What just a week of junk food can do to your brain

Indulging in a Western-style diet for 7 days impaired the brain function in healthy young people and made them want to overeat, researchers find.

Hot on the heels of research concluding that a Mediterranean diet does wonders for the gut microbiome, a new study looks into what a Western-style diet does to the brain ... and it isn't exactly surprising and it certainly isn't pretty.

The researchers found that after a week of adding high-fat and high-added-sugar foods to previously healthy diets, volunteers' memory and learning performance declined, as did their resistance to junk food.

“After a week on a western-style diet, palatable food such as snacks and chocolate becomes more desirable when you are full,” said professor of psychology at Macquarie University, Richard Stevenson, as per The Guardian. “This will make it harder to resist, leading you to eat more, which in turn generates more damage to the hippocampus and a vicious cycle of overeating.”

The Western-style diet is one that is abundant in highly processed and refined foods – with a lot of added sugar, sodium, and unhealthy fats. I refer to it as "junk food" in the title because both are characterized by calorie-rich foods lacking in nutrient density. As The Guardian points out, the Western diet has been identified as "a major contributor to the development of obesity-related diseases including type 2 diabetes, high blood pressure, and cardiovascular disease. The Western-style diet has also been associated with an increased incidence of chronic kidney disease."

For the study, the researchers recruited 110 college students who were "lean, healthy and currently consuming a nutritious diet." Half were put in a control group, half were put on a Western diet.

For those on the Western diet, on the first and last day they had a breakfast of a toasted sandwich and a milkshake in the lab, high in saturated fat and added sugar. On the days in between, they were instructed to eat two Belgian waffles for breakfast or dessert on four of the days, and to eat a main meal and drink/dessert from a set of options from a popular fast-food chain on the other days. Aside from those instructions, they were asked to otherwise maintain their normal diet.

The control group also had breakfast in the lab on the first and last day; theirs was also a toasted sandwich and milkshake, but low in saturated fat and added sugar.

Before and after these breakfasts, the participants took word memory tests and also did a "wanting and liking" test to score a range of high-sugar foods, like Coco Pops and Froot Loops. After a lot of testing and analyses, they found that,

One week's exposure to a WS-diet [Western-style diet] caused a measurable weakening of appetitive control, as measured by the two key ratings on the wanting and liking test.

In addition, the authors write,

We also found that a WS-diet induced a decline in HDLM performance in the WS-diet group.

HDLM is the measurement of hippocampal-dependent learning and memory.

“The more desirable people find the palatable food when full, following the western-style diet, the more impaired they were on the test of hippocampal function,” Stevenson said.

Thankfully, the difference were no longer significant when tested again three weeks after the study. "However," write the authors, "it is unclear whether this reflects a deterioration in performance in the controls or recovery in the WS-diet group."

Nonetheless, the authors conclude that that a Western diet causes "neurocognitive impairments" following short-term exposure. And meanwhile, we know that in the long term, this kind of eating leads to obesity, diabetes, and other conditions of poor health. That the short-term effect leads to increased desire to eat more, it's easy to see how a short-term cycle could lead to long-term habits.

“Demonstrating that processed foods can lead to subtle cognitive impairments that affect appetite and serve to promote overeating in otherwise healthy young people should be a worrying finding for everyone,” Stevenson said, adding that he believes that eventually governments will come under pressure to better regulate processed food. Holding Big Junk Food accountable is something that TreeHugger has been talking about for years – and something that sadly seems to be going in the opposite direction under the current (Western-diet-loving) administration.

“The new thinking here is the realisation that a western-style diet may be generating initial and fairly subtle cognitive impairments, that undermine the control of appetite which gradually opens the way for all of these other effects down the track,” Stevenson said.

The study, "Hippocampal-dependent appetitive control is impaired by experimental exposure to a Western-style diet," was published in Royal Society Open Science.