I’ve been doing some longer (50-70 mi) training rides lately, and I notice that when I’m dragging a bit, I pop a gel (either a GU or a Hammer Gel–the others I’ve tried seem hard to get down), and my speed almost immediately jumps 1-2 mph with what seems like the same effort. Is it possible that this is really due to the gels, or is it all in my head?
I’m no nutrition expert so I won’t say it’s in your head but I’ve never got an instant 1-2mph-for-the-same-effort boost from anything I eat or drink… not even Infinit.
Sounds like the placebo effect to me. Do they have caffeine in them? Caffeine (in my experience) is fairly fast-acting and reduces your perceived effort. However, most gels don’t really have caffeine in large enough amounts to cause that much of a difference.
depends what your blood sugar levels were like prior to you taking a gel. If you were ‘bonking’ then yes, sugar does have a great lift effect.
Now, how immediately does your velocity jump 1-2mph? If it is within the second you rip open the gel package then there might be some placebo effect involved 
its in your head, it takes 15-20 seconds to get down your throat and into your stomach. so its not going to break down anything that quick, unless its got a lot of cafine in it, there might be the caffine but even then its doubtfull. also maybe salt, how much sodium?
There was some research recently which showed a performance impact from just rinsing the mouth with a Carbohydrate solution.
http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=15570147&dopt=AbstractPlus
They argue its a mental, rather than metabolic effect, although clearly you can absorb certain chemicals through the mouth and gums.