A new US study has found that new mothers of young children are heavier and eat more fatty and high-sugar foods than women without children.

The University of Minnesota researchers collected data from 1520 adults with an average age of 25, including parents with children younger than five years old, and found that parents were less active, the Associated Press reported.

The researchers found that mothers ate more fatty foods and drank about seven sugary drinks weekly, compared to about four among childless women.

The mothers surveyed also consumed an average of 9910 kilojoules a day, around 1550 more kilojoules than women without children, and mothers exercised less than their childless counterparts.

As a result, mothers had a slightly higher average body mass index (27) than childless women (26).

Fathers included in the study were found to eat the same daily amount of kilojoules as childless men and both had an average BMI of about 25, but fathers also did less physical activity.

Study co-author Dr Jerica Berge said the research "wasn't about blame" but "about identifying ... a very high-risk time period [for parents]". She said doctors should be aware of the heightened risks so they can provide appropriate advice to parents.

The researchers, who publish their results in the Journal of Pediatrics, said the solution could include diet advice, parent-child exercise classes, or simply getting parents to take walks with their kids.

The researchers took race, income and other factors into account, which may have affected participant's diet.

But the study did have limitations, including limited data on the women who had recently given birth and could still be holding pregnancy weight and information about single parents was not included.

American Dietetic Association spokeswoman Sarah Krieger, who works with new mothers, said some of those involved in the study may be suffering from postpartum depression, which could have affected their eating and exercise habits and the results of the survey.