I have been getting a lot of questions asking me what intermittent fasting actually is. This article will explain what intermittent fasting is about with respect to longevity.

However, from the comments section in the previous article on intermittent fasting, there seems to be some confusion with a type of muscle-building exercise regimen that is designed to cycle in and out of carbs for an efficient increase in muscle to fat ratio. So I will devote some time at the end of this article to explain how and why this muscle building process actually works.

For the purposes of increasing longevity, the terminology of “intermittent fasting” describes an eating pattern that achieves greater success than calorie restriction diets in prolonging life. Markers of metabolic and aging diseases are improved: lower blood glucose, higher insulin sensitivity, increased efficiency in burning fat, lower triglycerides, lower LDL particle count, higher HDL levels, lower oxidative stress, lower inflammation and lower hypertension.

And that does not even cover half of the benefits. Read on to find out.

What is Intermittent Fasting About?

So, what is the intermittent fasting regimen relevant for longevity?

We must be clear about the macronutrient primarily implicated in accelerating the aging process:


Even worse, what we have today in the proliferation of refined carbohydrates is an abundance of food but a scarcity of essential micronutrients. It is important to understand this before moving on because the latest research is debunking the myths about what we should eat. Technology and data are much better today, and disingenuous research is no longer easy to pass.

For a good primer on why carbohydrates are the primary target of intermittent fasting, read the following:

  1. Calorie Restriction and Longevity: the Role of Sugar
  2. Calorie Restriction and Longevity: Glycemic Load
  3. And the Best Diet to Lose Weight Fast

The last article on weight loss is a popular subject. So let’s review what is actually happening to induce this weight loss.

Not to fret, I will shortly describe a few intermittent fasting diet plans. But to understand why they are designed the way they are and why they work, let’s go over the effects of this feast and famine eating pattern.

Intermittent Fasting Weight Loss

Intermittent Fasting Weight Loss

Bodybuilders often cringe at the thought of forgoing carbohydrates because they are necessary for muscle building. They work by triggering the master hormone, insulin, which regulates absorption of glucose in the blood into muscle and fat cells. Bodybuilders have the capacity for glycogen storage that most of us don’t, and refined carbohydrates are the quickest to be absorbed into fat cells.

So what does intermittent fasting do?

It is a form of carbohydrate restriction that works to keep insulin levels lower for longer periods of time. Weight loss happens on 3 fronts:

  1. The kidneys are no longer impaired by the insulin signaling and water retention is decreased
  2. Fat cells begin to release fatty acids for the liver to convert into ketones
  3. Proteins are also broken down into glucose in the process

The last part on protein breakdown is extremely important to understand from a longevity perspective. The scientific term is autophagy.

Autophagy and Fasting

Autophagy and Fasting

This is what bodybuilders fear: muscle wasting from lower insulin levels. Some of them go to extreme measures of injecting insulin directly into their muscles to speed up the process of glycogenesis.

However, this fear is misplaced, and its misunderstanding does more harm than good. What autophagy does is allow the body to repair itself. Evolution has given us a wonderful design whereby damaged tissue is prioritized for catabolism.

Autophagy further stimulates cell repair because dysfunctional cellular tissue is broken down as a source of fuel. This induces stem cell growth in the affected areas, where regeneration of tissue happens.

Intermittent Fasting and IGF1

The breakdown of damaged tissue also provides the raw materials in the form of amino acids required to build younger and healthier tissue. One of the most remarkable discoveries in experiments comparing intermittent fasting to calorie restriction was that insulin-like growth factor (IGF-1) levels increased under fasting conditions, as opposed to decreasing under simple calorie restriction.

To be clear, IGF-1 works in the same way as insulin amino acid anabolic processes. The hormone stimulates cell growth and proliferation. It also inhibits programmed cell death, which is pro-longevity.

Cancer risk is normally increased by this promotion of cell proliferation and growth. With intermittent fasting, however, this is not the case. In research experiments, even direct injection of IGF-1 into intermittently fasting mice did the exact opposite: it restricted cancer growth. The likely reason is the restriction of glucose on an intermittent fasting diet plan.

Fasting and Brain Function

Fasting and Brain Function

Fasting produces a stressed environment in neurons in the same way as exercise does in muscle tissue. It leads to a reaction by the central nervous system to enter a protective and regenerative mode. One of the mechanisms by which we know this works is that fasting induces the production of neurotrophic factors (BDNF), which increase the mitochondria in neurons.

Neurons develop resistance to dysfunction and degeneration that lead to many neurological diseases.

