Published by Paul Thompson |
Fact-checked against peer-reviewed sources | Updated March 2026

# Ketosis Explained

Understanding Your Body's Natural Fat-Burning State

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Ever wondered how your body can switch from burning carbs to burning fat? It's called ketosis - and understanding it is the key to making the keto diet work for you.

### Your Body's Two Fuel Systems

Think of your body like a hybrid car - it can run on two different fuels

🍞
Glucose Mode

Default fuel from carbs
Burns sugar for energy
Stores excess as fat

→
🔥
Ketone Mode

Activated by low carbs
Burns fat for energy
Produces ketones

## What Exactly Is Ketosis?

Ketosis is a natural metabolic state where your body switches from using glucose (sugar) as its primary fuel to using ketones - molecules produced when your liver breaks down fat.

This isn't some new diet trick - it's how humans survived for thousands of years when food was scarce. Your body is designed to do this.

### The Science Made Simple

When you drastically reduce carbs, your glucose stores deplete within 3-4 days. Your body then turns to fat - both dietary fat and stored body fat - breaking it down in the liver to produce three types of ketones: acetoacetate, beta-hydroxybutyrate (BHB), and acetone. These ketones can fuel almost every cell in your body, including your brain.

## How Long to Enter Ketosis?

Days 1-2

Your body uses up stored glucose (glycogen) from liver and muscles

Days 3-4

Ketone production begins as fat breakdown increases

Week 1-2

Full ketosis achieved - body efficiently burning fat for fuel

Week 3+

Fat-adapted - your body becomes highly efficient at using ketones

## The Keto Macros

To enter and maintain ketosis, you need to dramatically shift what you eat:

Fat: 70-75%
Protein: 20%
Carbs: 5-10%

This typically means keeping carbs under 50g per day (some aim for 20g). For perspective, that's less than a single bagel or two bananas.

## Why Ketones Are "Super Fuel"

⚡
More ATP
Ketones produce more energy per molecule than glucose
🧠
Brain Fuel
Ketones easily cross the blood-brain barrier
🎯
Steady Energy
No blood sugar spikes and crashes
🍽️
Less Hunger
Ketosis naturally suppresses appetite

### 2024 Research Discovery

Stanford researchers recently discovered a new metabolic pathway - BHB-amino acids - that explains why ketosis suppresses appetite and promotes weight loss. This "shunt pathway" directly links ketones to energy regulation in ways scientists didn't previously understand.

## The "Keto Flu"

During the first week, some people experience temporary symptoms as their body adapts:

- Headache and fatigue
- Brain fog
- Irritability
- "Keto breath" (fruity or metallic taste)

This usually passes within a week. Staying hydrated and keeping electrolytes up helps significantly.

#### Important Note

Nutritional ketosis is safe and different from diabetic ketoacidosis (DKA). In ketosis, ketone levels are controlled and blood remains at normal pH. DKA is a dangerous condition in diabetics where ketones build to harmful levels. If you have diabetes, consult your doctor before starting keto.

### Ready to Try Keto?

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