Are Blood Sugar Spikes Dangerous? Why “Blood Sugar Control” Is Essential for Dieting and Health

*This article is a translation from Japanese into English.

Feeling sleepy after meals, unable to stop craving sweets, or finding yourself exhausted by the afternoon…

If you’re experiencing these symptoms, you may be experiencing “blood sugar spikes” behind the scenes.

Blood sugar spikes are an “often-overlooked warning sign” deeply linked to weight gain, uncontrollable appetite, fatigue, and health risks.

In this article,

・ What is blood sugar?

・ Why do blood sugar spikes cause weight gain?

・ How can you prevent them?

We’ll break it all down and explain it in an easy-to-understand way.

By understanding the actual mechanisms at work in your body,

you’ll be able to confidently explain it to others.

If you’d like to skip ahead to the conclusion,

you can start reading from section “9. Blood Sugar Control Habits You Can Start Today” in the table of contents.

📝【目次】

1. What is blood sugar?

2. What Are Blood Sugar Spikes? Is Post-Meal Sleepiness and Fatigue a Warning Sign?

3. 3. Why Do Blood Sugar Spikes Cause Weight Gain? How Blood Sugar Levels Lead to Fat Storage

4. Is blood sugar the reason I can’t stop craving sweets?

5. Why do blood sugar spikes increase the risk of disease by 1.5 to 2 times?

6. Skin Problems (Aging, Dryness, Worsening Acne)—Could They Actually Be Caused by Blood Sugar Spikes?

7. 7. Is stress linked to blood sugar levels? People who get angry easily are more likely to develop high blood sugar and high blood pressure without even realizing it.

8. Habits for Managing Blood Sugar You Can Start Today

9. Summary: Why Stable Blood Sugar Levels Lead to Successful Weight Loss

1. What is blood sugar?

The amount of glucose (energy) present in the blood.

Carbohydrates from food, such as rice, are digested and broken down into glucose, which then flows through the bloodstream.

You often hear people say, “If your brain feels tired, it’s good to eat some Ramune (glucose).”

Glucose is an essential source of energy for the brain. (It’s also used by the rest of the body.)

When the amount of glucose reaching the brain decreases (low blood sugar), brain function declines,

and symptoms commonly known as hypoglycemia appear (such as feeling dazed or lightheaded).

Translated with DeepL.com (free version)

See a more detailed explanation of blood sugar levels

Technically known as “blood glucose concentration,”

it is carried through the bloodstream to the entire body as a source of energy.

Any excess that isn't used

is stored in the muscles and liver as “glycogen” and can be converted back into blood glucose as needed.

*The brain consumes approximately 120 grams of glucose per day.

When glucose is insufficient, the body breaks down its glucose reserves—glycogen—to replenish it.

If that is still not enough, a defensive response called “gluconeogenesis” occurs,

in which fat is broken down to produce glucose,

and in extreme emergencies, the body enters a stage where it breaks down muscle to produce glucose.

2. What Are Blood Sugar Spikes? Is Post-Meal Sleepiness and Fatigue a Warning Sign?

A “blood sugar spike” refers to

the phenomenon where blood sugar levels rise sharply after a meal and then drop suddenly.

When this sharp drop occurs,

it can cause symptoms such as:

• severe drowsiness after meals

• lethargy

• cravings for sweets

• irritability

• difficulty concentrating

• increased tendency to gain weight

• difficulty falling asleep

• waking up in the middle of the night

and more.

It is an important sign that is also linked to future health risks.

Post-meal drowsiness and lethargy are classic signs of hidden spikes.

In fact, “a sudden drop in blood sugar levels leads to an energy shortage in the brain,” resulting in symptoms such as decreased concentration, drowsiness, and irritability.

The practice of “eating a light lunch to stay focused” makes perfect sense.

If you struggle with difficulty falling asleep at night or nightmares, you may also be experiencing blood sugar spikes, so it’s worth trying the blood sugar control methods described below.

