Nurses treating children in poor areas see first-hand the skin and lung infections that may be linked to poor diet.
"We get a lot of students in every week who haven't had food to eat: no breakfast, they don't bring lunch," said Teresa Mountain, a nurse at Sir Edmund Hillary Collegiate, which serves children from Years 1 to 13 in Otara, South Auckland.
"They lack energy and vitality. They also can get a lot of sores and boils because their immune system is very low.
"We are fortunate in that we have breakfast programmes we run here through all the schools and in the middle and junior schools a resource room with fruit donated."
Her nursing colleague Cheryl Grbic said that although some students came to class hungry, eating unhealthy food - such as meat pies from the dairy on the way to school - was a greater problem than actual hunger.
Researchers have found links between poor nutrition and a number of illnesses in children, particularly pneumonia and bronchiolitis.
Some also suspect there may be a connection to New Zealand's high rate of serious skin infections and rates of acute rheumatic fever which, for Maori and Pacific children, are some of the highest in the world.
A third of New Zealand children are obese or overweight. Obese children are at increased risk of deficiencies of iron and vitamin D, a substance we derive mainly from exposure to sunlight as well as some from diet. Iron deficiency increases the likelihood of also being short of zinc and vitamin A.
An Auckland study identified deficiencies of iron and vitamins A and D in at least 10 per cent of young children, leaving them at risk of conditions including rickets, physical and mental development problems and, in extreme cases, blindness.
A separate study found zinc intake was insufficient for some. Zinc deficiency may be linked to an increased risk of infections.
Dr Cameron Grant, associate professor of paediatrics at the University of Auckland, said research on hospitalised New Zealand children with pneumonia showed that although heavier than the world average for their height and age, they were lighter than other New Zealand children, raising questions about diet.
"In order to have sufficient nutrients from diet to be protected from pneumonia, we have to eat a diet that contains excessive energy in New Zealand. I think our diet is energy rich, but nutrient poor.
"The relationship may be that poor nutrition in early life results in you having more frequent and more severe infections, altering the way that the body's immune system responds to infections."
Professor Grant said many European countries fortified foods with vitamin D, but he could not give advice on this until the completion of a study that was giving vitamin D supplements to pregnant women and infants.
"If you don't have much money for food, then you are not going to be able to afford some of the foods that have the best nutritional value, like fresh fruit.
"The United States' solution has been to provide free nutritious food to pregnant women and young children."