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Even though around 25 percent of formula-fed American babies take some form of soy formula, we recommend that parents begin their baby on a standard cow's milk-based formula unless advised otherwise by their doctor. Soy formulas became popular as an alternative formula in infants who are allergic to cow's milk. Some babies are less allergic to the soy protein than to cow's milk protein. Yet, we have the following reservations about soy formulas:
Even though soy-based artificial baby milks may be less allergenic for some babies, between 30 and 50 percent of infants who are allergic to cow's milk are also allergic to soy.
There is no precedent in nature for feeding young mammals a plant-based protein. In the early 1970s it was discovered that soy proteins are deficient in some amino acids that babies need. For this reason, methionine, carnitine, and taurine have to be added from other sources. Not only is soy protein deficient in some amino acids because plant protein in general does not provide the same growth equivalent as animal protein, but more needs to be added so that soy formulas have a higher level of this protein to make up for its lesser quality. According to the amino acid profile, at least in All-Soy, there is no carnitine or taurine. Even though current biochemical knowledge has fixed some of the previous problems with soy protein for babies, we are still tampering with Mother Nature's recipe, leading us to conclude that feeding soy protein to growing babies is still experimental. Plant protein is a good protein for older infants and adults, but the protein made by big mammals for little mammals is ideal for babies.
Another problem with soy is that the protein itself contains phytates, substances that bind calcium and phosphorus. To prevent calcium deficiencies and consequent deficiencies in bone mineralization, the calcium content of soy formulas is generally 20 to 30 percent higher than the calcium content of milk- based formulas.
These phytates also bind iron and zinc. As a result of this finding, artificial soy baby milks, such as Carnation, Allsoy, and Mead Johnson's Prosobee, have added extra iron and zinc. Isomil's Soy formula (made by Ross Laboratories) does not have more zinc or iron than the company's cow's-based formulas. Studies done by Ross Laboratories show that the blood-mineral profile of babies on cow's milk and soy formulas are no different.
In 1996 the Committee on Nutrition of the American Academy of Pediatrics voiced some concern about the relatively high content of aluminum in soy-based formulas and the possible toxicity to infants. Although the American Academy of Pediatrics concluded that the elevated aluminum levels in some soy formulas do not seem to be harmful for term infants, the fact is no one really knows. Because of this worry and studies showing less bone mineralization in preterm infants on soy formula, the Committee of Nutrition of the American Academy of Pediatrics recommended that soy formula be reserved for term infants and not be used for preterm or small-for-date infants.
Soy formula was once routinely recommended for infants with a family history of milk allergy in hopes of preventing allergies from developing. Research has failed to support the idea that starting a newborn on soy formula will decrease the later incidence of allergy. Also, recent research has disproven the belief that babies are less colicky with soy formulas. Studies comparing cow's milk- based and soy formula showed that soy formula does not lower the risk of infant colic. For this reason, the Committee on Nutrition of the American Academy of Pediatrics recommends against the use of soy formulas in the routine management of colic or in infants who are potentially allergic to cow's milk. Instead of soy, hypoallergenic formulas are recommended.
Giving an infant soy in the early months before intestinal closure may predispose the infant to soy allergies later on. Since soy is used as a filler in so many foods in the American diet, this is a serious concern.
Soy formulas contain around 33 percent more sodium than standard cow's milk- based formulas, and formulas in general are saltier than human milk. It is nutritionally unwise to shape young palates to get accustomed to salty tastes. It's unwise to give a baby a salty formula unless absolutely necessary.
Carbohydrate sources in soy formulas are even more of a concern. Just as there is a whey war going on between formula companies, there now seems to be a sugar war, too. Enfamil now advertises "no table sugar" in their soy formula, Prosobee, so they use corn syrup instead of sucrose. Does this make a big difference? Some nutritionists might prefer plain old table sugar to corn syrup. Corn itself is an allergen, and corn syrup is very sweet.
Because soy formulas are made with bean "milk" and not cow's milk, they are naturally lactose-free. The problem is that lactose is the sugar in human milk and in the milk of all other mammals. There is no basis in nature for feeding mammals lactose-free milk. Lactose is an intestinal-friendly sugar, enhancing calcium absorption and helping to colonize those little intestines with favorable bacteria. While the "lactose-free" nature of soy formulas benefit infants who are congenitally lactose intolerant (which is really quite rare in the first year of life), this is really tampering with Mother Nature. Because soy does not contain lactose, soy formulas are often recommended for infants who develop a temporary lactase deficiency following an intestinal infection. Studies as to whether or not this helps show mixed results. The American Academy of Pediatrics does not recommend the routine use of soy formulas in infants recovering from diarrhea, but suggests they be used only in babies shown to be temporarily intolerant of cow's milk-based formulas.
Our conclusion: Unless recommended otherwise by your baby's doctor, soy formulas:
Should not be routinely used in infants with a family history of milk allergy in hopes of preventing later allergy.
Should not be as a substitute for cow's milk-based formulas unless baby has been proven to be allergic to cow's milk-based formulas.
Should not be used to prevent or treat "colic" unless advised by your doctor.
Should not be used in preterm or small-for-date babies.
Even though we discourage the use of soy formula as a first-choice artificial baby milk, in some babies it is a necessary alternative to cow's milk-based formulas. Many of the objections to soy formula are perhaps more theoretical than practical (since studies have shown that healthy term babies grow just as well on soy as they do on cow's-milk-based formulas). It's what we do not know about soy that concerns us. The soy bean protein brings along with it a lot of other phytochemicals (plant nutrients), some of which may be healthful, and others we just don't know about. Cow's-milk-based formulas have been around for nearly a century. We don't have that much experience with soy, so be cautious.