Meanwhile, my niece Anya is turning six months on Thursday and her doctor already gave the go signal for her to start solids. My sister commented that during meal times Anya always stares at them and at the food. They are still deciding whether to start her as soon as she hits 6 months or at 7 months (which is actually 6 months adjusted).
Anyway, during one of the LATCH workshops, the resource doctor presented a study from the American Academy of Pediatricians which again referred to 4 months as the minimum age for starting solidds:

If you need a clearer copy of the guidelines/statement, the same is reproduced in this webpage. This policy statement actually referred to a study entitled “Effects of early nutritional interventions on the development of atopic disease in infants and children: the role of maternal dietary restriction, breastfeeding, timing of introduction of complementary foods, and hydrolyzed formulas.” Because of recommendation number 6 (as quoted above), a lot of doctors believe that there is not much difference if a baby starts solids at 4 or 6 months, as long as baby is at least 4 months.
I still strongly believe that baby needs to be at least 6 months to start solids and I was very happy to read about this news two weeks ago, that based on a Dutch study, “babies are less likely to develop a respiratory or gastrointestinal infection if they are exclusively breastfed for at least 6 months.”
According to the researchers: “We observed protective effects of breastfeeding on infectious diseases mainly in the first 6 months of life. Exclusive breastfeeding until age 6 months tended to be more protective, than exclusive breastfeeding until age 4 months.” I need to show my sister this study and hopefully, they decide to delay starting Anya on solids.

*Update: I had a conversation with Dr. Z last Saturday. Doctors generally recommend 4-6 months because that this time, babies are developmentally ready for solids. However, the WHO recommends 6 months because this recommendation is targeted to 3rd world countries where access to clean facilities, ingredients, water for preparing solid foods are not generally available. Thus, if you check the American Academy of Pediatricians’ recommendations, they state 4-6 months. Interestingly though, the US is a 1st world country – and we are not. This is why I still do not understand why our doctors here recommend starting at 4 months despite the WHO recommendation.