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Babies fuss, cry, spit up, and get gassy. When they have these symptoms frequently, it's up to their parents to figure out what's wrong. Often the first place parents will look for clues is the baby's diet.

In their quest to soothe a fussy baby, many parents try changing formulas, assuming that the symptoms are caused by a formula intolerance. Up to half of all formula-fed babies are switched to a new formula in the first six months of life. Yet research finds that only about 2% to 15% of babies actually have a formula intolerance.

So how do you know whether your fussy baby is really having formula problems? Here’s how to recognize the signs of formula intolerance, and when to consider switching formulas.

Formula Feeding Basics: Where to Start

There are four basic formula types:

  • Cow's milk formula with cow’s milk as the protein source and lactose as the carbohydrate source and typically enriched with iron. Soy-based formula with soy as the protein source and corn as the carbohydrate source and typically enriched with iron.
  • Hydrolyzed formula (also called hypoallergenic formula) is made with proteins that have already been broken down so they are easier to digest. Corn or sucrose is the carbohydrate.
  • Specialized formulas for premature babies or babies with certain disorders or conditions.

For most healthy infants, experts say cow's milk formula is the best place to start. "It's well tolerated, it's the cheapest, and it contains the nutrients babies need," says Ari Brown, MD, FAAP, a pediatrician in Austin, Texas, and co-author of Baby 411 and Expecting 411.

Try to stick with the same formula for at least six to eight weeks, even if your baby is crying, gassy, or spitting up. These aren't necessarily signs of formula problems -- they're just normal baby behaviors.

"All of the gassy, poopy stuff has nothing to do with the formula and everything to do with being a newborn," Brown says. "They are born with an immature gut and they eat 24 hours a day. If we ate 24 hours a day, we'd be gassy too." Most of the gassiness and other stomach discomfort should go away on their own by the time a baby is four to six months old.

Figuring Out Formula Problems

Most babies do just fine on cow's milk formula, but a small percentage of infants can't tolerate it because of lactose intolerance (an inability to break down the lactose sugar in milk) or an allergy to the proteins in milk.

Brown says it's very rare for babies to be born with lactose intolerance. Most of the time, lactose intolerance doesn't start until after a child's first birthday.

About 2% to 3% of babies have a milk protein allergy, in which the baby's immune system mistakenly sees the milk protein as a foreign invader and attacks it. Most babies eventually outgrow their milk allergy.

Common Baby Feeding Problems

Diet too spicy? Baby spitting up too much? Find out what's normal.
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