Research has shown that obesity can have a major effect on brain health, influencing everything from memory to executive function skills (the complex ability to initiate, plan, and carry out tasks). Studies have also revealed that middle-aged adults with obesity are at increased risk of dementia.
A recent investigation suggests, however, that it’s not too late for middle-aged adults who are overweight to turn things around through diet and weight loss.
The findings indicate that interventions to improve eating habits and manage central obesity (belly fat) targeted to people between ages 48 and 70 could help promote lasting brain health.
“These findings emphasize the importance of adopting healthier habits before significant cognitive decline occurs,” says lead study author Daria Jensen, DPhil, a postdoctoral fellow at the University Medical Center Leipzig and the Max Planck Institute for Human Cognitive and Brain Sciences in Germany. Dr. Jensen is also a visiting researcher at the University of Oxford in England.
Study Took a Close Look at Diet, Belly Fat, and Brain Health in Middle Age
To reduce the risk of dementia, World Health Organization guidelines recommend following a balanced diet with a high plant intake (such as the Mediterranean diet) and weight management.
The new analysis adds to existing evidence by looking at how changes in diet and waist-to-hip ratio during midlife could support brain structure and mental abilities later in life.
Waist-to-hip is the circumference of your waist divided by the circumference at your hips. Authors evaluated this measure rather than body mass index (BMI) because it focuses on abdominal fat, which is linked to higher risks of insulin resistance, type 2 diabetes, and cardiovascular disease — all factors related to greater dementia risk.
“BMI does not differentiate between muscle and fat, or indicate where fat is distributed in the body,” says Jensen.
Scientists examined data on diet quality for 512 participants and waist-to-hip measures in 664 participants. About 80 percent were male, with an average age of about 48. All participants were cognitively healthy at the study start.
Researchers took participants’ measurements five times over 21 years, and assessed their diet via questionnaire at three points over 11 years.
A higher diet score indicated a greater intake of vegetables, fruit, whole grains, nuts, legumes, omega-3 fats, and polyunsaturated fatty acids (found in fish, seeds, and nuts). Higher scores also reflected avoidance or low intake of sugar-sweetened drinks and fruit juice, red and processed meat, trans fat, sodium, and avoidance or low consumption of alcohol.
At an average age of 70, participants underwent brain magnetic resonance imaging (MRI) scans to assess the structure and function of the hippocampus, a part of the brain crucial for forming new memories and one of the first brain regions affected by dementia.
Researchers also evaluated white matter in the brain using an MRI technique called diffusion tensor imaging (DTI), which measures the movement of water molecules in the brain. White matter acts as the brain’s communication highways, facilitating efficient signal transmission between brain regions, according to Jensen.
At the time of the brain scans, researchers conducted cognitive tests to assess working memory, executive function, and fluency (the ease with which the brain processes information).
Healthy Eating and Slimmer Waists Tied to Better Brain Health
Jensen and her team found that higher diet quality in midlife and into older age was associated with better structural and functional connectivity of the hippocampus and better white matter integrity.
The research also tied lower waist-to-hip ratio in midlife to better performance on cognitive tests later in life. Conversely, a higher waist-to-hip ratio in midlife was linked with poorer working memory and poorer executive function.
Yuko Hara, PhD, director of aging and Alzheimer’s prevention at the Alzheimer’s Drug Discovery Foundation, notes that these results correspond with numerous studies in the past showing that better diets are associated with better brain health and function.
“Also, obesity in midlife is one of the 14 lifestyle risk factors for dementia reported by the 2024 Lancet Commission on Dementia Prevention, Intervention, and Care,” says Dr. Hara, who was not involved in the study. That means reducing fat around the waist can be vital in potentially cutting the risk of cognitive decline.
Exercise Can Also Help Cut Belly Fat and Boost Brain Health
Beyond sticking to healthy eating habits, people seeking to lose harmful abdominal fat will find that exercise is also key.
“By increasing physical activity, you can lose visceral [belly] fat and gain muscle mass, increasing your metabolism,” Hara says.
Hara recommends following World Health Organization guidelines regarding exercise: Adults should get 150 to 300 minutes of moderate intensity aerobic physical activity (or 75 to 150 minutes of vigorous-intensity aerobic exercise) per week, with two or more days of muscle-strengthening activities (such as weight lifting, push-ups, squats, or climbing stairs).
“By focusing on modifiable lifestyle factors, individuals can take proactive steps to enhance their cognitive resilience and overall well-being, ultimately contributing to a healthier aging process,” says Jensen.
EDITORIAL SOURCES
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Resources
Sui SX et al. Obesity and Brain Function: The Brain–Body Crosstalk. Medicina. September 24, 2020.
Williamson L. Obesity Harms Brain Health Throughout Life – Yet Scientists Don't Know Why. American Heart Association. January 12, 2022.
Jensen D et al. Association of Diet and Waist-to-Hip Ratio With Brain Connectivity and Memory in Aging . JAMA Open Network. March 12, 2025.
Risk Reduction of Cognitive Decline and Dementia: WHO Guidelines. World Health Organization. January 1, 2019.
Harris E. Study: Waist-to-Hip Ratio Might Predict Mortality Better Than BMI Author: Harris, Emily. JAMA. October 24, 2023.
Tom Gavin joined Everyday Health as copy chief in 2022 after a lengthy stint as a freelance copy editor. He has a bachelor's degree in psychology from College of the Holy Cross.
Prior to working for Everyday Health, he wrote, edited, copyedited, and fact-checked for books, magazines, and digital content covering a range of topics, including women's health, lifestyle, recipes, restaurant reviews, travel, and more. His clients have included Frommer's, Time-Life, and Google, among others.
He lives in Brooklyn, New York, where he likes to spend his time making music, fixing too-old electronics, and having fun with his family and the dog who has taken up residence in their home.
Don Rauf has been a freelance health writer for over 12 years and his writing has been featured in HealthDay, CBS News, WebMD, U.S. News & World Report, Mental Floss, United Press International (UPI), Health, and MedicineNet. He was previously a reporter for DailyRx.com where he covered stories related to cardiology, diabetes, lung cancer, prostate cancer, erectile dysfunction, menopause, and allergies. He has interviewed doctors and pharmaceutical representatives in the U.S. and abroad.
He is a prolific writer and has written more than 50 books, including Lost America: Vanished Civilizations, Abandoned Towns, and Roadside Attractions. Rauf lives in Seattle, Washington.
