I think it's less of a topic that you can find research about, and more of a philosophical paradigm shift you have to make.
From the very early days, the way breastfeeding works is supply and demand. This system is predicated on Mom nursing the baby on demand, and the baby regulating the supply. It felt like a huge leap to me when I threw away the notebook where I had been recording times/lengths of feedings and number of pees and poops and just started winging it, trusting my body and my baby to be in synch. What I learned from this experience is that you have to have faith that babies (WE) are born knowing what we need to eat. In a healthy, normal baby (most babies!) the baby knows just what he/she needs. It's sort of the essence of the nursing relationship that you just have to trust the process. One of the reasons you CAN trust the process is that human milk isn't like any other food. There's this amazing feedback going on between your body and the baby which is constantly readjusting the amount of protein, fat, etc. in the milk.
Whether, during breastfeeding, that need is physical or emotional is, admittedly, sometimes hard to separate. There's that study that you come across sometimes (not sure where to find a link) about a monkey being separated from his mother and given a choice of two substitutes: a prickly wire monkey that dispenses milk and a soft terrycloth one that had no food supply. The monkeys preferred the soft one. I have seen that study interpreted multiple ways including as evidence of the importance of attachment (physical touch needed for thriving). It is clear that babies need both food and comfort, and nursing provides both (how convenient!). So, one thing that I get out of that study is that it is an artificial imposition to separate the two. Babies and young children are meant to get both from the breast (evolutionarily speaking). Tranferrence to a blankie or pacifier or cookies (while apparently more generally culturally acceptable) is what is artificial. We're all imperfect parents, but it sort of gets my goat that people who give their one-year-old watered-down juice or arrowroot cookies or whatever would raise such a concern about breastfeeding.
The real danger is disrupting the body's natural ability to eat just the right amounts of the right foods is when very sugary or salty foods are introduced. From "My Child Won't Eat" a LLL book: (on the subject of letting your child choose his foods himself):
"But Won't He Stuff Himself With Chocolate?"
Sure! If he is allowed. Or at least that is what we think would happen although there are no scientific studies that demonstrate this....
...To understand why the control mechanism sometimes fails, we need to keep in mind the theory of evolution.... behavior that was valuable at one point may no longer be so good if living conditions change....
....What good was a preference for sweet and salty foods.... ? Not only did they (hypothetical cave children the author talks about earlier) not have chocolate, they also did not have salt or sugar. The sweetest thing they had was mother's milk, their main source of food, and fruit, which is full of vitamins. The saltiest was probably meat, an important source of iron and protein. Their preferences, therefore, helped them choose a varied and balanced diet. But now we have candy that is much sweeter than fruit, and snacks much saltier than meat, and our selection mechanism has gone a little haywire.
Even so, it is surprising just how strong the instinct to choose a healthy diet really is. Just look at the advertising: the less healthy a food is, the more they need to advertise it..... On the other hand, lentils, apples, rice or bread do not need to advertise much at all and people still eat them.
Eliminating food=comfort is not the real question. As someone who BFs but has also given her child a taste of lentils (yes!) and ice cream (uh-oh!) the real problem is how do you stay on track to let your child make his/her own choices among healthy foods despite all the pressure (and grocery aisles and ads) that say otherwise.