Tuesday, October 3, 2023

Benefits of intermittent fasting

The article covers the science behind fasting, various fasting formats, and their health benefits. It also discusses who should avoid fasting.

Executive Summary

Fasting means going without food for a period longer than normal. Intermittent fasting involves regular, alternating periods of feeding and fasting.

Fasting can help in diabetes, heart disease, cancer, brain disorders, inflammation, etc. The biggest benefit of fasting is to refurbish the immune system. All of these combined may help in improving longevity, too.

The benefits of fasting accrue only if the fast is long enough to push the body to switch from using glucose to ketones for its energy needs.

There are various types of fasting formats, as well as less demanding formats such as fasting-mimicking diets.

There are certain health situations in which one should avoid fasting. Read the full article to learn about them as well as the science behind fasting.

During a fast, an individual goes without food for a period of time longer than normal. Centuries ago, people used to fast to heal the body. Even today, many religious practices encourage fasting.

Fasting is different from starvation—the former is done by choice. So the fasting follows certain protocols about the acceptable foods and the timing of their consumption. On the other hand, starvation is caused by limited resources and can lead to malnutrition.

Just any kind of calorie restriction is not fasting. For a fast to be really helpful for the body, the duration of the fast is vital. Enter intermittent fasting, which is a type of fast where you alternate between periods of feeding and fasting at regular intervals.

Science Behind Fasting

Our body’s circadian rhythm synchronises with the daylight. The processes in the body ebb at nighttime, in general. Digestion is one of them. So the day is meant for food and the night is meant for sleep. In fact, many people who lived more than a hundred years don’t eat anything after the early hours of the evening. Read on this website: Diet secrets of centenarians.

When we eat, the carbohydrates are converted into blood glucose, which is used as fuel by body cells. If the next meal is delayed enough, this glucose gets used completely and the body needs to switch to an alternative source of energy.

From Glucose to Ketone

Once these glycogen stores are over, the body starts using fats stored in the fat cells and proteins from muscle tissues.

The stored fats are triglycerides, which are broken down into something called glycerol and free fatty acids. The liver converts glycerol to blood glucose. In parallel, the liver converts free fatty acids to compounds called ketones that also can generate energy.

Simultaneously, muscle proteins are broken down into certain amino acids (glucogenic amino acids) that are converted into glucose and some other amino acids (ketogenic amino acids) that are converted into ketones. That is one reason why too much and too frequent fasting can lead to muscle atrophy, which one needs to be careful of.

Eventually, as the glucose sources and stores in the body get even more depleted, the body cells start using more and more ketones for their energy needs.

The mechanism of the body going from using glucose to ketones for its energy needs is called metabolic switching. The fasting needs to be long enough to trigger the metabolic switch. Done often enough, the benefits of such fasting accrue over a period of time.

General Knowledge

Even during endurance events, such as running marathons, the body switches from glucose to ketones for its fuel requirement.

Our bodies store enough glucose (in the form of a compound called glycogen) to give about 2000 calories. Typically, a run of about 30 km is long enough to exhaust these glucose stores. So a marathon forces most runners to undergo this metabolic switch around the 30 km mark.

The energy production process from ketones needs 40% more oxygen than the one from glucose. As the body switches to ketones for its energy, the body’s oxygen requirements go up rapidly. Since one is already running hard in a race, one’s breathing rate and oxygen intake cannot increase. As a result, the runner’s speed drops by 30% all of a sudden as he hits this 30 km mark.

In the running lore, it is called hitting the wall and is the nightmare for every marathoner. Runners encounter it during a marathon (42 km) or beyond, but never in a half marathon (21 km). That is why a marathon is considered a completely different race than a half-marathon.

If this metabolic switch does not happen and the blood ketones are not elevated, the fast does not show its beneficial effects. Well, it may help in losing weight. But, other benefits do not accrue. Thus, true fasting should be done long enough that the blood ketone levels are raised. Read: Flipping the Metabolic Switch: Understanding and Applying Health Benefits of Fasting.


The presence of ketones in the blood triggers regeneration all over the body. It starts reducing the damaged white blood cells. Some scientists say that the body goes into conservation mode, protecting its limited resources by destroying imperfect cells.

This process is called autophagy, which involves systematic and natural destruction of malfunctioning or inefficient body cells. Some of the cell components are recycled back for later use. Discovering and studying this fascinating process, in fact, won the Nobel Prize in Medicine in 2018 for Dr. Yoshinori Ohsumi.

Rebooting the Immune System

Subsequently, when you eat again, the body senses that the period of nutrient scarcity is over. It turns on certain cells called stem cells. Stem cells can become any type of cells depending on certain triggers. They are like school kids, who can be trained to become doctors, lawyers, or architects, depending on the need.

As a result, the body regenerates new and healthy white blood cells. Since white blood cells confer immunity to the body, the fasting individual gets a revamped immune system.

