Prof. Thomas M. Badger, PhD/MD
Safety of Soy in Diet of Children
Soy beans are an excellent source of high quality protein. They are used worldwide in feed for animals. Animals have been fed high levels of soy-based feeds throughout life: before and during breeding; during pregnancy and lactation; and in offspring between weaning and adulthood. Soy foods have been consumed for centuries by adult men and women and by children in Asia as part of traditional diets.
For nearly 40 years, soy protein isolates have been used as the sole source of several commercially-available infant formulas. While the initial reason for developing soy formula was to meet the needs of infants with various medical conditions, such as adverse reactions to milk proteins or sugars, soy formula gained favor with many parents because of the reported health benefits of soy foods. In the United States, the numbers of infants fed soy formula has been estimated to be as high as 20-25% of all formula-fed infants. Sales of formula suggest that more than 20 million infants have been fed soy formula in the U.S. over the past few decades. These infants have been shown to grow and develop normally and there have been no adverse health effects reported in peer-reviewed medical journals.
Despite the long record of excellent growth and normal development of children who were fed soy formulas as infants, safety questions related to isoflavones continue to be raised. Isoflavones are phytochemicals physically associated with soy proteins. Under some experimental conditions, purified isoflavones have weak estrogenic activity and they have been labeled “phytoestrogens”. The reported estrogenic actions of isoflavones have led to concerns that consumption of soy foods, such as soy formula, may have adverse health effects. However, there is no scientific evidence that this is the case. In fact, the evidence supports the safe use of soy foods for children, starting with infant formula. So why are there conflicting views about the safety of soy foods for children? Much of the discrepancy lies in understanding the differences between soy foods and compounds purified from soy beans, such as the isoflavones. Children consume soy foods, not purified phytochemicals isolated from soy beans.
So what are the facts about isoflavones and children? Isoflavones are much less potent than naturally occurring estrogens, such as the major female hormone estradiol. It is estimated that between 1,000 and 400,000 times more isoflavone would be required in the human body to have the same biological effect as estradiol. In addition, the chemical forms of isoflavones that circulates in the blood are largely inactive conjugates produced during absorption by the intestine and during first pass metabolism in the liver. Active isoflavones (called aglycones or free isoflavones) represent only about 1% of the total isoflavones in human subjects (Gu et al, 2006). Furthermore, these aglycones must get inside cells to have biological effects and the cellular concentrations of these active forms are at least 100 times lower than the circulating form. Once within the cell where estrogens act, the estrogen receptors, isoflavones need to compete with the much more potent naturally-occurring estrogens in the cell. Importantly, isoflavones are not consumed in isolation, but as part of a soy-containing meal. Soy foods contain over 100 other phytochemicals and a number of bioactive peptides (Fang et al, 2003 and 2004). This complex mixture produces effects that are quite different from those of a pure isoflavones, because several other components in soy products are biologically active as well, such that the actions of purified isoflavones are modified or even blocked in the presence of these other components. So the bottom line is that it is highly unlikely that consumption of soy foods will cause “estrogenic” adverse health concerns.
One important area addressed by the Beginnings Study is brain development and function. Brain performance is assessed by several techniques, such as: standardized psychological testing; electroencephology (EEG); event related potentials (ERP); and power spectral analyses (SSA). Because the Beginnings Study is not completed, only preliminary data have been published in the form of abstracts (>40 published to date). These studies have demonstrated that:
1) in all standardized physiological tests, all children, including soy-fed children scored within normal range age-appropriate ranges;
2) most brain functions (as assessed by EEG, ERP and SSA) have the same pattern of activity and brain localization, but develop with a different temporal relationship (i.e., age at which these activities occur may differ between diet groups).
Therefore, some brain functions differ in children who were breast-fed as compared with formula feeding. For example, differences were found between breast-fed infants and milk-based formula infants in development of responses, processing capabilities and syllable registration (Jing, et al, 2007). Furthermore, both male and female breast-fed infants showed a biphasic change in the spectral power across age (highest at 9 months), but boys in both formula groups (milk and soy) had the highest spectral power at 12 months. While infants in the two formula groups had similar spectral power at each age, the spectral power for these groups was greater than that of breast-fed infants at 6 and 12 months (particularly in frontocentral areas) (Jing et al, 2008). These results suggest that the development of EEG activities is similar in infants fed milk-based and soy-based infant formulas, but the underlying time course for this development appears to differ in breast-fed infants. Understanding the neurophysiological basis for these differences and the long-term consequences will require further study.
