Avoid the feeding-time wail—look for these signs of a hungry baby.

It's no secret that feeding can be stressful for new parents. There are plenty of questions to ponder: How often should your baby be fed? How do you know if he's getting enough nourishment? Do his nutritional needs change from week to week?

The good news is that your baby is the single best authority for when he needs to be fed and when he is satisfied. His internal regulator for hunger and fullness is fine-tuned to his particular energy needs. That's why rigidly counting the ounces of formula or the number of minutes per breast-feeding session isn't the best way to calculate how much is enough. Instead, pay attention to his cues; his behavior will tell you when he's hungry and when he's full.

Research shows that when caregivers are responsive to feeding cues, infants will regulate their own energy intake. But when babies' cues aren't heeded, they're more likely to become confused about their sensations of hunger and fullness, possibly leading to preferences for less healthful (high-fat, high-calorie) foods and a greater risk for childhood obesity.

Signs That Your Baby Is Hungry

Crying. A hunger cry is usually short, low-pitched, and rises and falls. But crying is actually one of the later signs of hunger. You'll notice other behavioral cues first (such as those below). By the time a hungry baby is wailing, he may be too stressed to start eating easily.

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Waking up and acting restless. Before your baby launches into a full-throated hunger wail, he'll wake up and move around in his crib. He may also move his mouth and raise his hands to his face.

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Sucking on his fist, smacking his lips. If you feed a breast-fed baby when you see these signs, rather than waiting, he'll latch on more easily.

Rooting. During your baby's first weeks, when you stroke his cheek, his natural reflex will be to turn toward the bottle or breast and make sucking motions with his mouth. After 4 months of age, rooting becomes a voluntary action rather than a reflex.

Opening his mouth while feeding. Translation: "More, please!" A hungry baby may continue to show interest in sucking even after finishing the first breast or bottle.

Smiling during feeding. Babies older than 4 months will show their interest in continuing to eat by looking at you and smiling as they feed.

Signs That Your Baby Is Full

Closing lips. Just as a hungry baby suckles readily, a full baby zips his lips, as if to say, "No more, thanks."

Turning his head away. A more forceful version of closing his lips is to move his entire head away from the food source. If your baby turns away from your breast or a bottle, you shouldn't force him to eat.

Decreasing or stopping sucking. Some full babies will stay latched on to the nipple but not suck any more—at which point, it's time to gently end the session.

Spitting out the nipple or falling asleep when full. After about 15 to 20 minutes of feeding, a full baby will often act drowsy and may even fall asleep.

Showing increasing interest in surroundings rather than eating. At around 4 months old many babies begin to get distracted during feedings, as their awareness of the world around them grows. A hungry baby will put this curiosity on hold long enough to feel sated. When he begins looking around more distractedly, it's a sign he's had plenty.