Creatine: More Than a Muscle Supplement — What the Science Says About Energy, Strength, Aging, and Brain Health

Creatine is a naturally occurring nitrogen-containing compound that plays an important role in cellular energy metabolism.

It is not a hormone.

It is not a stimulant.

And despite a surprisingly persistent misconception, creatine is not an anabolic steroid.

Creatine synthesis occurs through a two-step biochemical pathway involving several tissues, with the kidneys and liver playing particularly important roles.

In the first step, an enzyme called arginine:glycine amidinotransferase (AGAT) transfers an amidino group from arginine to glycine.

This produces a molecule called guanidinoacetate.

This reaction occurs prominently in the kidneys and other tissues expressing AGAT.

Guanidinoacetate can then enter the circulation and travel to tissues including the liver.

There, another enzyme—guanidinoacetate methyltransferase (GAMT)—adds a methyl group to guanidinoacetate.

That methyl group comes from S-adenosylmethionine (SAM).

The result is:

Creatine.

Methionine participates in this process through the methylation cycle.

Methionine is used to generate S-adenosylmethionine (SAM), one of the body’s major methyl-group donors. SAM then donates the methyl group required to convert guanidinoacetate into creatine.

This makes creatine synthesis directly connected to methylation. Endogenous creatine synthesis represents a meaningful component of the body’s normal methyl-group demand. As SAM donates its methyl group during creatine synthesis, it is converted to S-adenosylhomocysteine (SAH), which can subsequently contribute to the formation of homocysteine. This creates an important biochemical connection among creatine synthesis, methionine metabolism, methylation, and homocysteine.

Once creatine is synthesized, it enters the circulation.

Creatine obtained through food or supplementation also reaches the bloodstream after intestinal absorption.

From there, creatine is transported into tissues through a specialized creatine transporter commonly called CRT1, encoded by the SLC6A8 gene.

Approximately 95% of the body’s creatine pool is located in skeletal muscle.

A substantial portion of the muscle creatine pool exists as phosphocreatine.

That distinction is central to understanding why creatine matters.

Plant foods generally contain very little creatine.

Vegetarians and vegans therefore typically consume substantially less dietary creatine and may have lower baseline muscle creatine stores than people who regularly consume meat or fish.

This can become relevant during supplementation.

Someone beginning with lower muscle creatine stores may have greater capacity to increase those stores when supplemental creatine is introduced.

A small portion of creatine and phosphocreatine is also continuously converted into creatinine, which enters the bloodstream and is ultimately eliminated by the kidneys.

That relationship becomes clinically important when interpreting kidney-function blood tests, which we will discuss later.

ATP stands for adenosine triphosphate.

ATP is the fundamental energy currency of the cell and is essential for nearly every energy-dependent biological process required to sustain life. Cells continuously produce, consume, and regenerate ATP to power the work necessary for normal cellular function and survival.

We obtain energy from food, but our cells cannot directly use the calories contained in a steak, bowl of rice, or stored body fat to contract a muscle, transmit a nerve impulse, maintain an ion gradient, or repair cellular structures.

Those nutrients must first be metabolized.

Their stored chemical energy is converted through a series of metabolic pathways into forms the cell can use—most importantly ATP.

At a broad level, the body generates ATP by extracting chemical energy primarily from carbohydrates and fats.

Protein can also contribute to energy production, particularly during fasting, calorie restriction, prolonged exercise, or other metabolic circumstances.

However, amino acids have numerous structural and metabolic roles and are generally not the body’s preferred primary fuel source under normal conditions.

Carbohydrates and fats begin their journeys through different metabolic pathways.

Eventually, much of their energy production converges on mitochondrial metabolism.

Dietary carbohydrates are broken down largely into glucose.

Glucose can circulate through the bloodstream and be used by tissues or stored as glycogen, particularly in the:

Liver

and

Skeletal muscle

These glycogen stores serve somewhat different purposes.

Liver glycogen can be broken down to help maintain blood glucose availability for the rest of the body.

Muscle glycogen primarily provides a local carbohydrate reserve for the muscle itself.

When cells metabolize glucose, one of the first major pathways is glycolysis.

Importantly, glycolysis occurs in the cytosol, not inside the mitochondria:

Glucose → Glycolysis → Pyruvate

Glycolysis can generate ATP relatively rapidly and produces a small amount of ATP directly.

