Obesity rates have tripled worldwide since 1975, and as of 2016, 39% of adults were overweight while 13% were obese.1 Associated health risks like heart disease and diabetes are well known, but many aren't aware that your brain may also be affected by obesity.
Rates of neurodegenerative disorders, including dementia, are also on the rise, with an estimated 115 million people expected to be living with dementia by 2050.2 It's possible that rising rates of obesity may be one driving force behind this growing burden — and one that's largely preventable at that.
Obesity May Shrink Your Brain
Research published in Radiology found that obesity may lead to alterations in brain structure, shrinking certain regions.3 Among men, higher total body fat percentage was linked to lower brain gray matter volume. Specifically, 5.5% greater total body fat percentage was associated with 3,162 mm3 lower gray matter volume.4
Gray matter is the outer layer of the brain associated with high-level brain functions such as problem-solving, language, memory, personality, planning and judgment. Among men, 5.5% greater total body fat was also associated with 27 mm3 smaller globus pallidus volume, an association also seen in women.
In women, 6.6% greater total body fat percentage was associated with 11.2 mm3 smaller globus pallidus volume. The globus pallidus is a brain region that plays a role in supporting a range of functions, including motivation, cognition, and action.5 Obesity was also associated with changes in white matter microstructure, which may be related to cognitive function.6
The researchers also noted, “[W]e showed that sex differences are manifest regarding negative associations of total body fat (TBF) percentage with regional subcortical gray matter volumes, including the globus pallidus and caudate nucleus, which have been associated with the reward circuitry of food-related stimuli.”7
Past research has also shown that people who are obese have higher concentrations of amyloid beta plaque in the brain, which is associated with Alzheimer's disease, compared to non-obese people.
In post-mortem studies, “Alzheimer-type neuropathological changes were frequent in our small sample of morbidly obese elderly individuals without a clinical history of cognitive impairment, approaching those seen in Alzheimer disease for some patients.”8
Belly Fat Also Linked to Brain Shrinkage
Excess body fat has been linked to brain changes for decades. In 2010, researchers found visceral (abdominal) fat is associated with lower brain volume, even among healthy middle-aged adults.9
In a separate study of more than 9,600 participants with an average age of 55, who received scores for both body mass index (BMI), a flawed formula that divides your weight by the square of your height, and waist-to-hip ratio (WHR), a connection was also found.
The participants received structural MRI, which provided brain images, allowing researchers to measure the volume of gray and white matter in the brain. After accounting for other risk factors, such as smoking and exercise levels, the researchers found a slight link between BMI and lower gray matter volume.
However, a much more significant connection was found for people with both high BMI and WHR. “The combination of overall obesity and central obesity was associated with the lowest gray matter compared with that in lean adults,” the researchers noted.10
Participants with a BMI and WHR in a healthy range had an average gray matter brain volume of 798 cubic centimeters. This dropped to 786 cubic centimeters among those with a high BMI and high WHR.11
How Does Obesity Harm Your Brain?
Obesity is associated with inflammation, and inflammation may increase your risk of dementia. Further, higher levels of inflammatory markers have also been associated with lower brain volume, including “greater atrophy than expected for age.”12
The authors of the Radiology study believed total body fat may be negatively associated with brain volume and microstructural integrity due to underlying systemic inflammation. “This has been supported by previous findings from the Framingham Heart study, which showed that several inflammatory biomarkers linked to obesity have also been associated with lower brain volume,” they said.13,14
Insulin resistance, a hallmark of obesity, is also thought to be involved in both cognitive impairment and Alzheimer's disease. Both diabetes and higher fasting glucose levels are linked with lower total brain volume,15 and even mild elevation of blood sugar is associated with an elevated risk for dementia.16
Writing in the New England Journal of Medicine (NEJM), researchers explained, “Higher glucose levels may contribute to an increased risk of dementia through several potential mechanisms, including acute and chronic hyperglycemia and insulin resistance and increased microvascular disease of the central nervous system.”17
Another one of the dangers of excess body fat, particularly visceral fat, is related to the release of proteins and hormones that can cause inflammation, which in turn can damage arteries and enter your liver, affecting how your body breaks down sugars and fats.
According to a study in the Annals of Neurology, “[A]dipose-tissue derived hormones, such as adiponectin, leptin, resistin or ghrelin, could also play a role in the relation between adipose tissue and brain atrophy.”18 Further, obesity may also be associated with lower volume in brain regions that regulate food-reward circuitry,19 possibly influencing overeating.
Are Your Neurons Making You Overeat?
