The Fascinating Mechanisms of Fasting: How the Body Changes and Adapts

In this video, the mechanisms and benefits of fasting are explored in detail. It is explained that fasting can lead to changes in the body’s energy metabolism, including the shift to using more fat for energy and the production of ketones. Fasting also stimulates the production of hormones like growth hormone and BDNF, which are responsible for brain repair and improved neural networks. Autophagy, a process of cell cleanup and rejuvenation, is also activated during fasting. The video discusses the timeline and duration of different fasting stages and suggests varying fasting durations depending on individual health goals, such as weight loss or disease prevention.

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How does this happen?

Key Insights:

– Fasting can have a profound impact on health by triggering various mechanisms and changes in the body.
– In the first 12 hours of fasting, the body starts shifting its energy metabolism to using more fat, resulting in the production of ketones.
– Ketones are not only a source of fuel but also signaling molecules that can reduce inflammation and improve DNA repair, especially in brain and nervous tissues.
– Fasting stimulates the production of growth hormone and BDNF (brain-derived neurotrophic factor), which promote brain repair and the creation of new neural networks.
– Autophagy, a process of cellular self-cleaning and recycling, starts around 18 hours of fasting and increases as fasting duration progresses.
– Fasting helps regulate insulin and reduces insulin resistance, leading to improvements in metabolic syndrome and cardiovascular health.
– Extended fasting periods of 72 hours or more can have additional benefits such as deeper autophagy, stem cell regeneration, and increased longevity.
– The duration of fasting can vary depending on individual goals and needs, ranging from 18 hours to multiple days.
– Fasting can be a sustainable lifestyle choice for weight management and overall health maintenance.


Hello Health Champions. How is it possible that even though food is the thing that keeps us alive, millions of people get healthier when they don’t eat for a few days? What are the mechanisms for that? How does the body change and cope and adapt when we don’t eat?

A lot of people have heard that fasting is good for weight loss, but they’re still concerned because there’s so much conflicting information out there. So today I wanted to explore these mechanisms of fasting in a little bit more detail to really help you understand what happens when you miss a few meals and how it can have such a profound impact on health.

In the first 12 hours, not a lot of changes take place. You’re going to be using up some of the stored carbohydrates in your body called glycogen your blood glucose will probably drop a little bit unless the 12 hours is at the end of sleep and you’re slightly insulin resistant then because of something called dawn phenomenon you might actually see the opposite your body temporarily makes some hormones in the early morning to get you ready for the day and you might see a little bit of an increase instead.

As you’re using up some of the stored glycogen, your body will gradually start shifting its energy metabolism into using more fat, and a byproduct of that fat is called ketones. Now this is barely detectable at this point but it’s a process that’s starting and what we want to understand about ketones is that this is completely normal everyone is going to gradually shift into this.

The problem is that oftentimes this is confused with ketoacidosis, which is a very dangerous condition that’s completely different. That’s if you have type 1 diabetes and absolutely no insulin in your body your blood sugar shoots up, your ketones shoot up, and that’s not going to happen unless you have no insulin. Instead, what this indicates is metabolic flexibility. That as one fuel starts to run lower, your body starts looking for another one. When you’re metabolically flexible, your body makes use of whatever fuel there is the most of.

Most of the changes that take place during fasting have to do with energy because we’re not eating anything that can turn into energy, so energy becomes super important. The only form of energy your body can use is something called ATP. Everything that you eat, all the food, whether it’s carbohydrate, fat, or protein, it eventually turns into ATP, which is a very specific molecule.

ATP is made up of an adenosine group and three phosphates. These phosphates are high-energy bonds or „springs“ that store energy. When the body needs more energy for anything, it releases one of these phosphates, and the spring releases that energy, leaving adenosine diphosphate (ADP).

So, how does ATP relate to the food we eat? In a mole of ATP, which is a huge number, we have seven calories. That means that one calorie you eat basically has 10^23 of these ATP molecules, or a hundred million trillion trillion molecules, in one calorie. And if we break that down to how much you need per second, you need about 2,300 trillion trillion of these ATP molecules per second. These are astronomical numbers, but if you think about the fact that you have about 40 trillion cells in your body, that means that every cell makes trillions of these molecules per second to keep you alive.

As soon as one of these phosphates is released, the body uses energy from food to create a type of energy that can be used to put the phosphate back on, a process called oxidative phosphorylation. This process happens in the mitochondria with the help of oxygen. The goal of the body is to keep almost all of these ATP molecules loaded all the time. But when energy levels start running really low, a few of the ATP molecules become ADP, which signals to an enzyme called AMPK (adenosine monophosphate-activated protein kinase) that the body needs to find other energy sources.

The first thing AMPK up-regulates is fat burning because, when you’re not eating, the majority of your energy comes from stored fat.

Now, let’s shift to the perspective of an athlete. When it comes to high-intensity exercise, such as sprinting, the body needs a lot more ATP. Usain Bolt, for example, uses up 29.1 times more ATP than the base rate during a sprint. However, the body is capable of up-regulating ATP production to meet these high demands.

When you go without food for about 18 hours, your body starts shifting into fat-burning mode and begins producing measurable amounts of ketones. Ketones are not only a source of fuel but also signaling molecules that reduce inflammation and improve DNA repair, especially in the brain and nervous tissue. During fasting, human growth hormone and BDNF (brain-derived neurotrophic factor) levels increase, promoting brain repair and the creation of new neural networks. Exercise can further accelerate these processes.

Around 18-24 hours into fasting, the body also activates a process called autophagy, which involves the recycling and removal of damaged or unnecessary cellular components. Autophagy increases with the length of the fast.

Skipping breakfast and extending the overnight fast to 18 hours can lead to improvements in weight loss, insulin levels, and inflammation. At 48 hours, growth hormone levels increase fivefold, and brain repair, increased longevity, wound healing, and cardiovascular health are observed.

At 72 hours, deeper levels of autophagy occur, and hematopoietic stem cell regeneration and rejuvenation begin. This process helps with immune cell production, and fasting has been found to protect against the damaging effects of chemotherapy on the immune system.

The duration of fasting depends on individual goals and health status. Intermittent fasting for 18-48 hours can be a sustainable lifestyle choice for weight management, insulin resistance, and overall health. Extended fasts of 72 hours or longer can be beneficial for disease prevention, rejuvenation, and reversing severe conditions.

It is important to strike a balance between feast and famine, finding an appropriate fasting routine that suits individual needs. Fasting should not be confused with eating disorders, as it addresses metabolic issues rather than distorted self-image.

By understanding the mechanisms of fasting and how the body adapts, we can harness its potential benefits for our health and well-being.