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Think of obesity and you likely picture a condition that contributes to diseases like diabetes and heart disease. But have you ever considered that obesity could impact your brain as well? A recent study in the Journal of Alzheimer’s Disease Reports found obesity can alter brain structure and speed the progression of Alzheimer’s disease. This adds to previous research exploring the connection between obesity and cognitive issues like memory loss. “There is a great deal of interest in understanding how the whole body influences the brain,” says Rozalyn Anderson, Ph.D., director of the metabolism and aging program at the University of Wisconsin School of Medicine in Madison, WI. Here's what we know so far.
In a nutshell, your weight has a direct impact on how your brain functions. Your brain is a complex organ, so there’s a lot to unpack here. But just to level set, we’re talking about diet-induced obesity caused by the prolonged, excessive consumption of processed, unhealthy foods. “It is important to make that distinction because obesity is complex,” says Cassandra Lowe, Ph.D., neuroscientist and senior postdoctoral fellow at Western University in Ontario, Canada. Obesity can also be caused by certain illnesses or medications and exacerbated by factors like genetics, stress, or lack of sleep.
Before we dive in, it’s important to remember that scientists are looking at the broad data. “Not all cases of obesity are associated with problems in metabolism, elevated inflammatory tone, or indeed with imminent risk for disease,” Anderson says. The goal with much of today’s research is to better understand the role that diet and lifestyle play in the health of your brain. After all, if dementia or Alzheimer’s could be partially prevented or delayed in onset through diet, that would be a game-changer for millions of people. Let’s break down the different ways in which diet-induced obesity can alter cognition.
Executive function refers to the part of your brain that helps you achieve your daily tasks. It includes things like problem solving, attention span, and working memory. “Think of working memory as your immediate workstation,” says Ranjana Mehta, Ph.D., an associate professor who studies obesity and cognition at Texas A&M University in College Station, TX. “You’re working with pen and paper, and you keep a book to the side so you can grab it really quickly to retrieve information. Working memory is that: what you can store in your immediate memory for quick thinking, information processing, and execution.”
Research shows that obesity has a detrimental effect on working memory, which impacts your ability to make decisions about the food you eat. In one study, people with obesity reported difficulty with making dietary choices. “Junk food is rewarding, and we see increased activation in brain regions associated with reward processing when we are exposed to these foods,” Lowe says. “Executive functions help us override these reward responses to make better choices.” This helps explain why obesity is a tough cycle to break; your brain has rewired itself to favor certain foods, while losing its power to veto bad decisions.
“Changes in brain structure caused by obesity can speed up the brain aging process by as much as 10 years,” Lowe says. In addition to the 2021 study linking obesity to Alzheimer’s disease, a recent report in Neurology found that obesity in middle age contributed to the onset of dementia years later. The Lancet included obesity as one of 12 modifiable dementia risk factors in its latest dementia report. All of this suggests that your choices right now can make a profound difference in how you age.
Studies have also found a link between midlife obesity and risk for developing Parkinson’s disease—but not necessarily obesity in the senior set. “The relationship between obesity and risk for dementia does not always hold among people who are older, perhaps because dementia itself is associated with weight loss,” says Barbara Bendlin, Ph.D., leader of the Research Education Component in the Wisconsin Alzheimer's Disease Research Center at the University of Wisconsin in Madison. Midlife obesity specifically is the indicator here, partially because it can come with other risk factors like hypertension and diabetes—all of which play a role in dementia progression.
“There is evidence to show that our brains function differently with obesity,” Mehta says. She has worked on research measuring mental and physical fatigue in people with obesity. “We published a paper where we looked at obese and non-obese individuals, and we physically fatigued them,” she recalls. Mehta’s team found that as participants were getting physically fatigued, those with obesity had more trouble sending signals from the brain to the muscles—meaning they also mentally fatigued earlier and more easily than others.
“Chronic inflammation is thought to be one of the pathways in which obesity impacts brain health and cognitive functions,” Lowe says. Diets high in processed foods increase the production of inflammatory cytokines (proteins that signal to cells to mount an inflammatory response). Lowe explains that this inflammation can weaken the connections between brain cells and eventually lead to a decrease in grey matter in your prefrontal cortex and hippocampus—regions of your brain that are essential for cognition and memory. “It can also impact white matter tracts, which are the connections between different brain regions,”
Though we understand the what—that obesity and cognition are linked—experts are still working to better understand the why and how. : “We need to start bridging disciplines like endocrinology, neurobiology, and psychology if we are to solve this. “More research is needed that focuses on the brain and body at the same time,” he says. The hope is that with a better understanding of obesity’s effects, scientists can pave the way for improved prevention and treatment of cognitive decline. “The brain can be trained to do anything,” Now that's food for thought.
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