Above we have been discussing infants fed soy formula because they consume more soy protein than any other segment of the human population. However, infants are not the only children exposed to soy foods. In fact, there are many more children over the age of 1 year fed soy foods worldwide than there are infants fed soy formula. Thus, there are centuries of experience with soy foods in children and there are no data to suggest adverse health effects in healthy children. There are data, however, suggesting that health benefits can be derived from consuming soy foods. For example, girls consuming soy foods during adolescence may have lower incidence of breast cancer later in life (Wu et al, 2002).
In conclusion, there are two main issues concerning efficacy and safety of soy foods fed to children. First, infants fed formula made with soy protein are clearly exposed to high levels of many soy bean-associated chemicals (phytochemicals). Of the millions of infants fed these formulas over the past 30-40 years, many peer-reviewed and high quality publications have documented normal growth and development, and they may have reduced disease risk as they age. There have been no adverse health effects reported for these people. Unfortunately, there have been no controlled prospective studies to document the health of these adults who as infants were fed soy formula. In the one retrospective follow-up study of such adults, no adverse health effects were attributable to soy formula consumption (Strom et al, 2000). Second, older children represent a different type of exposure to soy foods than infants fed soy formula. For example, children, like adults, consume soy foods in the context of an otherwise healthy and diverse diet. Since soy is an excellent source of high quality protein, this would be health beneficial. Furthermore, studies have suggested that other health benefits may occur from consumption of soy foods, such as reduced risk of breast cancer in women and lower cardiovascular disease in men and women.
Akingbemi BT, Braden TD, Kemppainen BW, Hancock KD, Sherrill JD, Cook SJ, He X, Supko JG. Exposure to phytoestrogens in the perinatal period affects androgen secretion by testicular Leydig cells in the adult rat. Endocrinology. 2007;148:4475-4488.
Badger TM, Ronis MJJ, Hakkak R. Developmental effects and health aspects of soy protein isolate, casein and whey in male and female rats. Internatl J Toxicol. 2001;20:165-174.
Brian L. Strom BL, Schinnar R, Ziegler EE, Barnhart KT, Sammel MD, Macones GA, Stallings VA, Drulis JM, Nelson SE, Hanson, SA. Exposure to Soy-Based Formula in Infancy and Endocrinological and Reproductive Outcomes in Young Adulthood. JAMA. 2001;286:807-814.
Fang N, Yu S, Badger TM. LC-MS/MS analysis of lysophospholipids associated with soy protein isolate. J.Agric.Food Chem. 2003;51:6676-6682.
Fang N, Yu S, Badger TM. Comprehensive phytochemical profile of soy protein isolate. J Agric Food Chem. 2004;52:4012-4020.
Gu L, House SE, Prior RL, Fang N, Ronis MJJ, Clarkson TB, Wilson ME and Badger TM. Metabolic phenotype of isoflavones differ among female rats, pigs, monkeys and women. J Nutr 2006;136:1215-1221.
Jing, H., Pivik, R.T., Dykman, R.A., Gilchrist, J.M., Badger, T.M. Effects of Breast Milk and Milk Formula Diets on Synthesized Speech Sound-induced Event-related Potentials in Three and Six Month Old Infants. Developmental Neuropsychology, 31: 349-362, 2007.
Jing, H., Pivik, R.T., Gilchrist, J.M., Badger, T.M. No difference indicated in EEG power spectral.
analysis in 3 and 6 months old infants fed soy- or milk-based formula. Maternal and Child Nutrition, 4: 136-145, 2008.
Pivik, R.T., Dykman, R.A., Jing, H., Gilchrist, J. M., Badger, T.M. The influence of infant diet on early developmental changes in processing human voice speech stimuli: ERP variations in breast and milk formula-fed infants at three and six months after birth. Developmental Neuropsychology, 31: 281-338, 2007.
Strom BL, Schinnar R, Ziegler EE, Barnhart KT, Sammel MD, Macones GA, Stallings VA, Drulis JM, Nelson SE, Hanson SA. Exposure to soy-based formula in infancy and endocrinological and reproductive outcomes in young adulthood. JAMA. 2001;286:807-814.
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