A new study in the BMJ reportedly shows that losing weight later in life correlates with a higher risk of dying. Could this be true? Do we want to avoid weight loss as we age to live longer?
Before we jump to conclusions, let's take a closer look at the study and what it really shows.
For starters, this was a retrospective observational study - one of the lowest quality types of evidence frequently referred to as "data mining." As we have mentioned many times, these studies suffer from unreliable data collections (in this case, it was self-reported weight which is subject to multiple sources of error) and uncontrolled variables (which will turn out to be important in this case). In addition, these studies cannot prove cause and effect, and instead can merely point out associations (most of which are statistically weak).
The authors evaluated the data from 36,000 people age 40 or older and had them estimate their weight at age 25 and at 10-years prior to their enrollment in the study. They then crunched the data to see if there were associations between risk of dying and weight changes.
Some findings shouldn't surprise us. Those who were heaviest at age 25 had the highest risk of mortality later in life, and those who had a stable "normal" weight had the lowest risk. The "stable obese" group, and those who gained weight from young-to-middle adulthood also had an increased risk.
But what is generating the most media buzz is the finding that those who lost weight from middle to later adulthood also had an increased risk of death. At first, this seems counterintuitive. Shouldn't losing weight be a good thing, and shouldn't they therefore lower their risk of dying?
Maybe. Unfortunately, this study did not differentiate between intentional weight loss and unintentional weight loss. In other words, those who went on a low-carb diet, started exercising and lost weight are treated the same as those developed burnt out diabetes and started losing weight, or those who became frail and sarcopenic as they aged. As you can see, that is a crucial difference that impacts our interpretation of the data.
We could probably assume that, in general, those who gain weight at a young age gain fat mass while those who lose weight later in life tend to lose lean body mass. But we don't know if that is true in this study or not. Did they measure waist circumference? DEXA scans or bioimpedance scales for fat mass? No.
So, even if the study shows an increased risk of dying for those who lost weight, the study cannot come close to telling us if it was actually the weight loss that increased the risk or if it was something altogether different.
In the end, we can conclude that it is likely better to stay "normal" weight your whole life. We cannot, however, conclude that purposeful weight loss as we age, especially in a manner that maintains lean body mass, is dangerous.
Also remember, weight is not the most reliable health marker. Instead, we suggest focusing on body composition, blood pressure, markers of metabolic health, how you feel, and other health markers. Read more about Weight, health and happiness: striking the right balance in our recently published guide.
Thanks for reading,
Bret Scher, MD FACC