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Fasting, extreme low cal diets, and the "starvation mode" myth...

I originally wrote this post in response to a question about an extremely restrictive diet. My fear was that, because there were so many posts under that thread already, the original poster would just get over whelmed and not read my post, which I worked really hard on! Kidding. I also do think this could be useful to others, as so many people seem to believe that there's a "starvation mode" that your body goes into when there's an extreme lack of food. It's not quite untrue...but it's not quite right either.

My sister is in medical school and studied nutritional sciences for her undergrad. She told me that when you don't eat for a day, or any other prolonged period of time, your body produces the energy it needs to live and move by "eating" your muscles instead. Muscle weighs more than fat, so when you step on the scale, you will see that you have lost weight.

Consider, however, that muscle takes the most energy for your body to maintain. A person with a lot of muscle mass burns more calories per day than a similarly built person who has less muscle, even if both are just sitting on the couch watching TV.

So, when someone stops fasting, he or she will have lost weight because they have lost muscle mass. However, his or her body will now burn less calories per day than it did before they started fasting. If that person were to start eating again as they did before the fast, he or she would now gain weight, where as before the fast, they broke even, and neither gained or lost.

It's quite possible that the same is true for when you eat an extremely low amount of calories per day. Your body needs energy to keep moving and living. It is not getting that energy from food, so it burns up some muscle, because muscle a) provides more nutrients than fat, and b) requires more energy to maintain, energy which your body no longer has.

The belief that your body goes into starvation mode, then, is a bit of a myth. Your body does not think "oh, no food, better lower my metabolism for a while". Your body is a machine really, it doesn't think much of anything at all. Eating too little, however, does lower your metabolism because your body is eating up its muscle mass. This is not a temporary change though, as the words "starvation mode" may lead you to believe. The lowering of your metabolic rate will be permanent until you exercise to build back the muscle you have lost.

Hope you found this interesting and helpful, and if anyone has anything to add to or counter the above, please feel free to post it below. Thank you.

Sun. Dec 7, 11:07pm

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I have a few points to counter.

Starvation DOES affect your metabolism. I am a pre-med in college and while I respect your sister's knowledge, I will give the benefit of the doubt that you are getting your information second hand, meaning you haven't learned it yourself.

The first few days during starvation there is an absolute change in your BMR. It is actually a tiny increase similarly related to 'overnight fasting' which is what we do every night when we sleep.

In 1950 a study was done, a very notorious Minnesota Semistarvation Study. ~40 young, healthy, lean men were put on what is considered a 'semi starvation diet', meaning less than 50% of their BMR caloric needs per day for 6 months. Their BMR dropped to about ~50% of what it had been. They did loose some muscle, but overall they lost mostly fat until their bodies reached the critical 5% body fat (critical amount of fat needed by males).

Starvation diets are usually used for morbidly obese/obese people. Obese people actually have a mechanism in their bodies that causes them to burn fat over muscle. A lean person and an obese person that are both on a starvation diet will lose weight very differently. The obese person will lose mostly fat, the lean person will lose mostly fat-free mass. 7e11.htm. (study that supports me)

Obese people have MORE lean body mass than a normal weight person (FORBES, 1987; JAMES et al., 1978). Up to over 30% more. Obese people need the greater vascular volumes and larger heart to pump blood through their entire body and need MORE muscle to move themselves.

When you do not eat for a long period of time, your body will release chemicals that tell the body to try and hold onto some fat, preferring muscle over fat. Burning muscle is EASIER than burning fat. That is why it's so hard to build muscle.

Monday, December 08, 2008, 12:20 AM

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If when starving people would not lose any fat then all those anorexics would be full of fat but they are not! They are skinny!

Monday, December 08, 2008, 5:52 AM

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Thanks, this is interesting stuff! My only concern is the date that this study was done, and the fact that it was done only on men. So many other things that people believed in the 50's have since been proved wrong, and women are physiologically different than men. Still, it may be relevant (unfortunately, I can't read the article, for whatever reason. It says it can't be found).

I'm sure you are correct, however, on the fact that obese people lose weight differently than people of a more normal weight. I haven't talked at length with sis about obesity. I was aware that the have more muscle than most, but that just makes sense. If I wore 100 pounds of extra weight on a daily basis, I would also have a lot more muscle.

I think this is neat stuff though. Does it say how long it took the men to get their BMR back up to what it had been? Just out of curiosity.

5:52 - yeah that was a point I was going to comment on, but it just got too long. I figured (solely on my own mind you) that, when your body has used up all the muscle you have to spare (ie, everything you don't use to get up in the morning, walk to the bathroom and take a shower, those kinds of everyday things) then it will start eating fat. Fat, however, is less nutritious than muscle, so at some point it will have to eat more muscle to get nutrients, and then go back to burning fat, and so on, until there's no more fat, and no more muscle, and then you body starts consuming bits of organs and will even go so far as to liquidate portions of your own DNA chain in order to keep going...of course by this point the person is beyond saving and will soon die (the DNA part was something my sister was amazed to learn, so that I'm fairly certain is true).

Anyway, this is cool stuff. Anyone else have something to add?

Tuesday, December 09, 2008, 10:53 AM

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Anorexics are "skinny"- I'd tend to go with gaunt. Completely lacking in tone and shape. And many prior to getting to that point are flabby.

Tuesday, December 09, 2008, 6:20 PM

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Most of the starvation diet myths were started by people trying to sell their own particular diet plans. People are always trying to make a buck off of fat people and claim that their own diet plan is the best. The one thing they all agree on is that starvation diets are bad, mainly because they won't make any money from people who fast or starve. But the truth is, fat is nature's protection against times of famine, and when people stop eating they are living on their stores of fat. They aren't even really starving, they are living off of their stored fat, just as if they were eating fat. Nobody ever died of starvation when they were fat. I repeat...NO FAT PERSON EVER DIED OF STARVATION. The body fat is used by the body as energy, and as long as you have fat, you have a source of nutrition. Only after the fat is used up does the body start to consume itself and enter starvation mode. As long as you have body fat, you will not starve. A 400 pound person can live for a year without eating. Fasting is a perfectly natural thing, and is by far the best way to lose weight. It shrinks the stomach which reduces portion size when you start to eat again. Fasting also re-sets the appetite switches so you don't pig out so much afterwards. Fasting is great, you really need to try it. And after 2 days of fasting you don't even feel hungry anymore, and the weight peels off FAST!!

Wednesday, March 11, 2009, 5:45 PM

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