It's important for you to know, too, that although I did nurse all three of my children, I supplemented my oldest with formula. If I were to try and answer "why" there would be many answers. Most of them all boiled down to one thing though, I didn't know better. I had PPD, my son was over 10lbs by the time he was a month old (9lbs 5oz at birth) and he nursed constantly! While normal babies are supposedly on a 2 hours nursing schedule - or at least that's what they say is average - he nursed for an hour at a time and only took 30-45 minute breaks between them. Plus I was dealing with sever dehydration and my body just couldn't keep up. Of course the doctors aren't going to tell you to get human milk, and at that time (8 years ago) I didn't have the resources I do today, so I didn't even know that was an option. Nor did I know how to make my own. So I went to WIC and got their formula checks and bought whatever brand they were using at the time (I believe it was Similac). Of course the formula usually bothered his stomach and added to his crying, which didn't help the PPD... Vicious cycle. But like I said, I didn't know better.
When my second son was born (14mos later) I was determined not to put him on the formula the way I did with my first. And since I wasn't working at all with this one (I was p/t with the first) and he was MUCH smaller (8lb 4oz at birth) he didn't need to nurse as often, so it wasn't an issue. The few times we did attempt to give him a bottle - either water or breastmilk - he would refuse it. He didn't even take a pacifier. He refused everything but the breast. In fact the one time I did leave him for any amount of time and left him a bottle of milk, he went 6 hours without eating (he was around 2mos), so I guess I didn't really have a choice.
Then my daughter came along, by this time I was a vet when it came to motherhood, and I had a much better support system (online) better resources and a good deal of research and practice behind me. I knew with her formula was just not an option. I never even considered it.
Of course I have found that I am the minority here. The vast majority of mothers are still giving their children baby formula rather than breastfeeding. That is changing! But slowly. Too slowly in my opinion.
Anyways, lets talk about formula. What IS baby formula? Well, it's highly processed and powdered milk solids (usually cow's and/or soy milk) mixed with a few dozen chemicals in an effort to mimic breast milk... But as usual, the imitations don't come close to the real thing...
While each baby formula has a different formulation, here's an idea of what you'll find listed on the back of the average formula can:
"Enzymatically hydrolyzed reduced minerals, whey protein concentrate, palm olein, soy, coconut, high-oleic safflower oils, lactose, maltodextrin, patoassium citrate, calcium phosphate, calcium chloride, salt, potassium chloride, magnesium chloride, ferrous sulfate, zinc sulfate, copper sulfate, manganese sulfate, potassium iodide, soy lecithin, mono and diglycerides, inositol, choline bitartrate sodium ascorbate, alpha tocophyeryl acetate, naicinamide, calcum pantothenate, riboflavin, pyridoxine hydrochloride, thiamine mononitrate, folic acid, phylloquinone, biotin, vitamin D3, vitamin B12, taurine, L-carnitine"You may read through those ingredients and think "Hmm, that's not so bad. I see words like Calcium and Potassium... That's good stuff!" And you'd not be entirely wrong. Calcium is great from newly growing bones. But Calcium Chloride, which happens to be the same salt used for icy sidewalks, is mildly toxic and known to cause digestive issues. Now, there's the argument that there is such a small amount of Calcium Chloride used in formula (and other foods) that it's not dangerous. But salts - ALL SALTS - including Calcium Chloride, collect in the body over time. Add to that the fact that an infant's body is more susceptible than an adults and you can see how any one of these chemicals, small doses or not, can easily affect them in ways they wouldn't affect an adults.
Similar warnings can be given for nearly every other ingredient listed above. More than that, it's important to know that while these chemicals often exist in natural foods - like fruits & vegetables - there is a difference between lab created chemicals and naturally occurring ones. It's the same reason a bottle of store bought aspirin comes with a warning label and White Willow Bark, an all natural aspirin, doesn't.
All of that sounds pretty bad, right?!? Well, it's not "good." Of course most of these same chemicals can be found in everything from breakfast cereals to prepackaged pasta dishes (like Hamburger Helper). So even though these ingredients are less than "healthy" whether or not they are actually "poison" or whether or not they, when combined, make a "poison" product, it debatable. The definition of poison, according to Dictionary.com is "a substance with an inherent property that tends to destroy life or impair health." Do these ingredients "destroy life or impair health?" Technically, yes. With prolonged exposure they lower the immune system, damage organs and inhibit healthy growth of the brain and nervous system. Which is why any physician worth half his pay will tell you processed foods are dangerous and should be avoided. My thinking is, if it should be avoided as an adult, it shouldn't even be considered for infants.
But how does formula compare to breastmilk? In my mind, it doesn't. There is simply no comparing them. Breastmilk is not just natural. It's actually the perfect food. Even mothers who have less than perfect nutrition produce milk which is full of minerals, vitamins and nutrition tailored specifically to their babies needs. Of course, in the effort of full disclosure, there are those on medications, with HIV or other illnesses, or who are dealing with sever malnutrition who shouldn't breastfeed. Their milk could either be dangerous to their infant, or in cases of malnutrition it may lack the proper nutrition for a growing infant. That said, malnutrition to those extents are extremely rare in the developed world.
Mature milk contains water, fat, carbohydrates, protein, vitamins and minerals, amino acids, enzymes, and white cells. Over the course of a feeding, breast milk changes from foremilk, high in water and lactose, to hindmilk, high in fat and calories. After the first few weeks of nursing, your breast milk will contain fewer white cells and more of another antibacterial enzyme, lysozyme, the level of which stays high as long as breastfeeding continues. In fact, breastmilk contains more than 200 beneficial elements, with more being discovered all the time! In fact, with the exception of those who nurse while on medications, after drinking a large amount of alcohol or with certain transmittable illnesses, there is nothing inside breastmilk which could be dangerous for baby.
SO it's clear why breast is best. Aside from the possible convenience of having someone else feed your baby when you're asleep or away, there aren't many benefits of choosing formula over breastmilk. But is it really poison? Well, like I said above, it could easily be classified that way. But so can a million other things on store shelves today. Formula is no more "poisonous" than Pringles potato chips or Pepsi cola. So while I can't endorse baby formula, and can't imagine myself doing so any time soon, I can honestly say I wouldn't necessarily classify it as "Poison." I would, however, classify it as "infant junk food!" Yes, it's better than starvation, but if the idea of a baby bottle filled with soda makes you cringe (the way it does me every time I see it) then so should a bottle filled with baby formula.