Energy Metabolism—MyKetoPal Knowledge Library E-Book

How the Body Creates Energy—and Why Fuel Choice Matters

Energy is the foundation of life. Every breath, heartbeat, thought, and movement depends on the body’s ability to convert food into usable energy. This process—known as energy metabolism—determines not only how energetic we feel, but how efficiently we age, heal, and resist disease.

Rather than focusing on calories alone, this article explains how energy is produced at the cellular level, why different fuels behave very differently in the body, and how ketogenic metabolism supports long-term metabolic health.

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What Is Energy—and What Is a Calorie?

Energy is the vitality derived from food that powers all bodily functions: breathing, digestion, circulation, movement, and brain activity.

A calorie is simply a unit of energy:

• Technically, it is the energy needed to raise 1 gram of water by 1°C

• Food labels list kilocalories (1,000 calories), though we call them “calories”

While the average person references a 2,000-calorie diet, true energy needs vary widely based on age, sex, body composition, and activity level.

What Is Metabolism?

Metabolism is the complete set of biochemical processes that convert food into energy (ATP).

It includes:

1. Digestion of food into smaller components

2. Absorption through the intestinal wall

3. Transport through the bloodstream

4. Cellular combustion inside the mitochondria

At rest, the body still burns a significant amount of energy to sustain vital functions such as brain activity, breathing, and circulation.

It Takes Energy to Process Food

Digesting food itself requires energy—this is known as the thermic effect of food.

• Carbohydrates and fats require ~5% of their calories to metabolize

• Protein requires ~30% of its calories to metabolize

This means protein yields fewer net calories and supports muscle maintenance, while highly refined carbs are metabolically inefficient.

Burning Fat vs. Burning Carbs

• Carbohydrates and protein provide 4 calories per gram

• Fat provides 9 calories per gram

Because fat is more energy-dense, a fat-based metabolism requires less total food volume to meet energy needs. This is one reason ketogenic diets often reduce hunger naturally.

Food is fuel—but not all fuel behaves the same once inside the body.

Do We Need Carbohydrates at All?

The human body requires a minimal amount of glucose:

• The liver relies on glucose

• Red blood cells can only use glucose

This minimum—about 14 grams per day—is easily supplied by non-starchy vegetables, particularly leafy greens. Fiber carbohydrates are not absorbed and do not spike blood sugar, making them ideal in a ketogenic framework.

How Fuel Reaches the Cells

Glucose travels through the bloodstream attached to red blood cells. Ketones, by contrast, float freely in the blood plasma, requiring no transport assistance.

The human body contains roughly 40 billion capillaries, delivering fuel and oxygen to every cell.

How Oxygen and Fuel Enter Cells

Oxygen enters cells through passive diffusion, requiring no energy.

Fuel entry differs:

• Glucose requires insulin to unlock cell receptors

• Ketones do not require insulin and pass directly into cells

This distinction is critical for individuals with insulin resistance.

Mitochondria: The Cellular Power Plants

Inside each cell are mitochondria—structures responsible for producing ATP, the body’s usable energy currency.

As we age, mitochondrial numbers decline, slowing metabolism and impairing cellular nutrition. Supporting mitochondrial health is essential for sustained energy and longevity.

Cellular Respiration: The “Change Machine”

Cells cannot use glucose or fat directly. These fuels must be converted into ATP.

A helpful analogy:

• Glucose is like a $10 bill, yielding ~38 ATP

• Fat (ketones) is like a $100 bill, producing far more energy

Mitochondria act as a change machine, converting fuel into ATP that powers every cellular process.

Glucose vs. Ketones: A Metabolic Comparison

Ketones offer several metabolic advantages:

• More stable energy production

• Lower oxidative stress

• Fewer free radicals

• Reduced insulin demand

This is why ketones are considered a cleaner-burning fuel at the cellular level.

The Ketogenic Diet as Metabolic Therapy

Originally developed at the Mayo Clinic in the 1920s to treat epilepsy, the ketogenic diet is:

• High in natural fats

• Moderate in protein

• Very low in carbohydrates

By restricting carbs, the body shifts from glucose dependence to fat-derived ketone production, a state known as ketosis.

Importantly, the quality of calories matters. Two foods with equal calories can have vastly different metabolic effects based on fiber, absorption, and hormonal response.

The “Magical” 120 Days

Red blood cells live approximately 120 days. Hemoglobin A1c (HbA1c) reflects how much glucose has attached to these cells over their lifespan.

Because of this:

• Blood sugar improvements take time to fully register

• A ketogenic or low-carb diet should be maintained for at least 120 days to accurately reflect metabolic change

Consistency—not short trials—is key.

So, What Is the Ketogenic Diet in Simple Terms?

A ketogenic diet trains the body to:

• Burn fat instead of carbohydrates

• Lower insulin levels

• Reverse insulin resistance

• Improve cellular energy efficiency

Proven benefits include:

• Improved metabolic flexibility

• Reduced inflammation

• Support against neurodegenerative conditions

• Weight loss without hunger

• Enhanced cellular resilience

Final Thoughts: Energy Is a Cellular Story

Calories alone do not determine health. How energy is delivered, processed, and used at the cellular level matters far more than raw calorie counts.

Metabolic health improves when the body is fueled in a way that aligns with human physiology—stable blood sugar, low insulin demand, and efficient mitochondrial energy production.