The Truth About Fat Cells: The 'Hormone Factory' That Controls the Whole Body and the Moment Metabolism Collapses

When we wish to 'lose fat,' we are simply looking for a change in appearance.
However, a much more dynamic and terrifying drama is unfolding inside the body.
Fat cells are not just 'bags of fat,' but the 'body's largest endocrine organ' that determines your lifespan.

1. The True Nature of Fat Cells: The 'Bank' and 'Command Center' of Energy

The role of fat cells can be broadly divided into two.

• Energy Bank: It stores excess energy overflowing in the blood as 'neutral fat (triglycerides).'

• Metabolic Command Center: It is also a chemical factory that secretes over 60 types of hormones, communicating the 'current energy state' to the brain, muscles, and heart.

80-90% of the content is neutral fat, but much of it is composed of oleic acid (omega-9), the same as olive oil. These are controlled by the liver and distributed to 'warehouses' throughout the body.

2. There Are 'Two Routes' for How Fat Increases

When fat increases, two different phenomena are occurring within the body.

1. Proliferation (Route B): The number of cells themselves increases. Since each one can remain small, it is relatively healthy.

2. Hypertrophy (Route A): A single cell swells up like a balloon. It grows to 20 to 30 times its original size.

In fact, this 'hypertrophy' is the root cause of all metabolic diseases.

3. The Barriers of Gender and Ethnicity: Why Even 'Thin' People Get Sick

What is important here is 'individual difference.'

• Women: They have a high ability to 'proliferate' fat cells, and tend to be less prone to metabolic breakdown even when storing a lot of subcutaneous fat.

• Asians (Japanese): Unfortunately, they are not good at 'proliferation' and quickly reach the limit of 'hypertrophy.'

For example, there are two people with the same body type and weight. Suppose both gain 10kg. One is Caucasian and one is Japanese.

In the process of gaining 10kg, the Caucasian person's number of fat cells increased.
In the process of gaining 10kg, the Japanese person's number of fat cells did not increase, but the fat cells themselves became larger.
The size of the Japanese person's fat cells reached their limit, making metabolic disease more likely to occur. On the other hand, from the perspective of metabolic disease, no problems occurred for the Caucasian person.

A guide to the 'accumulation amount' where metabolic dysfunction (disease) begins

The toxicity varies completely depending on where it is stored.

• Subcutaneous fat: Approx. 10kg (a relatively safe warehouse)

• Visceral fat: Approx. 2.5kg (scatters inflammatory substances)

• Liver fat: Just 250g (the critical point that destroys systemic metabolism)

Just 250g (the size of one steak) of fat accumulating in the liver is enough to make insulin ineffective throughout the body.

4. 'Malfunction' of the hormone factory: The loss of balance caused by hypertrophy

Hormones secreted by fat cells are not inherently 'bad guys.'
In fact, they are essential for maintaining our metabolism.

Currently, over 60 types of hormones secreted by fat cells (adipokines) have been discovered and they play a truly wide range of roles, including
appetite, blood sugar regulation, vascular health, and inflammation control.

The problem arises when
fat cells enlarge to their limit and their 'amount' or 'secretion balance' collapses.

Here, we introduce three representative hormones.

Leptin (appetite brake)

Leptin is an important hormone that originally sends a signal to the brain saying, 'I've eaten enough.'
However, when fat cells become excessively enlarged, leptin is secreted in large quantities, but
the brain becomes unable to receive that signal.

This is leptin resistance, which
causes a state where you cannot feel satisfied even after eating.

Adiponectin (hormone that protects blood vessels)

Adiponectin is a

• protective hormone

• that suppresses vascular inflammation and helps insulin function,

which is extremely important for metabolism.

However, when fat cells enlarge, it is also one of the hormones that decreases the most. As a result, the protective mechanisms for blood vessels and metabolism weaken.

PAI-1 (a factor that regulates blood coagulation)

PAI-1 is a substance originally necessary for stopping bleeding.
However, in hypertrophied fat cells, this PAI-1 is secreted in excess.

As a result,

• blood becomes more prone to clotting

• the risk of myocardial infarction and cerebrovascular disease increases

and other such problems occur.

The problem with fat cells is not that they 'release hormones,' but thatthe 'quality and balance' of the hormones break downwithin them.

Fat cells are reliable hormone factories in a healthy state, but when they become fully hypertrophied, that harmony is lost.

