MadSci Network: General Biology
Query:

Re: Can a 'fat' person survive longer without eating than a skinny person?

Date: Fri Nov 5 14:55:47 1999
Posted By: Carol Crouse, , Food Technology, The Food Chain Ltd.
Area of science: General Biology
ID: 940531184.Gb
Message:

Hello, Mr. Gillam.

It is hard to generalize about "a" fat person versus "a" thin person in the 
starvation question because it would vary with how fat and how well muscled 
the people were.  In a starvation situation, the human body can utilize 
protein or fat so it would just depend how much of a reserve of each there 
was.

There are three stages in the starvation process with the first taking 
place in a very short time - even just between meals for us.  Glucose is 
the fuel that the body uses if available, with over half of the daily glucose 
requirements going to the brain.  The rest of the glucose fuels e.g. the 
function/production of muscle tissue and red blood cells.  The body can 
obtain glucose from the breakdown of glycogen (first choice with small 
quantities being stored in the liver) and fat.  After the 
glycogen reserve is used up - still in this short term situation - the body 
begins to draw on fat to maintain blood glucose levels.  Of the 
fatty acids and glycerol derived from the fat breakdown, the glycerol is 
transformed into glucose that can go to the brain (fatty acids can not enter the 
brain.) The fatty acids can be used directly by all other body cells. The use of  
fatty acids in the cells swithches off the use of glucose in the same cell - 
with the result that parctically all the glucose available is used in the brain.

So during early starvation (say, 2-3 days after eating the last meal), we make 
extensive use of fatty acids as a fuel. Glucose is conserved and recycled and is 
reserved for almost exclusive use by the brain. However, with the brain using 
120 g glucose per day it is not going to take long for our carbohydrate stores 
to run out - what a pity we can't get the brain to make use of our
vast stores of fatty acids! 

Although the brain cannot use fatty acids, it can use short derivatives of fatty 
acids called KETONE BODIES. These are small, 4-carbon "mini-fatty acids" which 
CAN get into brain cells and can be split to give 2 molecules of acetyl CoA. 
Ketone bodies are produced from fatty acids in the liver after about 3 days of 
starvation. Essentially they are produced as acetyl CoA production reaches a 
maximum in this tissue. Their oxidation by the brain, cuts the brain's 
requirement for glucose from 120 g per day to about 30 g per day. Although the 
production and utilisation of ketone bodies is therefore a great help in 
relieving the pressure on our carbohydrate stores, it is still not really good 
enough - we still need to make that 30 g of glucose everyday from something! 
True we get 20 g of new glucose from glycerol everyday, but it still leaves a 
shortfall of 10 g - the difference must come from protein

After several days of exposure to low blood insulin concentrations, ALL our 
cells start to breakdown protein. This releases amino acids into the bloodstream 
which, as with glycerol and lactate, can be converted into glucose in the liver. 
Although this gives us all the glucose that we need for our brain, it should be 
realised that most cellular protein is ESSENTIAL to the survival of that cell. A 
cell cannot tolerate the loss of very much protein. Furthermore, the breakdown 
of proteins in cells is not very discriminatory. Prolonged low insulin levels 
are just as likely to breakdown lung cells as muscle cells. In addition, about 
2-3 g of protein has to be broken down to synthesise 1 g of glucose - so over 30 
g of pure protein is broken down each day just to keep our brain alive.

Eventually, after about 40 to 50 days of starvation, the loss of body protein 
reaches a stage at which important organs are irrevocably affected, and death 
results, regardless how many fat reserves are still present.

If the fat store has been depleted earlier, the body enters the final stage 
three in the starvation process earlier As the main source of energy switches to 
protein muscles deteriorate and cell function is impaired. The brain once again 
adapts to utilize some amino acids.

The ultimate cause of death would probably be due to arrhythmia or cardiac 
arrest brought on by tissue degradation and electrolyte imbalances, if an 
infection didn't attack first.

So the bodies of both the fat person and the lean person would respond the 
same to starvation.  First the short term glucose/glycogen supply from the 
liver would be used with some energy coming from proteins and fats.  Then 
fat tissue becomes the primary supplier.  The fat person would hold at this 
stage two longer than the lean person could.  At stage three, both would 
finish up their protein reserve.

Who is going to live the longest? - As soon as one has fat reserves for more 
than 2 months (and aery single normal healthy american has) there is no 
difference between the lean an fat persons. Of couse, if one has only few fat 
reserves (mostly people in 3rd world countries) then a few gram of fat can 
prolong your survival time during starvation considerably. 

I know this answer became rather convoluted but, as you now see (- I 
hope-), the answer to your question has a number of variables that come 
into play.  Anyway, it's time for me to stop my stage one starvation and 
head off for supper!  Have a good day.

Carol Crouse
Food Technologist
The Food Chain Ltd.  

This answer was edited for clarity by J. Ziesmann








Current Queue | Current Queue for General Biology | General Biology archives

Try the links in the MadSci Library for more information on General Biology.



MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci


MadSci Network, webadmin@www.madsci.org
© 1995-1999. All rights reserved.