Could a 'junk food' diet cause long-term damage to the brain?

So-called junk food is consumed across the world and is particularly prevalent in the Western diet. But in recent years it has increasingly been linked to serious health concerns, including obesity, type two diabetes, heart-related problems such as cardiovascular disease, high blood pressure, high cholesterol and certain types of cancer.

Now, new research from scientists at the University of Southern California (USC) is linking a junk food diet to long-term damage to the brain.

What is junk food?​

Though there is no exact definition of the term ‘junk food’, the general consensus is that it comprises foods, which are high in fat, sugar and salt (HFSS), with little or no nutritional value.

The Oxford English Dictionary defines the term junk food as, “food that has low nutritional value, typically produced in the form of packaged snacks needing little or no preparation."

Foods such as processed meats, chocolate, crisps and fizzy drinks are examples of foods often referred to as junk food.

Is junk food damaging to brain health?​

A recent study, led by researchers at the University of Southern California, suggests that consuming a diet high in junk food during teenage years could have long-lasting effects on memory function.

The study observed rats on a high-fat and high-sugar diet, which is typically associated with junk food.

“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,” said Scott Kanoski, professor of biological sciences at the University of Southern California Dornsife College of Letters, Arts and Sciences.

The study raises further concern as it appears these effects are long lasting and cannot easily be reversed.

“If you just simply put them on a healthy diet, these effects unfortunately last well into adulthood,” adds Professor Kanoski.

How was the study conducted?​

The study followed on from previous scientific research, finding links between poor diet and Alzheimer’s disease. It has previously been found that people who suffer from Alzheimer’s disease tend to have lower levels of a neurotransmitter called acetylcholine in the brain. Acetylcholine is essential for memory and brain functions such as learning and attention.

The research team considered what this could mean for younger people who may be consuming a diet high in fat and sugar, particularly during adolescence when their brain is undergoing significant development. By tracking the impact of the diet on the rats’ levels of acetylcholine, and running the rats through some memory testing, they realised that they could learn more about the important relationship between diet and memory.

The researchers tracked the acetylcholine levels of a group of rats on a high fat and high sugar diet alongside a control group of rats by analysing their brain responses to certain tasks designed to test memory. The team also examined the rats’ brains post-mortem for signs of disrupted acetylcholine levels.

The memory tests involved letting the rats explore new objects in a scene set up for them. The rats were then reintroduced to the scene several days later. The scene was the same, except for the addition of one new object. Rats on the junk food diet showed signs they could not remember which objects they had previously seen and where they had been placed, while those in the control group showed familiarity.

“Acetylcholine signalling 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 Anna Hayes, lead author of the study. “That signal appears to not be happening in the animals that grew up eating the fatty, sugary diet.”

Professor Kanoski went on to emphasise that 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.”

However, the team found that intervention could perhaps improve signs of damage to the brain. Professor Kanoski explained that in another round of the study, the research team examined whether the memory damage in rats raised on the junk food diet could be reversed with medication that induces the release of acetylcholine.

The team used two drugs on the study rats, PNU-282987 and carbachol, and found that when administered directly to the hippocampus, a brain region that controls memory, the memory ability was restored.

Professor Kanoski said more research is needed to know how memory problems from a junk food diet during adolescence could be reversed without pharmaceutical intervention.

Source: Western diet consumption impairs memory function via dysregulated hippocampus acetylcholine signalling
Published online: 8 March 2024
DOI: https://www.sciencedirect.com/science/article/pii/S0889159124002952?via%3Dihub
Authors: Anna M.R. Hayes, Logan Tierno Lauer, Alicia E. Kao et al.