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Metabolic Changes During Fasting and Starvation

October 12, 2019


hey everyone Dr Mungli here so in
this video I will be explaining you the metabolic changes that are going on in
our body during fasting condition and starvation during fasting conditions
when we are going to say a person is in fasting condition strictly speaking
fasting condition it begins 10 minutes after the meals
that’s strictly speaking otherwise loosely speaking so we just say two to
three hours after meals it says a person is in fasting condition
actually that is post absorptive condition anyway for our purpose here so
in this video I will be considering 2 to 3 hours after your last meal as a
fasting condition that’s what I have written here so two hours after meals
and then 12 hours after meals and up to 24 hours after the meals I have this
written it as a fasting condition here and then after that it is in days and
then in weeks now anyone who is not taking food more than 24 hours then they
just get into starvation that is what is referred as starvation fasting is within
24 hours we are not taking anything for 24 hours that is in fact that is
basically fasting and if you don’t take anything more than 24 hours that is
basically referred as starvation okay now what happens during fasting
condition or two to three hours after the meals so two to three hours after
meals our blood glucose level falls down so I’m going to write down the blood
glucose concentration so blood glucose it continuously falling down and then it
will just make the constant phase okay so this is what happens under fasting
conditions and the blood glucose this is this line is indicative of blood
glucose all the things that I’m writing here is in the blood so I will write it has
glucose here so glucose levels fall so as you can see continuous fall in the
glucose level and then it just maintains a constant phase there now as the blood
glucose level falls your insulin levels will also fall down as the insulin level
fall so you all know glucagon levels will rise so look I’m going to write a
glucagon level so the insulin is coming from beta cells of pancreas and glucagon
is coming from alpha cells of pancreas and generally insulin has got a negative
effect or inhibitory effect on alpha cells of pancreas so as the insulin
levels fall so the glucagon level will rise so that will be rise in the
glucagon levels and the insulin level is falling down so it will be like this so
we have glucagon here so now what is the metabolic effect of glucagon on our
body so you know glucagon is a catabolic hormone as opposed to insulin insulin is
a anabolic hormone now a person is in fasting conditions a two to three hours
after meals so slowly insulin is dropping down and glucagon is rising
so this glucagon is going to break down or energy sources
what are the energy sources that we have so we have glycogen in the liver we have
glycogen in the skeletal muscle and other tissues so glucagon it is going
to go and binds to glucagon receptors in the hepatocytes and it’s going to break
down glycogen by stimulating an enzyme called glycogen phosphorylase enzyme now
this degradation is going on in the liver so Im going to write that glycogen degradation now so it starts two to three hours after meals and it Peaks
by 12 hours and it basically it is depleted by 24 hours of
fasting so glycogen degradation this is the glycogen degradation here mediated
by glycogen phosphorylase and that is stimulated by glucagon hormone so glycogen degradation starts two to three hours of the meals peaks by twelve hours
and depletes completely by 24 hours it can vary from person to person depending
on their carbohydrate previous carbohydrate intake some people their glucose and
glycogen can last only for 12 hours and some other it can last for 24 hours in a
person who is taking well-balanced diet who is 70 kg in those people so glycogen
can lost for 24 hours so this glycogen which is breaking down into
glucose 1-phosphate further it is converted into glucose and that will
maintain the blood glucose level under fasting condition so basically
person will have a fasting blood glucose level so now what else is going on here
so as the glucagon is increased here so as the glucagon is increased here glucagon not only breaks up glycogen
stores it is also going to break a lipid store present in our body and where do
you have a lipid store where is the lipid stored in our body it is stored
beneath our skin that is adipose tissue adipose tissue has got white adipose tissue has got triacylglycerol and this triacylglycerol can be
broken down to give energy for ourselves so glucagon it is going to go and
activate hormone sensitive lipase glucagon is binding to glucagon receptors on the adipose tissue and it’s going to activate hormone sensitive
lipase and that hormone sensitive lipase it is going to release free fatty acids
and glycerol into the blood and free fatty acids will be taken up by
peripheral tissues almost all tissues in our body except red blood cells and the
brain so they can use free fatty acids for their energy so they will conduct beta oxidation process skeletal muscles cardiocytes all other tissues
