In the last Post #63, I described that:

  1. Lysosomes in our cells collect garbage and covert that for reuse.
  2. Do more of autophagy and body heals itself. Less of autophagy leads to diseases.
  3. Fasting is currently the only way to get the body into autophagy.

Concept of fasting, of course, has been around for thousands of years.

Our hunter gatherer ancestors had to live with unpredictable access to nutrition and routinely experienced periods of fasting and eating. Most religions of the world have some concept of fasting – Lent in Christianity, Ramadan in Islam, ta’anit, taanis or taʿanith in Judaism, a variety of fasting in Hinduism and Buddhism.

However, science of fasting is relatively new, though it is  a popular subject for research these days. I just did a quick search on the word “fasting” on the National Library of Medicine PubMed site and it produced 3,392 citations.

Michael Greger, M.D., who publishes his research summaries on the website NutritionFact.org, recently read and has summarized 1,250 of these papers. I attended the first half of his summaries in a 3-hour webinar last week.

Since weight loss is a major topic of interest around the world, a lot of research has focused on fasting for weight loss and its impact on popular bio-markers such as cholesterol, glucose, blood pressure. There is some research also available on the impact of fasting on longevity., although not as much as for weight loss.

All fasting methods consist of some variations of these variables:

  • What you eat or not eat,
  • How much you eat or not eat,
  • When you eat or not eat, and
  • How frequently you repeat the process.

And, with these variables you can make all kinds of combinations. For example, you may have seen or heard of the following popular combinations:

  1. Water only Fast for, say, 1, 3, or 5 consecutive days; alternate day fasting; 5:2 fasting: fasting for 2 days and eating the other 5 days of the week.
  2. Calories Restricted Diet: 20% fewer calories per day, e.g., 1,600 calories per day when 2,000 is your regular intake
  3. Time-Restricted Feeding: 8:16 fasting: eating for 8 hours and fasting for 16 hours; 4:20 fasting, where you eat for 4 hours and fast for 20, etc.
  4. Fasting-Mimicking Diet: During fasting, you still eat but with certain restrictions on carbs and protein, so your body feels as if you are fasting.

So, what option is optimal for you or I? Well, in biology nothing seems that simple. Answer always seems be: It depends.

The answer as to what is best for you or I, depends on a variety of variables including: state of your health, state of your fitness, your goals, your ability to follow the process in the short term or long term, any medicines you are taking, age, BMI.

Here are some principles, I have been able to tease apart from various research summaries, pod-casts of experts and books I have read so far. In human biology, there is always more details. So, these are, of course, simplified versions.

Principle I: Multiple Energy Sources: Our bodies have three main energy sources: a) immediate energy from the food we eat, b) Glycogen stored in liver, and c) fat stored in the body.

On typical days, we are constantly eating multiple meals a day that equal to or exceed the energy requirement of our body. Body simply takes macro and micro nutrient content from the digested food, and stores excess in liver as Glycogen or as fat in fat cells.

If we eat less than what our body needs, body takes excess first from the glycogen store in the liver and converts into glucose for use by the cells.

When glycogen stores are depleted, body starts to convert store fat into energy, through a process called Ketosis and uses Ketones as source of energy.

Which of these stores are being used when, depends on all those variable I mentioned above. For example, when body will start dipping into glycogen store may depend upon how big the last meal you had and what you ate. Or, your body may go into ketosis relatively quickly if you are athletically trained to burn fat as fuel like distance runners.

Principle II: Autophagy: At some point after body is in ketosis, autophagy turns on more and more vigorously. In fact, different tissues in the body up-regulate autophagy at different times. In autophagy, the lysosomes start to convert garbage insides the cells, e.g., broken DNA strands, ill formed organelles, into sources of energy.

Body is always in autophagy at some level. Fasting just kicks it into higher gears. How long before autophagy goes into higher gears? You guessed it: it depends. Since autophagy happens insides the cells, it is not easy to measure.

In general, autophagy has been observed after 14 hours in time-restricted regimens. And, it is generally established that after three days of fasting autophagy definitely accelerates.

Principle III: Chronobiology: Body’s circadian clock dictates metabolism. So, metabolism is generally faster during the morning and slower in the evening. Studies have shown that in a 16:8 fasting, with same intake folks who ate between 6am to 2pm lost more weight than those who ate from 2pm to 8pm. Moreover, the bio-markers, e.g., LDL cholesterol, of the second group were worse than the first group.

So, the wisdom of eat breakfast like a king, lunch like a prince and dinner like a pauper holds.

Not to leave you hanging, but it does looks like that it will take at least one more post to share the benefits, downsides and my experiences of fasting so far.


  1. Several variables make up a fasting protocol: what, how, when and how frequently you eat or not eat.
  2. There are many types of fasting: water only fasts, calories restricted diet, time-restricted feeding, and fasting-mimicking diet. What is optimal for you depends on a number of factors related to your health, fitness, and goals.
  3. Three general principles that you can use as guide to choose a protocol that may best suit you are: multiple sources of energy, autophagy and chronology.

What do you think?

Have you an experience with fasting? Have you learned about autophagy?

I and the readers of this blog would love to hear from you and learn from you.

Please click on Comment to leave your comments or question so others can benefit from your input.