What is the relationship between concentration and food/snacks? How to choose based on blood glucose levels and drowsiness

Fluctuations in blood sugar are not the only cause of lapses in concentration

In the afternoon, you may suddenly feel sleepy and find it hard to get work done, wondering what you should eat to get back on track. Do you have questions like these? This article explains the relationship between blood sugar fluctuations and drowsiness, as well as other contributing factors.

The idea that blood sugar fluctuations are linked to drowsiness

After lunch, there are times when you suddenly feel very sleepy and stop what you are doing. A commonly cited explanation for this is the link between blood sugar fluctuations and drowsiness. According to materials from the Ministry of Health, Labour and Welfare, blood glucose is referred to as "blood sugar," and its concentration is the "blood sugar level" (Source: Ministry of Health, Labour and Welfare "Dietary Improvement Guidance Staff Manual"). The idea that significant fluctuations in blood sugar after a meal can cause drowsiness is widely recognized, but there is no strong evidence to support this definitively. In fact, a study comparing days with different breakfast nutritional compositions reported no significant differences in attention or concentration (Source: Paper published in the "Journal of the Japan Dietetic Association"). While the link between blood sugar fluctuations and drowsiness is often discussed, individual differences are significant, and it cannot be generalized.

Other factors such as hunger, lack of sleep, and caffeine withdrawal also play a role

Even if you have the same amount of snacks, there are days when you feel sleepy and days when you do not. It is natural that the timing and intensity of when you lose concentration differ between a day when you had a light lunch and feel very hungry around 3 p.m. and a day when you were sleep-deprived the previous night. You may also be more likely to feel sleepy if a significant amount of time has passed since you last consumed coffee or other caffeinated drinks. Blood sugar fluctuation is just one of these factors and is not the sole determinant. When choosing food or snacks, it is important to consider not only blood sugar fluctuations but also the level of hunger that day, sleep status, and the timing of any beverages consumed.

How should you choose snacks based on nutritional labeling?

By checking the nutritional information on the packaging, you can determine the amounts of carbohydrates and protein. However, what is shown on the label and how your blood sugar reacts after eating are different things. We will look at what can and cannot be determined, along with items you should verify.

While you can tell the "amount" of carbohydrates, you cannot judge how blood sugar will "rise" just from the label

The carbohydrate figure written on the nutritional information label indicates the amount of carbohydrates contained in the product. Materials from the Ministry of Health, Labour and Welfare also explain that carbohydrates are divided into net carbs and dietary fiber. In other words, what can be determined from the label is the content, not how quickly or how high your blood sugar will rise after eating. Even with the same amount of carbohydrates, the rise in blood sugar varies depending on the dietary fiber and fat content, as well as the speed at which you eat. It is good to remember that just because you choose a product with a lower carbohydrate figure, it does not guarantee a gentler rise in blood sugar.

Protein and fat affect satiety

The nutritional information label also lists the amounts of protein and fat. What is important to note here is that snacks consisting only of carbohydrates and those containing protein and fat provide different levels of lasting satisfaction. For example, the timing of when you feel hungry again may differ between eating only carbohydrate-based snacks during an afternoon break and eating something that also includes protein and fat. When choosing, checking the amount of protein and fat in addition to carbohydrates will help you understand the difference in how long you will feel full.

Checking the basic items on nutritional labeling

According to the Consumer Affairs Agency, the basic items for nutritional labeling are energy (calories), protein, fat, carbohydrates, and sodium, with sodium expressed as salt equivalent. When choosing snacks, it is important to look at these five items together rather than getting hung up on a single figure, such as just carbohydrates or just protein. Also, check whether the label is per bag or per 100g. Overlooking the unit can lead to a misunderstanding of the values for the actual amount you are consuming.

Checking the meaning of "No Sugar Added" labels

When you see "No Sugar Added" on packaging, it may look like a product low in carbohydrates. However, under Consumer Affairs Agency standards, to display "No Sugar Added," there are conditions such as not using ingredients or additives that act as sugar substitutes in addition to not adding sugar itself (Consumer Affairs Agency). In other words, it means "no sugar has been added," but it does not mean that carbohydrates naturally present in ingredients like fruit or milk are zero. If you want to know the amount of carbohydrates themselves, it is better to look at the carbohydrate or energy values on the nutritional information label rather than the "No Sugar Added" claim.

