Cyanidin 3-glucoside (C3G) is a polyphenol found in blueberries, grapes, black beans, and pretty much any fruit or vegetable that has a reddish blue or indigo cast to it.
Studies have shown it to have anti-diabetic effects, which means that it makes you more insulin sensitive so that nutrients can be preferentially shuttled off to muscle tissue. We also know C3G has anti-obesity effects (by raising levels of adiponectin) and improves exercise capacity by activating fatty acid oxidation.
Users of the supplement can actually eat more carbs without getting fat and, provided they're working out, have the energy provided by those carbs ferried off to fuel and build muscle. C3G also has phenomenal potential to fight diabetes, improve vision, and promote liver health.
Most C3G products have two huge problems. First, the substance is pretty expensive and manufacturers who sell to retail outlets have to price the product at about 4 to 6 times manufacturing cost to take care of all the middlemen. As such, they typically under-dose the product and the end result is an ineffective supplement that has no noticeable effect.
Secondly, while C3G seems to be absorbed by both the stomach and the intestines fairly well, the stuff is broken down really quickly and enters the bloodstream as metabolites rather than the whole compound. While these metabolites may have unique health benefits all their own, they're not necessarily doing all the same things as the parent compound (purging fat and helping build muscle).
An effective C3G supplement should provide at least 500 to 600 mg. of cyanadin 3-glucoside per serving. Since it's intrinsically so expensive, you need to get it from a company that sells direct to the consumer so as to avoid all those retail, pay-the-middleman charges.
Additionally, it should use an innovative delivery system to protect, enhance, and stabilize the parent compound. Gelucire does the job nicely. The compound is derived from mixtures of mono, di, and triglycerides and widely used in the pharmaceutical industry to improve the bioavailability of drugs. Indigo-3G® checks all the boxes.