Pure fruit juice is having its health rating slashed - putting it on the same, or even lower level, than diet coke.

Most New Zealand juices without any added sugar receive an automatic rating of five stars, but new Trans-Tasman rules mean they will be judged on their natural sugar content.

Nutritionists say the key message is that people should be drinking water.

Professor of Population Nutrition at Auckland University Cliona Ni Mhurchu Cliona Ni Mhurchu has been interviewed by RNZ and TV3 - Newshub about the decision and what it means for the food industry.

Listen to the RNZ interview here and TV3 here.