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Intermittent Fasting - The Ultimate Guide

"Fasting is the first principle of medicine; fast and see the strength of the spirit reveal itself"

- Rumi

Fasting 101

If we look back at history, we can gather that meals were consumed less frequently. Take the paleolithic era for example, as a civilization we were hunters and gatherers and the availability of food was scarce compared to today. Our body is well adapted to handle periods of starvation and utilize its stored form of fuel (fat) as a source of energy. Fasting is simply defined as a period of starvation. The term breakfast, literally means to "break the fast" we undergo during the night.

The body uses the energy it receives from the food it consumes and anything left over is stored as fuel. The stored form of fuel in the body is called glycogen, which is mainly stored in the liver. The liver has a limited capacity of storage and once the liver is fully saturated, the additional fuel is stored in the form of fat. The Standard American Diet recommends eating 3-6 times per day, which include both meals and snacks. This will put strain on our hormones to help regulate the frequent sugar spikes occurring with each meal. Overtime, this will lead to chronic illness.

The first concept of fasting is that we store energy in the forms of glycogen and fats. The stored form of glycogen is in both the muscles and predominantly the liver. The usage of stored energy mainly occurs when we are in the starvation period and is hormonally regulated, predominantly by Insulin. When food is ingested, especially carbohydrates, there is a subsequent rise in our blood sugar levels. This is then managed by the pancreas releasing insulin.

Metabolic Syndrome X is a chronic condition associated with high triglyceride levels, high blood pressure, abdominal obesity, and insulin resistance. This syndrome is the cause of poor nutritional choices and increased meal frequency. In order to help reverse diseases, like type 2 diabetes, we need to allow our body to naturally use its stored energy. The only way this is achieved is fasting and exercise. When researched, exercise, although increases strength and performance, was not as efficient in reducing weight and reversing disease.

checking body weight
Obesity epidemic

The take home message here is that fasting is a normal process our body is equipped to manage. Fasting occurs after you consume a meal and in order to see benefits of fasting, I recommend against consuming anything that will cause a rise in blood sugar levels, subsequently releasing insulin, a potent fat storing hormone. At minimum, I recommend at least 12 hours between your last meal and first of the day.

Fasting can be difficult initially because we are conditioned to eating frequently. We may undergo hunger pains, but we can combat the habit of eating by staying hydrated, or drinking beverages that help with satiety, yet don't break our fast. Remember, anything that causes a significant rise in blood sugar levels would classify as breaking the fast. I recommend drinking tea and coffee to help keep you satiated. They also are a source of antioxidants. Sugar and creamer can cause a rise in blood glucose so it is recommended to drink plain.

There are many different fasting protocols we can undergo. A few examples are the 16:8 method, where we consume food during an 8 hour eating window and fast for the remaining time. Alternate day fasting is another approach to this lifestyle. During this method, we undergo a longer period of fast every other day. The duration of time is up to you. The warrior diet and OMAD (one meal a day) are more advanced forms of fasting.

If you are on any medications, I recommend that you consult with your physician prior to starting a fasting protocol. This is especially important if you are taking medications for diabetes, as you can have a dangerous drop in blood sugar levels due to the effects of medications, and the starvation period. Medications often need to be adjusted prior to starting this journey. Please consult with your physician and make the appropriate adjustments prior to starting this journey.

Hormonal Response to Fasting

When you ingest a carbohydrate, the pancreas secretes insulin to help regulate blood sugar levels.

This concept is quite important to understand, because insulin is a potent fat storing hormone. The body has receptors that help determine when sugar is elevated in the bloodstream. Overtime the sensitivity of these receptors becomes diminished and eventually the pancreas will need to release more insulin to cause appropriate regulation to the blood sugar levels.

This is how our body develops insulin resistance.

This mechanism occurs quite frequently in our body because we develop tolerance. For example, if you take medications for joint pain or if you were to drink alcohol, the first time you consume the agent, you have an appropriate response, but overtime, with increased frequency of consumption, you may need a higher dosage to illicit the same response.

This is how diabetes is developed, and insulin secretion needs to be controlled in order to help heal ourselves from within. Fasting helps with this. When insulin is released to help regulate blood sugar levels, it takes the sugar and stores it in the liver in the form of glycogen. As discussed earlier, the liver has limited capacity to store glycogen, and eventually will undergo biochemical pathways to convert the additional stored energy into fats.

Think of this concept like a cup. If we take a cup and fill it with water, once the cup is full, any additional liquid will spill over the top. The only way to prevent this is by not adding liquid to the cup.

