The country's fibre deficiency is costing the country more than half-a-billion dollars every year.
A report has found $600 million spent on healthcare costs and lost productivity could be saved if adults ate another two servings of grains a day.
Nutrition Foundation CEO Sarah Hanrahan says it's not a quick fix.
"Not if we had serves of cereal tomorrow, bang wallop, there would be hundreds of millions of dollars saved - it's over time."
The report was compiled by an economist, and commissioned by breakfast food company Kellogg's.
More than $200 million could be saved in healthcare costs, and economic activity would be boosted by $403 million, the report claims.
Increasing grain intake reduces the risk of cardiovascular diseases, and type 2 diabetes.
Ms Hanrahan says there's simple ways to slip it into your diet.
"Things like high-fibre cereals; if you're having a lot of white bread, put some wholegrain bread into the mix; when you're having vegetables, put something grain-based in, like corn."
Men average around 22g of fibre a day a Ministry of Health survey found in 2009, but they need at least 30g. Women consumed 18g, well short of the 25g target.