TORONTO -- A new study suggests mothers who can't afford enough food are more likely to stop breastfeeding before other moms, even though nearly all begin at a similar rate.

University of Toronto researchers don't delve into the reasons why, but conclude that financially vulnerable women struggle significantly more to breastfeed and need more government support.

Nutritional sciences professor Valerie Tarasuk says poverty forces many infants to start life "way further behind," pointing to ample evidence that breast milk offers excellent nutrition and protection against disease.

And she says women who are living in poverty clearly know that, since 86 per cent of those surveyed tried to breastfeed. Nevertheless, more than half stopped before two months, while half of the more financially secure moms stuck with it for at least four months.

Tarasuk says these women reported trouble affording enough food for themselves and their family, which sometimes included other children. She says they were likely undernourished themselves, and "probably stressed out of their minds."

The study was based on the experiences of more than 10,000 moms who took part in the Canadian Community Health Survey between 2005 and 2014. The Canadian Medical Association Journal published the results Monday.

Seventeen per cent of them -- or one in six -- lived in households with food insecurity, meaning they worried about being able to serve a balanced meal, reduced serving portions or skipped meals entirely.

"It's very likely that these women's own dietary intakes are compromised in that setting. It would be very unlikely if they weren't," says Tarasuk, who notes that breastfeeding itself requires many calories to sustain. "But they're also probably stressed out of their minds."

They likely struggled to pay rent and afford other necessities, she says.

Adding baby formula to household expenses can be "a financial burden that food-insecure families can ill-afford," the study says.

Researchers don't know if these women were working at the same time, or whether they were even able to breastfeed, given their own likely nutritional deprivation.

Even for advantaged women, breastfeeding to six months "is a rare event," says Tarasuk, and can be impacted by social, psychological and emotional stresses.

Canadian public health programs promote breastfeeding as a secure, low-cost, food supply for infants, but the study notes there has been little data on the ability of women who are living in poverty to comply if they struggle to buy food.

The study notes there are resources for vulnerable women, including the Canada Prenatal Nutrition Program, which funds community-based efforts to support healthy pregnancies.

There is also the Canada child benefit payment, which was redesigned in 2016 -- two years after the most recent data in the U of T study. The government has said the 2016-17 benefits helped lift about 300,000 children out of poverty.

Still, Tarasuk's study questions whether Ottawa is doing enough to tackle food insecurity.

"It's outrageous that simply the act of having a child puts a family at higher risk of food insecurity than others. That's wrong. It should be the other way around," she says.

"Whatever the supports are that we have, they're not enough. We shouldn't be able to find data like this if we were effectively intervening on that life stage."

The research was supported by the Canadian Institutes of Health Research.