The Randle Cycle Explained: Why Choosing Fat as Your Primary Fuel Matters
The human body is designed to run on one fuel at a time. This is the essence of the Randle cycle, also known as the glucose-fatty acid cycle. It explains how fat and glucose compete inside your cells. Understanding this process gives you a clearer picture of why mixing sugar and fat is a problem and why choosing fat as your main energy source supports better health.
What Is the Randle Cycle?
In 1963, Philip Randle and colleagues described how cells switch between glucose and fatty acids as fuel. The cycle shows:
When fatty acids are present, your body favors burning them and suppresses glucose use.
When glucose is abundant, it blocks fat burning by raising malonyl-CoA, which stops fatty acids from entering the mitochondria.
The result is metabolic competition: your cells run on either fat or glucose, not both at once.
Bart Kay explains this simply: “If you give your body both fuels together, one has to be locked out. The cell shuts the door on one substrate while the other dominates.”
Why Mixing Fuels Is a Problem
Modern diets combine high amounts of fat and sugar in the same meal. Think of pastries, fries, pizza, or ice cream. These foods force your body into what Bart Kay calls “metabolic limbo,” where neither fuel is processed efficiently. The outcome is:
Fat stored instead of burned
High blood sugar and insulin spikes
Increased risk of metabolic disease
Over time, this leads to weight gain, insulin resistance, and energy crashes.
Why Choosing Fat Works Better
When you keep carbohydrates low and make fat your primary source of fuel, the Randle cycle works in your favor:
Your cells stop competing and run smoothly on fat
Blood sugar stays stable
Insulin levels remain low and steady
Fat is burned efficiently for energy instead of stored
As Bart Kay puts it: “Your body wants to run on one fuel at a time. Choose fat, and you get stable energy, better metabolic control, and freedom from constant cravings.”
The Takeaway
The Randle cycle is not theory. It is a fundamental principle of human metabolism. Mixing carbs and fat in the same diet disrupts your body’s ability to process energy. By choosing fat as your primary fuel, you align with your biology, reduce metabolic stress, and support long-term health.
Disclaimer: The content shared here is for informational and educational purposes only and should never be taken as medical advice.
In writing this blog post, my goal is to distill research findings into a clear, approachable format that encourages critical thinking and empowers you to make informed decisions about your health.
