Is afternoon drowsiness caused by blood sugar levels? How to tell and how to rethink your lunch

Why do you get sleepy in the afternoon? Understand the relationship with blood glucose levels

When you are suddenly overcome by strong sleepiness during a meeting or while driving, do you automatically assume it is because your blood glucose level spiked after lunch? This article explains the mechanisms behind afternoon sleepiness and discusses aspects that cannot be explained by blood glucose levels alone.

The mechanism of rapid blood glucose spikes and drops

If you consume a meal high in carbohydrates, such as a rice bowl or ramen for lunch, your blood glucose level will rise significantly after the meal. To lower the elevated blood glucose, your body releases a hormone called insulin, and the blood glucose level gradually drops over time. The sharper the rise, the sharper the drop tends to be. Conversely, if you combine vegetables and protein and avoid overeating, the change in blood glucose levels will be more gradual. Understanding this flow of blood glucose fluctuation itself is the starting point for considering your physical condition in the afternoon.

Internal rhythms and lack of sleep are also causes of sleepiness

Blood glucose is not the only cause of sleepiness. The human body has an internal clock, and the intensity of sleepiness during the day varies depending on the time of day. Additionally, if you slept for a short time the night before or woke up in the middle of the night, you are more likely to experience strong sleepiness during the day. If you find yourself inevitably sleepy while working at your desk, look back not only at that day's lunch but also at how much you slept the previous night.

Why blood glucose alone cannot fully explain sleepiness

The relationship between postprandial (after-meal) sleepiness and blood glucose levels is actually a field with few studies. In a scoping review published in 2025 (Scoping review published in Nutrients), nine studies met the criteria for research on postprandial sleepiness and blood glucose. Of these, six studies measured blood glucose levels and six measured sleepiness, but only one study investigated both blood glucose and sleepiness together. It is important not to assume that blood glucose fluctuation is the only cause of sleepiness, but to consider other factors such as sleep and the internal clock as well. The relationship between food/snack choices and concentration is also introduced in our article, Thinking about the relationship between concentration and food/snacks based on blood glucose and sleepiness, so please refer to it as well.

Is that sleepiness due to blood glucose? How to identify it and tips for keeping a record

Even if you feel "sleepy because of lunch," you cannot know the true cause unless you actually measure your blood glucose level. First, let's start by recording the time you get sleepy, your meals, and your sleep, and look at the guidelines for when to consult a professional if symptoms persist.

Try taking notes on the time you get sleepy, your meals, and your sleep

Keeping a record is a clue to identifying the cause of sleepiness yourself. A memo app on your smartphone is fine. Try writing down three things for about a week: the time you felt sleepy, what you ate immediately before, and how many hours you slept the previous night. For example, if you felt strong sleepiness on a day when you had a light lunch consisting only of noodles, and also on a day when you slept for 5 hours the night before, you cannot conclude that the meal alone is the cause. Conversely, if the intensity of your sleepiness changes depending on the contents of your meal even with the same amount of sleep, reviewing your lunch might be an effective clue. If you continue to keep records, you will start to see patterns regarding whether your sleepiness is due to your meals or a lack of sleep.

Blood glucose rise cannot be determined by sleepiness alone

In the aforementioned scoping review, there was only one study that evaluated both blood glucose and sleepiness. This indicates that the relationship between sleepiness and blood glucose has not yet been sufficiently verified. It is important not to decide on your own that "this is a blood glucose spike," but to identify it through recording.

When to consult a medical institution for persistent symptoms

Recording your sleepiness alone cannot tell you your actual blood glucose numbers. The Ministry of Health, Labour and Welfare (MHLW) lists the following as blood glucose criteria for diabetes: a fasting blood glucose level of 126 mg/dL or higher, a 2-hour value of 200 mg/dL or higher in a 75g oral glucose tolerance test, or a random blood glucose level of 200 mg/dL or higher (MHLW "New Diagnostic Criteria for Diabetes and International Standardization of HbA1c"). If strong sleepiness is accompanied by persistent symptoms such as thirst, frequent urination, or weight loss, we recommend not just relying on records but having your blood glucose level measured at a medical institution. If you can confirm it with numbers, you will know exactly what to do next.