including the liver it’s going to conduct the beat oxidation breakdown
fatty acids and releases acetyl CoA and acetyl CoA get into TCA cycle to
give energy okay so in the influence of glucagon so your free fatty acids floods
into the blood so I’m going to write that now so two to three hours after
meals so free fatty acid continuously they’re going to rise as the fasting
goes on and as the person gets into starvation free fatty acid rises so
these free fatty acids will be used by almost all tissues in our body except
red cells and the brain so let me gradual means there will be
continuous rise in the fatty acids in our body okay so now the
glycerol that is coming from triacylglycerol as the adipose tissue is
broken down into free fatty acid and the glycerol so glycerol is taken up by the
liver free fatty acids predominantly taken up by the liver and the other tissues glycerol
mainly it will be taken up by the liver so what liver does with the glycerol
glycerol it will be converted into glucose in the liver liver has glycerol
kinase enzyme glycerol 3-phosphate dehydrogenase enzyme and ultimately glycerol is going into glucose formation by a process called as gluconeogenesis so
not only glycerol coming from triacylglycerol gets into
gluconeogenesis gluconeogenesis can also be done with using lactate
lactate is coming from red blood cells because red blood cells they conduct
anaerobic glycolysis so in anaerobic glycolysis you get lactate lactate gets
into the blood it will be taken up by the liver and heart so in the liver what
happens the lactate is converted back into glucose by gluconeogenesis now some
of the amino acids can also be converted into glucose like out of 20 amino acids 18 of
them can be converted to glucose so let’s see what is the timeline for
gluconeogenesis gluconeogenesis it starts two to
three hours after meals but
it will be there at basal level so this is the gluconeogenesis line here it
will be there at the base level because you are still glycogen degradation is
going on so at 12 hours your glycogen degradation is at peak and it is
depleted by 24 hours and the glycogen degradation is depleted so the
gluconeogenesis that is going on at a very basal level here it will start to
rise or 12 hours by 12 hours it is steaming up and by 24 hours it is at peak gluconeogenesis is at peak by 24 hours by the time your glycogen
degradation is already down it is totally depleted so now the glucose maintenance
this is the glucose here so the maintenance of blood glucose level it
will be done by gluconeogenesis process now as the gluconeogenesis process
reaches peak here by 24 hours your gluconeogenesis is at peak by that time
you know that the glycogen degradation degradation is already down here or total depleted now the gluconeogenesis further it is
going to continue for at the peak level for another one week basically for one
week it will be on peak as you can see this is one week period here soon
gluconeogenesis is at peak and after that it is going to fall down
gluconeogenesis is going to drop by second week and then it just maintains
at a constant level okay so now what all the sources there you can see as the
gluconeogenesis is falling down even the blood glucose levels also falls
down and just maintaining a constant pace now what all the sources for
what all the precursors for gluconeogenesis under this condition so
initially from 2 to 3 hours and then 12 hours up to 24 hours in this particular
periods how the glucose is made it is made from by converting glycerol into glucose glycerol you know it is coming from triacylglycerol it is made from
converting lactate into glucose in the liver and also some of the amino acids
present in the hepatocytes and also amino acids coming from the muscle not
really because of breakdown of skeletal muscles of breakdown of skeletal muscle
doesn’t go on until more than 24 hours to 48 hours it takes 24 hours to 48
hours for our skeletal muscle proteins to undergo proteolysis
so the amino acids that are coming from skeletal muscle actually they are all
come they are all coming from the transamination process what happens
during transamination let me explain they
transamination so whenever person is in fasting condition see there is a
glucagon is elevated releasing free fatty acids
free fatty acids gets into the skeletal muscles
skeletal muscles will conduct the beta oxidation process and they will get acetyl CoA
from beta oxidation acetyl CoA level rises as the acetyl CoA level rises acetyl CoA will have a negative effect on pyruvate dehydrogenase complex
so that means the glucose which is converted to pyruvate which is further
is not converted to acetyl coa because excess acetyl CoA from beta oxidation
of fatty acids in skeletal muscle will have a negative effect on pyruvate dehydrogenase
complex there by pyruvate accumulates and this accumulated pyruvate it will
undergo transamination reaction so with the glutamate amino acid glutamate so in
this transformation what happens pyruvate is converted to alanine and
glutamate is converted to alpha keto glutarate you can watch my video on
