COLORADO SPRINGS, COLO. --

According to a study reported in the journal Pediatrics, 1 percent of all American girls now show signs of puberty, such as breast development or pubic hair, before the age of three. By the age of eight, 14.7 percent of Caucasian girls and almost 50 percent of African-American girls had one or both of these characteristics.

There aren't many in the medical field who will debate that trend. What they will debate, though, is what's causing children to experience puberty at much younger ages.

The one controversial cause FOX21 News explored was soy products.

"In Puerto Rico they had something of an epidemic of precocious puberty and they went in to look for correlations. What they found was the strongest correlation was having had soy formula as children," explained Sally Fallon co-founder of Weston A. Price, a nonprofit organization dedicated to "restoring nutrient-dense foods to the American diet through education, research and activism."

The concern with soy formula and other soy products, in this situation, centers around a natural ingredient called isoflavones, which has an estrogenic effect. "In females it's the estrogens that simulate the development, the sexual developments," explained pediatrician Dr. John Kucera.

"There has been research to say that this is not a major issue and soy could be used without concern. But I think when you look at all the research and you see the pros and cons and where the sources of this information are we know that it is a potential concern," offered Kucera.

New Zealand toxicologist Mike Fitzpatrick estimates that an infant exclusively fed soy formula receives the estrogenic equivalent (based on body weight) of at least five birth control pills per day.

Effect On Boys

In boys there is concern that the estrogen effect overwhelms the testosterone production, which can delay their physical maturation or even prevent the development of the sexual organs.

"There is a point when testosterone is supposed to surge and cause the developmental changes in the brain that make a male, you know a boy, a true male. The estrogen effect can override that and this is early on even before sexual development, this is the first year of life. Some of the early changes that cause discrimination and development of the brain that makes a boy a boy and a girl a girl can be inhibited by estrogens of any kind," explained Kucera.

Other Factors To Consider

Endocrinologist Dr. Shona Murray said there are many theories as to what environmental factors may be contributing to early onset puberty and while soy may be one factor she said it is not the sole or even leading cause.

Approximately 25 percent of bottle-fed children in the U.S. receive soy-based formula, but we're not seeing the same rate of precocious puberty, so there is certainly not a very strong link, but there may be a weak link.

What Murray and Kucera both believe has a much stronger estrogenic impact on children is the cumulative effect of their environment.

"There are a lot of things in the environment that may be giving the body the message of estrogen whether or not it's truly estrogen," said Murray.

One of the big concerns is that people forget about all the chemicals and toxins in our environment and they focus on soy which is a natural phytoestrogen and forget about the xenoestrogens," said Kucera.

Xenoestrogens are man-made compounds that mimic the behavior of natural estrogen in the body. They occur in everything from plastic baby bottle and food storage containers to shampoo, cosmetics, sunscreen, pesticides and insecticides.

"This is the larger problem, the environment that our children are placed in. So I don't think we should just focus on one substance, like soy, which may have some concern, and miss the big picture," said Kucera.

Is Soy Healthy At All For Kids?

Registered dietitian Martha Rosenau said 'soy is a very healthy addition to the diet if you're looking for a low fat protein source."

But when Rosenau says soy, she's talking about soy the food, products like tofu, miso or tempeh.

"Soy infant formula is a processed food it is in no way similar to the soy bean any longer," explained Rosenau. "When you take isolated soy protein, which again is not the food soy, and you make it into just a protein that you can deliver in a powder for infants, the isoflavone numbers are much higher." The problem or concern then becomes feeding a formula with an increased amount of estrogen to babies who have smaller and more sensitive systems. "Small children's bodies are extra sensitive to estrogen," said Rosenau.