Obese child Lu Zhihao
Lu Zhihao, 4, shows his empty rice bowl to his teacher during lunch time at a kindergarten in Foshan, Guangdong province March 29, 2011. Lu, who is 1.1m tall and weighs 62 kg, put on weight dramatically since his appetite grew when he was 3 months old. His worried parents took him to several hospitals, but the reason for his obesity remains unknown, though it is possibly due to his dietary habit, according to local media. Picture taken March 29, 2011. Reuters/Joe Tan

A new study debunks the common idea of public health experts that children who eat more vegetables and fruits are less likely to eat more junk food. Researchers found no evidence for the link between frequently eating healthy foods and eating less of unhealthy foods, and suggest children tend to consume foods high in sugar, salt and fat similar to the amount of healthy foods they eat.

The study, published in the Maternal and Child Health Journal, shows pre-schoolers from low-income neighbourhoods in Columbus in the US ate unhealthy foods as many times as they ate fruits and vegetables and drank milk each day. In addition, these children consumed junk foods similar to those who rarely ate healthy foods.

"We assumed that children who ate a lot of healthy foods would also be children who did not eat a lot of unhealthy foods," said lead researcher Sarah Anderson, an associate professor of epidemiology at The Ohio State University. "I just thought that was the way the world was and it turned out not to be the case."

The researchers noted the study needs to be replicated on a larger scale before making policy changes to fight childhood obesity. However, they believe the findings could lead to changes in conversations on improving children's diets and reducing rates of childhood obesity, they added.

The researchers suggest policymakers should soon consider the negative effects of increasing consumption of health foods. Health experts commonly advise adding "good" foods rather than avoiding "bad foods" to lower childhood obesity rate.

"There has been a kind of assumption there that if you encourage people to adopt healthy eating that it naturally leads to a decline in unhealthy eating," said co-author Phyllis Pirie, professor of health behaviour and health promotion at Ohio State.

The findings come from surveys with parents or guardians of 357 children aged two to five. Researchers categorised foods and drinks as healthy and unhealthy and asked about the children's diets.

Healthy food choices include fruits, vegetables and milk, while unhealthy choices include sweetened drinks, fast food, sweets and salty snacks.

Results show no evidence, regardless of the children’s age, that those who frequently ate healthy foods were less likely to consume unhealthy foods. However, Anderson said the findings does not mean parents and policymakers should stop efforts to increase intake of more-nutritious foods.

However,sc the study questions the idea that good automatically replaces bad, she added. The team is currently conducting a larger national study across the US to support their findings.