What is the difference between breast milk and formula?

First of all: breast milk isn't cheap! They don't call it "liquid gold" for nothing. Do you know how much of a mother's time and effort goes into making milk for her baby? If you feed the baby 8 times a day, for 15 mins each feed, you spend 2 hours a day doing that. And many mothers spend more time than that. If you value your time at a mere $6/hour, then you have "spent" $12 a day feeding your kid. That is more expensive than formula, by a LOT.

Breastfeed because you want to give something valuable from yourself to your baby, not because it makes economic sense.

People have different opinions on whether formula feeding vs breastfeeding is more convenient (I personally think it depends on the situation).

Nutritionally, they are interchangeable, since formula is deliberately designed as a substitute for breast milk. There isn't anything special missing from breast milk that a baby gets from formula.

So....of course a baby could be on formula, and then be switched to breast milk, provided there is a source of breast milk. It usually happens the other way around though, since if you stop breastfeeding you will lose your milk supply, and its very hard to get it back once it goes.

Even your clarification is quite unclear, but I believe you are asking if a mother can breast feed all the way through, and the answer is of course. Many mothers breast feed and have no use for formula. Formula is a replacement for breast milk. At no time in a child's development does it become superior to breast milk. Although some mothers choose to breast feed for a few months and then switch to formula, there is no reason to do so from a health, nutrition, or developmental standpoint. You do not need doctor approval to continue to breast feed, and if the baby was showing developmental issues then switching to formula would not necessarily solve them. Yes, the pediatrician will check development, weight gain, milestones, etc at each visit to see how baby is doing. It is rare for a mother to truly not be able to produce enough milk to support her baby, although it does happen sometimes. Many mothers, once they have made it through the first few months, will continue to breast feed through the first year or beyond.

I had three boys, one never had formula. I nursed all three to about 18 months old. On some occasions, if they were visiting relatives they might have had a formula bottle. I tried to pump, but couldn't get much of any breast milk out with the pump. The youngest child refused any baby bottles.

*** The doctor did not stand over me and watch me pump out to "see if I had enough". And no one tests to see if breast milk is "nutritious enough". Mother Nature made breast milk to be the perfect milk for baby in the right amounts. ***

Nursing has worked since the dawn of time. You know baby has eaten enough milk by counting the number of soaking wet diapers. A baby soaking about 6 or more diapers a day is eating more than enough milk.

As for weight gain, formula fed babies tend to overeat. Newborns suck down any milk given to them, even if they are full. With a breast fed baby, the milk supply naturally ends based on the age of the baby.

Doctors prefer that a mother nurses her baby. Its not only healthier for the baby, but also benefits the mother's health. Like I said, I nursed to about 18 months of age, I just did not want to deal with bottles and formula. With the oldest, I went through seven brands of formula samples to find the one he could handle a small bottle. (by then, he was almost 9 months old) Formula can be very hard for some babies to digest. And its expensive!

Some moms just do not want to nurse that long, and switch over to formula. This is mom's choice and not the doctor's.

NO idea what you are asking? Mothers who dont' breastfeed don't give formula because the doctor told them they weren't allowed to breastfeed. So what 'doctor approval' are you talking about?

It's usually possible for a formula-feeding mother to relactate -- but it's a LOT of work, and rarely possible from a practical POV.

EDIT: Ok. Now I sort of understand. You and your friend are both correct. It is generally recommended for a mother to breastfeed for a minimum of one year, after which time baby can be weaned to a general adult diet, with no need for formula. In actuality, many women do wean after a few weeks/months and switch to formula, but it's not usually because their doctor told them to. (Though yes, some doctor are poorly educated about breastfeeding and will tell a mother she has to wean and/or will be unable to provide the support and help necessary.)

What on earth would need to be approved by a doctor in order for a child to be on breastmilk in addition to formula?

What? You're so American it hurts.