Blood Sugar Before the Autumn Equinox: What Japan and Korea Are Each Eating

About 5 minutes xoxoxox Seasonal healthBlood sugarNattoAutumn drynessJapan and Korea

A relative asked on the phone: "That natto you mentioned last time — does it actually work?" I said I would look it up first. Only after hanging up did I notice that this week's trending lists in Japan and Korea had thrown up exactly these two things — in Japan "納豆" (natto), in Korea "혈당", which means blood sugar.

In autumn, blood sugar does tend to rise

Let me start with what I looked up myself. Research published in China suggests there are seasonal differences in HbA1c among people with type 2 diabetes: a study in Tianjin Medical Journal analysed the effect of seasonal and temperature changes on fasting blood glucose, and noted that similar studies report HbA1c as "higher in winter, lower in summer". Around a change of season, diet, activity levels and sleep all shift, and readings move with them — that in itself is not surprising.

The ancients never measured blood sugar, but they had their own account of the body in this stretch of the year. The Yellow Emperor's Inner Canon, Basic Questions, "四气调神大论" (On Regulating the Spirit in the Four Seasons) says "秋三月，此谓容平" — in the three months of autumn, this is called calm and level — describing autumn as a season of gathering in and settling, one that calls for sleeping early and rising early and for keeping the emotions a little contained. The "autumn dryness" so often invoked in later health writings sits inside that framework — the weather is dry and the person dries along with it.

In a Japanese kitchen: a pack of natto

Natto is a fixture of the Japanese breakfast: soybeans left to ferment, sticky, stringy, sharply scented. It keeps being brought up mostly because fermentation produces nattokinase and vitamin K2 — both of which have their own discussions in research, but neither is a switch that makes everything fine once eaten.

One thing should be said first: natto is rich in vitamin K, and for people taking anticoagulants such as warfarin, vitamin K interferes with the drug's effect. This does not mean natto must be given up entirely, but large amounts should generally be avoided, and you should not suddenly change your intake while on the medication, nor adjust the dose yourself; for how to arrange it, ask the prescribing doctor or pharmacist first. This is medication safety, a different matter from health lore.

The "혈당" near the top of Korea's list these days literally means blood sugar. Searches related to blood sugar have a steady volume there all year round, mostly pointing to interpreting health check reports and managing diet.

What is interesting is the guidance the Korean Diabetes Association gives the public, which reads almost entirely as "swap out the white rice first": eat at regular times and in set amounts, watch out for simple sugars, take in more dietary fibre, and replace refined white rice with whole grains and beans — because the local diet is rice-based and the share of carbohydrates is already high, so the post-meal curve naturally climbs more steeply. Japan's natto, Korea's multigrain rice — in the end they are two local versions of one thing: get the staple food in order first.

Separating "health maintenance" from "treatment"

My reply to the relative was simple: appetites are good in early autumn, but how to eat, how much to cut back on staples, how long to walk after meals — these are best settled under a doctor's or dietitian's guidance, especially for anyone on medication; if the numbers on the glucose meter have been off several times in a row, take the records to hospital and see an endocrinologist rather than toughing it out on a diet copied from the internet.

If you too have been feeling unable to sleep well or low on energy lately, get the tests done first before talking about conditioning. Seasonal health customs in folklore serve to remind you to watch how your body changes as the seasons turn; they do not diagnose and they do not treat.

Writing these troubles down clearly and lining them up in time order is also a way of turning unease into a list. Remember this: organising can help you see yourself more clearly, but it cannot replace a doctor's diagnosis; if symptoms persist, please seek medical care promptly.

This article's information is current as of 15 September 2026; medical content is subject to the opinions of medical institutions and professionals.

Disclaimer: This article covers traditional culture and folklore and is for entertainment and self-reflection only. It does not constitute medical, psychological, investment, legal or marital decision advice. Please do not submit sensitive personal information such as ID numbers or detailed addresses. If you are experiencing persistent insomnia, anxiety or physical discomfort, please seek medical attention or consult a professional promptly. This article does not constitute medical advice; for specific medication and treatment, please follow your doctor's instructions.

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