3. Why Do Blood Sugar Spikes Cause Weight Gain? How Blood Sugar Levels Lead to Fat Storage

When blood sugar levels spike, the body secretes large amounts of insulin to lower them.

Insulin has the effect of

stopping fat breakdown

and switching the body into “fat-storing” mode,

so the higher the spike, the more likely you are to gain weight.

More details on stopping fat breakdown

For fat to be burned,

fatty acids are released from fat cells into the bloodstream

→ transported to the muscles, where they are burned in the mitochondria

(the energy-producing organelles = the “power plants”) of the muscles.

However, when insulin levels are high, the process is halted at the initial stage to prioritize lowering blood sugar levels. (The fatty acids do not enter the bloodstream.)

Note: As cardiovascular and muscular endurance improve, the number of mitochondria increases, enhancing fat-burning capacity and making you less prone to fatigue.

More details on the “fat-storing” mode

When blood sugar levels are high (meaning there is too much sugar in the blood), the sugar that cannot be fully absorbed by the muscles and liver is sent to fat cells, where it is converted from sugar to fat and stored.

What physical reactions trigger the release of insulin? Tell me more.

This is known as homeostasis, the body’s self-regulating mechanism. When levels deviate from a certain range, the body automatically works to restore them to normal. For example, when blood sugar levels rise, the pancreas automatically detects this and secretes insulin.

What happens if blood sugar levels remain high?

・Damage to blood vessel walls

・Inflammation

・Weakening of blood vessels

・Blood becomes thicker and more viscous

・Atherosclerosis

・Increased risk of diabetes

・Increased risk of heart attack and stroke

・Peripheral neuropathy (numbness)

・Damage to the eyes and kidneys (diabetic complications)

When you develop diabetes, your body either produces less insulin or the insulin stops working properly, making it impossible to lower your blood sugar levels—which is extremely dangerous! (Insulin treatment becomes necessary.)

4. Is blood sugar the reason I can’t stop craving sweets?

When blood sugar drops rapidly, the brain interprets this as a sugar shortage—and therefore a crisis—and stimulates the appetite center, leading to

• intense hunger

• cravings for sweets

• irritability

“Feeling hungry right after eating” is a classic reaction to blood sugar spikes.

5. Why do blood sugar spikes increase the risk of disease by 1.5 to 2 times?

👉Case 1

A sharp rise in blood sugar after meals damages the vascular endothelium (damaging blood vessels)

→ Blood vessels harden, leading to poor blood flow

→ This leads to high blood pressure, cold extremities, and fatigue

→ Risk of atherosclerosis

→ The risk of heart attack and stroke increases by about 1.5 to 2 times

👉Case 2

① As the body continues to release large amounts of insulin in response to a sudden spike in blood sugar levels

→ The pancreatic beta cells (which produce insulin) become exhausted

→ The body becomes less able to produce insulin.

② The cells that receive the large amounts of insulin become exhausted

→ The body gradually becomes resistant to insulin

As a result, the body becomes unable to process blood sugar, leading to type 2 diabetes.

What happens to the body when insulin takes effect?

As insulin flows through the bloodstream,

it binds to insulin receptors

on the surfaces of

muscles,

the liver,

and fat cells.

(This is like a key—insulin—being inserted into a keyhole—the receptor.)

When this happens, a sugar receptor called “GLUT4” moves to the cell surface and welcomes glucose from the bloodstream into the cell.

As a result, as muscles, the liver, and fat cells take in glucose,

the amount of glucose in the blood decreases → blood sugar levels stabilize

👉Case 3

When insulin levels are high,

“lipogenesis”—the process by which the liver converts sugar into fat—is activated.

(Since the liver has limited capacity to store sugar, it converts the excess into fat.)

• Fatty liver

• Elevated triglycerides

• Increased visceral fat

• High blood pressure

and other conditions directly linked to metabolic syndrome.

What are the limits of the liver's capacity to store sugar and fat?

