Eating an Unhealthy, High Fat, High Carb Diet Is Also Very Bad for the Brain, Scientists Say

Eating an unhealthy, high carb and high fat diet does not only impact physical health—it also changes the part of the brain that controls the metabolism, a study in mice has revealed.

Scientists at Yale were able to prevent mice from gaining weight by deleting a special protein in cells found in the brain.

The central nervous system helps to regulate how the body metabolises energy and glucose by picking up and reacting to changes in the body—such as the lows and highs of hormones like insulin. The brain plays an important role in the process by helping us to know when and how much to eat, and by guiding the response of our metabolism.

Recently, scientists found that other cells in the central nervous system help neurons in this process. Glial cells—which make up more than half of the central nervous system and surround and support neurons—are now thought to be vital in processes linked to body weight and obesity.

To find out more about how diet affects the brain, researchers gave rodents diets high in fat and carbohydrates, while others were fed their regular mouse chow to act as a control.

Research has previously linked a high fat diet to inflammation of the hypothalamus—a part of the brain partly in charge of the metabolism—in mice after three days. This diet is thought to activate a type of glial called microglial cells, which clear away damaged neurons and infections in the central nervous system, as well as regulating inflammation.

In their paper published in the journal Cell Metabolism, the authors showed the high fat diet seemed to trigger changes in cell powerhouses—or mitochondria—of microglial cells, causing them to spring into action.

They believe a protein known as Uncoupling Protein 2 (UCP2), which helps the mitochondria decide how to use energy, shrunk the powerhouses in these cells. This, in turn, changed how the hypothalamus maintained a balance of energy and glucose in the body.

The effect of the microglia springing into action was that neurons received an inflammatory signal, leading the animals to eat more food. The animals became obese.

Building on this finding, the team was able to prevent weight gain in mice on the high fat diet by removing the UCP2 protein from the microglia. This appeared to prevent the changes in the mitochondria, and therefore stop the microglia from activating and making the hypothalamus inflamed. This made them eat less, and expend more energy.

They were able to show that the way UCP2 changes the mitochondria, and in turn how the microglial cells help to trigger inflammatory signals, could play a "pivotal role" in hypothalamic inflammation and metabolic problems.

Study leader Sabrina Diano, from Yale School of Medicine has been studying the role of the brain in regulating food intake, body weight and metabolism for almost 25 years. She told Newsweek her team was "intrigued by the fact that exposure to food rich in fats and carbohydrates induces a fast inflammatory response in the brain way before changes in body weight occur. It was unclear, however, what the mechanism was underlying this inflammatory response and its role in the development of obesity."

She explained: "When we think of the brain, we always think first of neurons. However, glial cells outnumber neurons. Here we show the important role of a specific subgroup of glial cells (called microglia) in sensing changes in nutrients and altering neurons that control metabolism."

Diano said in a statement: "There are specific brain mechanisms that get activated when we expose ourselves to specific type of foods. This is a mechanism that may be important from an evolutionary point of view. However, when food rich in fat and carbs is constantly available it is detrimental."

Next, more studies are needed to understand if the findings in rodents are applicable to humans, she said.

This article has been updated with comment from Sabrina Diano.

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Researchers have investigated how high-fat food, like the burger shown in this stock image, may affect the brains of mice. Getty