Dr. Deb Lonzer did not take part in the study, but is a pediatrician at Cleveland Clinic Children's Hospital.
"Solid foods were being started before four months in about half of those kids, and in about 10 percent of them, it was actually being started in the first four weeks of life," she said.
CDC researchers questioned more than 1,300 moms and found that 40 percent of them introduced solid foods before four months of age. The top three most commonly cited reasons were, "my baby was old enough," "my baby seemed hungry," and "I wanted to feed my baby something in addition to breast milk or formula."
"They get information from so many sources, from friends, to relatives, to the internet, that they're not exactly sure what to do," Dr. Lonzer said. "And they figure, 'hey, I may as well try some solid foods. Maybe the baby will sleep better and be happier that way.'"
The AAP recommends holding off on solid foods until 6 months to be sure baby is developed enough to handle them.
Babies may also have trouble swallowing solid foods before 6-months of age, and researchers say introducing solid foods early may increase the risk of some chronic diseases and could cut short the benefits of breastfeeding.
"Solid foods are going to be lower in the good nutrition and may be higher in calories," Dr. Lonzer said. "So there's a chance we're causing more obesity in babies. It can cause allergies or eczema, there may be a link to diabetes."
Dr. Lonzer says if you have a fussy baby who never seems to be satisfied, don't turn to solid foods. Instead, call your pediatrician.
"So if you have a baby who is under 6 months and is taking in enormous quantities of breast milk or formula or really seems unsatisfied with feeding or who is fussy all of the time, it may have nothing to do with feeding," Dr. Lonzer said. "It may be a variety of other behavioral or even medical issues."
Complete findings for this study are in the journal "Pediatrics."