You avoid that fast-food dinner because it could ruin your workout or mess with your training, but have you ever considered what it could do elsewhere in your body—perhaps in your brain? Your brain uses between 20 and 25 percent of the calories you eat each day, and if you spend every meal chowing down on junk food, well, your noggin could suffer. Here are five ways junk food could mess with your brain.
It Could Make You Lazy
In a 2014 study out of the University of California, Los Angeles, researchers placed 32 female rats on one of two diets for six months—one comprised of things like corn and fish meal (relatively unprocessed foods), and the other of foods significantly more processed and higher in sugar. The second group was meant to mimic a junk food diet. Not surprisingly, after three months, the rats on junk food were carrying significantly more fat than the rats on the unprocessed diet.
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As part of the study, the researchers had the rats press a lever to receive food or water. The lean rats completed the task nearly twice as fast as the overweight rats.
After six months, the researchers switched the rats' diets for nine days—the overweight rats ate the whole foods, and the lean rats ate the processed foods. At the end of the nine days, both groups again attempted the lever task. The change in diet did not affect the overweight rats competence with the lever task.
"Either the highly processed diet causes fatigue or the diet causes obesity, which causes fatigue," said Aaron Blaisdell, a professor of psychology in the UCLA College of Letters and Science, in a release.
It Could Mess With Your Memory
If you start eating it as an adolescent, that is. Research out of the University of San Pablo in 2013 showed that mice fed a normal-calorie, high-fat diet during their adolescent years displayed impaired spatial memory as adults. In the study, researchers compared the aforementioned group of mice with another group of adolescent mice, who were fed a more conventional diet. The high-fat mice consumed 45 percent of their calories from saturated fats.
A similar high-fat diet was assigned to mature mice to compare the effects of a high-fat diet during adulthood.
After eight weeks, the researchers tested the memory of the mice by placing them in an open-but-walled box, with one familiar object and one unfamiliar object. The mice explored the box for 10 minutes then returned one object. The adolescent mice on the high-fat diet took significantly longer to find the unknown object compared to the adolescent mice fed a conventional diet.
The high-fat mice did not demonstrate an improvement in memory when switched to a conventional diet, indicating that a high fat diet in adolescence could have long lasting effects.
Additionally, the researchers noted the mice with memory issues had changes in the structure of the neurons in the area of the brain associated with memory. The researchers surmise that the brain is at higher risk during adolescence due to all the hormonal changes taking place.
It Could Lower Your IQ
A 2012 study out of Goldsmith's University of London found children who ate more fast food during their youth had lower IQ's than their peers who chowed down on fresh cooked stuff. The researchers followed approximately 4,000 Scottish children from age 3 to age 5. Children who grew up with a higher socioeconomic standing were more often fed slow-cooked foods with fresh ingredients, which improved their cognitive ability. Children who grew up in a lower socioeconomic circle tended to eat more fast foods, which lowered their intelligence.
"It's common sense that the type of food we eat will affect brain development, but previous research has only looked at the effects of specific food groups on children's IQ rather than at generic types of meals," said Sophie von Strumm, PhD, one of the researchers, in this release. "This research will go some way to providing hard evidence to support the various high-profile campaigns aimed at reducing the amount of fast food consumed by children in the UK."
It Could Inflame Your Brain
Research presented at the Endocrine Society's 93rdannual meeting in 2011 suggested that a typical American diet could lead to inflammation in the brain. In the study, researchers fed groups of between six and 10 mice and rats high-fat diets for periods between one day and eight months. They then "performed detailed biochemical, imaging and cell sorting analyses on the animals' brains," according to this release.
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Rats and mice both gained weight during the course of the study, and the animals also developed an inflammation in the part of the brain that contains the neurons that control body weight. At the same time, scavenger cells, called microglia, and support cells, called glia, accumulated in the same area. Both of these inflammatory responses (called gliosis) subsided after a few days, but they re-emerged four weeks later.
"Gliosis is thought to be the brain equivalent of wound healing. It is typically seen in conditions of neuronal injury, such as stroke and multiple sclerosis," said presenting author Joshua Thaler, MS, PhD, in a statement. "We speculate that the early gliosis that we saw may be a protective response that fails over time."
It Could Become Addictive
Like, legitimately: 2010 research out of the Scripps Research Institute and published in the journal Nature Neuroscience suggests the molecular mechanisms that push people toward drug addiction also cause them to overeat junk food. In the study, researchers offered rats either standard rat feed or high calorie foods like bacon, cake, chocolate and sausage. Not surprisingly, the rats preferred the unhealthy options to the healthy ones.
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"The body adapts remarkably well to change—and that's the problem," said Paul J. Kenny, PhD, in a release. "When the animal over stimulates its brain pleasure centers with highly palatable food, the systems adapt by decreasing their activity. However, now the animal requires constant stimulation from palatable food to avoid entering a persistent state of negative reward."
Basically, what he's saying is the more junk food you eat, the more you need to eat to elicit those same pleasurable feelings.
Even more surprising was the fact that, when the researchers associated a painful shock with a light signal, the obese rats (the ones who had been eating junk food) simply ignored the pain and kept gorging, while the leaner rats avoided the junk food.
"These findings confirm what we and many others have suspected," Kenny said in a statement, "that overconsumption of highly pleasurable food triggers addiction-like neuroadaptive responses in brain reward circuitries, driving the development of compulsive eating. Common mechanisms may therefore underlie obesity and drug addiction."