Swedish researchers have found a way to improve people's lifetime incomes, increase their chances of getting a university education and even make them grow taller.
The secret is to simply give them a free lunch while they're in primary school, whether their families are rich or poor.
"Our study shows that universal efforts that provide children with nutritious meals can be seen as a long-term investment," said Dan-Olof Rooth, professor of economics at the Institute for Social Research (SOFI) at Stockholm University, who co-authored a new study into the Swedish school lunch programme.
"In other words, ensuring that children eat well also pays off later in life in terms of health, education and income."
The Swedish school lunch programme was rolled out in the mid-20th century, providing all students with a healthy feed - regardless of their parents' incomes. The researchers looked at data from 1959 to 1969, during which the programme expanded to cover 265 different municipalities.
Comparing outcomes with those students who lived in areas without access to the programme, they found a 3 percent improvement in lifetime earnings, a small increase in the likelihood of attending university and a height advantage of almost 1cm.
"We also noted some interesting differences in the effects, where children from poor households benefited the most, even if children from all households benefit to a certain extent," said lead author Lund University economist Petter Lundborg.
"Students from poor families had a 6 percent higher lifetime income, and students from other households had about a 2 percent higher lifetime income. The reform thus benefited all students, from both poor and rich families."
The researchers said the improved nutrition for those getting lunches at school was directly responsible for their improved health, and therefore height, and previous research has found a link between height and income.
Introducing lunches didn't improve attendance, which was already high in mid-20th Century Sweden so it's suspected that having a belly full of healthy food made students "more receptive to what they were being taught".
The New Zealand Government launched its lunches programme in 2019, focusing on "students in schools with high levels of disadvantage". By the end of this year, it's estimated the Ka Ora, Ka Ako programme will be in schools covering 215,000 students, some of them secondary - about 25 percent of all schoolkids in the country.
Prime Minister Jacinda Ardern in May said she wasn't opposed to rolling it out nationwide, but called it "quite costly". Its initial funding in 2019 was $220 million for two years. The maximum cost is $5 per meal for primary school students and $7 for secondary.
The study notes Sweden wasn't a poor country at the time the scheme was rolled out, and most parents could afford nutritious meals - they just didn't make them.
"The program was introduced in a wealthy country, where school children did not face food insecurity but where parents lacked knowledge about healthy food habits. The reform changed the nutritional content of the lunch meals and made pupils switch away from less nutritious lunch bags or lunches at home. This is of relevance for many countries today that plan to improve, or have improved, the nutritional content of the food served in schools."
The overall economic benefit of the programme was four times what it cost, the analysis showed.
"Our results show significant long-term economic benefits of school meals," said Prof Lundborg. "You get a lot of 'bang for your buck' - it is extremely well-invested money."
An earlier attempt to introduce school lunches by then-Green Party leader Meteria Turei and recently departed Mana MP Hone Harawira was voted down in 2014, then-Prime Minister John Key saying there wasn't a widespread problem that school lunches would fix.
The Children's Commissioner has called universal free lunches a "birthright" whose benefits are "incalculable".
The Swedish research was published in journal The Review of Economic Studies.