A similar regeneration process happens in multiple body systems. That can have huge implications for certain diseases that involve body or organ degeneration. With fasting, the damaged cells in an organ can be replaced with new working cells. Then the refurbished system may start working properly. At least, that resetting is what should happen in theory.

Fasting Formats

There are different formats for fasting. Broadly, they fall into two categories: intermittent fasting and fasting-mimicking diets.

Intermittent Fasting

In Intermittent fasting or IF, nothing is consumed (except water, black coffee, green tea, lemon water, etc) for a certain period of time. The idea is to provide zero calories to the body during the fasting period.

It is hypothesized that increased levels of insulin are responsible for many degenerative actions in the body. The longer you can keep the insulin levels down, the better will be the triggers for body processes that heal. So even a low-calorie input such as eating salads or drinking a glass of milk will stop the body repair. That is why a complete fast is an integral part of intermittent fasting.

Black coffee, green tea, and lemon water are essentially zero-calorie flavoured waters and so are acceptable as a part of intermittent fasting.

Among intermittent fasting formats, the popular ones are:

  1. Complete fasting: Here, you fast on alternate days.
  2. Time-Restricted Feeding or TRF: Here, one eats only for a few, limited hours in a day. This has three main themes:
    • Early Time-Restricted Feeding or E-TRF: This involves eating for a few hours in the morning;
    • 8–16 Fasting: This involves eating in an 8–hour window out of 24 hours. This window of time need not be in the morning;
    • 2–Meals Format: Here, you eat only two times a day. Neither of these eating periods should last more than 55 minutes.

    All these formats involve a complete fast during the fasting times. So, they are harder for many individuals. They are not even advisable if the person has a medical condition such as diabetes. For such individuals, fasting-mimicking diets are useful.

Fasting-Mimicking Diet or FMD

In a fasting-mimicking diet or FMD, a low amount of calories is eaten in a day. It avoids a complete fast, in which nothing is consumed except water. Among fasting-mimicking diets formats, the popular ones are:

  1. 5 days a month: For five days every month, the participants eat between 800 to 1,100 calories a day. For the rest of the month, they can eat anything.
  2. 5–2 fasting: In this fasting format, one eats anything one wants for 5 days a week and 500 calories each for the remaining two. It is important that these two low–calorie days are consecutive.

Benefits of Fasting

All fasting formats offer benefits for multiple health conditions. Intermittent fasting formats help more because they are stricter than the fasting-mimicking formats. But each one helps as long as the metabolic switch happens from glucose-based energy production to ketone-based energy production. So one should fast long enough to finish the calories obtained from the previous meal.

  • Obesity: Fasting helps reduce or prevent obesity. Fasting also increases a neurotransmitter called norepinephrine, which can raise metabolic rate leading to weight loss.
  • Diabetes: Frequent fasting and glucose-lowering reduce insulin resistance, which is the main culprit behind diabetes. Improves blood glucose control.
  • Thinking: Fasting reduces brain fog and brings more clarity into the thought process.
  • Memory: Verbal and working memory were found to improve in humans and rats, respectively, in different studies. Obviously, we may never know if fasting rats can improve verbal memory. 😌
  • Endurance: Contrary to logic, fasting leads to higher endurance in physical tasks. Of course, while one is fasting, one may not be at one’s best. However, frequent fasting improves endurance. Fasting raises the secretion of a hormone called human growth hormone or HGH, which can increase strength and growth.
  • Heart Health: Fasting helps improve many heart-related markers, such as blood pressure and resting heart rate, improve. Reduces fat that can cause fatty deposits. Also reduces triglycerides, LDL-cholesterol and total cholesterol.
  • Inflammation: Fasting reduces inflammation in most parts of the body. This can help many inflammatory conditions, such as irritable bowel syndrome and arthritis. Chronic and excessive inflammation is linked to many lifestyle disorders such as heart disease and cancer.
  • Immunity: As discussed, the biggest benefit of fasting is rebooting the immune system.
  • Longevity: Finally, the biggest claim about fasting is that it can increase longevity. But I feel it is impossible to design a clinical trial that can be completed in our lifetime—at least mine—to know this for sure.

    However, if you look at the benefits of various fasting formats in lifestyle disorders, logically, fasting should increase longevity. After all, these days, our medical science has improved so much that major killers in the developed world are lifestyle disorders such as cancer, heart disease, diabetes, and brain disorders.

Of course, improved health may not always mean improved longevity. But as the saying goes,

It is better to have more life in your years, than have more years in your life.

