A diet heavy on cheap, modern food like instant noodles that fills bellies but lacks key nutrients has left millions of children unhealthily thin or overweight in Southeast Asia, experts say.

Not only do foreigners like the taste of instant noodles, they also enjoy experimenting with different ingredients to create unique dishes. Photo: Li Hao/GT

The Philippines, Indonesia and Malaysia have booming economies and rising standards of living, yet many working parents do not have the time, money or awareness to steer clear of food hurting their kids.

In those three nations, an average of 40 percent of children aged five and below are malnourished, higher than the global average of one-in-three, according to a report out Tuesday from UNICEF, the UN children's agency.

"Parents believe that filling their children's stomach is the most important thing. They don't really think about an adequate intake of protein, calcium or fiber," Hasbullah Thabrany, a public health expert in Indonesia, told AFP.

UNICEF said the harm done to children is both a symptom of past deprivation and a predictor of future poverty, while iron deficiency impairs a child's ability to learn and raises a woman's risk of death during or shortly after childbirth.

To give some sense of scale to the problem, Indonesia had 24.4 million children under five last year, while the Philippines had 11 million and Malaysia 2.6 million, UNICEF data show.

Mueni Mutunga, UNICEF Asia nutrition specialist, traced the trend back to families ditching traditional diets for affordable, accessible and easy-to-prepare "modern" meals.

"Noodles are easy. Noodles are cheap. Noodles are quick and an easy substitute for what should have been a balanced diet," she told AFP.

The noodles, which cost as little as 23 US cents a packet in Manila, are low on essential nutrients and micronutrients like iron and are also protein-deficient while having high fat and salt content, Mutunga added.

Indonesia was the world's second-biggest consumer of instant noodles, behind China, with 12.5 billion servings in 2018, according to the World Instant Noodles Association.