Ketone bodies are also the preferred fuel for the brain, which is why many dieters report having mental clarity and a generally positive and energetic mood when fasting. Ketone bodies are evolution’s answer to the pattern of food scarcity that humans had to endure for prolonged periods of time. Ketones are permeable to neuron membranes, which is why fatty acids cannot be broken down in neural cells and instead have to pass through the liver first.

Fasting and DNA Repair

Intermittent Fasting and DNA Repair

Fasting gives us the ability to accelerate the repair of DNA. From a biological perspective, three meals a day is not the healthiest eating schedule for an eating pattern. Fasting also regulates the genes that extend longevity. It works through its restriction of carbohydrates, whereby epigenetic modifications are significantly reduced.

Fasting also works to protect DNA because there is less oxidative stress, in which DNA is also oxidized by free radicals generated in glycolysis. In general, reducing energy intake and metabolism is protective for cells and DNA.

What do longevity scientists mean by intermittent fasting?

Now that we have covered the basic building blocks, it will be easier to explain what is intermittent fasting is about.

It is about entering a state of nutritional ketosis, in which the body runs primarily on fat. There is a period of adaptation in which the liver becomes more efficient at the process of breaking down fatty acids into ketone bodies.

This is not an abnormal way of eating. In fact, it’s quite the opposite because our high carbohydrate food infrastructure was only built in the last century. Prior to modern food processing, humans depended on a lot more fat in their diet.

What are typical intermittent fasting plans?

The good news is that not everything is restricted during a fast to achieve the desired effects. In fact, the longer the fasting period, the better it is to be consuming liquids with high mineral content, collagen, salt and even fat.

With low insulin levels, the kidney secretes a lot more salts and water than with a typical diet. To avoid side effects, these micronutrients must be replenished with plenty of liquids. Collagen is an important building block for tissue repair, and dietary fats, especially in the form of medium chain triglycerides (found in coconut oil), accelerate the body’s adaptation to ketosis.

In the article on the bone broth diet, Dr. Kellyann Petrucci’s 21-day bone broth diet was advocated as a coherent application of this low-carbohydrate principle. The end result is a generally low insulin environment, which solves most of our age-related illness.

Dr. Kellyann Petrucci also presents several variations of the fasting plan in her book, but her premise is the same: namely to restrict carbohydrates during the fasting windows.

There are other varieties of intermittent fasting, and research experiments are also diverse in their interpretation of the fasting period. These varieties include:

  • The 5:2 Diet
  • Alternate Day Fasting
  • Ketogenic diet


The last one is a special case because a follower of a ketogenic diet is in a permanent state of nutritional ketosis. For some longevity dieters, this option is ideal because the uncomfortable adaptation period in between cycles is no longer an issue.

Your choice of the intermittent fasting plan will have to take into account your genetics, objectives and lifestyle. If you are an athlete, for example, it will be quite a challenge to maintain the same level of intense exercise while in ketosis; you will also find it challenging to maintain muscle mass without breaking ketosis with too much protein intake.

Carb cycle does not mean high carb

It is important to note that none of these variations ever interpret the “feasting” part to be high in carbohydrates. The objective is to balance the nutrients missing when targeting nutrients that target nutritional ketosis.

In fact, for some intermittent fasting diet plans, like the alternate-day fasting, it would be nearly impossible to go back into ketosis within 24 hours if a significant amount of carbohydrates are ingested.

Final note on the muscle-building carb load

We mentioned in the beginning of the article that some people utilize a form of intermittent fasting to increase the muscle to fat ratio. This modification for high-intensity exercise is still better than the standard diet. In fact, in experiments where calorie count was identical, the one that overloaded meals during a “feast” cycle ended up losing weight.

This is contrary to what we are told by most nutritionists and politically supported guidelines. Never skip breakfast, right? Absolutely rubbish!

What carb-cycle loading does is suppress the mTor pathway during the fasting window, which signals autophagy to take place. On feeding, the mTor pathway activated by proteins and a higher level of insulin turns the process backwards into rebuilding muscles and tissue. Recall that IGF-1 was elevated during the fasting cycle, which stays elevated during the feast. IGF-1 is less volatile than insulin and will generally stay high for much longer with this pattern of eating.

This regimen works to increase the muscle to fat ratio as long as the fat flux is negative. That means there is a point that you can fool yourself into thinking you are experiencing weight loss from fat metabolism, as opposed to the loss of retained water. So on feeding, you only need enough carbohydrates to replenish the depleted glycogen stores. Once that buffer fills, your body begins to turn glucose in the blood into fatty acids and ships it off for storage in fat cells.


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