I have read that whole foods rich in carbohydrates may also contain the amino acid Tryptophan. Eating the carbs first may give Tryptophan a head start to the blood-brain barrier where it will cross and cause sleepiness and also block amino acids from the protein from crossing. Eating the protein first--so long as it is not rich in tryptophan (turkey being rich in tryptophan as an example) may give other amino acids a head start to the blood-brain barrier and block the action of tryptophan that may be present in carbohydrate foods.
So, it depends if you want to be sleepy or peppy... if you are not sure you can also pop a taurine or tyrosine cap about 15 min before the meal and the action of either will block tryptophan from crossing the blood-brain barrier. Either taurine or tyrosine will bring elevated mood and energy.