Eating an unhealthy diet during adolescence can have long-term negative consequences for the brain and impair memory, as suggested by the results of a study led by researchers at the University of Southern California (USC) who, after feeding rats with a diet rich in fats and sugars, similar to what is considered junk food for humans, they found that the animals presented memory deficits that were maintained over time.
“What we observed, not only in this study, but also in other recent research, is that the rats that grew up on this junk food diet have memory deficits that persist. These effects, unfortunately, continue into adulthood, even if you switch to a healthy diet,” said Scott Kanoski, professor of biological sciences at the USC Dornsife College of Letters, Arts and Sciences.
In developing the study, Kanoski and lead author and postdoctoral fellow Anna Hayes took into account previous research that has shown a connection between poor diet and Alzheimer’s disease. People with Alzheimer’s typically have lower levels of acetylcholine, a neurotransmitter essential for memory and functions such as learning, attention, arousal, and involuntary muscle movement.
Impact of a Western diet high in fats and sugars on the brain
The team investigated the possible implications of a Western diet high in fat and sugar for young people, especially during adolescence, a stage of significant brain development. By monitoring acetylcholine levels in rats and performing memory tests, they sought to delve deeper into the relationship between diet and memory.
The researchers monitored acetylcholine levels in a group of rats on a high-fat, high-sugar diet and in a control group, analyzing their brain responses to specific tasks designed to test their memory. They also examined the rats’ brains after their death for signs of altered acetylcholine levels.
The memory test consisted of allowing the rats to explore new objects in different locations. Days later, the researchers reintroduced the rats to a nearly identical scene, but with the addition of a new object. Rats on a junk food diet experienced difficulty remembering which object they had previously seen and where, while those in the control group recognized the objects.
“The rats raised on this junk food diet have memory deficiencies that persist and are maintained into adulthood, even if they switch to a healthy diet.”
“Acetylcholine signaling is a mechanism that helps them encode and remember those events, similar to ‘episodic memory’ in humans that allows us to remember past events. That signal does not seem to occur in animals that grew up eating the diet rich in fats and sugars,” Hayes explained.
Kanoski emphasized that adolescence is a period of great sensitivity for the brain, when important changes in development occur. “I don’t know how to say this without sounding pessimistic,” he said, “but unfortunately, some things that might be more easily reversible during adulthood are less reversible when they occur during childhood.”
There is some hope for intervention. Kanoski mentioned that, in another phase of the study, the research team evaluated whether memory damage in rats fed junk food could be reversed with drugs that induce the release of acetylcholine. They used two drugs – PNU-282987 and carbachol – and discovered that by administering these treatments directly to the hippocampus, a region of the brain that controls memory and is altered in Alzheimer’s disease, the rats’ memory capacity was restored.
However, without that special medical intervention, Kanoski said more research is needed to understand how memory problems stemming from a junk food diet during adolescence can be reversed. The results of the study have been published in the journal Brain, Behavior, and Immunity.
