Your Brain is a Dishwasher During Sleep—and Your Diet Can Junk It Up
You’ve heard about the lymphatic system—that’s the network that helps our body get rid of toxins and waste. But have you heard about the glymphatic system?
Your central nervous system (CNS)—made up of your brain and spinal cord—is highly active, producing lots of waste. But unlike the rest of your body, the CNS doesn’t have any lymphatic vessels. Still, your brain needs to get rid of all that cellular garbage somehow. That’s where the glymphatic system comes in.
Danish scientist Maiken Nedergaard discovered this system, and the vital glial cells for which it’s named. These cells form tunnels that insulate the brain’s neurons and form channels for waste disposal through which cerebrospinal fluid travels. These channels distribute vital substances throughout the brain, including “glucose, lipids, amino acids, growth factors, and neuromodulators.”
There’s a catch, though: The glymphatic system—and remember, this is the brain’s primary method for waste disposal—seems to primarily function during sleep. In the words of Max Lugavere, researcher and author of Genius Foods, “Your brain becomes a dishwasher while you sleep.”
Max Lugavere explains how the brain cleans itself.
Sleep is the mechanism that activates the glymphatic system. Without sleep, our brains begin to build up harmful waste products, including the β-amyloid peptide, a plaque deposit that can accumulate in the brain and eventually result in Alzheimer’s disease.
We had Lugavere walk us through how the glymphatic system works. He noted that there is “growing suspicion that amyloid plaque may be more a consequence of an underlying dysfunction than the smoking gun.” In other words, we need to figure out what’s causing amyloid build-up to solve Alzheimer’s. Knowing that amyloid plaque is linked to disease is not the same as knowing why amyloid build-up happens.
With this in mind, Lugavere says, “Scientists have taken a step back and asked: ‘How do we prevent our brains from becoming an amyloid landfill?’ ”
The answer lies in diet—and in sleep.
“When insulin is elevated—due to frequent high-carbohydrate meals or excessive caloric intake—our ability to break down amyloid becomes handicapped,” Lugavere says. Insulin-degrading enzymes (IDE) break down insulin, but they also help degrade β-amyloid. “Unfortunately, IDE supply is limited, and it has a stronger preference for degrading insulin than it does for amyloid.”
Put simply, elevated insulin means IDEs don’t have the capacity to break down β-amyloid peptides, so amyloid plaque starts building up in our brains.
Sleep goes hand-in-hand with diet. In Lugavere’s words:
“Much of the brain’s custodial work occurs while we’re off in la-la-land. Thanks to the newly discovered glymphatic system, your brain essentially becomes a dishwasher while you sleep, whooshing cerebrospinal fluid around and flushing out amyloid protein and other by-products.”
“Insulin interferes with the body’s housekeeping tasks, and that includes the cleanup that takes place while you sleep. One way to optimize this critical brain cleaning is to stop eating two to three hours before bed to reduce circulating insulin.”
“If you’ve ever put a dried bowl of day-old oatmeal into a dishwasher only to find the oats stuck like paste on the bowl even after it runs, you understand the importance of a basic chemical concept: solubility. Amyloid is like oatmeal in the brain. For it to be flushed, it requires that the protein stay soluble, so that it can be dissolved in the cerebrospinal fluid that pulsates through the brain.”
“What makes amyloid as insoluble as dried-out oatmeal? Sugar binds wantonly to nearby proteins, and amyloid beta is no exception. When amyloid is glycated it becomes stickier and less soluble, and thus less easily chopped up and flushed away.”
Sugar both captures the resources of IDEs and binds to waste proteins, making them harder to dispose of. A 2015 study in Alzheimer’s & Dementia demonstrated the danger of elevated blood sugar and insulin levels.
Lugavere summarized the study: “The more severe the insulin resistance in the body—signaling chronically elevated blood sugar—the more plaque build-up there was in the brain of cognitively normal subjects.” This connection held up even among non-diabetic people, Lugavere notes, “meaning just slight insulin resistance is enough to increase amyloid deposition.”
Our last note before we move on to what you can do to maintain your own glymphatic system:
Balancing fed and fasted states is crucial to solving insulin resistance and avoiding plaque build-up in the brain.
“Our bodies are adapted to carry out important maintenance tasks in each of these states,” Lugavere says. “We would find little argument that modern life tilts the scales far toward the fed state, which appears to increase brain plaque burden while also preventing important fuels like ketones from reaching the brain.”
That means finding a healthy balance between being fed and being fasted, so you can ensure your brain is getting squeaky clean while you sleep.
4 ways to ensure a well-oiled glymphatic system.
Now for the good stuff: How can you ensure that your own glymphatic system is working like clockwork, so you can avoid pesky amyloid build-up and keep your brain working well, even in old age? We’ve got a few suggestions:
- Don’t eat for at least three hours before bed. This reduces your insulin levels when you fall asleep, meaning your brain’s IDEs can put their full energy into breaking down amyloids, instead of putting their focus on breaking down insulin.
- Improve your sleep habits. More and better sleep allows the dishwasher to get a full cycle (see our Sleep Guide for tips). The longer you sleep, the more time your glymphatic system has to do its job and dislodge all those harmful waste products that it would otherwise build up over time.
- Manage your insulin resistance well. Reducing blood sugar spikes reduces amyloid beta production to begin with, and also helps your brain spend more time cleaning up plaque and other waste products. You can start by eliminating processed carbs and moving toward a whole-foods diet.
- Build in periods of fasting. Fasting allows the body to rest and repair by sending all of your IDEs off to deal with waste. This is the reason many people like intermittent fasting—it helps the body do the housekeeping more easily.
Max Lugavere is a science journalist and author of the New York Times best-selling book Genius Foods. After his mother was diagnosed with a mysterious form of dementia, Lugavere put his media career on hold to research the workings of the human brain. Genius Foods, a deep dive into how diet affects our brains, is the product of that research.
In the book, Lugavere talks about 10 foods that are best for brain health and explains the science of how our brains work, why standard Western diets are creating disease in our brains, and how you can halt the aging of your brain with the right foods and healthy habits. We found Lugavere’s book an intensely interesting read—if you’re interested in learning more about how food influences brain function, we highly recommend you snag a copy!