What does your brain want you to eat?
Everyone talks about the effect of diet on the body, but we often overlook how food choices impact our brain function. This is surprising, considering a large chunk of the calories we eat are used by the brain; in fact, the brain uses around 20% of the calories we consume, despite being only 2% of our body weight.
Research suggests that diets high in fat and sugar can impair cognition, our ability to think and make decisions, and impact memory. This may be even more of a threat when the brain is still developing in childhood and early teen years, a time when people tend to consume the most food high in fats and sugars.
In a new study from Western University, researchers show that diets high in fats and sugars impact brain cells differently based on the age at consumption. The study, published in March 2021 in the journal Scientific Reports, was led by Research Fellow Dr. Amy Reichelt and two trainees, Claire Lemieux and Oren Princz-Lebel, in the Translational Cognitive Neuroscience Lab at Western.
Dr. Reichelt fed adolescent and adult mice one of two diets for five weeks straight. The first diet was a standard mouse food that has a normal level of fat and sugar content. The second was a diet high in saturated fat and refined sugars – termed high fat high sugar (HFHS) – and is representative of the typical “Western diet”that is associated with obesity and diabetes. As expected, mice that ate the HFHS diet weighed around 6 grams more than the mice eating the standard diet at the end of the five weeks. Six grams may not sound like much but would be the equivalent of gaining 24 lbs to a 150 lb human.
Next, the researchers wanted to see how this HFHS diet affected the brain. Specifically, they looked at brain areas that are critical for cognition and memory, and have previously been shown to be impacted by unhealthy diets. These areas were the prefrontal cortex, which helps control our attention and the process through which we think and make decisions, and the hippocampus, which plays a major role in learning and memory.
To locate specific brain cells within these regions, the authors used a technique called immunohistochemistry. Immunohistochemistry can be thought of as a way to mark or tag specific cells based on their identity. This allows the researchers to count all the cells of a particular type and compare them between different conditions.
In the study, the researchers specifically looked at brain areas that have previously been shown to be impacted by diet. These areas were the prefrontal cortex, which controls our attention and the process through which we think and make decisions, and the hippocampus, which plays a major role in learning and memory.
The authors used a technique called immunohistochemistry to locate specific cells. Immunohistochemistry can be thought of as a way to mark or tag specific cells based on their identity. This allows the researchers to count all the cells of a particular type and compare them between different conditions.
Dr. Reichelt and colleagues found that HFHS-fed mice had changes to a group of cells in the hippocampus called parvalbumin-expressing cells. These cells are responsible for inhibiting the activity of other hippocampus cells and their loss may lead to dysregulation of the entire brain region. The hippocampus is involved in spatial memory, which is what helps you remember how to get to work from your home. Interestingly, previous research has shown spatial memory is hindered by obesity, and these cells could be one of the reasons why.
The researchers were also curious whether diet-related brain changes could affect the developing brains of younger animals. It is well known that there are key ages for brain development, called “critical periods”, when the brain prunes away connections that are not needed, which in turn enhances communication efficiency between brain areas. This “pruning” is carried out by a group of immune system-related brain cells called microglia, which are crucial for healthy brain development. Microglia have another role to clean and get rid of any potential threats (e.g., viruses, bacteria) in the brain.
Interestingly, the researchers found more activated microglia in the brains of younger mice, but not older mice, that were fed the HFHS diet compared to the standard diet. While this may mean that the microglia of younger mice are protecting the brain from the effects of HFHS diets, it could have long term effects on brain development. Microglia should be busy during this time window, pruning brain connections that aren’t needed to make the brain more efficient. However, if microglia are activated and responding to diet-related immune threats, they may be distracted from their main role of pruning which could interfere with healthy brain development. More research is required to determine the long-term effects of these findings.
In humans and mice, adolescence is a key time period where the brain is changing and developing in response to the environment. This study suggests that HFHS diets can not only alter memory-related brain cells, but may also cause overactivation of the brain’s immune cells. This in turn, can change the trajectory of brain development, highlighting the importance of a balanced diet during this key time period.