By ages 4 to 6 months, most babies are ready to begin eating solid foods as a complement to breast-feeding or formula-feeding.

What's so magic about ages 4 to 6 months? It's around this time that babies typically stop using their tongues to push food out of their mouths and begin to develop the coordination to move solid food from the front of the mouth to the back for swallowing.

It's also at age 6 months that babies need complementary food to support growth, satisfy hunger and help meet energy and nutrient needs. For babies who are exclusively breast-fed, waiting until age 6 months before introducing solid food can help ensure that they get the full health benefits of breast-feeding.

Starting solids too early — before age 4 months — might:

• Pose a risk of food being sucked into the airway (aspiration)
• Cause a baby to get too many or not enough calories or nutrients
• Increase a baby's risk of obesity

Also, starting solids before age 4 months hasn't been shown to help babies sleep better at night.

Starting solids too late — after age 6 months — poses another set of issues. Waiting too long might:

• Slow a baby's growth
• Cause iron deficiency in breast-fed babies
• Delay oral motor function
• Cause an aversion to solid foods

Postponing the introduction of highly allergenic foods, such as peanuts, eggs and fish, beyond 4 to 6 months of age hasn't been shown to prevent eczema, asthma, allergic rhinitis or food allergy. In fact, early introduction of peanuts might prevent peanut allergy.

In addition to age, other signs can show you that your baby is ready for solid foods. Can your baby hold his or her head in a steady, upright position? Can your baby sit with support? If you answer yes to these questions and your baby's doctor agrees, you can begin supplementing your baby's liquid diet.