Pyruvate can then enter the mitochondria and be converted into:

Acetyl-CoA

Acetyl-CoA subsequently enters the citric acid cycle, also known as the Krebs cycle or TCA cycle.

This is an important misconception.

Human metabolism does not operate through a simple system in which the body burns carbohydrate for the first 20 or 30 minutes of exercise and then suddenly switches to fat.

Carbohydrate and fat are generally being used at the same time.

What changes is their relative contribution.

During lower-intensity and longer-duration activity, fat oxidation can supply a greater proportion of the body’s energy requirements.

As exercise intensity increases, the body generally becomes increasingly dependent on carbohydrate because carbohydrate metabolism can support more rapid ATP production.

Fat represents the body’s largest stored energy reserve.

Most stored body fat exists as triglycerides within adipose tissue.

When energy is required, triglycerides can be broken down and fatty acids released into the circulation.

Those fatty acids can be taken up by tissues and transported into mitochondria.

Within mitochondria, fatty acids undergo beta-oxidation.

Beta-oxidation progressively breaks fatty acids into acetyl-CoA while also generating high-energy electron carriers.

Acetyl-CoA then enters the TCA cycle.

Carbohydrate and fat therefore begin through different metabolic pathways but ultimately converge on much of the same mitochondrial machinery for ATP production.

However, they are not interchangeable energy sources.

Carbohydrate can support ATP production at a much faster rate, making it particularly important when energy demand rises rapidly, such as during high-intensity exercise. Glucose can also generate ATP through glycolysis before mitochondrial oxidation occurs, allowing carbohydrate to contribute to ATP production especially quickly.

Fat, in contrast, is a slower fuel to mobilize and oxidize, but it is an extraordinarily energy-dense fuel capable of yielding substantially more ATP per molecule than glucose. Fat therefore becomes particularly valuable for sustained energy production when ATP demand does not exceed the rate at which fatty acids can be mobilized and oxidized.

In most aerobic tissues, mitochondrial oxidative metabolism provides much of the ATP required during rest and sustained activity.

Inside mitochondria, acetyl-CoA enters the TCA cycle.

Rather than producing enormous amounts of ATP directly, the TCA cycle captures much of the energy derived from fuel in high-energy electron carriers, particularly:

NADH

and

FADH₂

These molecules deliver electrons to the electron transport chain located along the inner mitochondrial membrane.

As electrons move through this system, their energy is used to pump hydrogen ions—protons—across the mitochondrial membrane.

This produces an electrochemical gradient.

Those protons then flow back across the membrane through an extraordinary molecular enzyme called ATP synthase.

ATP synthase uses the energy contained within that gradient to drive:

ADP + phosphate → ATP

This process is called oxidative phosphorylation.

Oxygen plays a critical role at the end of the electron transport chain by accepting electrons and ultimately participating in the formation of water.

This is one of the fundamental reasons humans require oxygen.

The oxygen we breathe allows the mitochondrial electron transport system to continue operating efficiently, supporting sustained ATP production.

The larger picture can therefore be simplified:

Food or stored energy → metabolic fuel → cellular metabolism → ATP → cellular work

ATP consists of adenosine attached to three phosphate groups.

When cells require energy, ATP can undergo hydrolysis:

ATP + H₂O → ADP + Pi + energy

ATP becomes adenosine diphosphate (ADP) and inorganic phosphate (Pi).

The free energy associated with this reaction can then be coupled to cellular work.

In skeletal muscle, ATP is required at several points in the contraction-relaxation cycle.

ATP interacts with myosin, the molecular motor protein that generates force against actin during muscle contraction.

ATP is also required to pump calcium back into the sarcoplasmic reticulum and to maintain ion gradients necessary for repeated electrical signaling and muscle contraction.

ATP therefore helps muscle fibers:

Contract → Relax → Reset → Contract again

Despite continuously producing and consuming ATP, skeletal muscle does not maintain a large reserve of ATP.

ATP must therefore be continuously regenerated from ADP.

The body’s major energy systems differ in both speed and capacity.

This is the central reason creatine matters.

Inside skeletal muscle, creatine can accept a high-energy phosphoryl group and become phosphocreatine.

When ATP availability is adequate:

Creatine + ATP → Phosphocreatine + ADP

Energy can therefore be temporarily stored within the phosphocreatine pool.

The human body has enormous stores of potential energy.

A relatively lean adult still stores tens of thousands of calories in adipose tissue.

