Will fasting metabolize "waste material" before healthy tissue?

October 3, 2005 5:23 PM

"Within 24 hours of curtailing food intake, enzymes stop entering the stomach and travel instead into the intestines and into the bloodstream, where they circulate and gobble up all sorts of waste matter, including dead and damaged cells, unwelcome microbes, metabolic wastes, and pollutants." [cite] Could this possibly be true? I know that eventually the body will start metabolizing itself, but is the process selective in its initial stages to only metabolize "waste matter" and not healthy tissue?
posted by Asef Jil to Health & Fitness (19 answers total)

There are tons of enzymes in the cells in your body that do their specific 'jobs' regardless of you fasting or not.

Enzymes act on specific substances and are contained in special containers--your cells--that they don't start destroying you inside-out nilly willy.

(although, if you stop eating for a long time, obviously, that can have some detrimental effects.)
posted by scalespace at 5:31 PM on October 3, 2005

I personally have enjoyed the benefits of fasting in various different ways and have never experienced any harmful side affects (other than those which stem directly from the elimination of toxins themselves such as irratability, dry mouth etc). It makes sense to me that the body would first look to clean out excess buildup and old waste, and that cannibalizing itself is a last resort. If you are concerned about this still, try a juice fast, in which you will still see many benefits but is much easier to maintain and easier to stay healthy on.
posted by sophist at 5:47 PM on October 3, 2005

Elimination of toxins? Benefits of toxins? Metabolizing waste first? Come on guys.

The body will first start metabolizing the extra glucose in the liver. When that runs out it will go to the fatty acids using the Kreb cycle. I believe you can continue to fast as long as glucose levels remain above a certain point. After that your nervous system fails and you die.

Waste products are exactly that, waste. We can't burn soot, our body can't burn its byproducts in a pinch.

Correct me if my fasting data is off.
posted by geoff. at 5:55 PM on October 3, 2005

Sophist, with all due respect, can you cite some actual scientific evidence that fasting eliminates "toxins"? As far as I'm aware, studies do show that fasting temporarily relieves arthritis inflammation, but this has nothing to do with "toxins".

"Detoxification" is an alluring, but irrational, concept.
posted by footnote at 5:57 PM on October 3, 2005

including dead and damaged cells, unwelcome microbes, metabolic wastes, and pollutants."

Sounds like the spleen, immune system, and liver, respectively--you don't need to fast for those organs to do those things.
posted by Brian James at 6:04 PM on October 3, 2005

The explanation has mixed two different processes.

Fasting doesn't work because enzymes are being redirected from the stomach. It works because when you reduce the toxic load on your eliminative organs (wherby the main source of toxins is that junk you're eating and drinking) they are freed up to process other toxins already stored in your system.

The mechanism for toxin elimination is distinct from energy metabolism. When we say that a body "cannibalizes" itself, this tends to refer to the process whereby, when deprived of energy, the body will not only metabolize fat but also protein in the muscles.
posted by missbossy at 6:11 PM on October 3, 2005

It's complete garbage. First of all, the release of digestive enzymes into the stomach and small intestine is triggered largely by the consumption of food. No eating means no digestive enzyme release. But more importantly, these enzymes do NOT enter the bloodstream at any point in an active form. After they've served their purpose they're either broken down into their component amino acids and reabsorbed, or -- to be blunt -- shat out. So yeah, the whole "gobbling of waste matter" thing is just not possible. I'm not denying that fasting might have benefits, but this ain't how it works.

And on preview, what missbossy said.
posted by purplemonkie at 6:15 PM on October 3, 2005

I guess a lot of people listened to This American Life (see: "Promised Land") this weekend. [RealAudio stream]
posted by TonyRobots at 6:24 PM on October 3, 2005

Great link, footnote.
posted by LarryC at 6:33 PM on October 3, 2005

This detox stuff is straight bunk. No science to see here folks, move along.
posted by drpynchon at 7:47 PM on October 3, 2005

Fasting may or may not have benefits, but its effects do not include the release of digestive enzymes into the bloodstream.

That's a load of malarkey, not to put too fine a point on it.
posted by ikkyu2 at 8:55 PM on October 3, 2005

Dr. P: does medical science recognize any physical benefits to short periods of fasting?
posted by agropyron at 9:07 PM on October 3, 2005

Dr. P: does medical science recognize any physical benefits to short periods of fasting?

I'm guessing... weight loss?

