Is There a Link Between Obesity and Brain Function?

Being obese comes with a long list of health risk factors that include diabetes, hypertension, heart disease, Alzheimer's disease, lung disease and 13 types of cancer. For decades, these effects have been well known. Lately, researchers have discovered a new link between obesity and brain function.

Because Oklahoma is on track to become the nation's most obese state by 2030, according to projections by the New England Journal of Medicine, this blog will go into more detail about the effects obesity has on brain function.

The science behind weight gain

Weight gain is straightforward – you consume more calories than you burn. Each day, your body burns a baseline amount of calories by performing routine tasks such as breathing and digesting food. The remaining calories are typically burned by basic movements and physical activity. People who either eat too many calories or don’t exercise enough take in more calories than they burn.

The food you eat contains nutrients in the form of carbohydrates, proteins and fats. Once it reaches the gastrointestinal tract, your body then digests and processes the food for immediate and long-term use. Eating a high-fat, high-calorie diet causes the body to store extra sugars – carbohydrates are broken down into blood sugar – and fats in your liver and muscle tissue. Over time, you gain weight.

Effects of obesity on the brain

Over the years, a variety of research studies on both small and large groups of children and adults. Studies have found obesity impacts brain volume, executive function skills, cognitive development and can lead to a higher risk of dementia and Alzheimer’s disease.

Lower brain volume

As you age, brain volume naturally decreases. But now there is a link between obesity and brain volume as part of neurodegeneration. In 2010, the Boston University School of Medicine sampled 733 adults and found body mass index (BMI) and total brain volume were inversely related. In other words, people with more body fat had lower brain volume. 

Another study published in the Neurobiology of Aging compared brain scans of 500 adults. The research found white matter – a network of nerve fibers deep in your brain – to be lower in overweight or obese people. In fact, being obese increased brain age by 10 years.

Further, a study of 2,170 young- to middle-aged adults who were obese had lower total cerebral brain volume compared to the non-obese group, according to the Journal of the American Heart Association.

Why is this significant? Your brain uses neurons and neurotransmitters to communicate with various parts of the body to complete everyday tasks. As brain volume and these chemical messengers decrease, you’re more likely to have problems with tasks such as thinking and memory.

Obesity and executive function

Executive function skills are high-level cognitive skills used in thinking, memory recall, self control and planning of tasks – all areas needed to complete tasks each day. Executive function skills are controlled by the brain’s frontal lobe.

Data from a study published in the International Journal of Obesity detailed the negative link between obesity and neurocognitive functioning, such as executive functioning, attention, visuospatial skills and motor skills.

These obesity-related deficits in executive function have shown up as early as childhood. A study analyzed the brain scans of more than 3,000 American children between the ages of 9 and 10 and found lower cortical thickness in children who were obese. In total, 18 cortical regions had lower volume, and the prefrontal cortex was most affected.

Obesity and Alzheimer’s disease

The flow of blood to and from organs is known as the cardiovascular system, which helps deliver nutrients and oxygen to your cells.

As with any other organ, the brain relies on blood to carry out many tasks. Obesity can cause arteries to narrow, restricting blood flow to the brain and causing cells to die – two factors that increase the risk of Alzheimer’s disease. 

A study published in the Journal of Alzheimer’s Disease analyzed brain scans of 17,721 people to track how blood flowed to 128 regions of the brain. Researchers discovered people with a higher BMI had less blood flow to the temporal lobes, the parietal lobes, the hippocampus, the posterior cingulate and the precuneus – all areas of the brain prone to developing Alzheimer’s disease.

Poor eating behaviors

More than one in five (22 percent) of young people ages 2 to 19 are obese, according to the State of Childhood Obesity. 

Becoming obese as a child can create a vicious cycle when it comes to eating behaviors. The International Journal of Obesity found obese children had a more difficult time saying no to foods compared to healthy children. This lack of inhibitory control can lead to overeating, which fuels excess fat storage and causes more weight gain.

Even if obesity doesn’t develop until later in adulthood, you can still experience poor eating habits as a result of changes to your brain. A study published in the Journal of Neuroscience discovered the brain’s striatum was less active in women who gained weight. The striatum, found in the subcortical basal ganglia of the forebrain, plays a critical role in reward perception when eating. When you eat, the amount of pleasure you receive comes from dopamine released. People who are obese have a lower signaling capacity, meaning they need to eat more food to feel the same reward.

Cognitive effects of obesity

A small study of 60 people ages 18 to 35 revealed higher BMIs were linked with structural and functional neural changes that led to memory deficits – both the ability to form or retrieve memories. Other research points to a correlation between obesity and verbal learning – delayed recall and recognition of words.

Another study of 138 severely obese individuals found waist circumference – due to excess fat in the abdomen – was significantly associated with a decrease in cognitive function.

Why does this happen?

While the research indicates a negative relationship between obesity and brain function, it is less clear why this occurs.

Anecdotally, obesity is tied to many diseases that can affect the brain, such as diabetes, high blood pressure and high cholesterol. For example, chronic high cholesterol leads to the development of fatty deposits in blood vessels. Typically, blood flows through arteries free of any obstacles or interference. However, the fatty deposits make it harder for blood to flow to your brain. Plus, the deposits can also form a clot that restricts flow altogether, causing a stroke and subsequent brain damage.

In fact, one large study identified a relationship between high BMI and decreased blood flow to the brain, according to the Journal of Alzheimer’s Disease. Researchers analyzed 35,442 brain scans across 17,721 adults and saw decreased cerebral perfusion pressure, also called blood flow to the brain, especially to the hippocampus. 

In addition to blood flow, there is also a belief that people who eat a diet high in fat and sugars are more prone to having a weaker blood-brain barrier in certain areas such as the hippocampus. The hippocampus is found in the temporal lobe and plays an important role in learning and memory formation. Damage to the hippocampus can lead to a variety of neurological disorders.

What you can do to prevent obesity-related changes

Currently, there are more than 1 million obese adults in Oklahoma, and 32 percent of children ages 10 to 17 are either overweight or obese. However, it’s never too late to make changes that can impact you or your child’s health in a positive way. 

A few simple changes are needed, and they start with diet and exercise.

Diet: Calories in and calories burned play a critical role in weight gain. How many calories you or your child should consume depends on age, gender and lifestyle. For example, the U.S. Food and Drug Administration recommends active two-year-olds consume 1,000 calories per day. A sedentary 20-year-old male should consume about 2,400 calories per day, while an active 20-year-old male should consume about 3,000 calories per day. For context, sedentary in this case means no physical activity, and active means walking – or another similar activity – three miles per day. You can find a full chart of estimated caloric needs here.

All calories aren’t the same, though, in terms of nutritional value. Choose whole fruits and vegetables, whole grains and lean meat. Stay away from packaged foods, processed meats and foods high in added sugars. Healthy carbs are your friend.

Exercise: Movement is key, especially for children. For children in preschool, aim for three hours of activity a day and try to limit screen time. Children and adolescents (ages 6 to 17) should have 60 minutes of activity each day. Once you reach adulthood, you should incorporate 150 minutes of activity each week. As a guide, try to break this down over the course of seven days (about 20 minutes per day). Exercise doesn’t always have to mean strenuous activity. It can be a brisk walk or playing a sport.

If you or a loved one are struggling with losing excess weight, don't hesitate to contact the INTEGRIS Health Weight Loss Center at INTEGRIS Health Baptist Medical Center. We also offer online weight loss seminars to get you started on your weight loss journey.