I just read your posting and pulled an article from my files written by Dr. James Scala, a noted authority on nutrition and biochemical research. He has lectured at Georgetown Univ. School of Medicine and Dentistry and is the author of more than 50 published articles on food, nutrtion and health.
Nature always favors the survival of the offspring.
The developing child will extract whatever nutrients it requires from the mother. A seriously inadequate diet may affect fetal development, however, just as it affects the health of the mother. Consider some of the additional demands created by a full term pregnancy. Approximately 300 extra calories per day. Protein needs are increased by 30 grams a day.