But seriously, the idea that stomach enzymes would just get dumped into the bloodstream like that is just silly.
posted by delmoi at 9:29 PM on October 3, 2005

Come on. I'm not sure whether fasting does have medical benefits, but that's the second time tonight the quackwatch article on fasting has been posted, and it does a horrible job of debunking. It's merely a rundown of some claims from fasting advocates, followed by a claim that it's "irrational":

"It can be terrifying to believe that one's body is being poisoned by toxins from within. But if this were true, the human race would not have survived, says Vincent F. Cordaro, M.D., an FDA medical officer. "A person who retained wastes and toxins would be very ill and could die if not treated. The whole concept is irrational and unscientific."

Well, when I look at the National Center for Health Statistics' stats I'm thinking that the majority of those deaths are caused by wastes and toxins in the body. How, exactly, if the concept of being "poisoned by toxins from within" irrational and scientific?
posted by jgee at 10:05 PM on October 3, 2005

Well, when I look at the National Center for Health Statistics' stats I'm thinking that the majority of those deaths are caused by wastes and toxins in the body. How, exactly, if the concept of being "poisoned by toxins from within" irrational and scientific?
posted by jgee at 10:05 PM PST on October 3 [!]

Well, it's irrational because people seem oddly eager to believe completely unscientific claims that they are beset by "toxins"--it seems to be fruit of an imagined fear of contamination rather than a rational decision. I for one will adhere to the opinion of the FDA officer quoted in the Quackwatch article (which is admittedly thin), rather than that of "Shirley's Wellness Cafe."

Also, I have no idea why you are "thinking" that the list of the causes of death may be attributed to "toxins." Are you just making that up out of thin air? That's just the kind of irrational "thinking" Quackwatch is talking about.
posted by footnote at 8:33 AM on October 4, 2005

agropyron, I've never read or heard of a single peer-reviewed, well-designed study that shows any benefit to fasting in the form of detoxification. Which is not to say that such benefits may never be discovered. But the advocates of these practices who draw on pseudo-scientific buzz words are not representing the literature (or lack there of) on this matter.

That said there certainly is some evidence that drastic reduction in caloric intake throughout an animal's life may in fact lead to increased longevity, but the jury is out on if that can be applied to humans. And of course, cutting your calories in half for your entire life isn't the same as a 3-day fast once a year.

Well, when I look at the National Center for Health Statistics' stats I'm thinking that the majority of those deaths are caused by wastes and toxins in the body. How, exactly, if the concept of being "poisoned by toxins from within" irrational and scientific?

That's not the irrational part. The irrational part is when one more or less ignores human physiology, the function of the liver and kidneys, the difference between high and low levels of a molecule in the blood stream, etc.

Our bodies are constantly taking in, circulating, breaking down, and removing molecules, ALL of which can be considered toxins. The natural byproducts of our own cell's can be considered toxins. And even when we fast, our metabolism is designed to make adjustments in dealing with this. The reasoning that suggests that a few days of ketosis every now and then is a good thing is irrational because of the time-scales we're dealing with, not to mention the fact that ketosis itself may actually be a more toxic state than baseline.
posted by drpynchon at 8:39 AM on October 4, 2005

The digestive enzymes that work in the stomach and intestinal track will not work in the blood stream for the simple fact that they are designed to work only at the pH levels that are present in the organs in which they are found. For instance, the main stomach digestive enzyme pepsin is only converted into its active form in the presence of hydrochloric acid and works only at pH levels less than 2 (I believe, it may be lower). If your blood pH is around 2, you've got bigger problems than digestive enzymes in your blood -- you're dead.
posted by The Bishop of Turkey at 11:01 AM on October 4, 2005

I assume that detox is crap, but it's a fact that a lot of environmental toxins are kept in the body in fat and elsewhere. Whether fasting would help at all is another question.
posted by abcde at 11:23 AM on October 4, 2005

Yes, this is all complete malarky.

Digestive enzymes are specialized for digesting different things (ie. starch-->simpler sugars, proteins-->peptides, &c&c) and are not involved in clearing up "toxins" (if only these types of snake-oil salesmen would define what a toxin is).

The immune system has a subclass of cells called phagocytes who's main job is to gobble-up and remove dead cells (yours as well as microbial).

Potentially (chemically) reactive breakdown products (ketones, aldehydes, &c) are eventually eliminated from the body through the kidneys. Other reactive small molecules (ie., oxidants) can be rendered unreactive by, you guessed it, antioxidants (which are more "appealing" than other molecules) and then eliminated through the kidneys.

Drinking lots of water/juice/sports drink and vitamin C would probably do more for "detoxification" than fasting.
posted by PurplePorpoise at 3:30 PM on October 4, 2005