Comparing how to choose by snack and food type

Convenience store shelves are stocked with standard snacks like nuts, chocolate, gummies, and yogurt. Although they may look similar or seem equally sweet, the types and amounts of carbohydrates, protein, and fat contained in each food differ when you look at the nutritional information label.

Differences between staples: Nuts, chocolate, gummies, yogurt, etc.

When you feel a bit hungry, you might struggle with what to eat. Standard nuts are made of almonds, walnuts, etc., contain protein and fat, and are relatively low in carbohydrates. Chocolate contains both carbohydrates and fat. It is also a food where the amount consumed at one time tends to vary depending on whether it is a chocolate bar or individually wrapped pieces. On the other hand, gummies contain almost no fat or protein and are primarily carbohydrates. For yogurt, there is a large difference in carbohydrate content between sugar-free and sweetened versions, but protein is contained regardless of the type. These differences can be confirmed by looking at the nutritional information label.

Distinguishing between what can and cannot be said based on "strength of evidence"

The carbohydrate, protein, and fat amounts written on nutritional information labels are facts that can be compared between foods. This much can be stated definitively. However, as mentioned above, there are individual differences in the relationship between blood sugar fluctuations and drowsiness, and one cannot predict the rise in post-meal blood sugar based solely on the label's figures. Therefore, statements like "nuts are less likely to make you sleepy than gummies" cannot be said to have strong evidence. All that can be said is the factual statement from the label that nuts are foods that contain protein and fat. Make a habit of distinguishing between what is fact and what is speculation.

Even with the same "carbohydrate amount," satiety varies by food

When comparing carbohydrate amounts on nutritional labels, one bag of gummies and one bag of nuts might have almost the same value. However, the contents are not the same. While gummies are mostly carbohydrates, nuts also contain protein and fat. If you are unsure which to choose for an afternoon break, it is better to check the protein and fat columns in addition to just looking at the carbohydrate amount. Even with the same "Xg of carbohydrates" displayed, looking at the breakdown will reveal the specific differences between foods.

How true is it that certain foods "increase concentration"?

Glucose and chocolate are often discussed as foods that "increase concentration." However, it is not widely known what the basis for such claims is or under what conditions they do not hold true.

Do glucose or ramune candies increase concentration? Evidence and points of caution

Some people consume ramune or glucose before exams or studying. It is a fact that the brain uses glucose as energy, but there is no strong evidence to suggest that eating a bag of ramune candies will immediately increase your concentration on the spot. What you should be more careful about is what happens after eating. If you choose ramune or glucose, it is best to decide on the amount to eat at once and observe whether or not drowsiness occurs afterwards.

Conditions under which chocolate is more likely to have the opposite effect

Chocolate contains carbohydrates and fat, making it a food that is easy to feel satisfied with even in small amounts. On the other hand, if you eat several chocolate bars in a row, your carbohydrate intake increases all at once. According to Ministry of Health, Labour and Welfare materials, the guideline for carbohydrate intake from meals for adults is approximately 300g. When choosing chocolate, we recommend deciding on the amount to eat at one time.

One cannot say that concentration differs based on breakfast content alone

You may also hear that changing the nutritional balance of breakfast will increase morning concentration. However, in a paper published by the Japan Dietetic Association, no significant differences in attention or concentration were seen even when comparing days with different breakfast nutritional compositions (Japan Dietetic Association "Journal of the Japan Dietetic Association"). Instead of expecting a difference in concentration by changing only the content of breakfast, it is important to look at multiple factors in combination, such as sleep duration and meal timing.

What should be the criteria when choosing at a convenience store?

Choosing snacks at a convenience store involves more than just taste and nutritional content; important criteria also include whether the food will make your hands or desk dirty and whether there is an overlap in sugar or caffeine with your beverages. Let's look at specific items that are easy to eat during work or study.

Choosing items that don't make your hands dirty and don't have strong odors

Sometimes you eat snacks while turning pages of meeting materials or trying not to take your hands off the keyboard. In such situations, it is difficult to choose foods that make your hands dirty. Chocolate melts easily at room temperature, and the oil left on your palms can easily get onto documents or screens. On the other hand, individually wrapped nuts, gummies, and protein bars can be eaten straight out of the package and leave little residue on your hands.

Odor is another criterion that is easily overlooked. Snacks with curry or grilled meat flavors have a strong aroma, which may make you feel self-conscious in meeting rooms or libraries. Conversely, yogurt and protein bars tend to have subtle scents and are generally easy to eat regardless of the location. If you are eating at your desk or in a meeting room, we recommend choosing snacks that are individually wrapped, won't make your hands dirty, and don't have a strong odor.

