University of Otago research suggests the "glycemic index" (GI) which can put the diet-conscious off potatoes might not be a good measure to follow.
GI relates to carbohydrates' effects on blood sugar levels.
Low GI carbohydrates such as pasta are touted by food manufacturers as not producing blood sugar spikes.
Advice based on GI also featured in diet books.
Researcher Dr Bernard Venn, of the Department of Human Nutrition, said a study of 30 adults found the GI of carbohydrates changed when eaten with other food in a meal.
In the study, three meals were tested; the meals all contained chicken, peas, carrots, kumara and gravy, together with potato or white rice or spaghetti.
The GI for each meal was lower than expected.
It was difficult to predict the GI values in meals and it was unknown why foods' GI changed in combination.
It was possible the way people chewed affected food GI; foods were usually tested by themselves for GI and it was possible this affected how people chewed them, he said.
Dr Venn believed the quantity of food eaten was the key to a healthy diet.
"I don't think people should be too afraid of putting high-GI foods into their meals - our work suggests that having a small amount of potato with a meal isn't going to drive your blood sugar crazy."
The research has been published in this month's American Journal of Clinical Nutrition.
Nova Cafe chef Michal Roth said any food could be unhealthy or healthy depending on the way it was cooked and the quality of ingredients.
