How long can a baby survive without being fed?
"They have enough to survive for the 24 to 48 hours without much in the way of feeding. I am surprised: six days seems a long time to me." After six days the baby was likely to be suffering from low blood sugar and at risk of getting cold. "It's possible, it's surprising.
In the first few weeks of life, breastfeeding should be "on demand" (when your baby is hungry), which is about every 1-1/2 to 3 hours. As newborns get older, they'll nurse less often, and may have a more predictable schedule. Some might feed every 90 minutes, whereas others might go 2–3 hours between feedings.
Newborns typically lose between 5 and 10 percent of their body weight, depending on delivery method, in the days after birth. They need to spend the first few weeks gaining it back. Not eating enough in the first few days can also lead to complications linked to jaundice and low blood sugar.
It depends. If baby is close to 12 months of age and has a varied and well-balanced diet that is rich in iron-rich foods, then it may be safe to wean off of formula.
However, every mother is different and every breast has a different storage capacity. A few moms might be able to go 10 to 12 hours between their longest stretch, while others can only go 3 to 4 hours.
Stage 1 Sleeping Through the Night Without Feeding (6 - 8 hours): Around 4 months of age is when most parents will start to see signs from their babies that they're able to sleep in longer stretches. Getting up to 5 and 6 hours by this point is very likely.
Babies who are not fed enough eventually develop dehydration, low blood pressure and hypoglycemia, better known as low blood sugar. She says that all of these conditions will cause brain injury if not corrected.
From a developmental perspective, babies are able to sleep through the night — defined as a six- to eight-hour stretch — without eating when they're between 4 and 6 months old. In this age range, most babies reach the 12- to 13-pound mark, the weight where they no longer metabolically need nighttime feedings.
Newborns who sleep for longer stretches should be awakened to feed. Wake your baby every 3–4 hours to eat until he or she shows good weight gain, which usually happens within the first couple of weeks. After that, it's OK to let your baby sleep for longer periods of time at night.
The amount of sleep an infant gets at any one stretch of time is mostly ruled by hunger. Newborns will wake up and want to be fed about every three to four hours at first. Do not let your newborn sleep longer than five hours at a time in the first five to six weeks.
Can babies sleep through hunger?
If your baby is older than 6 months, and/or weighs more than 15 pounds, then barring any medical issues, they are absolutely capable of sleeping through the night (11-12 hours) without needing a feed. But this is only true if they are able to take in their entire caloric needs during the daytime hours.
Before the invention of bottles and formula, wet nursing was the safest and most common alternative to breastfeeding by the natural mother.

Before the era of "modern" medicine, breastfeeding was the preferred method of feeding infants, just as it is today. But if a mother's milk supply was inadequate or she chose not to nurse, the family often employed a "wet nurse" to nourish infants.
Parents who could not afford a wet nurse turned to alternative baby foods. In early modern Europe and early America, caregivers mixed animal milk, water, or broth with flour, bread, or other grains, much like the Wabanaki blend of nut milk and cornmeal.