Insulin is well known to reduce protein breakdown and can lead to a higher overall net protein balance - helping to increase muscle growth.
The point of the review article Dr S posted is that there is NO evidence Insulin itself exerts an anabolic benefit on SKM.
Because if that's the case it's one heck of a leap to assume it's use in a cycle improves, enhances, induces or accelerates muscle hypertrophy.
Thus while it's obvious insulin does exert a certain degree of anti-catabolic activity does NOT mean "it's inclusion in a cycle" affords the user ANY benefit. Why is that? Bc the amount of insulin needed to restrict catabolism is already produced endogenously and no net gain is achieved thru supplementation. Why is that? Bc supplementation reduces endogenous insulin production in a proportional manner!
That's one huge difference bt insulin and TT and GH both being relatively specific, compared to insulin, for their SKM anabolic properties. That's bc the endogenous production of both of these drugs is relatively small and exceeding ones baseline production is relatively easy and with limited adverse effects, the same most certainly can NOT be said for insulin.
So how much insulin should be used to improve anabolism thru "a reduction of catabolism" obviously that would depend upon one's diet and basal metabolic demands but somewhere around 30 to 50 units daily!
How many BB are using those doses, close to NONE. Just as important what type of insulin affords the greatest benefit, Humalin R, Humalin NPH, Lente or Ultra Lente?
How much and how long would someone have to use insulin before "insulin resistance" occurred and does the development of HR predispose the user to DM?
For these reasons and many others I don't believe there is ANY reason one can justify the use of insulin as an adjunctive anabolic agent. The risks FAR outweigh any potential benefit and apparently the WADA concurs, whom have never even considered insulin (above a certain level) a potential PED.