Updated 16 September 2014

Does obesity affect the brain?

Health problems associated with overweight and obesity are well known – and there might be even more bad news: Being overweight could affect your intelligence!


Although it is well known that being overweight or obese increases our risk for a large number of diseases and conditions, the effect that carrying extra weight might have on our cognitive abilities has received much less attention.

Until very recently in human history, life was a struggle for survival. Most of our forefathers died from exposure, attacks by wild animals, disease and hunger long before they had to face the ravages of old age.

In the last few millennia, life has become a lot more secure for the majority of people on earth, and especially hunger and starvation have become the exception rather than the rule.

In fact, in the twenty-first century more deaths are linked to overweight than underweight, and nowadays most of us have access to more food than we need.

Let’s look at the facts

According to the World Health Organisation, worldwide obesity has nearly doubled since 1980. In that year, 35% of adults, 20 and older, were overweight, and 11% obese. In 2012, more than 40 million children under the age of 5 were overweight or obese.

Read: Why kids get overweight

Overweight and obesity, which were previously considered a problem mainly in wealthy countries, are rising at an alarming rate in low- and middle-income countries, especially in urban environments.

Overweight and obesity are caused when more calories are consumed than expended. All over the world, people are eating more high-fat and energy-dense foods and getting less exercise because of sedentary work and motorised transport. 

Read: Even women who exercise sit too much

Health problems associated with overweight and obesity are well known and include the following:

·         High blood pressure (hypertension)
·         Diabetes
·         Gallbladder disease
·         Certain kinds of cancer
·         Heart disease and stroke
·         Osteoarthritis
·         Gout
·         Asthma
·         Sleep apnoea

And as if this isn’t enough bad news, there may be even more – being overweight may affect your intelligence!

It's all down to bad connections

Gaining weight doesn’t only increase your risk for disease; it may decrease your brainpower!

Researchers have found that obese people’s brains don’t work as efficiently as those who weigh less.

According to Timothy Verstynen, a professor at Carnegie Mellon University in the US, the connections in the sections of the brain responsible for decision-making and memory are hyperactive in overweight people because hypertension (high blood pressure) and inflammation irritate the brain and reduce its efficiency. It’s like having a bad telephone connection.

In 2006, French scientists established a link between obesity and reduced cognitive function. In an article in the journal Neurology, researchers, led by Dr Maxine Cournot of Toulouse University Hospital, speculate that diabetes or cardiovascular disease could explain their findings, but that hormones produced by the fat cells may also affect the brain.

Cournot also found that overweight people could develop a greater risk for dementia as they grow older.

Read: Boost your brainpower    

The brains of obese people are especially bad at controlling impulsive behaviour, which makes it difficult to say no to unhealthy food, causing a vicious circle.

As people gain weight, they may also become less sensitive to the pleasure they derive from sugary and fatty foods – like drug users who need to take more and more of their favourite poison to achieve the same high.

Sugar is the new nicotine 

Lower sex drive

Apart from reducing your brainpower, obesity and fatty food can reduce your quality of life in other ways. It can interfere with your sex life by lowering your testosterone levels, cause depression and increase your chances of developing Alzheimer’s.

Testosterone deficiency

In a study published in Human Brain Mapping, a study led by UCLA Professor of Neurology, Paul Thompson, compared the brains of overweight, obese and normal senior citizens and found that on average the obese test subjects had 8 percent, and the overweight 4 percent less brain tissue, than the control group.

Dr Thompson mentioned that this was the first study to establish a link between overweight and “severe brain degeneration”. “That’s a big loss of tissue, and it depletes your cognitive reserves, putting you at much greater risk of Alzheimer’s and other diseases that attack the brain,” he added.

Read: What is Alzheimer’s disease

Using neuroimaging, Thompson and his team found that the obese and overweight individuals had lost tissue in several areas of the brain. “The brains of obese people looked 16 years older than the brains of those who were lean, and in overweight people, they looked eight years older,” Dr Thompson said.

Going pear shaped

Overweight has also been associated with poor memory. The Journal of the American Geriatric Society reported in a survey of women between 65 and 79 that women who carry excess weight around their hips and are “pear shaped” experienced greater memory loss than those with an “apple shape”.

The doctor who led the study said that fat could impair memory by restricting blood flow to the brain.

Read more:
Memory loss not normal ageing
Obesity and diseases
Smart foods to boost your brain power


The Society of Neuroscience 
US National Library of Medicine
NorthWestern University 

Image: Confused fat man from Shutterstock

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