Lee Seung-hoon, a neurology professor at Seoul National University Hospital, emphasizes proper sleep habits and a healthy diet as the core secrets to brain health and the prevention of chronic inflammation. In particular, he explains the importance of the glymphatic system, which clears waste from the brain, and its connection to deep sleep, recommending quality sleep as the first step toward dementia prevention. He also stresses that a diet which reduces simple-sugar intake and increases good protein is essential for preventing the accumulation of visceral fat and reducing chronic inflammation, and he warns about the causes and dangers of "skinny obesity" among Koreans.
1. The Glymphatic System That Rinses the Brain, and the Importance of Deep Sleep 😴
Professor Lee explains that he once considered sleeping a waste of time, but in reality, not sleeping poses a major threat to health. The reason is precisely that the Glymphatic System, which cleans the brain, operates during sleep. Similar to the lymphatic system, this system removes waste products from the brain. For a long time it was believed that the brain had no lymphatic system, but its recent discovery is considered so significant that it is mentioned as a candidate for a Nobel Prize.
The professor explains how the glymphatic system works by comparing it to an office worker cleaning up the office after finishing for the day. During the day, while the brain is actively at work, waste accumulates, and during sleep these waste products are cleaned away.
"During sleep, the brain gets thoroughly rinsed out. The brain literally gets washed. That's why people think it's almost worthy of a Nobel Prize — this thing called the glymphatic system was discovered."
In particular, the glymphatic system is activated during stages 3 and 4 of deep sleep among the sleep stages. Therefore, sleeping in short naps or waking up frequently interferes with the brain's cleaning. Adenosine, the fatigue-causing substance produced in the brain, can only be removed through the glymphatic system. Caffeine merely blocks the receptors that sense this fatigue for a while; it does not remove the underlying fatigue substance, he explains.
"If you sleep in short naps, or keep waking up and dozing off, then your brain doesn't get cleaned."
"The only way to eliminate adenosine is the glymphatic system, and it can only happen while you sleep."
Beyond that, the glymphatic system is also known to play an important role in clearing away amyloid, the substance that triggers dementia. Therefore, deep sleep is also very important for preventing dementia, and he emphasizes that getting good deep sleep starting in middle age is the key to preventing dementia.
"If you don't want to get dementia, getting good deep sleep starting in middle age is truly important."
The key to healthy sleep is to sleep at least seven and a half hours or more, without waking up in the middle, and to maintain deep sleep.
2. Eating Habits That Block Inflammation: Avoid Simple Sugars and Increase Protein 🍎🍗
As the basic principle of healthy eating, the professor recommends reducing simple-sugar intake, avoiding excessively fatty foods, and following a diet centered on protein and fiber. He says this goes beyond a mere declaration that something is "good for your health" — it is important to understand the underlying reasons why our bodies reduce inflammation.
The most important thing is to avoid simple sugars. The professor explains the dangers of consuming simple sugars and emphasizes the importance of whole grains.
"Reducing simple sugars basically means: eat grains. Eat whole grains. What does this mean? It's a really interesting point. It means eat carbohydrates that the body finds hard to digest."
When we eat rice, the stomach does strenuous work to digest it, and it is slowly broken down into glucose and absorbed. In this process, the body gets exercise, and because blood sugar rises slowly, it is beneficial to health. But desserts high in simple sugars, such as ice cream, are already broken down into glucose and fructose, so they are quickly absorbed into the bloodstream without any digestion process.
"It's sweet the moment you eat it. Wow, it feels so good. Why do you feel it's sweet? Because the body loves it. Because there's no need to digest it."
The problem is that such simple-sugar foods induce overeating. The brain responds to delicious foods, especially intensely flavored ones, and demands more food. As the saying goes, "there's always room for dessert" — simple-sugar foods expand the stomach so that you can keep eating.
"If it's delicious, you overeat, so it's unconditionally bad for your health."
"Our country has the unhealthiest food culture in the entire world. It's a big problem precisely because it's so delicious."
Therefore, Professor Lee offers a somewhat humorous but essential piece of advice for health: "Eat blandly." Bland food prevents overeating and doesn't expand the stomach, making it easy to feel full.
He also emphasizes the importance of protein intake, saying that vulnerable groups in particular — the elderly, cancer patients, and people with chronic illnesses — must consume enough good-quality protein.
"Our country has too much of a diet that lacks protein. You need to eat good protein well, and the more vulnerable the group, the more they need to eat good protein well."
In conclusion, the most important thing in a diet is to decide on your own calorie intake and eat a balanced variety within that limit. Overeating caused by simple-sugar intake is the main cause of obesity, and obesity is the cause of all metabolic abnormalities and atherosclerosis.
3. Koreans' Skinny Obesity and the Dangers of Visceral Fat 🚨
Professor Lee explains the causes and dangers of skinny obesity, which appears especially often in Koreans. Asians, including Koreans, have a genetic trait of smaller body frames and weaker pancreatic function compared to Westerners. In the past, they lived having adapted to eating little and to small body types, but after the 1900s, as Western food culture flowed in, they began consuming high-calorie foods.
Because people with weak pancreatic function find it difficult to fully digest and store excessive calories, the body stores the surplus calories as visceral fat. For this reason, skinny obesity arises, where the arms and legs are thin but only the belly protrudes.
"Even a thin person, by constitution and genetics, is someone who can't gain weight. That person can't gain weight... The people who take all of it in and gain weight are the ones with good pancreatic function."
"The other organs have no intention of taking it in, and because they won't accept more than the genetically determined size, only the belly sticks out."
This visceral fat goes beyond simple fat accumulation; it is an active hormonal organ that secretes hormones that trigger chronic inflammation in our bodies. Unlike subcutaneous fat, visceral fat has very active metabolic function, and when it accumulates excessively, it becomes the driving force that amplifies inflammatory responses.
"Visceral fat releases various hormones related to obesity in our body, which are called adipocytokines. Among these adipocytokines, except for just one component called adiponectin, all the rest are hormones that amplify inflammatory responses."
Therefore, even if the body mass index is normal, skinny obesity — where the waist circumference exceeds 90 cm for men and 85 cm for women — is regarded as a very harmful form of obesity. We must keep in mind that both diabetes caused by excessive carbohydrate intake and obesity caused by excessive fat intake are key factors that trigger chronic inflammation.
Closing
Professor Lee Seung-hoon emphasizes that for a healthy life, it is important to keep the brain clean through quality sleep, and to prevent the accumulation of visceral fat — the main cause of chronic inflammation — by avoiding a diet centered on delicious but intensely stimulating simple sugars and increasing intake of good protein. He delivers the message that we need to understand our bodies' genetic traits and the dietary changes of modern society, and to make a conscious effort to maintain healthy lifestyle habits.