While the body can store only about 100–120 grams of sugar, it can store almost unlimited amounts of fat!

This is because fat cells can not only enlarge but also multiply!

Given the significant health risks involved, that’s likely where the limit lies...

👉Others

Dementia (Alzheimer's)

It is also said that vascular damage combined with insulin resistance promotes inflammation in the brain and increases the risk of dementia.

6. Skin Problems (Aging, Dryness, Worsening Acne)—Could They Actually Be Caused by Blood Sugar Spikes?

Excessive insulin secretion stimulates the sebaceous glands,

leading to increased sebum production → which makes pores more prone to clogging.

Furthermore, “glycation”—the process by which glucose binds to proteins—triggers severe inflammation,

• Skin redness

• Worsening acne

• Prolonged inflammation

and other issues, becoming a cause of chronic skin problems.

Glycation causes collagen in the skin to harden

→ As a result of the loss of firmness and elasticity, the following issues are more likely to occur:

• Wrinkles

• Sagging

• Dullness

• Loss of skin elasticity

Controlling blood sugar levels is essential for beauty as well.

7. Is stress linked to blood sugar levels? People who get angry easily are more likely to develop high blood sugar and high blood pressure without even realizing it.

Case 1：Fast-acting type

Stress Stimulus Activated (Psychological/Physical)

→ Sympathetic nervous system (autonomic nervous system) activated

→ Adrenal medulla secretes adrenaline

→ Powerfully promotes the breakdown of sugar (glycogen) in the liver

→ Sugar (glycogen) stored in the liver is rapidly released into the bloodstream.

→ Blood sugar & blood pressure rise

👉 This is what causes sudden spikes when you get “flustered” or feel a “jolt.”

Case 2：Stays angry for a long time

Severe or prolonged stress causes cortisol levels to rise

→ Cortisol is secreted from the adrenal cortex

→ Muscles are broken down (catabolic effect)

→ Glucose is produced in the liver (gluconeogenesis) and released into the bloodstream

→ Blood sugar levels rise

Furthermore, cortisol reduces insulin sensitivity, making it harder for blood sugar levels to drop.

In fact, people who get angry easily experience simultaneous increases in both blood pressure and blood sugar levels, even when they haven’t eaten.

Note: When muscle breakdown occurs...

• Slower recovery

• Easier to lose muscle mass

• Harder to see results from training

It’s also terrible for dieting...

⚠ Lack of sleep + stress are your biggest enemies

8. Habits for Managing Blood Sugar You Can Start Today

◆① Pay attention to the order in which you eat

Eat in the following order: vegetables (fiber) → protein → carbohydrates

That’s all there is to it 👌(※1)

Some studies have shown that this approach can reduce the rise in blood sugar levels by 20–30%.

More information

When you eat vegetables (especially those rich in soluble dietary fiber) first,

the “volume” and “viscosity” of the stomach contents are established early on.

Furthermore, when some of this reaches the small intestine, hormones such as GLP-1 (etc.) are secreted,

sending a signal to say, “Please release the contents from the stomach little by little.”

As a result, the pylorus (the exit of the stomach) does not open fully,

and even staple foods like rice and bread are sent to the small intestine slowly from the very beginning.

Differences Based on the Order of Eating

Sample Meal: White Rice + Meat + Vegetables

When starting with white rice

・30 minutes after eating: Blood sugar level 140–160 mg/dL

・60 minutes after eating: 120–140 mg/dL

・High insulin secretion

When eating in the order of vegetables → meat → white rice

・30 minutes after eating: 100–120 mg/dL

・60 minutes after eating: 100–115 mg/dL

・Insulin secretion is low and stable

◆② Do some light exercise after meals

Take a light walk immediately after eating

(Simply avoiding sitting still makes a big difference)

Post-meal blood sugar fluctuations 👇

・Blood sugar begins to rise about 10–15 minutes after you start eating

・It tends to peak 30–60 minutes after you start eating

→ Light exercise immediately after eating or within 30 minutes can lower the peak

(If moving immediately causes indigestion or an upset stomach, it’s fine to wait 5–10 minutes after eating)

According to recent studies, simply walking for 10 minutes right after a meal has been shown to be highly effective. (*2)

Light exercise causes muscles to absorb glucose, lowering blood sugar levels with almost no use of insulin.