Differences between nuts, gummies, small-portion chocolates, and protein bars

Nuts contain fat and protein and have a chewy texture even in small amounts, making them suitable for when you want to eat slowly. However, keep in mind that some are high in salt or oil, and eating too many can easily increase your fat intake. Gummies are mostly carbohydrates and contain almost no fat or protein. They provide a quick sugar boost, but they do not keep you full for long. Small-portion chocolates make it easy to adjust the amount per piece and are convenient when you want a small amount to feel satisfied. Protein bars differ from nuts and gummies in that they contain a high amount of protein, and depending on the type, there are differences in how carbohydrates and raw materials are used. For those who want to compare raw materials, carbohydrates, and protein amounts, you can check product differences at How to Choose an Additive-Free Protein Bar? | Comparing Raw Materials, Carbohydrates, and Protein.

Be careful about the overlap of caffeine and sugar in beverages

Many people have snacks while drinking coffee or tea at work. What is easy to overlook here is that you are taking in sugar or caffeine from both the beverage and the food. Sweetened coffee and soft drinks contain carbohydrates themselves. If you combine these with sweet gummies or chocolate, your total carbohydrate intake is the sum of the drink and the food. The same is true for caffeine; if you stack caffeinated soft drinks or energy drinks on top of coffee, your intake will add up. When choosing a beverage, it is important to consider what you plan to eat as a snack and make adjustments for the combination as a whole, such as choosing an unsweetened drink or limiting yourself to one caffeinated beverage.

What to choose based on the situation

What is easy to choose as a snack and the actions you should take change depending on whether it is a short break, a meeting, or immediately after feeling sleepy. Let's look at what to prioritize in each scenario.

What to choose for short breaks and gaps in time

If you have about a 10-minute break, items in amounts that you can finish without leaving your seat are suitable. Bite-sized nuts or chocolates can be eaten as soon as you open the package, so you don't spend the majority of your break time eating. Conversely, snacks that require peeling or dividing from a bag might still be in your hands by the time your break is over. For spare moments, we recommend individually wrapped items that can be finished in a small amount.

How to manage long periods where you cannot move, such as meetings or exams

During meetings or exams, you cannot leave your seat and the timing for eating is limited. In this situation, it is important to decide in advance what to eat and when. Instead of eating everything at once just before the start, it is better to consider dividing the timing, such as having a small amount during a break in the meeting or eating only once before the exam. In situations where you cannot move for a long time, you cannot eat again, so be sure to estimate the required amount in advance.

Differences between responding to the moment you feel sleepy and prevention

Taking a snack after feeling sleepy will only get you through the moment; it will not prevent drowsiness itself. As mentioned above, there are individual differences in the relationship between blood sugar fluctuations and sleepiness, so eating the moment you feel sleepy does not guarantee that you will recover immediately. Taking a small amount before you feel sleepy, for example, 30 minutes before you start a task, is a better way to avoid being reactive. If you are already feeling sleepy, you should also consider methods other than food, such as standing up and moving your body.

Eating amount, timing, and eating habits to avoid

The impression of a snack changes not only by "what you choose" but also by "how much and when you eat it." Here are some guidelines for amounts and specific examples of eating habits to avoid.

Guidelines for the amount to take before studying or work

For snacks before starting a task, using an amount that fits in the palm of your hand makes it easier to prevent overeating. For example, a small bag of nuts or two to three pieces of a chocolate bar are easy units to understand. Since nutritional information labels list values either per bag or per 100g, check which unit it is first to see the amount you are actually going to eat.

If you carry a bag around without deciding on an amount, you may find yourself reaching for pieces little by little between tasks, and before you know it, you might have eaten the whole bag. If you portion it into a small dish or a small bag in advance, you can see the amount you are consuming.

Avoid eating only sweets all at once and watch out for excessive caffeine

Eating only high-carbohydrate snacks such as ramune or gummies at once is said to sometimes lead to sleepiness, as the body's subsequent reaction is not uniform. Be careful, as habits like opening several individually wrapped snacks at once or working with a large bag left open make it difficult to grasp the quantity.

Also, there are situations where people take energy drinks or coffee together with sweet snacks, but if the beverage also contains sugar, the total carbohydrate amount may be higher than expected when combined with the snack. As for caffeine, since some products contain it in both beverages and snacks, it is good to check the package labels. By the way, for those who consume caffeinated drinks multiple times during the day, it is easy for the amount to pile up, so we recommend being mindful of the daily total.