How does lunch content change sleepiness?

Even if you have the same "lunch," the way you feel sleepy in the afternoon changes depending on what you choose. Here, we introduce tips you can try from today, including the difference between rice bowls and set meals, the order of eating, and how to combine items at convenience stores.

Differences between rice bowl/noodle lunches and set meal styles

Lunches consisting only of beef bowls, pork cutlet bowls (katsudon), or ramen tend to be carbohydrate-heavy menus. This is because the amount of meat or vegetables is often small relative to the amount of rice or noodles. On the other hand, a set meal style naturally includes rice, a main dish, a side dish, and soup. Since you will be consuming protein and dietary fiber at the same time, it is less likely that you will be consuming only carbohydrates all at once. On days when you choose a rice bowl or ramen at a restaurant, adding just one small side dish such as a salad, chilled tofu, or an egg can change the balance to something closer to a set meal.

How the rise in blood glucose changes with the order and amount of eating

As mentioned above, meals high in carbohydrates tend to raise blood glucose levels rapidly. This rise can be influenced by the order in which you eat. If you eat vegetables and protein first, and carbohydrates such as rice or noodles later, your blood glucose level will rise more gradually. Also, reviewing the quantity itself is important. If the amount of carbohydrates increases due to large portions or extra helpings, the rise in blood glucose will be correspondingly larger. It is a good idea to start by eating vegetables and soup first, and keeping the rice to a normal portion.

Tips for combinations at convenience stores

Even with convenience store bento boxes, you can approach a balance closer to a set meal depending on how you choose. A lunch consisting of a single item, such as just one rice ball or just pasta, is a combination that tends to be carbohydrate-heavy. Adding a salad chicken, an egg, or vegetable sticks to a rice ball can supplement protein and dietary fiber. On days when you choose a sandwich, adding a low-carb hard-boiled egg or yogurt is one way to go. We recommend the habit of adding one more item rather than settling for a single item, especially when you are too busy to take time to choose.

What should you do when you feel strong sleepiness before driving or a meeting?

When you experience strong sleepiness while driving or in a meeting, there are things you should do before trying to pinpoint the cause. Here, we introduce emergency responses to ensure your safety and how to rest on days when you are feeling very sleepy.

Quick ways to wake up (light exercise, cold water)

If you feel sleepy right before a meeting, try standing up and moving your body lightly. Just rotating your shoulders or walking up and down a flight of stairs can change your mood. Washing your face with cold water or drinking a cold beverage are also easy methods to incorporate. If you are driving, try the same after parking your car in a place where you can do so. Even just opening the window to let in outside air can change how you feel about your sleepiness. However, these are just stopgap measures. Since they don't necessarily eliminate the strong sleepiness itself, it is important to check your condition before moving on to the next action.

Prioritize naps or breaks on days when sleepiness is strong

If sleepiness does not go away with light interventions, do not force yourself to proceed with your schedule; prioritize a nap or a break. If it's a meeting, leaving your seat for even a few minutes to close your eyes can make a difference; if you're driving, parking in a designated spot and taking a 15-minute nap can help. Especially when driving, it is more dangerous to continue driving while fighting sleepiness. If days with strong sleepiness continue, do not just treat it as a one-time issue, but look back at your records to see on what kind of days you feel especially sleepy.

Related content is also introduced in How long does sleepiness from a blood glucose spike last? Causes and countermeasures, so please refer to it as well.

Choosing afternoon snacks and the ingredient comparison of BRAIN PRO

When you get hungry around 3:00 PM, what you choose will change how your blood glucose rises. Let's look at how to choose snacks that are not biased towards carbohydrates and specifically look at the nutritional components of BRAIN PRO.

