A health expert is warning cutting out high fibre grains and cereals unnecessarily could have serious consequences.
Virtuous eating and exercise regimes paraded on social media have given rise to niche diets like gluten free.
Gluten is a mixture of two proteins naturally found in cereal grains like rye, barley and wheat.
It's mainly found in baked goods, like bread, pizza cakes and pastries, as gluten gives dough its elasticity.
Wellington dietitian Sarah Elliott has seen increasing numbers of clients becoming low in iron and fibre after going gluten-free without the right advice.
She said a gluten-free diet is not necessarily healthy, especially if it still contains a lot of processed foods.
"We have people coming in, becoming gluten free and then becoming more constipated because their fibre intake has come right down so we need to teach them to get enough fibre in their diet," she said.
Ms Elliott pointed to a mass of misinformation available on the internet about what's good for you and what's not, as a reason for the rise in people adopting diets without seeing a health professional first.
"I have really intelligent sensible people come to see me and say I don't know what to eat for breakfast anymore."
'The fad has become a trend'
Food retailers have capitalised on the growth in gluten-free demand, striving to provide a wider product range for customers.
Food giant Nestle last week launched a gluten-free plant in its South Auckland factory, and Wellington store Commonsense Organics has worked to stock better quality gluten free products.
According to the store's merchandise manager Teva Stewart, "we've seen the nutritional value of the products increase exponentially so now you can get pasta made with mung beans and bread made with cassava flour".
"Gluten free was probably considered a fad about 15-years-ago, but 15-years-later it's still here," he said.
"The fad has become a trend the trend has become a lifestyle."
It is estimated about 1 in 70 New Zealanders has Coeliac disease, which means they must adhere to a strict gluten free diet for medical reasons as gluten can damage their intestines.
Coeliac New Zealand president Catherine Murray said anyone with symptoms – like bloating, gas, constipation, fatigue and abdominal pain should get tested before starting a gluten free diet.
"Eighty percent of those (1 in 70) aren’t diagnosed or don’t know they have the disease."
Coeliac Awareness week is coming up in May.