Points for children and those with underlying health conditions

Many households may be choosing snacks for children with the same feeling as adults. Snacks centered on carbohydrates, such as ramune and chocolate, can easily account for a large proportion of a child's single snack intake even in small quantities, so it is better not to apply adult guidelines directly.

Also, for people who need to manage their blood sugar, such as those with diabetes, the movement of post-meal blood sugar can change depending on the amount and type of carbohydrates contained in the snack. Because what and how much you can eat depends on the state of your underlying condition, it is appropriate to consult your doctor or a registered dietitian rather than judging the content of snacks by yourself.

Care is also required for beverages and snacks containing caffeine. Children and pregnant women cannot apply the same intake standards used by adults. If a product has a caffeine content listed on the package, check the label before purchasing.

If you have allergies, checking the raw material label is also essential. For snacks using specific ingredients such as nuts or chocolate, it is a good habit to check where and what is written on the ingredient label every time.

How is BRAIN PRO different from nutritional supplements and bar foods?

Nutritional supplements and bar foods include several categories, such as soy bars and balanced nutritional foods, in addition to protein bars. Let's look at the differences with other categories by checking the raw materials and nutritional information label of BRAIN PRO.

BRAIN PRO's raw materials and nutritional information label

BRAIN PRO contains 190 kcal, 11.1g of protein, 13.5g of fat, 7.1g of carbohydrates (4.9g sugars, 2.2g dietary fiber), and 0.4g of salt equivalent per 35g bar. The ingredients are almond paste, pea protein, almonds, soy puffs, cocoa powder, coconut oil, cacao butter, inulin syrup, agave syrup, lion's mane mushroom powder, rock salt, flavoring, and sweetener (stevia). Allergen labeling includes soy and almonds. White sugar, preservatives, wheat, casein, trans fatty acids, animal-derived ingredients, and artificial coloring are not used.

BRAIN PRO contains 11.1g of protein and 13.5g of fat. It is suitable for those who want to finish their snack with one bar before a meeting in the afternoon or while out and about. Since it does not use animal-derived ingredients, it is also a suitable choice for those refraining from dairy or meat.

Comparison table with other nutritional supplements and bar foods

Nutritional supplements and bar foods include several categories, such as soy bars primarily made from soybeans and balanced nutritional foods with added vitamins and minerals. Even with the same term "protein bar," the raw materials and values listed on the nutritional information labels vary by product. It is important to compare by looking at the values per bar.

Product	Content	Sugars	Artificial Sweeteners	White Sugar	Protein (Source)
Calorie Mate Chocolate	80g (4 bars)	39.7g	Not used	Used	8.7g / Soy, Wheat
Cream Genmai Bran Cacao	36g	17g	Not used	Used	5g / Soy
1-Pon Manzoku Protein Strong Caramel	70g	17g	Used (Sucralose)	Used	30g / Soy, Milk
SAVAS Soy Protein Bar Bitter Chocolate	45g	Not listed (4.2g sugars)	Used (Sucralose)	Used	16.5g / Soy
BRAIN PRO	35g	4.9g	Not used	Not used	11.1g / Plant-based (Pea)

The values for each product are based on nutritional information listed on the official manufacturer's websites as of September 25, 2026. These may change due to product revisions.

Many protein bars prominently display the protein amount, and soy bars are primarily products using soybeans as the main ingredient. Balanced nutritional foods often display added vitamins and minerals. We recommend checking the nutritional information label for each before purchasing rather than judging solely by the category name. For those who want to avoid artificial sweetness or those concerned about whether animal-derived ingredients are present, it is best to choose after checking the ingredient label of BRAIN PRO.

Summary | How to choose food and snacks when concerned about blood sugar and drowsiness

While fluctuations in blood sugar are considered a factor related to drowsiness, it is better to assume there are large individual differences because other factors such as hunger, lack of sleep, and caffeine withdrawal also overlap. What you can tell from nutritional labeling is the amount of carbohydrates and protein; you cannot determine how your post-meal blood sugar will rise just from the label. When choosing, we recommend deciding the amount and timing yourself based on the values on the label. When in doubt, please refer to the criteria for choosing at a convenience store and the comparison between BRAIN PRO and other nutritional supplements and bar foods. Please consult your doctor regarding any concerns.