The Simple Science of Fasting

If you're anything like me, the thought of diving straight into the science behind intermittent fasting (IF) can be daunting. This may explain why so many people approach fasting halfheartedly, without fully reaping its benefits, and eventually give up. They feel overwhelmed by the sheer amount of information available and don't know where to start. Trust me, we’ve been there! That’s why we’re here to break it all down into the simplest version possible—the way we wish someone had done for us when we first embarked on our intermittent fasting journey.

Our interest in fasting began when we started learning about what happens to the body after you eat and how carbohydrates impact our internal systems. It amazed us that we had never given it much thought before! Understanding metabolism, digestion, and the profound effects of food on our hormones has forever changed our lives. We truly believe we should be taught about these things from a young age. Perhaps if we were, the Western world wouldn't be dealing with the massive obesity epidemic it faces today. Just sayin’.

When you fast, your body stops using glucose for fuel and starts metabolising fat.

As soon as we eat, our bodies start breaking down the food into energy. However, the type of food we consume and the amount of it matters a great deal. Eating the wrong foods or consuming too much can lead to various health problems. Our digestive system releases hormones through glands into the bloodstream, regulating key functions like sleep, metabolism, mood, hunger, and even reproductive health. Among the most important of these hormones is insulin. Most of us have heard of insulin, but many aren’t aware of its crucial role. After we eat, insulin signals the body to store energy from the food, initially as sugar, which is quickly accessible, and then as fat for long-term storage.

Carbohydrates, in particular, cause a rapid spike in blood sugar, prompting the release of insulin. Carbs are essentially chains of sugars. Some of this sugar is used immediately for energy, but the excess gets stored as glycogen in the liver. If there's more glucose than the liver can store, it converts to triglycerides, which are then stored in fat cells.

So, how does fasting fit into all of this? When we fast and reduce carbohydrate intake, the body's glycogen reserves become depleted, and it has to turn to fat stores for energy. This metabolic shift is why fasting, combined with a reduction in carbs, is so powerful. But fasting does more than just deplete glycogen—it regulates your hormones. It’s not just another diet; it resets your body’s internal systems, allowing them to function optimally.

When we refrain from eating, insulin levels drop, signaling to the body that it’s time to burn stored fat for fuel. After 12-16 hours without food, the body naturally transitions into fat-burning mode, using fat as its primary energy source. This process shows that intermittent fasting is both safe and effective for most people (though there are exceptions which I touch on here).

Intermittent fasting activates key hormones in the body that promote fat burning, enhance metabolic flexibility (the ability to switch between fuel sources), and help maintain a healthy weight. It also has numerous other positive effects on weight control and overall health. When your hormones are in balance, fasting can even boost your metabolic rate, making it easier to lose and maintain weight.

This is the simplest way we can explain the science behind intermittent fasting. There's certainly more in-depth information out there if you want to dive deeper, but this should give you a good foundation to start with.

For a deeper dive, here you’ll find a collection of books, podcasts, and articles that have been instrumental in my journey to better understanding our amazing bodies.