5. One cause of insulin resistance is the 'rejection' by fat cells

Insulin is a 'moving company' that tries to push blood sugar into fat cells. However, when cells swell to 20-30 times their size and become 'fully booked,' the cells physically begin to reject insulin, saying, 'Not another drop can fit!'

Insulin continues to try to push blood sugar into the fat cells, but unlike before, the fat cells no longer accept it.

This is the truth aboutinsulin resistance. A hellish loop begins where sugar that has lost its place overflows into the blood, and more insulin is released in an attempt to lower it.

When fat cells enlarge to their maximum size, they fall into a state of severe stress.
As a result, from the fat cells themselves and the immune cells gathered around them,
substances that cause chronic inflammation (cytokines/adipokines)are secreted.

Representative examples are as follows.

• TNF-α (Tumor Necrosis Factor-α)
  A representative inflammatory cytokine that inhibits insulin signaling and directly worsens insulin resistance.

• PAI-1 (Plasminogen Activator Inhibitor-1)
  Makes it harder to break down blood clots, increasing the risk of arteriosclerosis and cardiovascular disease.

• Resistin
  Secreted mainly by immune cells, it promotes insulin resistance through inflammation.

• MCP-1
  Attracts inflammatory cells to adipose tissue, further worsening local chronic inflammation.

6. Detecting the 'Screams of Fat Cells' through Blood Data

To understand the limits of fat cells, the TG (triglyceride) / HDL (good cholesterol) ratio is a very useful indicator.

In fact, many studies have reported that this ratio shows a strong correlation with insulin resistance and cardiovascular disease risk. A large-scale study published in Scientific Reports in 2024 also shows that the higher the TG/HDL ratio, the significantly higher the risk of cardiovascular events and cardiac death. [nature.com]

Guidelines for the TG/HDL ratio

• 1.0 or less: Ideal. Fat cells are small and metabolism is stable

• 2.0 or more: Caution. Possibility that fat cell hypertrophy has begun

• 3.0 or more: Danger zone. Insulin resistance and chronic inflammation are likely to progress

However, judging everything solely by the TG/HDL ratio is insufficient. When fat cells approach their limit, their 'cries for help' appear in other test items as well.

Important indicators to check in conjunction

• Triglycerides (TG): 150 mg/dL or higher
  A sign that fat is beginning to overflow into the liver and visceral fat.
  Strongly associated with insulin resistance and fatty liver. [pmc.ncbi.nlm.nih.gov]

• HDL cholesterol: less than 40 mg/dL
  A decrease in good cholesterol is likely to reflect
  fat cell hypertrophy and chronic inflammation. [pmc.ncbi.nlm.nih.gov]

• ALT (GPT): 30 U/L or higher
  In recent years, even values within the 'normal range' are considered high, and it is emphasized as an
  early sign of fatty liver (fat overflow into the liver). [pmc.ncbi.nlm.nih.gov], [kanagawamed.org]

• Visceral fat area ≥100 cm² on abdominal CT
  When visceral fat exceeds this level, it is highly likely that fat cells have almost certainly hypertrophied to their limit. [NOVO NORDISK]

7. Solution: Shrink fat cells

3 approaches to burning fat

7-1. Lower insulin and unlock fat burning

― Switching to Ketone Mode ―

The biggest factor hindering fat burning is chronically high insulin.

When insulin levels are high, the enzyme that breaks down fat (HSL) is locked, and the body works strongly in the direction of 'storing' rather than 'burning'.

In other words, the reason fat doesn't decrease is not a matter of willpower, but simply that it is locked in a state where it cannot be burned.

Foods that easily raise insulin

The following foods, in particular, are likely to strongly raise insulin.

• Sugar

• Refined carbohydrates

• Ultra-processed foods

You don't need to reduce these to 'zero,' but reducing them as much as possible is the shortcut to fat burning.

When insulin drops, the body finally gets permission to 'burn fat'.

The human body has 'two types of fuel'

The human body, especially the brain, consumes 20% of its energy despite weighing only 2% of the total body weight. And its fuel consists of the following two types.

• Glucose

• Ketone bodies

Many people who eat a lot of carbohydrates or are prone to obesity live their daily lives using 'only glucose' as fuel.

In this state, fat is preserved as emergency energy and is rarely used.

When insulin drops, the body switches to using fat as fuel

When calorie intake is restricted or a low-carbohydrate state continues, insulin in the body decreases, and glycogen (stored glucose) in the liver decreases.

Once in this state, the body switches its energy source, breaks down fat to create ketone bodies, and begins to use them as energy.

