For 5-year-old Anthony Guest one 67th of a teaspoon of gluten can cause internal bowel damage.
This week is Coeliac Awareness Week, which draws attention to the growth in the number of Kiwis diagnosed with coeliac disease, and the related demand for verifiable gluten-free food.
Anthony's mother Lizzy Guest said her son was diagnosed two years ago, the week before Coeliac Awareness Week, after they took him to the doctor because he had stopped growing.
The first coeliac test came back negative, though tests did show Anthony was low in iron.
Six months later, another coeliac test returned positive.
Mrs Guest said before Anthony went gluten free his symptoms would include lethargy, stomach pain and joint pain.
After cutting out gluten a lot of things improved with his behaviour, he started sleeping better, his stomach pains disappeared and in about six months he started growing again, she said.
Mrs Guest said they were now "pretty much gluten free as a household" and the main difficulty was eating out, as it was hard with cross-contamination.
It could be a bit tricky with the likes of goodie bags or bake sales at school, she said.
"He just likes to be able to join in like everybody else does."
She said managing her son's diet "just takes a bit more planning" and could be tricky until you got the hang of it.
Anthony is part of the Coeliac Kids Club, run by the Rotorua branch of the Coeliac Society. Mrs Guest said they met regularly to do fun activities, such as learning how to make gluten free sauce.
Coeliac New Zealand general manager Carl Sunderland said the group has developed a gluten free accreditation programme for eateries.
"Simple things like dining out, sports trips, air travel, or even Friday night takeaways become magnified by the risk of gluten slipping into the food."
He said for people living with the disease the threat of being accidentally "glutened" was nerve-racking, and even the tiniest crumb could cause symptoms such as diarrhoea, bloating, severe stomach pain, headaches and vomiting.
"Our new Dining Out Programme will ensure that eateries offering gluten free selections can substantiate their claims - an important aspect in a marketplace where electing to eat gluten free has become quite trendy and many eateries and manufacturers are simply jumping on the bandwagon."
Hard to stomach:
- 65,000 Kiwis have it
- 80 per cent of people do not know they have the condition
- Serious condition that can be diagnosed at any time
- A lifelong auto-immune disorder
- It damages the gut lining and ability to absorb nutrients