transamination the link for that is appearing right now on the right upper
corner now with pyruvate undergoing transamination it is converted to a
alanine and the alanine is coming into the blood and that will be taken up by
the liver and that will participate in gluconeogenesis process that is what
happens within 24 hours of this gluconeogenesis period so the major
sources or the precursors for gluconeogenesis within that 24 hours i
would say it is glycerol lactate and the amino acid coming from the muscle
specially from transamination reaction which is coming from pyruvate okay after
24 hours what happens so after 24 hours 24 to 48 hours period so it is the
proteolysis that can go on in the skeletal muscle especially because by
that time even the cortisol will be elevated because the person is in
starvation it’s a stressful situation so the cortisol will build up in the blood
so that cortisol can lead to proteolysis in the skeletal muscle and skeletal muscle proteins will be broken down to release more amino acids so that amino
acids will go to the liver and in the liver some of these amino acids go into gluconeogenesis process to maintain blood glucose level and also
some amino acids in the liver can be going into protein synthesis to make
essential proteins that are needed for anabolic processes in the liver that is
why the skeletal muscle protein acts as a source for amino acids in the liver
but so far that happen the starvation has to be 24
48 hours and then continues there until like 7 days after that you see
there is a drop in these gluconeogenesis because by that time 50 to 60% of the
skeletal muscle is already proteolysed so growth hormone comes in and it will
decrease the proteolysis and thereby gluconeogenesis this drops and continues
and the constant phase and in this gluconeogenic precursors are
glycerol and lactate again because glycerol is coming from continuous
degradation of triacylglycerol into free fatty acids and glycerol and the lactate
is coming from anaerobic glycolysis so this is what happens in relation to
gluconeogenesis process now see a the free fatty acids are coming
into the liver so liver is conducting beta oxidation beta oxidation will give
you acetyl CoA and acetyl CoA will saturate TCA cycle once TCA cycle
is saturated so excess acetyl CoA they will be diverted into ketone body
formation ketone bodies for formation note like 12 hours after fasting
they basically are at the baseline you won’t really see them much in the blood
but after 24 hours so they start to appear in the blood so by the three days
as you can see there is a significant appearance of ketone bodies and they
are going to rise as the starvation like fasting and going into starvation as the
starvation occurs ketone body rises this is the ketones here so ketones
will rise they will appear significantly twenty four hours after starvation and
they are continuously rise as long as free fatty acids are available then it
now you have most of our cells when when a person is in fasting condition
they are all like adopted like they’re using free fatty acids as the
ketone bodies are appearing in the blood so our cells will adopt themselves
to use ketone also specially the brain brain takes two to three days to
adopt for ketone bodies and start using ketone bodies as the brain start using ketone bodies by third day like around 30 percent of the energy needs of brain
will come from ketone bodies that means it is
going to save this glucose for red blood cells so because it knows there as the
days goes you know gluconeogenesis is going to fall down
blood glucose level goes to go down that means by that time your brain is
already adapting itself to use ketone bodies by one week brain is almost using
ketone bodies as its energy source it is sparing glucose for red blood cell
in the same way the skeletal muscle and other tissues like heart they
all will use ketone bodies eventually they will revert back to use of fatty
acids because ketone bodies are predominantly used by the brain after
one to two weeks of starvation it so this is how the metabolic adaptations
will go on in our bodies for that there will be a lot of hormonal changes
going on so insulin dropping glucagon increasing and later on cortisol
coming in and then growth hormone coming in so all these hormones they will alter
the metabolic pathways and make sure that our cells will get all the energy
that they need so in one or the other form it initially it will be coming from
a glycogen giving glucose after that gluconeogenesis giving glucose and then
the free fatty acids giving energy and later body getting into keto adaptation
process so this is all about metabolic changes that are going on during fasting
condition and starvation I hope this video has helped you in understanding
this concept if you have any question so kindly let me know about that in the
comment section below I will answer to them as soon as possible so thanks for
watching and for regular updates you can consider subscribing to this CHANNEL and also click on the bell button there so that you get the notification as in
when I upload the video thanks again and have a good day!!!

