To clarify- I'm the one who used the term 'junk food' and as I stated before, it was probably a poorly chosen term, but it was the term used by the Vet who was scolding me (A teenager) for feeding too many worms to my turtles.
I don't really care about "junk food" as a term being used. There are foods that humans eat that are referred to as junk food, and I don't think there's any harm in using it for snakes.

What's important here is:

1) What are the nutritional requirements of snakes.

2) What is the nutritional value of food items being fed to snakes.

Turtles may very well have different dietary requirements than snakes. I have 23 turtles and have been keeping them for a very long time (I've had one for 27 years). I have never heard of feeding a turtle too many earthworms, unless of course it causes the turtle to become overweight.

I have also dealt with a fair number of vets over the years - when it comes to reptiles, some know what they are talking about, while others clearly don't (in my opinion). So I wouldn't swallow everything a vet says hook, line and sinker.

So to get back to the topic at hand, without knowing the nutritional components of worms, how can they be termed an inferior food source? For all we know Euro-worms might be more nutritious than native worms...or they may not.

RodentPro has a chart on their website breaking down the nutritional components of vertebrate prey. If such a thing existed for invertebrate prey, then some comparisons could be made.

Of course in addition to the chart, we'd also need to know the nutritional requirements of garter snakes.

I think the issue here is that we have neither a chart which covers the nutritional components of invertebrate prey, nor a thorough understanding of what the nutritional needs of garter snakes are.

Having a theory that Euro-worms are somehow insubstantial is just that - a theory. Currently it cannot be proven one way or the other.

I will toss out this anecdote: There's a small snake native to the west coast known as a Sharptailed Snake. The Sharptail Snake feeds mainly on slugs. It will readily eat European garden slugs of the genus Arion and, in fact, seems to prefer them over native slugs (Rossi and Rossi, 1995). Shaw and Campbell (1974) state that the snake's range may actually be expanding due to the introduction of these slugs by humans.

And just for kicks, here's a Sharptail Snake that I found a couple years ago: