Not so. Here, the myth is that the tryptophan in turkey causes the drowsiness. This amino acid is known to cause drowsiness, but the truth is that there’s as much tryptophan in pork and cheese as there is in turkey. What’s more, researchers noted that for tryptophan to promote sleep, you need to ingest it on an empty stomach (with no protein present) – something that’s unlikely at Thanksgiving or Christmas dinner. Other factors are probably to blame for post-meal drowsiness: any big meal can make you sleepy because of a decrease in blood flow and oxygenation to the brain. Your body is desperately trying to handle the sheer volume that is the Thanksgiving Meal!