This is what is known as 'ketone body mode'.

The important thing is that ketone body mode is not a special diet method, but

👉 a natural metabolic state where fat burning is unlocked

is what it is.

Ways to make it easier to enter ketone body mode

• Fasting

• 12-16 hour time-restricted eating

• Avoiding late-night meals

These are all methods to lower insulin and
return the body to fat-burning mode.

In this state, the proportion of
fat used as an energy source at rest increases.

Fat that is easily affected first

Since ketone bodies are produced in the liver,
in this mode, fat stored in the liver is preferentially used more easily.

As this decreases,

• improvement in insulin sensitivity

• stabilization of blood glucose and lipid metabolism

and other systemic metabolic improvements occur in a chain reaction.

7-2. Consuming fat 'directly' through aerobic exercise

Aerobic exercise such as walking or light jogging
does not have a high immediate effect, but is extremely important in the long term.

• Increasing the ability to use fatty acids as energy

• Improving insulin sensitivity

While exercise alone won't lead to dramatic weight loss, it
becomes the foundation for building a body that burns fat easily.

7-3. Building muscle to increase basal metabolism

Muscle is the body's largest 'fat processing plant'.

When muscle mass increases,

• you consume energy even while doing nothing

• the 'receptacles' that accept glucose and fat increase

As a result, it becomes
easier to avoid rebounding and maintain a healthy weight in the long term.

8. Supplement: What happens in the body when fuel switches

There is a
set order for the body to start using fat as its primary fuel.

8-1. The first thing to decrease is 'liver glycogen'

The first thing consumed is
glycogen (stored glucose) stored in the liver.

• Amount estimate: approx. 80-100g

• Role: 'Ready-to-use energy' to keep blood sugar constant

When periods without eating continue, this glycogen is used preferentially.

Generally,

• it begins to decrease within a few hours

• and drops significantly in about 8 to 24 hours

(there are individual differences depending on activity level, physique, and diet).

8-2. When glycogen decreases, hormones switch

When liver glycogen levels decrease, the body determines that 'glucose alone is not enough.'

That is when a hormonal shift occurs.

• Insulin ↓

• Glucagon ↑

This combination acts as a major metabolic switch.

• Insulin decrease → The command to store fat weakens

• Glucagon increase → A command is issued to mobilize stored energy

8-3. Lipolysis proceeds, and fatty acids are released

As insulin levels drop,

• in fat cells, lipolysis is activated

• fat is released into the blood as free fatty acids

and begins to circulate.

The released fatty acids split into two routes:

• being used directly by the muscles

• and flowing into the liver

.

8-4. The liver begins to produce 'ketone bodies'

When a large amount of fatty acids flows into the liver while glucose is in short supply, the liver begins to produce

ketone bodies from the fatty acids.

This is what is known as 'ketone body mode'.

✅ Important point
Ketone body mode does not occur at the 'exact moment glycogen hits zero,' but rather

It is a state that
gradually intensifies from the stage where glycogen has significantly decreased and insulin has dropped sufficiently.

So, 'when' do ketone bodies start to increase?

As a general guideline:

• Around 12 hours:
  Glycogen depletion + fatty acid utilization begins to become noticeable

• 16 to 24 hours:
  Ketone body production clearly increases, and
  many people start using them for their brain and muscles

*Individual differences apply
(varies depending on typical carbohydrate intake, obesity level, and muscle mass)

Fat most easily affected first in ketone body mode

Since ketone bodies are produced in the liver, what is particularly likely to be used in this mode is fat stored in the liver.

By reducing liver fat,

• improvement in insulin sensitivity

• stabilization of blood glucose control

• reduction in triglycerides

such metabolic improvements tend to occur in a chain reaction.

To summarize the key points

• Fuel switching does not happen through 'willpower'

• Glycogen depletion → hormone switch → fat utilization
  is a natural physiological reaction

• Ketone body mode is not a special method, but
  
  a highly rational mechanism that the body inherently possesses

Summary

Shrinking fat cells is not about enduring, but about changing how the body uses fuel.

• Returning to a body that can burn fat

• Give insulin a rest

• Create a state where fat 'naturally decreases'

This accumulation will gradually return enlarged fat cells to a healthy size.

Depending on how you treat them, fat cells can become your 'greatest ally' or your 'worst enemy.' Before your cells swell to the point of bursting and screaming for help, give insulin a rest and switch to a body type that can burn fat.