Plant-based milks are popular alternatives to regular cow’s milk — and they can be great options for some adults, especially those who have lactose intolerance.

But are non-dairy milks like soy milk good for babies and young children too? Here's what you need to know about soy milk for babies.

What is soy milk?

Soy milk is made from cooked soybeans, and contains soy protein, natural or added sugars, and fiber. While the nutritional content can vary from brand to brand, a 4-ounce glass of soy milk contains about 40 calories, 3 to 4 grams of protein, 2 grams of fat and a half-gram of sugar.

It also contains minerals like calcium, iron and potassium.

Should babies drink soy milk?

Babies under the age of 1 shouldn’t drink cow's milk, soy milk or any other plant-based milks, and stick to only breast milk or formula (with a little water after they start solids). 

Cow’s milk contains too many proteins and minerals for babies’ stomachs to handle, and most plant-based milks aren’t adequate sources of the many nutrients babies need early on.

Between the ages of 1 and 5, doctors recommend that children drink mainly cow's milk and water. However, fortified soy milk is an acceptable alternative to cow's milk, since it's nutritionally equivalent.

So if your child does drink soy milk before the age of 5 and after age 1, make sure it's fortified and unsweetened. Children ages 1 to 2 should have two to three cups of whole milk each day.

If your child has a medical problem — for example, she has a dairy allergy or is lactose intolerant — or if your family doesn’t eat animal products, fortified soy milk is an appropriate substitute for cow's milk.

Is soy milk good for babies?

You shouldn’t give soy milk to babies under the age of 1. Unlike soy milk, breast milk and infant formula contain all the nutrition babies need.

After the age of 1, your little one should stick to whole, plain cow's milk, but fortified, unsweetened soy milk is an acceptable alternative if your family is vegan or your child has a milk sensitivity or other underlying medical issue.

Work with your pediatrician to determine the best kind of soy milk for your child. Not only can the nutritional content of soy milk vary by brand, but experts also point out that our bodies may not be able to absorb nutrients from plant-based milks as well as they can from dairy milks, so be sure that the kind you're choosing is one recommended by your doctor.

Is soy milk safe for babies?

Babies under the age of 6 months should only drink breast milk or infant formula; after you start to introduce solid foods into her diet, she should still stick to only a few sips of water between meals — not cow's milk or soy milk.

After the age of 1, you should only give your little one regular, unflavored cow's milk or if she has a milk allergy or intolerance (or eats a vegan diet) fortified, unsweetened soy milk.

Cow's milk is an important source of protein, calcium, potassium and vitamins A, D and B12. But plant-based milks can have a varying amount of nutrients, and — with the exception of certain fortified soy milks — aren’t an ideal replacement for the dairy varieties. 

When can I give my baby soy milk?

If your child has a milk allergy or intolerance, or you're raising her vegan, you can give her a fortified soy milk recommended by your pediatrician starting at the age of 1.

If your child doesn’t have a medical issue, however, or if your family eats animal products, then you’re better off avoiding plant-based milks until she’s older. The leading children’s health organizations in the United States tell parents not to substitute plant-based milks — like oat milk or almond milk — for cow’s milk in children under the age of 5, with the exception of fortified soy milk.

Soy milk vs. cow's milk for babies

Other than certain fortified soy milks, experts point out that cow’s milk contains more nutrients, cup for cup, than plant-based milk. For example, 1 cup of whole milk contains 149 calories and about 7 to 8 grams of protein compared to the 105 calories and 6 grams of protein in soy milk. 

Whole milk contains more fat and sugar, too. One cup of cow’s milk contains 8 grams of fat and 12 grams of sugar; one cup of soy milk contains about 3.5 grams of fat and 9 grams of sugar. 

As for vitamins and minerals, 1 cup of whole milk contains 276 milligrams of calcium and 322 milligrams of potassium, whereas the same amount of soy milk contains 300 milligrams of calcium and 298 milligrams of potassium.

Soy milk and phytoestrogens

Soy milk contains compounds called phytoestrogens, also known as plant estrogens or isoflavones. While there have been reports over the years about phytoestrogens possibly being linked to breast cancer, other studies have shown that isoflavones might be protective against diseases like breast, endometrial and prostate cancers.

As for reports that excessive amounts of phytoestrogens could have a hormonal effect on kids, Pediatrics (the American Academy of Pediatrics' journal) points out that there is no evidence that the isoflavones in soy have any negative effect on their hormones or development.

Should I give my baby soy milk if she has a dairy allergy?

If your baby has a milk allergy — which is somewhat rare, affecting only about 2 to 3 percent of babies — or an intolerance to lactose (a type of sugar found in milk and dairy products), you can give your child a fortified soy milk if she's over the age of 1.

But because plant-based milks like soy milk can vary depending on the brand, it’s important to work with your pediatrician or a registered dietitian to choose the right type for your child.

Soy milk and calcium

While some soy milks contain a little more calcium than cow’s milk, they also contain natural compounds called phytates, which can interfere with your child’s ability to absorb calcium. If your little one is drinking soy milk instead of cow’s milk, ask your pediatrician whether you should add other calcium-rich foods like spinach and fortified cereals to her diet.

When to call the doctor

Milk allergies in babies are rare, but it’s worth knowing how to spot the signs. Babies who are breastfed can have an allergic reaction to the milk in their mothers’ diets, whereas babies who are formula-fed are reacting to the milk proteins found in the formula itself.

Some of the symptoms of a milk allergy in babies include frequent spitting up, signs of abdominal pain, vomiting, diarrhea, blood in the stool, wheezing, trouble breathing, coughing and itchy, watery or swollen eyes. Call your pediatrician if you believe your child might have a milk allergy. 

While fortified soy milk might be an appropriate milk substitute for a small percentage of children, experts recommend that almost all children drink regular cow's milk until at least the age of 5. Babies under the age of 1 should drink only breast milk or formula (with a little bit of water after they've started solids around 6 months), and tots aged 1 and up should stick to unflavored cow’s milk.