• Jasmine Blake Hollywood, MS, HHP

Intermittent Fasting: Biochemical Review

Updated: Sep 18, 2020

Controversies of Intermittent Fasting

We all need energy to survive. However, we do not need as much as we think we need. It is certain, the best way to argue this topic is to be as uncomplicated as possible. There is much debate about fasting, therefore writing about it has to be accurate and punctual.

People read that Intermittent Fasting (IF) should be practiced at random times every day, and there is a definitive answer. They read it is good for the body, and they read it is bad for the body. They also read statistics stating that IF is beneficial for weight reduction, but if they do not eat, they will gain weight. Beyond the controversies of what the internet flushes around, this blog post will have references to back up the findings.

What does Biochemistry have to do with it?

When most people see the word "fast," they think that this caloric reduction is also a reduction in fuel in the body. Interestingly, this type of health practice provides more energy when appropriately utilized. All of this subject matter has to do with biochemical processes. So, explaining the biochemical pathways should give people a better perspective as to how it works.

Bio means doing anything that relates to life or organic matter, such as a living thing. Chemical means being able to relate to the interaction of substances. Together, biochemical means to understand the inner processes of a live body and how to understand the processes that keep a living thing alive. Let us take a look into how fasting is suitable for a living thing like a human.

What is Intermittent Fasting?

According to studies, most people only fast overnight when they sleep, for about 8 hours. IF is newly discovered health practice that involves eating at specific periods and fasting the rest of the day. This practice includes fasting overnight, as well. The process of IF involves usually skipping the first meal of the day or the last meal of the day. The goal is to restrict eating until a certain point in the day. People who practice IF tend to restrict eating for 12 to 16 hours usually.

When people practice IF, they only eat within a window of opportunity. If they were to fast in the morning, they would get benefits of utilizing fuel storages that have been reserved by the body and see a reduction in weight. This reason is that they have not eaten all night. The body needs energy, so it will use its stores because the person has not put any food in their body yet. [6]. As well, studies say stomach acids is at its highest in the evening and is reduced in strength in the morning. [11].

  1. Practice in the Day

  • For example: If I sleep at 10 pm and wake at 8 am, I have already fasted for 10 hours. If I choose to fast for 16 hours, I will have to add 6 hours to the 10 hours I have already fasted for. 8 am plus 6 hours equals 2 pm. Therefore I will not eat until 2 pm.

From experience, it has not been unheard of a person to fast in the evening. Besides, clinical studies say people should stop eating a couple of hours before they go to bed. [5]. However, this is due to the massive amounts of food they take into the body right before bed. Taking in more substantial amounts of food is said to adverse health consequences like being overweight, dyslipidemia, problems with glucose intolerance, and issues with gastric emptying. [5]. Therefore eating in the morning could be more beneficial.

  1. Practice in the Night

  • For example: If I sleep at 10 and wake at 8 am, I should technically stop eating around 8 pm. If this were the case, then I would have fasted 12 hours. If I still wanted to fast for 16 hours, I could add 6 hours to the evening instead of the morning. So, if I were to sleep at 10 pm, I will have to deduct 6 hours from then. 10 pm minus 6 hours equals 4 pm. In this case, I could eat when I wake up at 8 am and eat until 4 pm. Then I would not eat for the rest of the day.

Difference between the Fasting State and Fed State

According to Lieberman and Peet (2018), the fasted state is a biochemical pathway of the human body. [6]. It is natural for the body to fast. Fasting is usually activated inside our bodies in about two to four hours after eating a meal. [6]. Fasting means we have already eaten, broken down the foods, and now the food is digested. The food no longer fills our stomachs. It means our bodies are refraining from eating or digesting food currently. The fed state is just the opposite. [6].

The fed state occurs typically around an hour after eating. [6]. The fed state is when our stomachs are full of food. There is no need to eat. In the fed state, our bodies are entirely nourished with the nutrients we need. The body will begin to use the food we have eaten to disperse nutrients provided to different parts of the body. During the fed state blood glucose levels will rise. [6].

Harnessing Energy

Researchers and scientists have concluded that when a person eats, they are technically considered to be in the fed state. [6]. This state allows for the body to breakdown the ingested macronutrients (CHO, FAT, PRO) into smaller particles. [6]. During digestion, these particles are broken into molecules, absorbed, and the initial stage of glycolysis begins.

Glycolysis is the breakdown of glucose into usable carbohydrates. During glycolysis, the body then breaks down glucose into pyruvate. [6]. Pyruvic acid is the simplest form of keto acids. [6]. Pyruvate is then processed into the citric cycle and used for energy (ATP). [6]. Once the body utilizes the ATP it needs to maintain survival, the body will store the rest as additional metabolic energy.

Fat Stores

Fat or adipose tissue is the body's way of storing metabolic energy between meals or over some time. [6]. After continuing to eat meals and energy not being used, the body decides to keep putting it away for later use. To use energy, a person's input of energy has to equal their output of energy. If we take in more than we are using, then this how we accumulate more mass into fat stores.

More mass equals a higher number in weight on the scale. More weight equals larger clothing sizes and health complications. It is well known that the majority of the people in the world are already overweight. According to the Institute for Health Metrics and Evaluations, nearly ⅓ of the world’s population is, in fact, overweight. [8]. Also, to be descriptive, being overweight is defined as "an abnormal or excessive fat accumulation that presents a risk to health." [9]. This definition clearly defines the process of energy storage.

Give the Body Time to Use the Energy it has Harnessed

Since researchers have found that it takes approximately 2 to 4 hours to complete the fed state cycle, it is easy to know when the fasted cycle is ready to begin. [6]. Once a person has achieved the fasted state, the body begins to utilize the energy it has stored. [6]. Using the stored energy can ultimately result in weight loss and disease reversal. Unfortunately, most people choose to eat or drink before the 4 hours mark.

Some people even ingest foods and beverages regularly throughout the day by sipping on beverages and eating snacks. Indulging in these types of practices continuously interferes with their body's ability to use the stored fuels it has harnessed. By utilizing IF, a person's body gets a way to access the energy they have stored and continuously see results.


Usually, the liver will generate glucose via gluconeogenesis. [6]. Gluconeogenesis is when the body uses other from means to make fuel besides carbohydrates. [6]. After long periods of starvation, the body becomes exhausted, and fuel will need to produce. [6]. In short, gluconeogenesis begins to evolve.

The body will need to use gluconeogenesis to produce more glucose to fuel cells like red blood cells (entirely dependent on glucose) and the brain. [6]. In this process, the body will search for specific non-carbohydrate sources that are useful, while preserving the functions of other vital tissues and organs. [6]. Therefore the body will begin to degrade primary carbon sources such as amino acids, lactate, pyruvate, and glycerol to provide this fuel. [6].

At the point of fasting, the body is only using emergency stores for a short period. At the point of starvation, the body has u