While it's true that warm milk and chamomile tea help induce sleepiness, more than eight ounces of liquids within four hours of bedtime can disrupt sleep. (motherscircle.net)
That suggested that it might induce sleepiness by inhibiting the activity of those neurons. (sciencemag.org)
The carbs induce sleepiness and the protein maintains blood sugar until the next meal. (swanling.com)