Which Fuel Does Your Body Really Prefer—Glucose or Ketones?
- Richelle Lecourt
- Apr 16
- 3 min read
Updated: Apr 17
Our bodies are brilliantly designed to adapt to different fuel sources, and the two main players in this energy game are glucose (from carbs) and ketones (produced from fat). But did you know that certain organs actually prefer ketones over glucose? And others thrive on a steady stream of sugar?
Let’s take a closer look at who prefers what—and why that matters for your health, energy, and mental clarity.
Organs That Prefer Ketones
1. The Brain
Contrary to popular belief, your brain doesn’t need carbs to function. While some parts do require glucose, the majority of the brain can run beautifully on ketones—especially beta-hydroxybutyrate (BHB). In fact, during extended fasting or a ketogenic/carnivore state, ketones can supply up to 70% of the brain’s energy needs.Why it matters:Ketones are neuroprotective, reduce inflammation, and provide a cleaner, more efficient fuel source for the brain.
2. The Heart
Your heart is a high-performance organ that works non-stop—and it runs more efficiently on ketones than on glucose.Why it matters:Ketones boost cardiac output and lower the amount of oxygen needed to generate energy, meaning your heart can do more with less.
3. Muscles (Especially During Low-Carb States)
Skeletal muscles are metabolically flexible, but during periods of low carb or fasting, they shift toward using ketones and fatty acids.
Why it matters: Using ketones helps preserve glycogen and supports endurance and recovery, especially in fat-adapted individuals.
4. Kidneys
Your kidneys also take in ketones during states of ketosis, helping to maintain acid-base balance and even contribute to gluconeogenesis (making new glucose as needed).
Why it matters:Ketones support kidney function without the glucose swings.
Organs That Prefer Glucose
While ketones are an amazing, clean-burning fuel, some parts of the body still require glucose, even during ketosis:
1. Red Blood Cells
RBCs lack mitochondria, so they rely solely on glucose through anaerobic metabolism.
2. The Retina & Certain Brain Cells
Some specialized brain and eye tissues need glucose for proper function.
3. Intestinal Mucosa
The lining of the gut uses glucose for regeneration and maintaining a healthy barrier.
But here's the kicker:Even on a low-carb or carnivore diet, your body can make all the glucose it needs through gluconeogenesis—so you're never actually in danger of "not getting enough."
So Which Fuel Is Better?
Glucose pros:
Quick, accessible energy (especially in emergencies or high-intensity effort)
Supports anaerobic activity (like sprinting or explosive lifting)
Some cells require it (RBCs, retina, etc.)
Ketone pros:
Clean-burning and anti-inflammatory
Supports cognitive clarity and stable mood
Enhances endurance, heart efficiency, and mitochondrial function
Reduces oxidative stress and brain fog
The Beauty of Metabolic Flexibility
In a healthy body, you’re able to switch between glucose and ketones as needed. But many people today are stuck in sugar-burning mode—reliant on constant carb intake, with blood sugar roller coasters and energy crashes.
By tapping into ketones—whether through fasting, carnivore, or keto—you unlock your body’s original backup generator. One that’s not only efficient, but also healing.
Bottom line:
Glucose is useful. But ketones? They’re powerful, restorative, and preferred by some of your most vital organs. When your body has access to both, it thrives. When it’s free from sugar dependency, it begins to heal.
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