If it has a high fat content, it would slow it down.
I make my Ovaltine and protein mix with 1% milk, just so the sugar is not slowed down!
Sure I understand we are not the same for insulin and all of that. I am not disconnecting for as long as you, which makes a difference too.
If you are worried about a spike, I would suggest an IM shot when you are done swimming, to speed it up. I really think that would help you reduce the spikes. And more carbs will help reduce the crazy drops.
I can run 15 miles and not drop after. Because I am sucking down a crazy amount of carbs.
Do you remember this Easter thread I posted, of the carb equivalents for 15 miles?
easter-candy-carb-equivalencies/
You have got to replace that fuel! Your body uses fat and glucose (in the form of muscle glycogen, blood sugar, and liver glycogen). The harder you are swimming, the higher the percentage your body is using the glucose forms for energy.
If you swim 2 hours, you need to replace it!