But having energy stored somewhere in the body is not the same thing as being able to convert it into ATP instantaneously.

Extracting energy from fat requires fatty-acid mobilization, transport, mitochondrial entry, beta-oxidation, the TCA cycle, electron transport, and oxidative phosphorylation.

Carbohydrate can support faster ATP turnover, particularly through glycolysis, but still requires metabolic processing.

This makes the phosphocreatine system particularly important during the first seconds of intense muscular activity, including:

• Heavy resistance exercise
• Sprinting
• Jumping
• Explosive acceleration
• Repeated high-intensity contractions

Imagine beginning a heavy set of squats.

The moment the muscle begins producing substantial force, ATP consumption increases dramatically.

The small amount of ATP already present inside the muscle is immediately available.

Almost immediately, phosphocreatine begins transferring phosphate to ADP to help regenerate ATP.

As the set continues, phosphocreatine concentrations decline.

Glycolysis contributes increasingly to ATP regeneration, while mitochondrial oxidative metabolism continues contributing as well.

Eventually, the ability to sustain the required rate of ATP regeneration becomes one of several factors contributing to fatigue.

The phosphocreatine system is important not only during muscular contraction but also during recovery.

After an intense effort, phosphocreatine stores must be replenished.

ATP produced largely through oxidative metabolism can be used to re-phosphorylate creatine:

Creatine + ATP → Phosphocreatine

Creatine supplementation does not create energy from nothing.

It does not replace glucose.

It does not replace fat.

It does not replace mitochondria.

And it does not function like a stimulant.

Instead, supplementation increases the amount of creatine available within the muscle’s creatine-phosphocreatine energy-buffering system.

That can increase the amount of phosphocreatine available for rapid ATP regeneration.

A single additional repetition may seem insignificant.

But muscle adaptation occurs through repeated training over time.

An additional repetition here, slightly greater resistance there, or better performance during later sets can accumulate across hundreds of sets and months of training.

That is one of the most important ways creatine can ultimately contribute to strength and muscle development.

Creatine is sometimes discussed as though it directly builds muscle in the same way that anabolic hormones influence muscle protein synthesis.

That is not an accurate description of its primary established mechanism.

Creatine does not provide the amino acids needed to construct new muscle proteins.

And taking creatine without an appropriate training stimulus does not reproduce the adaptations produced by resistance training.

One of the earliest changes some people notice after beginning creatine is an increase in body weight.

This is frequently misunderstood.

Creatine is osmotically active.

As creatine concentrations increase within skeletal muscle, intracellular water can increase as well.

At R2 Medical Clinic, we frequently emphasize that successful weight loss should not be judged by the scale alone.

The goal is generally not simply to become lighter.

The goal is to reduce excess body fat while preserving as much healthy skeletal muscle, strength, and physical function as possible.

That distinction becomes particularly important when weight loss occurs rapidly.

To lose stored body fat, the body must ultimately expend more energy than it receives over time.

That creates an energy deficit.

This is necessary for fat loss.

But the body does not exclusively remove energy from adipose tissue while perfectly protecting every other tissue.

The goal should therefore not simply be:

Lose as much weight as possible.

A better goal is:

Lose excess body fat while preserving as much functional lean tissue as reasonably possible.

Creatine does not independently prevent muscle loss.

And it cannot compensate for inadequate protein or the absence of resistance training.

Its potential value becomes more logical when we consider the physiology we have already discussed.

Consider someone who is simultaneously:

Losing body fat

while

Preserving more muscle

and

Increasing intracellular muscle water after beginning creatine.

The scale may move less than expected.

If we looked only at total body weight, we might conclude that progress was inadequate.

The creatine discussion becomes increasingly interesting with age.

Beginning in midlife and progressing with aging, humans tend to experience gradual declines in skeletal muscle mass, strength, and physical performance.

Age-related loss of muscle is often discussed in the context of sarcopenia, although modern definitions emphasize strength and physical function in addition to muscle mass.

Resistance training and adequate dietary protein therefore become increasingly important with age.

Creatine may enhance some of the adaptations produced by resistance training.

Meta-analyses generally suggest that adding creatine to resistance training in older adults can provide additional benefits for strength and may support improvements in lean tissue.

Effects vary among studies, and outcomes related to physical function are less consistent.

Creatine should therefore not be promoted as something that independently prevents aging or sarcopenia.

Creatine is sometimes incorrectly viewed as primarily a supplement for men.

There is no biological reason to think of it that way.

Women rely on the same creatine-phosphocreatine energy system.

Skeletal muscle is not the only tissue requiring rapid and reliable ATP availability.

The brain is one of the most metabolically demanding organs in the body.

Possibly in certain circumstances—but the evidence is considerably less established than it is for muscular performance.

Systematic reviews and meta-analyses have reported potential improvements in certain measures of memory, attention, or information-processing speed.

However, benefits have not been demonstrated consistently across every cognitive domain or population.

Researchers have proposed that creatine may become particularly relevant when cerebral energy demand is increased or baseline creatine availability is relatively low.

Creatine metabolism has an important relationship with methylation.

As discussed in our previous R2 Medical Clinic articles on methylation and homocysteine, methyl groups are continuously transferred among molecules throughout the body.

One of the body’s most important methyl donors is S-adenosylmethionine, or SAM.

Earlier, we discussed how the body synthesizes creatine:

Arginine + Glycine → Guanidinoacetate

Guanidinoacetate must then receive a methyl group before it becomes creatine.

That methyl group is donated by SAM through the enzyme guanidinoacetate methyltransferase (GAMT):

Guanidinoacetate + SAM → Creatine + SAH

When SAM donates its methyl group, it becomes S-adenosylhomocysteine (SAH).

SAH can subsequently be converted into homocysteine.

The significance of this pathway is not simply that creatine synthesis happens to require a methyl group.

Endogenous creatine synthesis represents a substantial component of the body’s normal SAM-dependent methylation demand.

In other words, synthesizing creatine internally requires the body to continually use methyl groups.

This makes creatine synthesis one of the meaningful metabolic pathways drawing from the body’s methylation system.

That becomes particularly interesting when supplemental creatine is introduced.

The body regulates its own creatine synthesis.

When more creatine is supplied through supplementation, feedback mechanisms can reduce endogenous creatine synthesis.

The body therefore does not need to synthesize as much creatine from arginine, glycine, guanidinoacetate, and SAM.

This can reduce some of the methyl-group demand associated with endogenous creatine synthesis.

This is where biochemical plausibility needs to be separated from demonstrated clinical outcomes.

Because creatine synthesis consumes methyl groups and contributes to SAH and homocysteine formation, it is reasonable to investigate whether suppressing endogenous creatine synthesis through supplementation could influence homocysteine concentrations.

But that does not mean creatine supplementation has been proven to reliably lower homocysteine in everyone.

This is also a useful example of a broader principle:

Understanding a biochemical pathway does not automatically mean that manipulating one part of that pathway will produce a predictable clinical outcome.

Creatine does not remain in the body’s creatine pool indefinitely.

A small portion of creatine and phosphocreatine continuously undergoes spontaneous conversion into creatinine.

Creatine and creatinine are not the same molecule.

Creatine participates in cellular energy metabolism.

Creatinine is a breakdown product formed from creatine and phosphocreatine.

This conversion occurs spontaneously and does not require a specific enzyme.

Because approximately 95% of the body’s creatine pool is located in skeletal muscle, muscle mass can influence creatinine production.

This is one reason a muscular individual may naturally have a higher serum creatinine concentration than someone with substantially less muscle mass.

Once creatinine enters the bloodstream, the kidneys remove it primarily through glomerular filtration, with some contribution from tubular secretion.

Under relatively stable conditions:

Creatinine production → bloodstream → kidney filtration → urine

If kidney filtration declines, creatinine clearance generally decreases and serum creatinine rises.

But decreased filtration is not the only reason serum creatinine can increase.

Creatinine can also rise because production has increased.

This distinction becomes particularly important in someone taking creatine.

Creatine supplementation increases the body’s creatine pool.

Because a portion of creatine and phosphocreatine continuously becomes creatinine, supplementation can modestly increase serum creatinine in some people without representing actual kidney damage.

One of the most commonly reported measurements of kidney function is estimated glomerular filtration rate, or eGFR.

Most routine eGFR calculations use serum creatinine.

If creatinine increases because production has increased rather than because filtration has declined, a creatinine-based eGFR may appear lower even when actual kidney filtration has not meaningfully changed.

Importantly, creatinine itself is not damaging the kidneys. An increase in serum creatinine is clinically important because it can be a marker of reduced kidney filtration—but when creatinine rises because its production has increased, as can occur with creatine supplementation, the higher value does not necessarily represent kidney injury.

