The Phantom of Kohada Koheiji

The Phantom Paradox of Obesity and Brain Function

Two serious health concerns – obesity and loss of brain function – intersect in curious ways. Good evidence suggests that obesity in early and mid life can have a negative effect on cognition. But later in life, the story is a bit fuzzier. In fact, some researchers have suggested the opposite might be true for older persons. That is, they have found hints that a bit of overweight or obesity might prevent cognitive decline. Some have gone so far as to call this an obesity paradox.

However, a recent paper in PLOS One tells us that this is likely a phantom paradox. A careful analysis shows that the supposed benefits had more to do with weight changes associated with illness and recovery.

Longitudinal Data From SHARE

Judith Kronschnabl and colleagues used longitudinal data from the Survey of Health, Ageing and Retirement in Europe (SHARE) for their analysis. The survey tracked 58,389 persons between 2006 and 2016. The researchers found complex relationships and investigated them thoroughly.

For example, at low levels of BMI, weight loss predicted declines in cognition. This was mainly due to health conditions that affected both brain function and BMI. But overall, the relationship between weight gain and cognition was not significant. Only people who had lost weight previously (again because of illness) had improvements in cognition when they gained weight.

Setting Aside a False Paradox

Kronschnabl explained the importance of their findings:

“Persistent weight gain or weight gain at already high levels of BMI eventually becomes detrimental. It has been suggested that higher weight or weight gain in older age may become beneficial for keeping up cognitive performance. We find no evidence for this.”

Neurology professor David Knopman calls this an excellent and thoughtful analysis. He told Medscape:

“This study removes the false expectation that obesity somehow protects against dementia. It does not. All of these statements can be made regardless of adult age.”

In short, the relationship between obesity and brain function can be convoluted as people age. People may lose weight when they have a difficult illness and regain it when they recover. At the same time, such illnesses can affect cognition. None of this, though, suggests an obesity paradox. That “paradox” is a phantom we can dismiss.

Click here for the Kronschnabl paper and here for further perspective. For recent data on obesity and cognitive decline, click here.

The Phantom of Kohada Koheiji, painting by Katsushika Hokusai / WikiArt

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May 27, 2021