Here’s another worry to add to parents’ long list: a new study published in Molecular Psychiatry suggests that a high-fat diet could lead to cognitive problems in developing brains, including impaired memory and loss of key cells in parts of the brain.
The research was co-directed by researchers from ETH Zurich in Switzerland and the INMED Institute in France, and looked at populations of mice fed one of two diets, a high-fat diet where 63 percent of calories came from fat, or a control diet where about 5-10 percent of calories came from fat.
To put those numbers into perspective, the recommended fat intake for adult humans is around 20-35 percent, Marie Labouesse, first author of the study and a Ph.D. student in Behavioral Neuroscience at ETH Zurich, told Paste, and slightly higher—about 25 percent-35 percent—for adolescents. A regular size “Big Breakfast” at McDonald’s, she added, is made up of about 58 percent fat, says Labouesse.
Each diet was fed to an adolescent population of mice and an adult population of mice to determine the different effects the diet had on their brains. Researchers then tested the mice’s memory and cognitive skills using a series of tasks, including the navigation of mazes.
The results of the experiment were stark: Adolescent mice fed the high-fat diet showed cognitive impairments such as poorer memory and a reduced ability to switch tasks. Crucially, the brains of the adolescent mice also showed a 35 percent reduction of a key type of brain cell, called reelin neurons, in the prefrontal cortex. The prefrontal cortex is a brain region responsible for important tasks such as decision-making and self-control.
Strangely, though, adult mice showed no such impairments, suggesting that adolescent brains are particularly vulnerable to these dietary changes. In fact, the prefrontal cortex is the last brain region to reach full maturity in both humans and rodents.
More research is needed to determine whether the results would apply in humans, and not just in mice. In the meantime, here are a few tips for making sure that high-fat diet doesn’t affect you or your loved ones’ developing brain:
Labouesse notes that more research is needed to determine the precise level of fat per day that is healthy for growing humans. However, in the meantime, it couldn’t hurt to pay attention to cutting back on fatty foods like french fries and pizza.
Total calories consumed is important, too. It’s possible, Labouesse says, that the negative effects of the high-fat diet might have been because mice on that diet—finding the diet tastier than the low-fat control diet—ate more than the other mice. Additional studies would need to tease apart the relationship between fat consumed, calories consumed, and effects on the brain.
Overeating can cause not only weight gain, but health problems including fatigue, joint pain and heart disease. Therefore, make sure to watch not only overall fat intake, but overall calories as well.
Labouesse noted in her study that we’ve moved, in modern times, toward a more high-calorie, highly processed diet. This diet include elevated levels of saturated fatty acids, which can have negative health effects.
The solution? Try to look for healthy, whole foods, such as fresh fruits and vegetables and whole grains, and skip the processed takeout.
Teens, Labouesse says, are particularly vulnerable to unhealthy diets, given many are just starting to make diet decisions for themselves. They may be influenced by peer pressure and media advertisements pointing them toward less-healthy options.
To combat this, parents and teens should educate themselves about healthy food options, so teens can make informed decisions as they take more responsibility for their diet and their health.
Not all fats are created equal. “The type of fat matters with respect to how it effects the brain,” Labouesse acknowledges, noting that high levels of saturated fatty acids (found in foods such as butter, fatty meat and salami) are generally associated with cognitive impairment. However, polyunsaturated fatty acids, especially omega-3 fatty acids (found in foods such as flaxseed, fatty fish and walnuts), are associated with a lower risk of cognitive decline in humans and improved memory in mice.
Labouesse’s study featured a diet with a mix of fats, including a high amount of unhealthy saturated fats. It’s possible, she noted, that a diet featuring a higher amount of healthier fats may have led to different results.
So, when choosing a brain-healthy meal, even one higher in fat, reach for foods low in saturated fatty acids and high in polyunsatured fatty acids—such baked salmon and veggies versus pepperoni pizza.
Stephanie has a degree in the History of Science from Harvard University, and has written for publications including Quanta, Live Science, and NY Mag. In her spare time, she also writes children’s books.