Newborns dont't go into deep sleep for very long and it's with good reason - to avoid apnea whereby a baby can stop breathing. This is due to the nature of a newborn's lung system. Light sleep helps a baby to prevent that by ensuring that when s/he does stop breathing, they can be easily awaken on their own to continue breathing.
This is why a lot of docs advise against too much warmth for a newborn because warmth gets them all cosy thus going into deep sleep for long periods. Warmth here refers to too much clothes and so forth, not so much diet.