A new USC-led study of rats feasting on a high-fat, high-sugar diet raises the possibility that a junk-food-filled diet in teenagers could disrupt their brains' memory abilities for long periods of time.
“What we see not only in this paper, but in other recent work, is that if these rats are raised on this junk food diet, they have memory deficits that don't go away,” says Scott Kanoski. professor of biological sciences at the USC Dornsife College of Letters, Arts and Sciences. “Unfortunately, if you just put them on a healthy diet, these effects last well into adulthood.”
The research appears in the May issue of the journal Brain, behavior and immunity.
In developing the study, Kanoski and lead author and postdoctoral researcher Anna Hayes believed that previous research has shown a link between poor nutrition and Alzheimer's disease. People suffering from Alzheimer's disease typically have lower levels of a neurotransmitter called acetylcholine in the brain, which is essential for memory and functions such as learning, attention, arousal and involuntary muscle movements.
The team wondered what this might mean for younger people who eat a similar high-fat, high-sugar Western diet, especially during adolescence, when their brains are undergoing significant development. By monitoring the impact of the diet on the rats' acetylcholine levels and putting the rats through a series of memory tests, they were able to learn more about the important relationship between diet and memory.
The researchers monitored the acetylcholine levels of a group of rats on a fatty, high-sugar diet and of a control group of rats by analyzing their brain responses to certain tasks designed to test their memory. The team examined the rats' brains post-mortem for signs of disturbed acetylcholine levels.
In the memory test, the rats had to explore new objects in different locations. Days later, the researchers reintroduced the rats to the scene, which was virtually identical except for the addition of one new object. Rats on the junk food diet showed signs of not being able to remember which object they had previously seen and where, while those in the control group were familiar with it.
“Acetylcholine signaling is a mechanism to help them encode and remember these events, analogous to 'episodic memory' in humans, which allows us to remember events from our past,” explains lead author Hayes. “That signal doesn't seem to happen in the animals raised eating the fatty, high-sugar diet.”
Kanoski emphasized that adolescence is a very sensitive period for the brain when important developmental changes occur. “I don't know how to say this without sounding like Cassandra and doom and gloom,” he said, “but unfortunately some things that are more easily reversible in adulthood are less reversible when they occur in childhood.”
There is at least some hope for intervention. Kanoski said that in another round of the study, the research team examined whether memory damage in rats raised on the junk food diet could be reversed with drugs that induced the release of acetylcholine. They used two drugs, PNU-282987 and carbachol, and found that those treatments delivered directly to the hippocampus, a brain region that controls memory and is disrupted in Alzheimer's disease, restored the rats' memory ability.
But without that special medical intervention, Kanoski says more research is needed to know how to reverse memory problems caused by a junk food diet during adolescence.
In addition to Kanoski and Hayes, the team included other USC Dornsife researchers Logan Tierno Lauer, Alicia E. Kao, Molly E. Klug, Linda Tsan, Jessica J. Rea, Keshav S. Subramanian, Cindy Gu, Arun Ahuja, Kristen N. Donohue and Léa Décarie-Spain; Natalie Tanios of USC's Keck School of Medicine; as well as Anthony A. Fodor, Shan Sun of the University of North Carolina-Charlotte.
The work was supported by the following: National Institute of Diabetes and Digestive and Kidney Diseases grant DK123423 (SEK, AF), National Institute of Diabetes and Digestive and Kidney Diseases grant DK104897 (SEK), Postdoctoral Ruth L. Kirschstein National Research Service Award from the National Institute on Aging F32AG077932 (AMRH), National Science Foundation Graduate Research Fellowships (separate awards for LT and KSS), Quebec Research Funds postdoctoral fellowship 315201 (LDS) and the Alzheimer's Association Research Fellowship to Promote Diversity AARFD-22 -972811 (LDS ).