How your blood glucose rise changes based on what you choose for a snack

Sweet snacks and juices are absorbed quickly and push up blood glucose levels in a short time. On the other hand, foods that contain protein and dietary fiber are known to slow the absorption of carbohydrates. For example, there is a difference in the actual amount of carbohydrates you consume between a snack consisting of just one sweet bread versus a snack combined with a hard-boiled egg or nuts. When choosing a snack, it is better to look at how much protein and dietary fiber it contains rather than just its sweetness. For those who are unsure what to choose for a snack while working, please also refer to Recommended snacks for work | How to choose and easy-to-eat products.

Product comparison table based on the balance of carbohydrates and protein

Convenience stores and supermarkets are lined with many products that boast high protein and low carbohydrate content. Even for the same "protein bar," the amount of carbohydrates and protein per bar varies by product. For example, some products keep carbohydrates to around 10g, while others keep them to around 5g, and protein amounts range from around 10g to nearly 20g. When choosing, it is a good idea to look at the nutritional information on the package, compare the carbohydrate and protein figures, and decide based on which one you want to prioritize.

Product	Content	Carbohydrates	Artificial Sweeteners	White Sugar	Protein (Origin)
Calorie Mate Chocolate Flavor	80g (4 bars)	39.7g	None	Used	8.7g / Soy, Wheat
Myprotein Layered Protein Bar Birthday Cake	60g	21g	Used (Sucralose)	Used	20g / Milk, Soy
1-pon Manzoku Bar Protein Vitality Baked Cacao	45g	12g	Used (Aspartame, Sucralose)	None	10g / Soy, Milk
SAVAS Protein Bar 1/2 Day Iron Royal Milk Tea Flavor	38g	Not listed (Sugars 6.4g)	Used (Sucralose)	Used	14.7g / Milk, Soy
BRAIN PRO	35g	4.9g	None	None	11.1g / Plant-based (Pea)

The figures for each product are based on the nutritional information posted on each manufacturer's official website as of September 25, 2026. They may change due to product revisions.

Let's look at the ingredients and nutritional components of BRAIN PRO

BRAIN PRO contains 190 kcal, 11.1g of protein, and 4.9g of carbohydrates per 35g bar. It uses agave syrup, inulin syrup, and stevia sweetener for sweetness, and does not use white sugar. Ingredients include almond paste, pea protein, almonds, and soy puffs, as well as yamabushitake (Lion's Mane) mushroom powder. It does not use preservatives, coloring, trans fats, or animal-based ingredients. However, as it contains soy and almonds, those with allergies should check the ingredient list before choosing. BRAIN PRO is recommended for those who want to avoid white sugar and animal-based ingredients, and for those who want to consume protein while keeping carbohydrates low in their afternoon snacks.

Frequently Asked Questions

What are the signs that blood glucose levels are dropping?

Even if you feel that your sleepiness has faded or your body feels lighter, it is difficult to judge that your blood glucose level has dropped based solely on that physical sensation. Because the intensity of sleepiness is also affected by sleep deprivation and your internal clock, it is difficult to distinguish it from blood glucose movement based on sensation alone. If you want to confirm it numerically, we recommend having your blood glucose measured at a medical institution rather than relying on your own judgment.

When is a blood glucose spike difficult?

"Blood glucose spike" refers to a state where blood glucose levels rise rapidly and fall rapidly after a meal. Many people associate this term with feelings of intense sleepiness or lethargy after a lunch of just rice or noodles. However, this is just a guess based on how you feel; unless you actually measure your blood glucose level, you won't know if the cause of your discomfort is actually blood glucose. Continue to keep records of your sleepiness, meals, and sleep, and compare the patterns.

Summary

Afternoon sleepiness is related not only to blood glucose levels but also to sleep and your internal clock. Whether blood glucose is the cause is best distinguished by keeping a record of your sleepiness, meals, and sleep, rather than relying on intuition. If strong sleepiness interferes with driving or work, do not force yourself and prioritize taking a break, and if symptoms persist, we recommend having your blood glucose confirmed at a medical institution. Reviewing the contents of your lunch and snacks is also one of the ways to make your afternoon more comfortable.