While I haven't seen the published manuscript yet, I find this conclusion somewhat implausible clinically and flawed based on the thumbnail descriptions of the methods of study used.
The researchers interviewed 132 women who consulted for a breast lift or breast augmentation. The women were, on average, 39 years old; 93 percent had had at least one pregnancy, and most of the mothers--58 percent-- had breastfed at least one child. Also evaluated were the patients' medical history, body mass index, pre-pregnancy bra cup size, and smoking status.
The results suggested no difference in the degree of breast ptosis (the medical term for sagging of the breast) for those women who breastfed and those who didn't. However, researchers found that several other factors did affect breast sagging, including age, the number of pregnancies, and whether the patient smoked.
Quantifying something as subjective as this is hard to do under most circumstances (and I give the doctor's credit for writing something interesting), but unless you study these women prospectively (rather then retrospective as was done here) and get better characterization of their baseline breasts size/shape, skin quality, body weight, and breast tissue tone (ie. firm vs fatty) then you really can make no valid conclusions about their hypothesis.
You get breasts that hang for a number of reasons including:
- gravity (no explanation needed!)
- thinning of the skin with age
- attenuation of the internal soft tissue support of breast tissue (aka Cooper's Ligaments)
- "tissue expansion" phenomena from weight gain or engorgement during lactation
Now in re. to ptosis and lactation, the tissue expansion effect is what I'd say predominates. Now as a lactating breast will be swollen for a longer time, it's pretty intuitive and obvious that it's going to affect the breast shape more. I'm skeptical from this intuitive POV plus an (occupational) observational basis on this idea that there's no difference after breast feeding.
One of the more common sub-groups in the breast augmentation or breast lift group are women in their early or mid 30's who present with "involutional ptosis" (our fancy words for saggy breasts after pregnancy). During my residency at the University of Louisville (KY), I can remember spending time with one of my favorite surgeons, Dr. Marc Salzman, who was kind enough to let me accompany him during his cosmetic surgery consults. There was a pretty girl ~ 33 years old who came in, and when describing what she did not like about her breast declared, "Dr. Salzman, after having my babies, my breasts now look like Squidworth's nose!". He was kind of puzzled by her comment, but I burst out laughing aware (due to having small children) that Squidworth is Sponge Bob Squarepant's boss on the popular cartoon show.
Pictured below is Squidworth. And you know what? Her breast looked exactly like Squidworth's nose. :)