If your eating very high carbs, the argument can definitely be made that insulin use has the opposite and actually prevents diabetes.
Eating high carbs and high volumes of food all the time leads to consistent high blood sugars, which makes your body need to increase insulin output, which can take a toll on the beta cells in your pancreas and can burn them out. Burned out beta cells = lower and less efficient insulin production.
Adding exogenous insulin relieves stress of high work load on your pancreas beta cells so your body doesn't burn out the cells that create natural insulin.
There are arguments to be made for both sides of the issue,
I first read about non-diabetics use of insulin in Dr Jason Fung's book "the diabetes cure", he quoted studies that showed fairly rapid onset of insulin resistance, which if left unchecked could lead to diabetes. Makes sense, with the homeostatic mechanism of the body trying to keep too much glucose from being stuffed into the cells.
But there are non diabetic uses in legitimate medical settings, like wound healing, aftercare for surgery, and to help prevent muscle wasting in temporarily bedbound patients.
This was a paper published in the U.S. but it was by Indian physicians so... I don't know how often it's used in Western clinical settings.
I'm particularly skeptical of it's use by psychologists to facilitate better therapy sessions by dis-inhibition of the "higher cognitive functions"
I know psychiatrists, in the past, used high doses of insulin to initiate seizures before and alongside electro-shock, but I even the paper mentions that insulin shock therapy is considered too dangerous now, even though as a side note electro-shock is still used, albeit rarely, in cases of intractable depression.
Here's the paper. (God I love the internet.)
This brief communication reviews the non-diabetic uses and utility of insulin. It highlights the lesser known uses in medicine, psychiatry, suregery and diagnostics that this versatile peptide has. Keywords: Applied pharmacology, insulin, ...
www.ncbi.nlm.nih.gov