Japanese researchers have discovered that feeding fruit flies a high-fat diet disrupts both intermediate and long-term memory. Their study, published in PLOS Genetics, set out to explore why previous research has linked high-fat diets to cognitive decline. What they found was that excess fat clogs the brain’s cleanup system, slowing its ability to remove waste and allowing harmful proteins to accumulate.

According to Study Finds, the scientists used fruit flies — creatures that share many of the same brain maintenance systems as humans. After just seven days on a high-fat diet, the flies showed problems with autophagy, the brain’s natural waste-clearing system. The fatty diet caused this critical process to fail, leading to a buildup of cellular “garbage” inside neurons, especially in regions tied to memory.

Normally, autophagosomes (which collect waste) fuse with lysosomes (which break it down) to keep the brain clear of debris. But in flies fed a fatty diet, this connection broke down. Cleanup stalled, leaving toxic clutter scattered throughout the neurons.

The researchers then tested how this impacted memory. Fruit flies can usually be trained to avoid certain smells associated with an electric shock and remember the connection for up to a day. But those on a high-fat diet forgot within hours, repeatedly suffering shocks. By the next day, their long-term memory also weakened.

The good news: scientists were able to reverse the damage by:

• Turning off a protein called Rubicon, which slows autophagy.
• Over-activating another protein called Atg1, which jump-starts the cleanup process.
• Feeding the flies rapamycin, a drug that helps cells recycle waste.

All three methods successfully restored balance in the brain, and the flies regained their memory. According to Technology Networks, these same strategies could one day help counteract cognitive decline in humans linked to high-fat diets. If our brain’s “cleaning crew” can’t keep up, damaged proteins may accumulate and interfere with memory.

“Our findings suggest the diet-induced cognitive decline is not irreversible and may be improved by lifestyle interventions that promote autophagy,” said study co-author Associate Professor Ayako Tonoki.

However, the researchers caution that their study was limited. They tested only male fruit flies and used just one type of fat — coconut oil. Different fats may affect the brain differently, and the results may not translate directly to human memory decline.