A study examining data from over 58,000 European participants calls into question the cognitive "obesity paradox," a controversial belief that higher weight in older age can protect against cognitive decline, which has taken hold among some clinicians in recent decades.

In the study, published Wednesday in PLOS One, researchers at the Munich Center for the Economics of Aging at the Max Planck Institute for Social Law and Social Policy analyzed longitudinal data from the Survey of Health, Ageing and Retirement in Europe (SHARE) to show that previous investigations may have suffered from several methodological shortcomings. In particular, the researchers found that some of the associations between weight loss and cognitive decline may have been closely related to the physical deterioration that can accompany many kinds of disorders linked to aging rather than to any health benefits from increased weight alone. Their findings suggest that doctors should no longer encourage weight gain later in life in an effort to preserve patients' cognitive abilities. 

Thorsten Kneip, a sociologist at the Munich Center for the Economics of Aging and a co-author in the study, said it was important for the researchers to reevaluate the obesity paradox because it could potentially have wide-ranging implications in how patients are advised to treat cognitive health problems, such as dementia. "It's about addressing potentially false beliefs," Kneip told The Academic Times. "If people keep on believing that it might be better to be a little overweight, or even obese, because everyone, including their general practitioner says, 'Don't worry about your weight — it's actually good,' that may be harmful, because we know from other studies that there are a lot of adverse effects of [being] overweight." Those negative health effects could include "diabetes, heart disease, stroke, and some types of cancer," according to the Centers for Disease Control and Prevention.

It had been posited that obesity could improve the outcomes of older patients with broad health concerns ranging from cardiovascular issues to kidney disease. Several underlying mechanisms have been suggested to explain the apparent contradiction, including overweight individuals' ability to store harmful chemicals in adipose tissue, or body fat, and their potential propensity to receive more comprehensive, optimal treatments in response to certain medical issues. Meanwhile, other studies have investigated the potential causes for an obesity paradox in cognitive outcomes, in particular, finding that the presence of adipose tissue can help preserve executive function.

Judith M. Kronschnabl, the corresponding author of the study and a doctoral candidate in sociology who specializes in the socioeconomic and behavioral aspects of aging, said the findings indicate that doctors should apply a personalized approach, taking extra care to determine why particular older adults are gaining or losing weight, rather than suggesting a one-size-fits-all solution. "Saying that once you're older, you should not lose weight, period, is just something that should not be promoted anymore. It's not backed by data," she said. "One has to take a closer look as to why someone is losing weight. Is it due to an illness or due to a deliberate change in behavior? Is he or she losing muscle mass or fat mass?"

There are some rare cases, according to the study, when weight gain could be a sign of health improvements. "Weight gain may point to recovery from a preceding illness, particularly in the oldest [of the] old," Kneip explained. 

From 2006 until 2016, the SHARE project tracked the health of an international cohort of adults aged 50 and over. The Munich Center for the Economics of Aging researchers were intimately familiar with the data because some had already served in administrative roles in the data-collection process itself. This allowed them to use multiple measures to assess participants' body weight and health.

Some previous studies had looked at body mass index — a rudimentary tool for categorizing patients as underweight, normal weight or overweight — in isolation. But as the researchers explained in their study, BMI has several limitations, including the tool's inability to reflect the differences between lean muscle mass and body fat, which can sometimes cause misleading results.

To combat these shortcomings, the team also assessed volunteers' grip strength, a secondary measure that helps establish correlations between overall strength and lean mass. They also tracked observable diseases that could cause fluctuations in weight gain, irrespective of other health factors. The team indicated that future studies could use other measures to track body weight, such as using bioelectric impedance analysis or measuring waist circumference, in order to identify whether their results can be replicated in other settings. 

The team was careful not to dismiss the obesity paradox altogether, but they suggested that many of the factors that lead to unintentional cognitive benefits in obese people may stem from correlational factors rather than a clear causal mechanism. The majority of the researchers have a background in sociology, Kneip noted, so they brought a uniquely humancentric perspective to the study, centered on correcting a potential misunderstanding that has spread throughout the medical community.

"This common notion somehow made it out into the world," Kneip said. "And since we are mostly social scientists, and we usually deal with research that has real-life implications, it's really a motivation for many of the things that we do, to provide sound evidence, to give good counseling and to eventually improve people's lives."

The study "Bodyweight change and cognitive performance in the older population" published April 21 in PLOS One, was authored by Judith M. Kronschnabl, Thorsten Kneip and Luzia M. Weiss, Munich Center for the Economics of Aging; and Michael Bergmann, Munich Center for the Economics of Aging and Technical University of Munich.