A recent study using mice has revealed that a diet high in fat and sugar, similar to a typical Western diet, can quickly and significantly reduce blood flow in the brain of adolescent mice. However, the research also found that adding omega-3 fatty acids, like those found in fish oil, to this unhealthy diet could reverse these negative effects and restore normal brain blood flow. These findings suggest that diet during adolescence may have a profound and lasting impact on brain health, and that specific dietary changes could offer a way to protect the brain from the harmful effects of unhealthy eating habits.
The research, which was published in the International Journal of Obesity, was motivated by growing concerns about the increasing rates of childhood and adolescent obesity worldwide. Obesity, often driven by diets rich in unhealthy fats and sugars, is known to harm various organs, including the heart, liver, and pancreas. Scientists have also observed that obesity can affect brain function, including thinking skills and sensory processing.
A key aspect of healthy brain function is the ability to regulate blood flow. When brain cells become more active, they require more energy and oxygen, which is delivered through increased blood flow. This process is called functional hyperemia. Problems with functional hyperemia have been linked to conditions like stroke and dementia. While previous research has examined the effects of obesity on brain blood flow in adults and older individuals, less was known about how a Western diet impacts brain blood flow specifically during adolescence, a critical period of brain development.
“Childhood and adolescent obesity is rising at an alarming rate worldwide. We became curious about how the Western diet, which is high in fat and sucrose, might affect brain function,” explained study author Hirac Gurden, a neuroscientist currently working at French National Centre for Scientific Research and Paris Cité University. “Specifically, we focused on a critical aspect of brain health: vascular supply. To investigate this, we employed a groundbreaking functional ultrasound imaging technique to track cerebral blood flow in adolescent mice on a Western diet.”
“We found that cerebral blood flow rapidly decreases after starting the Western diet and does not recover in adulthood. However, when we altered the fat content by balancing harmful omega-6 fatty acids with protective omega-3 fatty acids (found in fatty fish, soybean oil, and nuts), cerebral blood flow was no longer impaired. In short, we discovered that nutraceutical protection of cerebral blood flow is possible.”
For their study, the researchers used young male mice, around the age of six weeks, which is considered adolescence in mice. They divided the mice into different groups and fed them various diets. One group received a standard, healthy rodent diet. Another group was given a Western diet, which was high in fat and sugar, designed to mimic the unhealthy eating patterns common in Western societies.
To examine the effects of diet over time, the researchers studied these groups of mice at different points: after one week, two weeks, three weeks, two months, and ten months on their respective diets. A separate group of mice was also fed a Western diet supplemented with docosahexaenoic acid, or DHA, an omega-3 fatty acid. This was done to see if balancing the ratio of different types of fats in the Western diet could have a protective effect.
Throughout the study, the researchers performed several measurements on the mice. They regularly monitored the body weight and body composition of the animals, specifically looking at fat and lean mass. To assess metabolic health, they measured fasting blood glucose levels, and conducted glucose tolerance tests and insulin tolerance tests. These tests help determine how well the body regulates blood sugar and responds to insulin, a hormone important for glucose control. Elevated blood sugar and insulin resistance are common problems associated with obesity and can be signs of pre-diabetes or diabetes.
To examine brain blood flow, the researchers used a sophisticated imaging technique called functional ultrasound. This technique allowed them to non-invasively measure cerebral blood volume, a measure of blood flow, in the brains of the mice while they were alive and under anesthesia. They focused on the somatosensory cortex, a brain region that processes sensory information, specifically using the part related to whisker sensation.
To stimulate this brain area, they gently vibrated the whiskers of the mice at a specific frequency. This whisker stimulation caused increased activity in the somatosensory cortex, and the researchers measured the change in blood flow in this region in response to the stimulation. This allowed them to assess functional hyperemia, the brain’s ability to increase blood flow when needed. They compared the blood flow responses in mice fed the different diets at various time points.
The researchers observed that the mice fed the Western diet quickly developed metabolic problems. After just three weeks on the Western diet, these mice showed significant weight gain, increased fat mass, elevated fasting blood glucose, glucose intolerance, and insulin resistance. These metabolic changes worsened over time, persisting into adulthood and middle age.
The Western diet also had a rapid and negative impact on brain blood flow. As early as three weeks after starting the Western diet, the adolescent mice showed a reduced blood flow response in the somatosensory cortex during whisker stimulation. This impairment in functional hyperemia was sustained over time and remained in adult and middle-aged mice that continued to eat the Western diet. This indicated that the unhealthy diet caused early and long-lasting damage to the brain’s ability to regulate blood flow.
But the researchers found that supplementing the Western diet with DHA, an omega-3 fatty acid, had a remarkable protective effect. Mice fed the DHA-supplemented Western diet did not show the same impairment in functional hyperemia as the mice on the regular Western diet. In fact, their brain blood flow responses were similar to those of mice fed a healthy regular diet. Furthermore, the DHA supplementation also improved metabolic health in the mice, restoring glucose tolerance and insulin sensitivity, despite the fact that these mice still gained weight and fat mass similar to those on the standard Western Diet.
“Our results were surprising in that we didn’t anticipate such a rapid, profound and sustained negative effect of the Western diet on a vital brain function like cerebral blood flow, which delivers oxygen and nutrients to neurons,” Gurden told PsyPost. “We were also pleasantly surprised by the powerful protective effects of omega-3 fatty acids on brain health.”
“The diet provided to children and teenagers should be carefully considered, with input from parents. A high intake of fast food, which is rich in omega-6 fatty acids and lacks protective omega-3s, should be avoided. This kind of diet can harm brain function in the long term, particularly by negatively affecting the brain’s vascular system.”
The researchers also observed interesting changes in brain blood flow in the mice fed a regular diet as they aged. They noted a natural decrease in functional hyperemia as the mice developed from adolescence to adulthood and middle age. However, the decline in blood flow was much more pronounced and occurred much earlier in the mice fed the Western diet, suggesting that the unhealthy diet accelerated the aging process of the brain’s blood vessels.
The researchers acknowledged some limitations to their study. One important point is that the study was conducted in mice, and while mouse models are valuable for understanding biological processes, the findings need to be confirmed in humans. While other brain imaging studies in humans have shown similar vascular impairments in teenagers with obesity, further studies in humans, particularly those that follow individuals over time, would help to confirm the results.
“Our findings should be validated by longitudinal studies in humans, particularly those beginning in adolescence,” Gurden noted.
Understanding how diet impacts brain health, particularly during critical developmental periods like adolescence, is essential for developing effective ways to promote healthy brain aging and prevent diet-related brain disorders.
“Our long-term goal is to identify protective strategies that can prevent the harmful effects of the Western diet on brain function, such as the impairment of cerebral vascular supply and memory,” Gurden explained. “Omega-3 fatty acids are one potential strategy, but incretins could also offer a promising medication whenever necessary.”
“While it may seem obvious, it’s important to remind parents to carefully monitor the quality of food they provide to their children,” he added.
The study, “Western diet since adolescence impairs brain functional hyperemia at adulthood in mice: rescue by a balanced ω-3:ω-6 polyunsaturated fatty acids ratio,” was authored by Haleh Soleimanzad, Clémentine Morisset, Mireia Montaner, Frédéric Pain, Christophe Magnan, Mickaël Tanter, and Hirac Gurden.
