I really enjoyed the TDF glimpses into the feed bags of the riders, those Spanish guys had hardly anything in their feed bags, of course there may be misinformation and product placement here.
I monitor my calorie (estimated) out my 910 (imperfect science) but flat centuries don't even use 2000 calories for me, in a 6 hr century ride with an average HR of 140 (resting 55). So between liver and muscle glycogen and some calories in my bottle and breakfast, and my capacious fat stores. it is all good LOL.