<<while there is a very marked effect of bloat and lethargy after consuming
carbohydrate. And I certainly did notice a feeling of faintness after
consuming an unaccustomed large wheat flour tortilla recently.>>

This is a common symptom of wheat sensitivity.  I feel the same way after
eating bread.

<<I am extremely fit, and I am sure that I do not have any food allergies or
any kind of insulin resistance.>>

Fatigue after eating carbs can be an indication of food
allergies/sensitivities.  Why not try pulse testing after eating different
carbohydrates to rule out allergies/sensitivities
www.alternate-health.com/pulse.html ?

<<There seems to be an underlying assumption that eating food gives
you energy. This is clearly false -- eating food consumes energy,
obviously.>>

Both are true.  Above, you said, "I do not detect any effect after consuming
fat and protein."

Allergies + sensitivities www.mothernature.com/ency/Concern/Allergies.asp

Rob