Food for thought: High-fat, sugary diets in teens may permanently harm memory, study flags

16 Apr 2024 --- A mouse-model study suggests that teenagers who consume a diet high in fats and sugars may experience long-term disruptions in their brain’s memory function. Led by a team from the University of Southern California (USC), US, the study delved into previous research that links poor diet to Alzheimer’s disease.

The research team notes that individuals with Alzheimer’s often exhibit lower levels of a neurotransmitter called acetylcholine in the brain, which is crucial for memory and other cognitive functions. The neurotransmitter also powers important memory functions that occur within the hippocampus.

“Acetylcholine signaling is a mechanism to help them encode and remember those events, analogous to ‘episodic memory’ in humans that allows us to remember events from our past,” explains the study’s lead author, Dr. Anna Hayes. “That signal appears to not be happening in the animals that grew up eating the fatty, sugary diet.”

Diets’ effects on the brain
The study, published in Brain, Behavior and Immunity, sheds light on the potential impacts of junk food-filled diets on cognitive health. 

To explore the effects of a high-fat, sugary diet on memory, the researchers tracked rats’ acetylcholine levels while feeding them a “junk food cafeteria-style diet” (CAF). Examples of the diet include potato chips, chocolate-covered peanut butter cups and sugary beverages. The caloric value of each rat’s diet was calculated to coincide with the average calorie intake by weight of an adolescent child.

The researchers also conducted novel location recognition (NLR) and novel object-in-context (NOIC) memory tests to assess the subjects’ cognitive functions.

The NLR test consisted of habituation subjects to a specific object in a room, moving the object to different locations and gauging how long each group of rats in the test and control spent investigating the “familiar” item to assess spatial recognition memory — a type of memory that relies on the hippocampus which is powered by acetylcholine.

The NOIC procedure consisted of placing the same object in a different room or context over a period of days and calculating how long each group of rats spent investigating the familiar object in an unfamiliar context to assess hippocampus-dependent contextual episodic memory.The study reveals that adopting a healthier diet later in life cannot undo the effects of eating poorly when young.

Struggling with spatial memory
During the memory tests, rats fed the junk food CAF diet struggled to remember objects and their locations compared to rats in the control group. The researchers emphasize that this suggests the unhealthy diet negatively impacts the animals’ long-term memory function.

Post-mortem examinations of the rats’ brains were also conducted to identify any signs of disrupted acetylcholine levels. For rats given the CAF diet at a young age, acetylcholine production was lower than the control and remained low even after a healthy diet intervention.

“What we see not just in this paper, but in some of our other recent work, is that if these rats grew up on this junk food diet, then they have these memory impairments that don’t go away,” says Dr. Scott Kanoski, a professor of biological sciences at USC and coauthor of the study. “Even if you put them on a healthy diet, these effects unfortunately last well into adulthood.”

Hope for the hippocampus
The study does offer a glimmer of hope for intervention. In a subsequent phase of the research, the team investigated whether memory deficits in rats fed a junk food diet could be reversed with medication that stimulates the release of acetylcholine. Administering acetylcholine agonists directly to the hippocampus restored the rat’s memory function.

Despite these promising findings, the study’s authors underscore the importance of dietary habits during adolescence and their potential long-term effects on cognitive health. As the prevalence of high-fat, sugary diets among teens continues to rise, understanding the impact on brain function is vital for public health initiatives that promote healthy eating habits to prevent cognitive decline later in life.

“I don’t know how to say this without sounding like Cassandra and doom and gloom,” Kanoski concludes. “But unfortunately, some things that may be more easily reversible during adulthood are less reversible when they are occurring during childhood.”

Edited by William Bradford Nichols