Researchers followed 190 teenagers to see if babies fed soy-based formula grew up differently than babies fed cow’s milk formula or breast milk. At age 14, they measured the teens’ height, weight, body fat, heart health, and pubertal development. The good news: teenagers who were fed soy formula as babies looked very similar to those fed other types of formula or breast milk. All groups had similar weight, body composition, blood pressure, and cholesterol levels. The only notable difference was that breast-fed teens had slightly less body fat than those fed cow’s milk formula. Overall, soy formula appears to be just as safe and healthy as other feeding options.

The Quick Take

  • What they studied: Whether babies fed soy-based infant formula grow up with different body size, weight, heart health, and puberty timing compared to babies fed cow’s milk formula or breast milk.
  • Who participated: 190 teenagers (average age 14 years old) who had been tracked since infancy. The group included 52 who were fed soy formula, 76 who were breast-fed, and 62 who were fed cow’s milk formula as babies.
  • Key finding: At age 14, teenagers who were fed soy formula as babies had nearly identical growth, body composition, heart health markers, and pubertal development compared to those fed cow’s milk formula or breast milk. The only meaningful difference was that breast-fed teens had slightly less body fat than those fed cow’s milk formula.
  • What it means for you: If your baby was fed soy formula, this research suggests it’s associated with normal, healthy development through the teenage years. However, this is one study with a relatively small group, so parents should continue following their pediatrician’s recommendations about infant feeding.

The Research Details

This was a follow-up study that tracked children over many years. Researchers started with babies who were fed different types of formula or breast milk, and then checked in on them at age 14 to see how they had grown and developed. At the 14-year visit, the teenagers had their height and weight measured, their body fat calculated using special imaging, their blood tested for heart health markers, and their pubertal development assessed by a doctor. The researchers used statistical methods to account for differences between the groups, such as the mother’s education level and the baby’s birth weight, to make fair comparisons.

The study was careful to measure many different aspects of health. They looked at how much the teens ate, what types of foods they chose, their blood pressure, blood sugar levels, cholesterol, and markers of inflammation. For girls, they also recorded when they started their period. For both boys and girls, they measured reproductive organ development.

This approach is valuable because it follows real children over a long period of time, rather than just looking at short-term effects. It also includes multiple feeding groups, which allows researchers to compare soy formula not just to cow’s milk formula, but also to breast milk, which is considered the gold standard.

Long-term follow-up studies like this are important because infant feeding decisions can seem to have immediate effects, but parents really want to know about long-term health. By following children from infancy into the teenage years, researchers can see whether early feeding choices affect growth, body composition, and important health markers like heart health and blood sugar control. This type of study is more reliable than short-term studies because it captures real-world development over many years.

This study has several strengths: it followed children over many years, it included multiple feeding groups for comparison, it measured many different health outcomes, and it used statistical methods to account for other factors that might affect results. However, the sample size of 190 is relatively modest, which means the results might not apply perfectly to all children. The study also relied on information collected from the past about how babies were fed, which could be less accurate than information collected at the time. Additionally, the study was conducted in the U.S., so results might differ in other countries with different populations or feeding practices.

What the Results Show

When researchers compared the three groups of 14-year-olds, they found almost no differences in body size or composition. Teenagers who had been fed soy formula weighed about the same as those fed cow’s milk formula or breast milk. Their BMI (a measure of weight relative to height) was similar across all groups. The amount of body fat, including dangerous fat around the organs, was comparable between groups.

Heart and metabolic health markers were also very similar. Blood pressure, blood sugar levels, cholesterol, and inflammatory markers (signs of inflammation in the body) showed no significant differences between the three feeding groups. This is reassuring because these are important indicators of long-term health risk.

Pubertal development—the physical changes that happen during puberty—occurred at similar rates and times across all three groups. For girls, the age when they started their period was comparable. For both boys and girls, the development of reproductive organs was similar.

One interesting finding was that teenagers who were breast-fed had slightly lower rates of cardiometabolic risk factors (conditions that increase heart disease risk) compared to those fed cow’s milk formula. However, those fed soy formula had rates similar to breast-fed children.

When researchers looked at what the teenagers ate, they found that overall diet quality was similar across groups. However, teenagers who had been fed soy formula or breast milk consumed slightly less fat in their diet compared to those fed cow’s milk formula. This difference was small and may reflect dietary patterns rather than effects from infant feeding. Energy intake (total calories) and other nutrients were comparable across all groups.

This study adds important information because previous research on soy formula has been limited, especially for long-term outcomes in teenagers. Most concerns about soy formula have focused on compounds in soy that act like estrogen (a female hormone), but this study found no evidence that soy formula affected pubertal development or reproductive organ development. The findings align with other research suggesting that soy formula is safe, while also providing new data on teenage outcomes that hadn’t been thoroughly studied before.

The study included 190 teenagers, which is a reasonable size but not huge—results might be different in a larger group. The study only followed children to age 14, so we don’t know about health effects in adulthood. The researchers had to rely on parents’ memories about how babies were fed, which could be inaccurate. The study was conducted in the U.S. with a specific population, so results might not apply to all children worldwide. Additionally, the study couldn’t prove that soy formula caused the outcomes observed—it only showed associations between infant feeding type and teenage health.

The Bottom Line

Based on this research, soy-based infant formula appears to be a safe feeding option associated with normal growth and development through the teenage years. Parents who used soy formula should feel reassured by these findings. However, this is one study, and parents should continue to follow their pediatrician’s recommendations about infant feeding. If parents have concerns about any feeding choice, they should discuss them with their child’s doctor. (Confidence level: Moderate—this is good evidence, but more research would strengthen these conclusions.)

Parents who used or are considering soy formula should find this reassuring. Healthcare providers who counsel families about infant feeding options will find this useful. Teenagers who were fed soy formula and their parents may be interested in knowing their long-term health appears normal. People with concerns about soy formula safety will find this research helpful. However, this study doesn’t change recommendations for families who prefer breast milk or cow’s milk formula—all three options appear healthy based on this research.

This study measured outcomes at age 14, so these are the long-term effects visible by the teenage years. Parents shouldn’t expect to see dramatic changes from infant feeding choices—growth and development happen gradually over years. If concerned about a child’s growth or development at any age, parents should consult their pediatrician rather than waiting for teenage years.

Want to Apply This Research?

  • Track your child’s growth measurements (height and weight) at annual check-ups and compare to growth charts. If your child was fed soy formula, you can monitor that their growth follows normal patterns and discuss any concerns with your pediatrician.
  • If you’re a parent considering infant feeding options, use the app to research and compare different feeding types. You can log your feeding choice and track your child’s growth milestones to ensure healthy development. Set reminders for regular pediatric check-ups to monitor growth and health.
  • For long-term tracking, record annual height and weight measurements in the app and watch for consistent growth patterns. Monitor key health markers like blood pressure and cholesterol when measured at doctor visits (typically starting in teenage years). Track dietary intake and quality as your child grows to ensure balanced nutrition regardless of infant feeding history.

This research suggests soy infant formula is associated with normal development, but it is not a substitute for personalized medical advice. Parents should consult with their pediatrician about infant feeding choices and any health concerns. This study was conducted in a specific U.S. population and may not apply to all children. If you have concerns about your child’s growth, development, or health, please speak with your healthcare provider. This summary is for educational purposes and should not be used to diagnose or treat any medical condition.