It may shock many people to know that T3 is NOT catabolic per se. Corticosteroids are catabolic drugs that attack muscle tissue directly; T3 does not. It is a very potent calorie burner and it does not discriminate between carbohydrates, protein and fat. Unlike DNP, it has no protein sparing properties. T3 is also more likely to burn muscle than fat in lean users (10-12% BF), but this can be said for any extreme drop in caloric intake and uptake such as starvation diets (Caloric intake <10 X BW).
This whole paragraph contradicts itself. It's not catabolic but it burns muscle??? You are comparing corticosteroids with T3 in the wrong way. Cortescosteroids are catabolic because that's what they do. T3 is used for something else, but is catabolic. It burns protein and muscle.
Definition of catabolic
This term is often used in reference to the breakdown of muscle. Dieting is catabolic because it causes muscle loss. The word catabolic can, however, be used to refer to any process in which a complex substance is converted into simpler substances. Lipolysis, for example, is a catabolic process because your fat stores are broken down into free fatty acids and glycerol
So, if T3 breaks down protein and muscle it is catabolic.