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22 Comments

  • Reply Ramchandra Suthar October 20, 2017 at 2:29 pm

    Very nice analysis sir

  • Reply Vimal Susee October 20, 2017 at 3:01 pm

    Nicely explained sir…

  • Reply Dr.Bala krish October 21, 2017 at 8:04 am

    Thank you for your lucid explanation!!!

  • Reply D Castle November 25, 2017 at 3:17 pm

    May I ask , if you are diagnosed with fatty liver disease and you would like to use a fasting protocol to help use the fats stored in the liver, at what point would the body start using the liver fat stores during a fasting schedule? I would like to use a fasting as a therapeutic form of health to help my husband and I, but I’m not sure if the duration. Thank you

  • Reply Brayton Carbine December 3, 2017 at 12:03 am

    Very informative. Thank you!

  • Reply Olafsos Huber April 3, 2018 at 5:09 am

    great explanations of the most important metabolic changes

  • Reply Mister EIE April 15, 2018 at 10:33 am

    Starvation? After only 24 hours? Uh, I dont think so.

    Starvation only occurs after a couple of months of fasting, when the body begins to break down organs for nutrition.

    The rest of your info is accurate, but your terminology is extreme.

  • Reply eviee April 26, 2018 at 6:44 pm

    Thank you so much! you are amazing!

  • Reply Aliya Zakir May 1, 2018 at 5:44 am

    professor is good but there are about 15 commercials in this video! very disruptive and annoying 🙁 watch if u want to get a headache

  • Reply Don Grant May 31, 2018 at 7:43 pm

    Starvation is just not as simple as going more than 24 hours without food. Humans can go weeks without food and not starve .

  • Reply Vida Verde Las Terrenas June 25, 2018 at 8:41 pm

    axoloacetate depletion – changed in glucose when glucose level is low and actyl coa is high – is the starting point of ketones production

  • Reply Synaptricks August 23, 2018 at 4:50 pm

    This was beautifully explained Dr. Mungli, thanks for sharing.

  • Reply nyile012 December 2, 2018 at 11:51 am

    Execellent !!!

  • Reply Humaira Khan December 7, 2018 at 1:41 am

    thank you soo much soo hepful

  • Reply Wesam Bassout February 11, 2019 at 3:50 pm

    Thank you very much for this comprehensive information

  • Reply Michael C February 28, 2019 at 5:24 pm

    I can think of 2 great additions to this presentation. 1. Mapping the autophagy process 2. Having a duplicate presentation (including autophagy) but beginning the process in a body that is already operating in ketosis from hour one.

  • Reply Steve Morris-Bond March 29, 2019 at 10:53 pm

    Starvation is the process by which your body breaks down muscle, body tissue and finally vital organs only after all body fat reserves have been depleted. Starvation takes weeks and sometimes, months to occur depending on how much body fat one has. It definitely doesn’t start 24 hours after fasting. Your body will enter gluconeogenesis 12 hours into fasting which will enable you to burn small amounts of body fat. 36 to 48 hours into fasting, you will enter Ketosis which will enable you to burn much more body fat.

  • Reply Nevena Dimanova May 26, 2019 at 7:02 pm

    Thank you very much for explaining everything so all of us can understand!

  • Reply GloryNourSufferings May 29, 2019 at 9:15 pm

    Thank you for this information Dr! Please pardon the ignorant people who seek to insult you.

  • Reply ran June 1, 2019 at 6:35 pm

    thank you sir! very helpful !

  • Reply Wild One June 4, 2019 at 3:47 am

    Great video,very detailed. I found information presented a bit too fast to take it all in though – while also getting used to the accent! 🙂 It would be good to have subtitles. I'm listening to it a second time and pausing and rewinding the bits I missed.

  • Reply John Coughlan June 4, 2019 at 5:00 pm

    Dear Doctor,I was water fasting for 24 hours and only eating at 6 pm once a day.
    After a few days i felt dizzy and unwell.
    All my blood test was normal except low phosphate 0.74(0.87-1.45)
    Is this dangerous and what caused it.
    Thankyou

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