What Happens When You Stop Eating?

Medically speaking, starvation occurs when a body doesn’t get enough calories and nutrients; Whether brought on by poverty, famine, being lost at sea, voluntary hunger strikes or medical conditions, the physiology of starvation follows the same process no matter the cause. And it really is a process: it takes time to starve to death. Without oxygen, our bodies shut down in five or ten minutes. Without water, we can last maybe a couple days — a week at most. But depending on the circumstances, a person might go as long as two months without any food at all. During this time the body passes through three distinct metabolic phases as it desperately tries to stay alive until it finds food again. phase one is where your body picks the
lowest hanging fruit, energy-wise through glucose burning. In your normal well-fed
state your body breaks down glycogen molecules to produce glucose: the
friendly carbohydrate that keeps your cells well-fed and functioning. The average person can typically go
about six hours after feeding in the glucose burning phase before they start
feeling hungry, and probably grumpy. At that point your
body has burned through all that lunchtime glucose and is turning toward
fatty acids: the building blocks of fat molecules
stored in your tissues to fuel itself. This, which kicks off the first big
metabolic shift as your body enters phase two of starvation: fat burning. The fat-burning phase can
last from days to weeks. During this stage called ketosis, our
livers metabolize fatty acids and the smaller fat-chain derivatives called ketone bodies; they replace
glucose as the main energy source. These compounds come in three different
water soluble configurations that move from the liver to the heart, brain, and
other tissues during periods of fasting to try to keep things going. Some people,
like hard-training triathletes or body builders are those on a super low carb
high protein diet are maybe in ketosis is pretty often. It
doesn’t mean they’re starving, it just means that
their bodies are running differently because either they’re not eating enough
carbs from which to get glucose, or they’re
quickly burning through them. But if you think that eating butter covered bacon
to burn body fat sounds like a good deal, you should know your brain might be less than amused. Your brain
can’t directly use those fatty acids as fuel because they’re too big to squeeze
through the blood-brain barrier. And our brains are a big energy suck —
they demand about 25 percent of our stored energy to function properly. The kind of greedy like that needing about a hundred and twenty grams of glucose a day to stay happy. That’s like three cans of coke: it’s like four
cans of coke if one of them’s diet. So in your first day or two without food while
the rest of your body starts fueling itself on fatty acids, the brain drains the last bit is stored glucose
until it really runs out. But you probably noticed that no one dies after just two
days without food: that wouldn’t make very much
evolutionary sense. Luckily, your brain is smart and it has a backup
plan. Within a few days have no food, your brain recalibrates its glucose
requirement from 120 grams to about 30 grams, and it changes the menu. The brain now
starts eating those processed ketone bodies, which, because they’re smaller
than fatty acids, can get through the blood-brain barrier. This is a great evolutionary trick to keep us alert enough no matter how hungry we are
to continue to look for food. But even if you are semi alert you’re definitely not in a
good mood. As a hungered is continually deprived of vital nutrient, it
gets to feeling depressed, anxious, lethargic, socially withdrawn, and starts
to have trouble concentrating and comprehending. The third, and final phase
of starvation begins when all your fat stores are burned up, and the body
switches to using its final reserves proteins. This phase is marked by a rapid
muscle depletion as your body cells start to break down their own proteins into amino acids which your brain now gobbles up. Proteins are essential for proper cell functioning, so
things go downhill pretty quickly as your body starts eating itself, basically, in a
process of internal self cannibalism called catabolysis. Still, your ever
optimistic body tries to run damage control by eating up your least vital
cells for as long as possible as it holds out hope for more food. But, after weeks of no food — once your
body has burned through all available glucose, fatty acids, and protein, muscle
mass, it’s got nowhere left to look, and the
end is near. even mind that by this point your body is so
grossly deficient in vitamins and minerals and has such a weakened immune
system not just about anything could kill you. In the end, the ultimate cause of death during
starvation is often cardiac arrest, due to excessive tissue degradation. The heart simply can no longer support
itself with such limited resources. It’s enough to make us all, I hope, really
appreciate everything we eat, at least for this one day. Thank you for
watching this episode of SciShow, if you have any questions, comments, or ideas for us where the comments, and on Facebook and
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