A junk food diet is often linked to obesity and increased risk of chronic health conditions such as diabetes and cardiovascular diseases. A recent study has revealed that indulging in a junk food diet during adolescence can leave a lasting impact on the brain, affecting memory function.

A high-fat, high-sugar diet in teenagers may lead to long-term memory damage, according to the results of a rat study conducted by researchers from the University of Southern California.

The researchers noted that adolescent rats that were on a junk food diet had significant memory issues that persisted into adulthood even after they switched to a healthier diet. The results indicate that a similar junk food-filled diet in teenagers may disrupt their brains' memory ability for a long time.

"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. If you just simply put them on a healthy diet, these effects unfortunately last well into adulthood," said Scott Kanoski, from the USC Dornsife College of Letters, Arts and Sciences.

Previous research connected poor diet with Alzheimer's disease. Additionally, an earlier study showed that people with Alzheimer's have reduced levels of a neurotransmitter called acetylcholine, which is essential for memory and functions like learning, attention, and muscle movement.

The researchers decided to explore the relationship between diet and memory in younger people when they are on a fat-filled, sugary Western diet, particularly during adolescence when their brains are undergoing significant development.

To understand the link, the researchers divided rats into two groups: one fed a fatty, sugary diet and another given a normal diet. They then administered memory tests and assessed their acetylcholine levels.

For the memory test, the rats were allowed to explore new objects in different locations, and days later, they were reintroduced to a similar scene that was nearly identical except for the addition of one new object. The rats in the test group that consumed the junk food diet showed difficulties recalling which object they had previously encountered and where. However, those in the control group showed a sense of familiarity.

The team tracked the levels of acetylcholine in each group by analyzing their brain responses to certain tasks designed to test their memory. Using a post-mortem of the rats' brains, they estimated the signs of disrupted acetylcholine levels.

"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. That signal appears to not be happening in the animals that grew up eating the fatty, sugary diet," lead author Anna Hayes explained.

In another phase of the study, the team tested if the memory damage in rats from the junk food diet could be reversed with the use of drugs that could induce the release of acetylcholine. During the experiment, the researchers administered drugs — PNU-282987 and carbachol — directly to the hippocampus, a brain area crucial for memory and often affected by Alzheimer's disease. They observed that these treatments restored the rats' memory abilities.

However, researchers cautioned that more studies are needed to understand how memory problems from a junk food diet during adolescence can be reversed.

According to Kanoski, adolescence is a very sensitive period for the brain when important changes are occurring in development. "I don't know how to say this without sounding like Cassandra and doom and gloom but unfortunately, some things that may be more easily reversible during adulthood are less reversible when they are occurring during childhood," Kanoski added.

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