Research on Aging)

A: I am a bit reluctant to “weigh in” (as you well put it), as this is truly a messy issue. First, not all fats are the same. As mentioned in the article, the fat that accumulates in your belly can be quite different than that distributed in other tissues or areas of the body. Fat droplets have been observed to increase in aging bones, for example, although it’s not clear what the significance of this is. There has also been a lot of discussion recently on “brown fat” and its role in health and disease. However, none of these distinctions were considered. Second, I don’t like these types of epidemiological studies. They are typically only correlative, and rarely get to the molecular or physiological underpinnings (if they exist at all). Third, only small differences were observed among the main weight groups (excluding the highly obese). Fourth, BMI is a very crude index. That said, the results of this study are still surprising and suggest that our notions of a healthy weight may need to be reconsidered. Most of us intuitively know this, as we have seen plenty of thin people who look unhealthy while many who fit the category of "somewhat overweight" look real healthy, robust and fit. I remember several years hearing from a seminar speaker that early Alzheimer’s’ patients weighed less than their age-matched non-AD controls. The speaker suggested there might be some type of abnormal metabolic disorder associated with AD that had not yet been identified as such.

With so many possible confounders and variables to consider, it’s pretty hard to make any serious conclusions. Eat healthy, be physically active and put away the scale? Sounds good to me.

— Brad (Professor Bradford Gibson, Buck Institute for Research on Aging)