A Comparison of Post-Meal Blood Sugar Levels in Numbers

According to a randomized controlled trial conducted in 2025

in which participants were given glucose to drink,

① No activity (sitting)

② Walking for 10 minutes immediately after ingestion

③ Walking for 30 minutes 30 minutes after ingestion

When these three conditions were compared, the peak blood glucose levels were

① approximately 182 mg/dL

② approximately 164 mg/dL

③ approximately 176 mg/dL

Thus, while condition ③ showed blood glucose levels nearly identical to condition ①,

the 10-minute walk immediately following intake in condition ② resulted in significantly lower levels.

This indicates that, compared to the amount of exercise, “the effect of moving immediately is greater.”

◆③ Limit foods that cause blood sugar levels to rise quickly (high-GI foods)

The glycemic index (GI) is

a numerical measure of how quickly blood sugar levels rise after eating a food.

Foods with a GI of 70 or higher are classified as

high GI,

those with a GI of 69–56 as

medium GI,

and those with a GI of 55 or lower as

low GI.

Here are some examples of replacing

high-GI foods that cause blood sugar levels to rise quickly

with low-GI foods.

For example, replace white rice (GI value approx. 85)

→ with brown rice, mixed grain rice, or glutinous barley (GI value approx. 55)

Replace bread (GI value approx. 90)

→ with whole wheat bread or rye bread (GI value 50–60)

Replace high-GI sweets with high sugar content with low-GI nuts, etc.

Even with high-GI foods, you can control blood sugar levels by paying attention to the order in which you eat them and chewing thoroughly.

◆④ Get Enough Protein

The Effects of Protein 👇

・Protein has virtually no direct effect on raising blood sugar levels

・It also slows down sugar absorption

・It also stimulates the secretion of satiety hormones (GLP-1, CCK)

Surprisingly, many people don’t get enough protein unless they make a conscious effort.

General guideline: Body weight (kg) = Protein intake (g)

Example: If you weigh 60 kg, aim to consume at least 60 g per day.

If you want to build muscle, you’ll need to consume even more (around 1.5 times that amount).

◆⑤ Improve Sleep Quality

Lack of sleep reduces insulin sensitivity.

Reasons:

・Chronically elevated levels of the stress hormone (cortisol).

・The sympathetic nervous system remains constantly activated.

・Levels of the appetite-stimulating hormone (ghrelin) increase, while levels of the satiety hormone (leptin) decrease.

・Growth hormone decreases, making it harder to burn fat and easier to lose muscle mass.

9. Summary: Why Stable Blood Sugar Levels Lead to Successful Weight Loss

• Insulin levels stabilize, making it easier to burn fat

• Appetite stabilizes, preventing overeating

• Weight gain caused by stress is reduced

• The risk of disease is also lowered

When blood sugar levels stabilize, both your body and mind are in a state that makes it easier to lose weight.

📚Source:

※1：

Imai S, Fukui M, Kajiyama S. Effect of eating vegetables before carbohydrates on glucose excursions in patients with type 2 diabetes. J Clin Biochem Nutr. 2014 Jan;54(1):7-11. doi: 10.3164/jcbn.13-67. Epub 2013 Dec 27. PMID: 24426184; PMCID: PMC3882489.

※2：

Hashimoto K, Dora K, Murakami Y, Matsumura T, Yuuki IW, Yang S, Hashimoto T. Positive impact of a 10-min walk immediately after glucose intake on postprandial glucose levels. Sci Rep. 2025 Jul 2;15(1):22662. doi: 10.1038/s41598-025-07312-y. PMID: 40594496; PMCID: PMC12216464.