London(CNN) Most yogurts have deceptively high levels of sugar, with organic yogurts among the worst offenders, a new study warned.
Researchers analyzed more than 900 yogurt brands found in UK supermarkets and found that only 9% can be classed as low in sugar -- containing less than five grams of sugar per 100 grams -- while just 2% of children's yogurts are low in sugar.
The study also warned of the "health halo" effect that leads consumers to automatically assume that organic products are healthier, despite this category of yogurt being the most sugary.
Organic yogurts contained an average of 13.1 grams of sugar per 100 grams, which is roughly equivalent to three sugar cubes, while children's yogurts averaged 10.8 grams. Greek and natural yogurts were the least sugary varieties, with an average of five grams per 100 grams.
Yoghurts marked as "desserts" contained the most sugar, with an average of 16.4 grams per 100 grams.
"While yogurt may be less of a concern than soft drinks and fruit juices, the chief sources of free sugars in both children and adult's diets, what is worrisome is that yogurt, as a perceived 'healthy food', may be an unrecognized source of free/added sugars," the authors wrote.
The NHS recommends that adults not exceed 30 grams of free sugar -- defined as sugar added to or naturally found in foods -- each day, while parents are encouraged not to give children under 4 foods with added sugar.
"A lot of people don't actually realize how much added or free sugars are in yogurt," Bernadette Moore, associate professor at the University of Leeds' School of Food Science and Nutrition and the study's lead researcher, told CNN. "If you're watching your weight, sugar is sugar, no matter what."
"Parents need to realize that all yogurt is not exactly the same, and it's the natural yogurts which are healthier," she added.
Moore also highlighted that all consumers should beware of the marketing of organic products.
"People do look at organic products and think they're better for them -- if you ask consumers, their responses are that they think they are healthier," she said.
In 2016, Public Health England (PHE) urged the food industry to achieve 20% cuts in sugar levels in everyday foods by 2020, with the goal of 5% within the first year. In May, the agency announced that yogurt manufacturers had met the target for year one.
Alison Tedstone, chief nutritionist at PHE, said: "The food industry has a key role to play in reducing the amount of sugar we buy and consume."
The yogurt category was the only one to surpass the 5% sugar-reduction target in the first year, and Tedstone expressed hope there would be further reductions posted in next year's report.