Introducing babies to food is terrifically fun (and also very messy). It's great to see babies grabbing up avocado or carrots and making adorable faces as they try new foods, but a new study indicates that most U.S. parents are introducing their babies to solid foods too early. Experts say parents should wait until six months to start introducing complementary food, which are foods other than breast milk and formula.

According to CBS News, the CDC recommends that babies consume only breast milk or formula for the first six months of life, but says at that six-month point, parents should start introducing complementary foods. The babies should keep drinking milk and formula until they're at least 12 months old, but they should also start getting a bit of solid food as well.

A new study published in the Journal of the Academy of Nutrition and Dietetics indicates that only 32.5 percent of U.S. babies are introduced to complementary foods while they are six months old. Most babies are getting complementary foods earlier. More than half of U.S. babies are being introduced to complementary foods at less than six months old. 38 percent of U.S. babies are getting complementary foods at four to five months old, and 16.3 percent of them are even starting to get complementary foods at less than four months old.

Experts don't recommend introducing a baby to solid food before six months, because they say that could keep babies from getting all the nutritional benefits from breast milk or formula.

"Introducing babies to complementary foods too early can cause them to miss out on important nutrients that come from breast milk and infant formula," said Chloe M. Barrera of the CDC's Division of Nutrition, Physical Activity, and Obesity, in a statement.

About 13 percent of U.S. babies are introduced to complementary foods at more than seven months old, and that also goes against current CDC and American Academy of Pediatrics recommendations. Introducing babies to food too late has been associated with pickier eating later in life, and also with a higher risk of food allergies and nutrient deficiencies.

"Conversely, introducing them to complementary foods too late has been associated with micronutrient deficiencies, allergies, and poorer diets later in life," Barrera says.

Figuring out when to introduce a baby to food is complicated, because the recommendations for when and what to give them have changed a lot over the years. In the 1950s, most parents were told to start giving food at three months. In the 1970s, that shifted forward to four months. In the 1990s, parents were told to wait even later and hold off until four to six months. Right now, the CDC and AAP say the best time to give a baby food is when it is six months old.