More than half of New Zealand infants have tried junk food like chips and sweets by nine months of age, but only a third have more than one portion of vegetables daily, a study has found.

The research, released as part of the Growing Up In New Zealand study, looked at how closely the Ministry of Health nutrition guidelines for infants are being followed.

Only 32.8 percent of infants met the vegetable intake recommendation of twice or more daily, 55.3 percent ate vegetables once a day, and 11.9 percent less than daily or never.

For fruit consumption only 48.2 percent ate fruit once a day and 14.7 percent ate fruit less than daily or never.

Just one in five infants were eating both fruit and vegetables at least twice a day and one in 16 infants did not eat fruit or vegetables daily.

On a more positive note, 80 percent of infants were meeting the guidelines for iron-rich food such as meat and other plant-based alternatives.

The study says 53 percent had tried food deemed inappropriate, such as sweets, chocolate, hot chips or potato chips and 39 percent had tried either coffee, cordials, juice, tea or soft drinks at nine months of age.

One of the research's authors, University of Auckland Associate Professor Clare Wall says this age was a critical window for growth and development.

"We know that not getting optimal nutrition in early life can have an effect on growth and development and can lead to unhealthy weight gain at a later age," she says.

She says foods high in sugar and salt are likely being given to infants because of food being eaten by the wider family.

"If those foods are available in the home and commonly eaten by other members of the family, then I suppose it's probably quite usual for infants to be consuming them as well," she says.

She says additional support may be needed for those families to make better choices for both their infants and children.