Well, this an interesting and very complex topic. I can give you some information, but a final answer has yet to be found.
Caffeine is a central stimulant that increases the release of catecholamines. Its pharmacological effects are predominantly due to adenosine receptor antagonism and include release of catecholamines. Caffeine can decrease insulin sensitivity in healthy humans. It was hypothesized that caffeine reduces insulin sensitivity, either due to catecholamines and/or as a result of blocking adenosine-mediated stimulation of peripheral glucose uptake. The latter could not be confirmed.
400mg of caffein taken first thing in the morning will lead to an immediate decrease of insulin sensitifity of about 15%.
So the peri-workout nutrition protocol will be less effective. Additionally, the workout itself will trigger catecholamine release, which will have a further negative impact on insulin sensitivity.
BUT: Studies show COFFEE consumption to be correlated to large risk reductions in the prevalence of type 2 diabetes. Such correlations are seen with decaffeinated and caffeinated coffee, and occur regardless of gender, method of brewing, or geography. They also exist despite clear evidence showing that CAFFEINE causes acute postprandial hyperglycemia and lower whole-body insulin sensitivity.
Coffee contains many beneficial compounds found in fruits and vegetables, including antioxidants. In fact, coffee is the largest source of dietary antioxidants in industrialized nations!
When green coffee is roasted at high temperatures, so-called Maillard reactions create a number of unique compounds. Roasting causes a portion of the antioxidant, chlorogenic acid, to be transformed into quinides, compounds known to alter blood glucose levels. Coffee consumption may also mediate levels of gut peptides (glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1), hormones intimately involved in the regulation of satiety and insulin secretion. Finally, coffee may have prebiotic-like properties, altering gut flora and ultimately digestion.
So, trying to give you an answer: I wouldn't recommend to take caffeine right before the workout or the peri-workout nutrition protocol, respectively.
The caffein will have a negative impact and make the protocol less effective (my guess would be around -15%, but we can't tell without an adequate study, which will never be done).
As for taking caffeine as an ergogenic aid for college students, I would suggest to rely on COFFEE, not caffeine pills, for it's health benefits.
By the way: individuals consuming >/=6 cups coffee per day have at least 50% less risk of developing type 2 diabetes than those consuming </=2 cups per day.
Just make sure you don't have coffee and/or caffeine (if you can't live without caffeine pills) 2-3 hours before starting the peri-workout nutrition protocol.
I known, this is not what has been said so many times before, that caffeine pre-workout is good and increases focus and strengh output, etc. It does. However, I consider the negative impacts of caffeine pre-workout (via increased catecholamines) to be far bigger than its positive potential.
Rely on Alpha-GPC to increase explosive strengh and use phosphatidyserine for its postive impact on ability to focus, etc. (search for my other post about it - athlete can use up to 2'000mg a day).
Hope that helped a bit.