How Being Fat Makes You Stupid

Packing on the pounds isn’t just bad for your body—it’s bad for your brain. According to researchers at Carnegie Mellon University, the brains of obese people work harder than those of normal weight people to achieve the same results.

Researchers quizzed 29 people who were having fMRIs and noticed a trend: The connections between the brain parts responsible for memory and decision-making were hyperactive in overweight people, but functioned normally in average weight people, says study author Timothy Verstynen, Ph.D., a professor at Carnegie Mellon University.

That’s because high blood pressure and inflammation—which go hand-in-hand with obesity—irritate your brain’s communication systems, making it harder for messages to come through, says Verstynen. It’s like your brain is trying to make a call when the phone lines are down.

And it’s a vicious cycle: The damage is particularly bad in areas responsible for controlling impulsive behaviors, like skipping dessert, says Verstynen. So your brain is making you fat (giving into the dessert), and then being fat is changing your brain, he adds.

Here are three more ways that being fat—and eating fatty food—messes with your brain. (Get rid of your gut for good with Speed Shred, the all-new workout DVD series from Men's Health!)

1. It makes you less manly.
Say goodbye to your T levels if you’re obese. A 2012 study in the journal Clinical Endocrinology found that testosterone levels in obese teenagers were 40 to 50 percent lower than those of healthy guys the same age. That’s because fat cells can convert testosterone into estrogen and interfere with how your brain calls the production of more testosterone. And low levels of the hormone can do everything from quash your sex life by lowering your libido to weakening your muscles. (Want to boost your levels? Pick up Testosterone Transformation to build muscle, boost sexual vitality, and reclaim your mental edge!)

2. It gives you the blues.
A 2010 study of 58,000 people found that obesity increases your risk of depression by 55 percent. Blame both physiology and psychology: Obesity causes inflammation, which research has shown can cause depression by damaging the brain’s circuitry. And the not-so-secret culprit? Fast food. According to a 2012 report in Public Health Nutrition, the top 25 percent of fast food eaters are more than 50 percent likely to suffer from depression.

3. It causes dementia.
Being obese in your middle age means you could be four times as likely to develop dementia when you’re older, according to a 2011 study in the journal Neurology. Researchers tracked the weight of 6,500 people over the age of 65 and found a link between those who were obese and those who had dementia. It’s believed that obesity-induced inflammation could actually kill part of your brain’s circuitry that's needed for memory.

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