I suspect that many women who “can’t” breastfeed, actually could…if they had adequate information and support. But they don’t get that information, they don’t get that support, they have helpful family members feeding the baby a bottle (for “bonding”, or because grandma just loves to feed babies, or whatever) when what the mother/baby pair really need is for baby to be suckling every hour around the clock during a growth spurt. The delicate demand-supply system gets screwed up, and lo and behold, mom doesn’t have enough milk. Or, mom can’t know how much milk baby is getting at the breast, and believes baby can’t possibly be getting enough. Or well-meaning grandmothers or grandfathers criticize at every turn, insisting that mother can’t possibly have enough milk and baby needs formula. Or, mom has a cesarean section or operative vaginal delivery, her milk is delayed coming in due to the impact of the delivery, and when she hasn’t got milk after 3 days, she’s told she has no milk and must start giving formula. There are a LOT of reasons why women who might well have adequate milk, become convinced they do not.
Some babies learn inefficient suckling techniques or ‘laziness’ from overuse of pacifiers, from early introduction of artificial nipples, or even from intra-uterine sucking habits (such as sucking on their own tongues). These babies may be difficult to transition to the breast. Some babies simply don’t get the whole suckling-at-the-breast thing (so it’s not the woman who cannot breastfeed, but the baby who will not.)
Many women experience extreme discomfort and even extreme pain in the early weeks, and find it more than they can deal with. In some of these cases, it is undiagnosed or inadequately treated yeast infection (thrush). Some doctors give very bad advice to women suffering from thrush. I was one of these, so I know exactly how bad some of the advice can get. That kind of pain is excrutiating beyond belief, and exceedingly difficult to persevere through. Yet, if it were treated promptly and aggressively, these women might well proceed to breastfeed.
There are women who do not have adequate milk. Some of these could produce some milk, and make up the difference with formula if they wished.
There are also women who produce no milk at all. I suspect this is rare, comparatively speaking, and will typically have a medical explanation such as anaplastic breasts or a piece of retained placenta.
I think…a lot of the women who say they cannot breastfeed, actually could if circumstances were different - if they had more support, more information, or no ready option for formula. And some women who cannot, cannot. But it’s hard for us to sort out what percentages, and of course we’re told that formula use is a lifestyle choice, and that we are not to judge people for their choices, so it can be very difficult to tell what is ‘choice’ and what is truly life-and-death necessity.