QUOTE from Dr Fung (emphasis mine):
“FASTING INCREASES ADRENALIN levels, starting at around twenty-four hours. Forty-eight hours of fasting produces a 3.6 percent increase in metabolic rate, not the dreaded metabolic shutdown so often seen in caloric-reduction strategies. In response to a four-day fast, resting energy expenditure increased up to 14 percent. Rather than slowing metabolism, the body revs it up instead. Presumably, it does this so we have energy to go out and find more food.” 
NOTE – What does it say?
Fasting increases the metabolic rate … which is a mystery. What circumstance would make the dreaded metabolic shutdown make sense?
Basal metabolic rate (BMR) is the rate of energy expenditure per unit time by endothermic animals at rest…. Basal metabolic rate is the amount of energy per unit time that a person needs to keep the body functioning at rest. Some of those processes are breathing, blood circulation, controlling body temperature, cell growth, brain and nerve function, and contraction of muscles. Basal metabolic rate (BMR) affects the rate that a person burns calories and ultimately whether that individual maintains, gains, or loses weight. The basal metabolic rate accounts for about 60 to 75% of the daily calorie expenditure by individuals. It is influenced by several factors. BMR typically declines by 1–2% per decade after age 20 … 
Forty-eight hours of fasting produces a 3.6 percent increase in metabolic rate
Energy available to us decreases during a famine because the understanding of the body is that there is no food to gather. So fat is not burned but rather conserved for survival. When any food is found, rather increasing metabolism and burning calories for energy, it is converted to fat; and when the famine ends, the body keeps the metabolic rate low in order to return fat storage to former levels or more, as more fat stored enhances survival in a famine. This is why consistent calorie reduction doesn’t work – it mimics a famine. We regain any weight lost, and more.
The body is a system, and systems seek to remain in balance, at homeostasis. Consequently, when food available in the environment decreases because of natural causes, as in a famine, the body lowers the metabolic rate such that the energy expended matches the food energy available. And, therefore, no weight is lost. If I understand Dr. Fung correctly, this is the inescapable result of every calorie restriction process except one – fasting. When a decreased calorie level is consistent, the body adjusts metabolic rate downward in order to conserve life and energy.
When no food whatsoever seems to be available … zero calories in … the body increases metabolism so that there is energy to go find food. Forty-eight hours of fasting produces a 3.6 percent increase in metabolic rate … In response to a four-day fast, resting energy expenditure increased up to 14 percent. The body consumes available calories from food eaten, then glycogen stored in the liver, and then enters keto and begins to burn visceral fat (liver, pancreas, abdomen) and then subcutaneous (under the skin) fat. Finding food as soon as possible is seen as necessary to survival.
Rather than slowing metabolism, the body revs it up instead.
The signal to the body to ramp up energy and go find some food is zero calories in. This signal is reached as the body enters a keto state – glucose in the liver is being consumed or has been consumed. The great difficulty I personally face is that “a few calories in” is the signal for a famine rather than a fast, and the body responds appropriately. A few glucose calories in stops the keto signal, resets the process and indicates a famine. Therefore, the calories from milk that I prefer in my coffee on the morning of a fast day may be hazardous to my health.
What gets my attention?
Do I understand the need or problem?
Do I understand the potential solution?
Do I understand how to apply that strategy?
What questions do I have for the experts? What might be the answers?
Who needs to hear this?
What do I do next?
SOURCE – Footnotes:
 Quote from The Obesity Code: Unlocking the Secrets of Weight Loss by Dr. Jason Fung; Greystone Books (March 3, 2016). Page . Kindle location: tk
 “Basal metabolic rate” From Wikipedia, https://en.wikipedia.org/wiki/Basal_metabolic_rate
Photo Fasting-a-glass-of-water-on-an-empty-plate, via Wikimedia Commons
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Key: Fung-10-30.29 Last Revision: 1-12-2021