Filling water in a cup
An example of caloric intake

This is how fasting works to help you lose weight, reduce insulin intolerance and achieve longevity. When you fast, your Insulin levels are at a minimum. When that occurs, our body has counter-regulatory hormones that help keep our body's blood sugar levels elevated to help prevent a crash due to hypoglycemia.

Counter- Regulatory Hormones

Our body has complex mechanisms to regulate our blood sugar levels. This involves many organs which secrete the hormones used to maintain homeostasis.

Many conventional medicines used to treat diabetes involve altering the natural responses of sugar metabolism. When you fast your body uses these regulatory hormones to keep you balanced and utilize the predominant stored form of energy, both glycogen and fats.

Overtime, either through diet or extended fasting, there is an additional form of fuel that our body can utilize called ketones. Once we enter this stage of fasting, known as ketosis, we maintain blood sugar levels adequately while simultaneously burning fat.

The Counter- Regulatory hormones are:

  • Glucagon, which is secreted by the pancreas and works by opposing insulin. It works in a balance and is considered to be the main catabolic hormone of the body. It works by releasing stored sugar (glycogen) from the liver through a process called glycogenolysis.

  • Epinephrine, secreted by the adrenal medulla, helps rev up the body during an episode of hypoglycemia. When your blood sugar is low, you may see it's effects when you become sweaty, tremble, or have a racing heart beat secondary to low sugar levels. This is the effects of Epinephrine to help signal your body to release more stored energy as fuel.

  • Cortisol, secreted by the Adrenal Cortex. This hormone stimulates gluconeogenesis, which synthesizes "new" sugar from non carbohydrate sources. This occurs mainly in the liver after a prolonged fast.

  • Growth Hormone, secreted by the pituitary gland, helps maintain lean mass both in muscles and bones. It boosts exercise performance and helps recovery from injury and disease.

The 5 Stages of Fasting

Have you ever wondered why we never fall ill during a prolonged fasting period? It has been documented that some people can fast for extended periods of time, under doctors supervision. The longest fast recorded was over a year long. What happens inside the body when we go through a prolonged fasting period? In order to know that, we must know how our body consumes energy.

It has been researched that over a long period of time, the body uses glucose through consumption of carbohydrates and triglycerides through the storage of fats as a form of energy. Throughout the 1900s, this was researched quite thoroughly. It was determined that the body has a third form of energy called ketones which was predominantly used by the brain during an extended fast.

Francis Benedict, through his study on prolonged fasting in 1915 researched this very theory on how our body adapts to fasting over a long period of time. He studied different durations of fasting and compared the consumption of energy between diabetics and non diabetics.

In the 1950s, Dr. George Cahill, an American scientist, piggybacked on this very topic. He evaluated our metabolism during the starvation period and determined that ketones were a very efficient form of energy that could cross the blood-brain barrier providing the nutrition required by our brains to function properly.

Through Dr. Cahill's research, we are able to determine what happens internally as we go through fasting. He came up with 5 stages of fasting, which included the feeding stage, the post absorptive stage, gluconeogenesis, ketosis, and protein conservation stage.

How long to enter ketosis
The 5 Stages of Fasting

1. The Feeding Stage, which occurs right after you ingest a meal. This stage can last up to 4 hours.

  • The feeding stage provides us with energy in the form of glucose. Glucose is used as fuel in every tissue in our body. The main hormones secreted during the feeding period is insulin to help regulate blood sugar levels. As discussed earlier, insulin's job of sugar regulation is by storing glucose within our bloodstream into our liver in the form of glycogen. The liver does not have a large storage supply of glycogen and after saturation, any additional glucose becomes converted into triglycerides (fat) via fatty acid synthesis.

2. Post-Absorptive State. This occurs 4 hours after ingesting a meal and lasts up to 16 hours.

  • This stage is regulated by the counter-regulatory hormones we discussed earlier. When blood sugars are normalized and the secretion of insulin is at a minimum, the body has other mechanisms to help keep the sugars regulated and balanced to maintain homeostasis. The counter-regulatory hormones, which include glucagon, cortisol, adrenaline, and the human growth hormone play a key role in this stage of fasting. This is where the 16:8 fasting protocol becomes relevant

3. Gluconeogenesis. This stage occurs 16 hours and can last up to 30 hours from your last meal.

  • In gluconeogenesis, our body utilizes non-carbohydrate sources of energy to create sugar. The source of energy is mainly proteins, but we have additional hormones that play a role to preserve muscle mass during the starvation period. Remember that the human growth hormone helps preserve muscle mass and bone health so fasting is well balanced to preserve strength, while burning fats as energy. The proteins used in this stage come from various sources, including connective tissues. This broad usage of protein is one of the reasons why intermittent fasting is not associated with excessive skin after moderate weight reduction.

