How Obesity Affects Your Brain
Diet-induced obesity can impact your memory, mental health, and even your long-term risk for dementia.
Think of obesity and you likely picture a physical health condition—one that contributes to diseases like diabetes and heart disease. But have you ever considered that obesity could impact your brain as well? A 2021 study in the Journal of Alzheimer’s Disease Reports explains how 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, decline in executive functioning, and early-onset dementia.
“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. “Traditionally, investigators worked either ‘above the neck’ or ‘below the neck,’ but it is so clear now that there is a great deal of cross talk between the two.”
In a nutshell, your weight has a direct impact on how your brain functions, and the more experts understand about the relationship between obesity and the brain, the closer they get to solving for cognitive diseases as well as physical ones. Here's what we know so far.
Defining Diet-Induced Obesity
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 as it relates to the brain. This is 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 does not always signal an unhealthy diet or lifestyle—it 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 the broad data we’re looking at doesn’t always apply to an individual person’s health. “Not all cases of obesity are associated with problems in metabolism, elevated inflammatory tone, or indeed with imminent risk for disease,” Anderson says. Weight stigma is real, and we are not here to shame you or make assumptions! We just want you to be your healthiest self, whatever that looks like for you.
Obesity and Brain Health
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.
Decline in executive function. 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 in industrial and systems engineering at Texas A&M University who studies obesity and cognition. “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 has shown that obesity has a detrimental effect on working memory, which ironically can lead to a harder time making rational decisions about the food you eat. In a 2018 study in the Journal of Behavioral Medicine, people with obesity reported difficulty with executive functioning, specifically as it related to making dietary choices. “Junk foods are very rewarding, and we see increased activation in brain regions associated with reward processing when we are exposed to these foods and when we eat them,” Lowe says. “Executive functions help us override these reward responses to food cues to make better choices.” This helps explain why obesity can be such a tough cycle to break; your brain has literally rewired itself to favor certain foods over others, while losing its power to veto bad decisions.
Acceleration in age-related dementia. “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 2020 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 2020 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 (not to be confused with the fact that Parkinson’s patients often lose weight as their disease progresses). “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, prediabetes, and diabetes—all of which play a role in dementia progression.
Mental fatigue. “There is evidence to show that our brains just 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. This can be hard to quantify because it’s a long-term, wide-ranging immune response that affects the whole body, including the brain. “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,” she says.
Stress also contributes to chronic inflammation, and societal weight stigma can put an emotional burden on people with obesity. “Because of the stigma associated with being overweight and obese, and the drive to maintain a certain ideal body type, persons with obesity may be under constant stress,” Lowe says. Some experts have pointed out that this psychological stress can lead to things like disordered eating and avoidance of exercise (not to mention bias by healthcare providers), which further endanger a person’s health.
Mental health issues. Along with general psychological stress, evidence has shown that people with obesity have increased risk of specific mental health conditions like anxiety and depression.
“There is some evidence that obesity-related brain changes can be a factor associated with the increased prevalence of mental health issues, but it could also be related to stress-induced effects associated with weight-stigma,” Lowe says.
The Mind-Body Connection
Though we understand the what—that obesity and cognition are linked—experts are still working to better understand the why and how. Anderson notes, for instance, that the effects of obesity on memory loss may be multifactorial. “I think it is too early to truly tease apart how much of this is due to, say, loss of motivation as opposed to some specific deficit in ability,” she says. “We will 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,” agrees Mehta. The brain is a flexible organ with the remarkable ability to bounce back, so the hope is that with a better uderstanding 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,” Mehta says. Now that's food for thought.
- Obesity Comorbidities: Centers for Disease Control and Prevention. (n.d.) “The Health Effects of Overweight & Obesity.” cdc.gov/healthyweight/effects/index.html
- Executive Function Study: Journal of Behavioral Medicine. (2018.) “Self-regulation and obesity: the role of executive function and delay discounting in the prediction of weight loss.” ncbi.nlm.nih.gov/pmc/articles/PMC6209053/
- Obesity & Alzheimer’s Disease: Journal of Alzheimer’s Disease Reports. (2021.) “Obesity and Brain Vulnerability in Normal and Abnormal Aging: A Multimodal MRI Study.” content.iospress.com/articles/journal-of-alzheimers-disease-reports/adr200267
- Middle-Aged Obesity & Dementia: Neurology. (2020.) “Body mass index, diet, physical inactivity, and the incidence of dementia in 1 million UK women.” n.neurology.org/content/94/2/e123.abstract
- Dementia Risk Factors: The Lancet. (2020.) “Dementia prevention, intervention, and care: 2020 report of the Lancet Commission.” thelancet.com/article/S0140-6736(20)30367-6/fulltext
- Obesity & Parkinson’s: International Journal of Neurogenerative Disorders. (2019.) “Obesity may Increase the Prevalence of Parkinson’s Disease while Parkinson’s may Reduce Obesity Index in Patients.” clinmedjournals.org/articles/ijnd/international-journal-of-neurodegenerative-disorders-ijnd-2-012.pdf
- Neuromuscular Fatigue & Obesity: International Journal of Obesity. (2014.) “Impacts of obesity and stress on neuromuscular fatigue development and associated heart rate variability.” nature.com/articles/ijo2014127
- Chronic Inflammation: StatPearls Publishing. (2020.) “Chronic Inflammation.” ncbi.nlm.nih.gov/books/NBK493173/
- Cytokines: International Anesthesiology Clinics. (2007.) “Cytokines, Inflammation and Pain.” ncbi.nlm.nih.gov/pmc/articles/PMC2785020/
- Weight Stigma & Psychological Distress: BMC Medicine. (2018.) “How and why weight stigma drives the obesity ‘epidemic’ and harms health.” ncbi.nlm.nih.gov/pmc/articles/PMC6092785/