Well there are a few articles I would like to Share with TRT that I have been able to find. Ill start with this one, I find it to be very informative, and usefull to where it all started.
Article pulled from Wetweb Media:
(The use of garlic for marine ich started when one person was examining the effectiveness of garlic against nematodes and Cestodes on infected puffer fish when they noticed a general decrease in Cryptocaryon irritans incidence and proposed feeding garlic to fish as a preventative. From there the legend of garlic has spread. Allicin, a.k.a. Diallyl thiosulfinate (or Diallyl disulphide-oxide), has been identified as the chief active pharmaceutical ingredient in garlic (Allium sativum). It has some antibacterial, antiviral and anti protozoal ability. Allicin further has a remarkable ability to permeate living tissue. It is hard to get garlic's smell off your skin after contact with the raw material. In a parasitic protozoan infestation similar to "Marine Ich", there are usually two major insults to the fish's physiology, the gross tissue damage committed by the Protozoans, and the secondary infection. There is speculation on the garlic's apparent ability to deliver damage to the parasites themselves -with numerous claims of outright detachment of C .irritans trophonts (the burrowing Protozoans) and tomonts (the "egg cysts") as a result. With its partially sulfurous chemical signature, there is the potential to mask the chemical cues that enable a parasite's recognition of the host, potentially confusing the invader and further suppressing the havoc itwreaks. This means garlic therapy could benefit even uninfected fish, allowing them to escape detection by host-hunting C. irritans tomites Allicin is unstable and highly reactive. Much of the potency has been lost in commercial preparation, and there is no shortage of neutralizing substances in the way to delivering the drug to the fish's infected parts. If the garlic is fed to fish, the acid in the stomach can irreversibly neutralize the alliinase. Even if some gets through, it must then bypass the liver, and interact with the blood resulting in a reduction of hemoglobin to methemoglobin, lowering oxygen transport (not a good thing). By adding the garlic directly to the water there is the problem of dilution, and the interaction with the biological soup of the tank water to neutralize any Allicin You can again either overwhelm this barrier via massive dosage; with the risk of impact this time on microorganisms throughout the aquarium, or you bypass contact with the water by mixing it with oily vehicles. This will just float to the surface, and the oil reduces the potency of Allicin by incarcerating it. On top of that there is no standard prescription formula like "X milligrams of garlic medication per Y grams of patient tissue, or water volume over Z days" like there is for conventional treatment with Cupramine where ingredients can be measured. As yet the effectiveness and safety of garlic has not been supported with proper science and reproducible clinical trials.) (Mike Lomb)
Now this is realy going in to the scientific behind Garlic.
There are several others I have and will provide that go in to other reasons for Garlic, such as an Immune boost, and general nutritional value.
Now the reason I reccomend doing so is my fish have proven to me time after time they eat vigerously when the food has been soaked in Garlic. Much more so then just regular feedings.
Methodology behid this, when you become ill it is important to keep your immune system in tip top shape to fight off infection, disease, virus and so on. So if you have a fish that has become ill and loss of appitight how are they keeping there immune system tip top with no nutrition??? Does Garlic provide added Nutrition to fish? Some articles suggest it does, but no scientific Data to prove this exists, atleast that I have found.
I feed Garlic to get them to eat, and stay interested in there food. The food its self will provide needed nutrition.