4. ketosis. This occurs 48 hours post meal and can last up to 7 days.

  • Ketosis occurs when all the glycogen stores within the liver are utilized and the effects of gluconeogenesis start to diminish. It is quite interesting that during this phase of starvation our hunger hormone, ghrelin, also starts to decrease, allowing for utilization of ketones as the predominant form of energy. This process takes place in the mitochondria (power house) of the cell.

  • Ketones are utilized by our brain more efficiently than sugar and during this stage many people feel a sense of mental clarity. During ketosis, we are optimizing the fat burning potential of fasting. Some diets help achieve ketosis faster than the 48 hours required through prolonged fasting. It is recommended to optimize weight loss with fasting by intaking a very low carbohydrate diet to promote fat loss. The carbohydrates that you do consume should be nutrient dense and full of antioxidants to help promote longevity.

5. Protein Conservation Stage. This stage occurs after one week of fasting.

  • This stage is predominated by the human growth hormone. Research states that the levels of HGH are 5 times the normal amount. When fasting for this long, I recommend consultation and supervision with your doctor to ensure you do not become malnourished. If you are taking any medications, especially for diabetes, these need to monitored closely.

Longevity Through Autophagy

Autophagy literally means to "self eat" and it is a mechanism used to recycle cellular waste via our lysosomes. These lysosomes are responsible to secrete digestive enzymes and help break down any cellular waste occurring within our body.

Autophagy through extended fasting
Intermittent Fasting

In 2016, Dr. Yoshinori Ohsumi was granted the Nobel Prize in Medicine and Physiology for his research on Autophagy. He researched this concept over the past 25 years, looking at yeast cells and how they break down waste. He presented these findings in the human body by correlating the same effects after a prolonged starvation period.

The benefits of autophagy include healthy aging, preventing disease, fighting pathogens, removing and recycling damaged proteins, and providing our cells with energy.

Autophagy is a self degradative process that is important for balancing sources of energy at critical times in development and in response to nutrient stress.

Autophagy is strongly induced by starvation and is the key component of the adaptive response of cells and organisms to nutrient deprivation that promotes survival until nutrients become available again.

Autophagy takes place after longer fasting regimens. Studies have shown that autophagy takes place between 17 to 24 hours into your fast, and peaks at approximately 48 hours. Autophagy is beneficial up to 72 hours.

To better understand this concept, consider a hoarder, who reads newspapers everyday. Instead of throwing them away, he keeps them in his house. Overtime, the house will be hard to maneuver through because of the excess papers laying around. Instead of keeping the newspapers, what if that same person recycled them into plates and cups to use?

This is similar to how Autophagy works. It uses old dysfunctional material and repurposes them to help us function better from within. This is cellular rejuvenation.

Sample Fasting Regimen

9am- Breakfast: In order to maximize weight loss, consider a low carb meal. Focus on healthy fats, that are nutrient dense and contain Omega-3 Fatty Acids. Example would be eggs with avocados.

5pm- Dinner: It has been 8 hours since your last meal, you do not need to count calories here. Consider foods that provide nutrition, lots of vegetables and healthy fats. You can eat til you are full. This is not a restrictive diet.

Beverages: Remember to consume drinks that don't raise blood sugar levels. Consider black coffee, plain tea, apple cider/vinegar to help with satiety until your next meal. Drink plenty of water throughout the day.

Exercise: Low to moderate resistance exercise is recommended. Maximize results with exercising during the fasted period, prior to breakfast.

Sleep: This may be the secret to achieving maximum benefits from any diet. Rest and digest with a good sleeping schedule. This help balance hormones that boost weight loss and achieve the most out of any dietary protocol.

Stress: Find ways to decrease your stress levels so that you optimize the benefits of fasting. Cortisol is a counter-regulatory hormone and beneficial for short periods of time to maintain your blood sugar levels, but when cortisol is secreted consistently, it can lead to central obesity, and stall your weight loss. Exercise and meditation is a great way to keep stress levels down.

Remember that fasting is considered an ACUTE stressor, it should be the exception to your weekly eating regimen, this allows for maximum results.

Disclaimer: For extended fasting, it is crucial that it is done under doctor supervision. Feel free to contact us at Florida Advance Medicine, where we help our patients optimize their health using lifestyle modifications including intermittent fasting.

We post health related articles twice a month, check out our blog to learn more about evidence based screening guidelines and up to date medical topics.


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