Like most parents, Andrea Thompson works hard to make sure her toddler eats nutritious foods.

The Toronto mother has been a vegan for four years and thinks carefully about the food she gives her two-year-old daughter, Everest Frenke. Sometimes she adds flax oil, peanut butter or hemp seeds to soy milk to ensure her daughter is getting important nutrients. 

"The soy milk I give her is fortified," Thompson said. "She doesn't drink it very often, mostly in her cereal or her oatmeal."

Recognizing that more families are reaching for alternative milks such as soy, almond or rice over traditional cow's milk, researchers in Toronto set out to see if it has an impact on growth — an indicator of optimal nutrition. 

The team at St. Michael's Hospital turned to their ongoing study of about 5,000 children aged two to six who were recruited from primary-care practices in the city.

The kids' heights and weights were measured and blood samples taken. Participating parents were surveyed about their child's diet to see if cow's milk offered a growth advantage over non-cow's milk.

Among the children in the study, 13 per cent drank non-cow's milk, including goat's milk and plant-based alternatives. The others drank cow's milk daily.

The researchers found that on average, a three-year-old having three cups of cow's milk a day grew 1.5 centimetres taller than a similar child consuming the same amount of alternative milk.  

The study's lead author, pediatrician Jonathon Maguire, and his co-authors reported the findings in Wednesday's issue of the American Journal of Clinical Nutrition.

Difference 'not tiny'

"When you are only 2.5 feet high and you are that different it is a fairly sizable difference," Maguire said. "How that plays out over childhood, what difference that makes to adult height, is not clear at the present time, but the difference at three years of age is detectable and not tiny."

What's driving the height difference? The investigators speculate that factors like certain proteins in cow's milk may contribute to height, based on other studies.

'It is a little bit unusual that the same standard isn't applied to the other alternative milks but they are marketed as being similar to cow's milk.'
- Dr. Jonathon Maguire

For instance, two cups of cow's milk contains 16 grams of protein, which meets 100 per cent of the daily protein requirement for a three-year-old child, the researchers said. Two cups of almond milk beverage typically contains four grams of protein, which is only 25 per cent of the daily protein requirement for a three-year-old.

Researchers can't fully explain the apparent height difference and what could be contributing to it. When they factored in age, sex, ethnicity, neighbourhood income and maternal height, the results did not change. 

In Canada, the nutritional content of cow's milk is standardized but non-cow's milk isn't, the researchers noted.

Almond and soy milk

In Canada, the nutritional content of milk is standardized but non-cow's milk isn't. (Melanie Glanz/CBC)

"I think the whole reason to standardize was to protect children and provide adequate nutrients," Maguire said. "It is a little bit unusual that the same standard isn't applied to the other alternative milks but they are marketed as being similar to cow's milk."

What's driving family's choices

The takeaway is that there's just an association between drinking non-cow's milk and height, but you can't say it makes you shorter, said Dr. Peter Nieman, a community pediatrician in Calgary who was not involved in the study. 

The number of children drinking non-cow's milk has been growing steadily over the past 10 years. In Nieman's practice, more families are avoiding dairy, more for medical reasons than social or environmental ones, although he says that's a growing segment. 

When talking to families, Nieman said it's important to know what's driving their decision.

"If they tell me they did it for environmental reasons, maybe they're vegan, I would have to respect that and work with them and help them follow a lifestyle that is healthy and that is safe," Nieman said.

'I can't tell you what to do, but because the neighbour is doing it or because more people and more people are doing it doesn't make it right necessarily.' - Dr. Peter Nieman

"If it's just something that's a fad because the neighbour's doing it, then I think you can work with those people and explain," he added.

"I can't tell you what to do, but because the neighbour is doing it or because more people and more people are doing it doesn't make it right necessarily."

Nieman said the findings stimulate conversation but more, longer-term information is also needed. 

For her part, Thompson is conscious about giving her daughter foods rich in protein and other nutrients, such as hummus, nut butters, tofu and tempe.

"I converse with many vegan parents," Thompson said. "We know that really store-bought almond milk is advertised as a diet food, low calorie, low fat. It is not a toddler food."

Thompson thinks much more research is needed before saying there's a true causal link between drinking alternative milks and shorter height.

The study was funded by the Canadian Institutes for Health Research and the St. Michael's Hospital Foundation.

With files from CBC's Christine Birak and Melanie Glanz