Many are marketed as being more advanced than traditional creatine.

But newer does not automatically mean better.

Creatine monohydrate remains the most extensively studied form of creatine.

It has decades of research supporting its effectiveness, safety, and ability to increase muscle creatine concentrations.

For most people, there is little evidence that more exotic—and often more expensive—forms provide meaningful advantages over creatine monohydrate.

Micronized creatine monohydrate is still creatine monohydrate. Its smaller particle size may improve how easily it disperses in liquid, but it does not fundamentally change the creatine molecule.

Probably not.

Creatine does not function like caffeine.

You do not take creatine immediately before exercising and suddenly experience a pharmacologic burst of energy.

Its effects primarily result from gradually increasing tissue creatine stores.

There is no established physiological requirement to cycle creatine.

Some supplement regimens historically recommended taking creatine for several weeks, stopping, and then restarting.

There is little evidence that this is necessary in otherwise healthy adults using conventional doses.

When supplementation stops, elevated muscle creatine concentrations gradually return toward baseline.

Creatine supplementation does not appear to permanently suppress the body’s ability to synthesize creatine.

This is another longstanding belief that has not held up particularly well under controlled research.

Creatine can increase water associated with muscle tissue.

But increased intracellular muscle water does not mean the rest of the body becomes dehydrated.

Research generally has not demonstrated that conventional creatine supplementation causes dehydration or increases muscle cramping in healthy individuals.

Normal hydration remains important—particularly during exercise, heat exposure, illness, or heavy sweating—but creatine does not appear to require extreme water consumption.

This claim largely originated from a small study reporting changes in dihydrotestosterone, or DHT, following creatine supplementation.

That observation eventually became widely repeated online as:

“Creatine causes baldness.”

That conclusion was not demonstrated.

Hair loss itself was not measured in that study.

Subsequent evidence has not established that creatine supplementation causes male-pattern hair loss.

At present, there is insufficient evidence to conclude that creatine causes baldness.

Creatine can increase body weight.

But body weight and body fat are not the same thing.

Early increases in body weight may reflect increased intracellular muscle water.

Longer-term increases may also reflect greater lean tissue when creatine is combined with resistance training.

Creatine itself has not been shown to meaningfully increase body fat.

This again illustrates why interpreting changes in scale weight without considering body composition can be misleading.

This is an area where marketing sometimes moves faster than science.

Creatine is increasingly included in discussions about longevity.

There are legitimate reasons for that interest.

Muscle strength, physical function, metabolic health, and preservation of lean tissue become increasingly important with age.

Creatine may support several of those areas—particularly when combined with resistance training.

Research into brain energetics, cognition, cellular energy metabolism, and other potential clinical applications also continues.

Resistance Training
Muscle requires a mechanical stimulus to maintain strength and adapt.

Adequate Protein
Muscle protein synthesis requires amino acids.
Creatine does not replace dietary protein.

Appropriate Energy Intake
Extreme caloric restriction can make muscle preservation more difficult.

Sleep and Recovery
Training adaptation requires recovery.

Hormonal and Metabolic Health
Testosterone, estrogen, thyroid function, insulin sensitivity, and other physiologic systems can influence body composition and physical performance.

Consistent Physical Activity
Strength is important, but cardiovascular fitness, mobility, balance, and daily movement also matter.

Creatine monohydrate has an extensive safety record in generally healthy adults, but supplementation should still be individualized.

Creatine is unusual in the supplement world.

Many supplements become popular first and are studied afterward.

Creatine has accumulated decades of human research.

Its fundamental physiology is well established.

In skeletal muscle, that can translate into improved high-intensity exercise capacity and greater training adaptation.

During medical weight loss, those effects may help support the resistance training needed to preserve muscle while body fat is being reduced.

With aging, they may complement strategies designed to preserve strength, muscle, and physical function.

In the brain, the same energy-buffering system has generated legitimate scientific interest, although cognitive benefits remain less certain.

And in clinical medicine, creatine provides a useful reminder that laboratory numbers require context: supplemental creatine can influence serum creatinine without necessarily representing deterioration in kidney filtration.

At R2 Medical Clinic, we view supplements as potential tools—not substitutes for physiology.

Whether the goal is medical weight loss, maintaining muscle during aging, improving physical performance, or optimizing overall metabolic health, the first question should not simply be:

“What supplement should I take?”