Several other intriguing links also exist between your brain, your body fat levels and your inclination to overeat. The prefrontal cortex (PFC), a region of your brain involved in complex thinking and self-control, is less active in those who overeat, whereas activation in the prefrontal cortex is associated with weight loss success.20 In a Trends in Cognitive Sciences Review, researchers explained:21
“In the modern environment, dietary self-regulation is especially dependent on the capacity of the PFC to exert modulatory control over food choices. Weaker modulation increases the likelihood that individuals will overconsume appetitive calorie-dense foods.
Over time, the persistent and sustained overconsumption of calorie-dense foods can lead to weight gain and, subsequently, obesity. Diet-evoked obesity can lead to marked and enduring changes in cognitive control and PFC functionality, which, in turn, drives the maintenance of unhealthy eating behaviors.”
Researchers at The Rockefeller University in New York City have also identified a group of neurons that reduce food intake when activated. The hippocampal dopamine 2 receptor (hD2R) neurons are activated by food cues and influence food-place associations.
However, hD2R neurons connect with the entorhinal cortex (LEC) and the septal area (SA), and the resulting circuit decreases food intake in mice. “Altogether these data describe a previously unidentified LEC > hippocampus > septal higher-order circuit that regulates feeding behavior,” the study found, highlighting the many ways that your brain plays an intricate role in your eating behavior and weight.22
“These cells keep an animal from overeating,” study author Estefania P. Azevedo, a researcher in the Laboratory of Molecular Genetics, said in a news release. “They appear to make eating less rewarding and, in that sense, are tuning the animal's relationship to food.”23
Being Obese May Age Your Brain Faster, but a Ketogenic Diet May Slow Aging
A study published in the journal Neurobiology of Aging also found structural changes in the brains of overweight and obese people — changes typically seen in far older individuals. In this case, it was white matter volume that decreased in relation to obesity, corresponding to an estimated increase of brain age of 10 years.24
It's increasingly clear that obesity appears to increase the risk of neurodegeneration, not only via inflammation but also by increasing oxidative stress. On the other hand, caloric restriction or fasting may help to protect your brain and slow aging, as may a ketogenic diet.
A ketogenic diet is high in healthy fats and low in net carbohydrates (total carbs minus fiber), prompting your body to start burning fat as its primary fuel, rather than sugar. This produces ketones, which not only burn efficiently but are also a superior fuel for your brain. Ketones also generate fewer reactive oxygen species (ROS) and less free-radical damage.
Recent papers have also demonstrated the benefits of nutritional ketosis for brain health. In one, researchers found a ketogenic diet improved neurovascular function, in part by improving your gut microbiome.25
In the second paper, the authors concluded a ketogenic diet acted as a veritable “fountain of youth” in their animal study by significantly improving neurovascular and metabolic functions, compared to the animals eating an unrestricted diet.26 Releasing ketones into your bloodstream helps preserve brain function and protects against cognitive impairment and other neurodegenerative diseases.27
KetoFasting, the program I developed and detail in my latest book, “KetoFast: A Step-By-Step Guide to Timing Your Ketogenic Meals,” combines a cyclical ketogenic diet and intermittent fasting with cyclical partial fasting to optimize health and longevity. Not only can KetoFasting help you to lose weight, but your cognition typically improves thanks to the biological cleansing and regeneration that occurs throughout your body, including your brain.
Tips for Avoiding Obesity and Boosting Your Brain
Eating a ketogenic diet helps protect your brain from free radical damage and supplies the cells with preferred fuel while also helping you to lose weight and avoid obesity. Also important is proper sleep.
Sleep problems like insomnia can have a distinct impact on your brain over time, causing it to shrink more rapidly compared to those who sleep well.28 Meanwhile, sleeping for less than five hours a night is linked to an increased rate of abdominal fat gain over five years.29 If you're not sleeping well, here are tips for a sound night's sleep.
Having elevated blood levels of the stress hormone cortisol can impair your thinking skills and memory over time.30 Previous research has also linked chronic stress with working memory impairment and an increased risk for early onset of Alzheimer's disease.31
Chronic stress may also increase your risk for visceral fat gain over time,32 which means addressing your stress levels is imperative for both your brain and maintaining your ideal weight. As the Radiology researchers explained:33
“More research is needed to assess changes in brain architecture in obesity over time, and metabolic influences such as insulin resistance and metabolic responses to fasting and exercise, and eating and resting conditions.
Further research is needed to investigate to what extent a greater amount of visceral adipose tissue (by a low grade systemic metabolic inflammation) leads to detrimental effects on brain structure and cognitive functioning above and beyond measures of general obesity.”
However, making positive lifestyle changes, including eating a ketogenic diet, getting proper sleep and addressing your stress, has no downsides and can only help you to achieve an ideal weight while supporting the health of your brain.