Great question, When I first started juicing I wondered the same thing.
Well first off juicing in general is an amazing "detox" because the vitamins, minerals, phytonutrients, etc are all beneficial to the major detox organs like the liver, kidneys, skin, and lungs.
The liver has the function of filtering the blood coming from the digestive tract. So we eat toxic foods then the toxins are in our blood stream momentarily but the liver will hold on to these toxins and will turn the fat soluble toxins into water soluble ones through enzymes. Fat soluble toxins pose more of a threat because well they will stay in your body for a long period of time while water soluble toxins will be filtered by the kidneys and ultimately excreted as urine. The other more concrete toxins that could not be made into water soluble are excreted through bile produced by the liver.
The liver however is very sensitive especially in the modern world today with the influx of environmental toxins. Liver's will get sluggish fast and start accumulating a surplus of toxins. So in a way you can imagine the liver as a sponge which is constantly being squeezed and pulsed, but then it gets sluggish... so the dirt water starts to build up a little more at a time (toxins) which slows down the liver even more and more and it turns into a snowball effect. Then the sponge becomes placid and it is full of dirty water. So by giving the liver an inpouring of vitamins minerals and enzymes, it will start to soak in these nutrients and get healthier and pulse a little bit and a little bit more until all the dirty water (toxins) is out and start to work normal again.
The liver when diseased, inflamed, fatty, sluggish will start to release toxins irresponsibly and the toxins will instead be stored in our fat cells which can cause longterm health complications.
Here is a more raw way to look at it:
Quote:
The liver plays several roles in detoxification: it filters the blood to remove large toxins, synthesizes and
gets rid of bile full of cholesterol and other fat-soluble toxins, and the live enzymatically eliminates unwanted
chemicals. The enzymatic process to dispose of toxins occurs in two phases: phase 1 (Oxidations) and phase 2 (Conjugation). Phase 1 neutralizes the toxin or changes the toxic chemical to form activated intermediates which
will then be neutralized by phase 2 of the enzyme system. This pathway converts a toxic chemical into a less
harmful chemical and is achieved by oxidation, reduction and hydrolysis reactions. During this process, free
radicals are produced and if there are too many it can damage the liver cells. With the help of antioxidant, it reduces
the damage caused by free radicals. One important antioxidant for neutralizing the free radicals produced in phase 1
is glutathione (GHS) is oxidized to glutathione disulfide (GSSG). This antioxidant is required for one of the key
phase 2 processes. When so many free radicals are produced from phase 1, the glutathione stops producing
oxidative stress or liver damage. The toxins are then transformed into activated intermediates; therefore the rate at
which phase 1 produces activated intermediates must be balanced by the rate at which phase 2 finishes their
processing. Phase 2 is called the conjugation pathway because the liver cells add another substance such as
cysteine, glycine, or a sulphur molecule to a toxic chemical to make it less harmful. As a result it makes the toxin
water-soluble so that it may then be excreted from the body via watery fluids such as bile or urine. There are six
phase 2 detoxification pathways:
1.Glutathione conjugation
2. Amino acid conjugation
3. Sulfation
4. Acetylation
5. Glucuronidation
These conjugation molecules join with specific enzymes to catalyze the reaction process. The liver is then able to
turn drugs, hormones, and other various toxins into substances that are secreted from the body. Read more:
http://people.cornellcollege.edu/bno...liverDetox.pdf
As far as specific juices go: There are two types of Detox juices. What I mean by this is there are juices that will target the vitamins and minerals the liver in particular will need and then there are those that will try to achieve a high alkalinity and sulfur level.
Juices that target the liver will pertain to the above process I talked about
The alkalinity theory is a bit more complicated. Basically in a nut shell the theory is that these toxins hold a acidic ph level and your body will create fat to house these toxins.
(this goes along with the theory that it isn't fattening foods that is causing obesity issues but rather the influx of toxins). So the liver is sick, and the toxins are released into the bloodstream so your body holds on to more fat so that it can house the harmful toxins because it wants the toxins out of the bloodstream as soon as possible.
Now these acidic toxins are stored in fat cells so by giving your body Alkaline foods like vegetables, the acids will be neutralized and released and with them the fat cells will be too. So with that the liver becomes less fatty and healthier and the Ph level in your body will go down and neutralize many of the toxins.
The Alkaline theory is a bit more subjective and exactly that, a theory but it does make a bit more sense to me at least the fat part. Many people try to lose weight through exercise but It rarely works, in part because I think the body wants to hold on to the fat to protect you from the toxins it has encapsulated.
The sulphur aspect is more concrete and I'll let you read about it here :
http://www.livestrong.com/article/317807-sulphur-detox/
Typically Juice Detox recipes will include a high alkaline through leafy greens while incorporating high sulfur produce like Onions and Garlic. Of course the leafy greens also play a double role by including very helpful vitamins to keep the detox organs healthy and happy.