Some Research Findings

In various clinical trials, different fasting formats showed benefits. Here is a summary of some research findings, to give you a glimpse of evidence in favour of fasting:

  • Animal research has shown that intermittent fasting can reduce obesity, and the risk of fatty liver, diabetes, and cancer.
  • Research from the 1980s showed that the rats who were made to fast on alternate days lived longer than the rats who had food available all the time.
  • Recent research showed that the rats who were fed all of their calories only once a day were healthier and lived longer compared to the rats who had access to food all the time.
  • People who were at diabetes risk saw their fasting glucose return to normal during a five-day fasting-mimicking diet. Their high levels of cholesterol and triglycerides decreased, along with other markers of heart disease. They lost abdominal fat while preserving lean muscle mass and metabolism.

    Interestingly, their levels of Insulin-like growth factor-1 or IGF–1 marker were also reduced. This is a complex factor that plays a role in ageing. Ideally, it should be kept at low levels and activated only under specific conditions.
  • Participants on a 5–2 fasting-mimicking diet also saw health benefits. Over a six–month period, they lost body weight. They also improved glucose regulation (a risk factor for diabetes) and lost belly fat (a risk factor for cardiovascular disease). Those, who ate similar average calories but ate on all days, saw weight loss, but no improvement in other risk factors.
  • A study revealed the health benefits of a time-restricted eating pattern in the absence of weight loss among pre-diabetic men.

Who Should Avoid Fasting

  • Diabetic people run a risk of getting in low blood glucose or hypoglycemia on fasting. Such people are better off with fasting-mimicking diets instead of complete fasting. But this is only if one’s doctor permits;
  • Pregnant and breastfeeding women need extra nutrients for the foetus or the baby. Cutting down on food is risky at this life stage;
  • Children and adolescents have fast-growing bodies needing extra nutrients for growth. Children don’t need protection against degeneration like the adults; and
  • If someone is suffering from eating disorders such as bulimia or anorexia, fasting can trigger complications.

My Views

  1. We have evolved as hunter-gatherers. Thousands of years ago, we had to stay hungry for long periods as the effect needed to hunt or gather food was extensive.

    After mankind became an agrarian society, food became more easily available. Yet, people did not eat for long hours of the night because we did not have lights.

    Nowadays, with bright lights and an abundance of easy food, we have many more hours of feeding time. Most of us don’t go into a high ketone state due to this. That is why we need to use fasting to regularly cleanse our immune system.
  2. Which fasting format is the best? The one that you can follow for life. That is just like choosing the best time to exercise, which is the one that works for you.
  3. The Nobel Prizes in Medicine in 2016 and 2018 were awarded for discovering two important body processes, autophagy and checkpoint inhibition, respectively. Both of these are important for healthy immunity and are triggered by fasting.

How to Start Intermittent Fasting

Here are a few simple steps to learn doing 8-16 intermittent fasting—8 daytime hours of feeding with 16 hours of fasting.

  1. Get your doctor’s clearance.

    If you have diabetes or any other medical condition, check with your doctor if you can start intermittent fasting.

  2. Calculate a 16-hour window before your typical first meal of the morning.

    If you eat breakfast at 8 am, you need to take your last meal at 4 pm the previous day. That is the eventual target.

  3. Get your family’s consent.

    After all, you are going to play with your meal that is normally taken with the family: dinner.

    If they are unsupportive, skip step 4 and implement step 5.

  4. Prepone your dinnertime by 30 minutes every week.

    You have to phase yourself into the IF regime. Gradually!

    If you normally eat dinner at 8 pm, start eating at 730 pm for a week. Then, 7 pm for another week, etc.

  5. If your schedule does not allow you to eat dinner earlier, start cutting down on dinner.

    Aim to stop dinner altogether. Gradually!

    Reduce eating carbohydrates in the dinner for a week.
    Next week, aim to stop most carbohydrates from the dinner.
    The week after, reduce the portions of proteins and fats and replace them with salads.
    The week after, replace salads with lemon water (unsweetened), etc.

  6. Eat bigger meals in the afternoon and the morning.

    Add more proteins to your meals. They keep you full and satiated for a long time.

  7. Avoid activities that may tempt you to eat in the 16-hour fasting window.

    Parties, dinner events, bar visits, and late-night work or TV-watching will prevent you from doing IF.

    Of course, allow some cheat days or occasional failures.

    Once you have mastered the IF technique, you will be able to participate in some of the above activities and still manage to do an IF. Intermittent fasting is not a life sentence; if you cannot do IF on some days, that is perfectly fine.

  8. If your schedule permits, postpone your morning meal by an hour or two.

    When you get up, you will not hungry even if you have fasted for many hours. It takes time for the appetite to work up after a good night’s sleep. So you can easily postpone your morning meal further by 1-2 hours.

  9. Persist! Give it time and you will be able to control your hunger for 16 hours easily.

    Most people underestimate what they can achieve in a year and overestimate what they can master in a month.

To Read More

First published on: 18th April 2018
Image credit: Markus Spiske on Pexels
Last edited on: 22nd June 2022


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