First and foremost, we recommend aiming to avoid all foods with added sugar listed in the ingredients list, which can be found on the food label.
Keep in mind that added sugar may sneakily be listed under less obvious names such as agave nectar, apple juice concentrate, barley malt syrup, cane juice, crystallised fructose, dextrose, fructose, fruit juice concentrate, maltose, molasses, sucrose, and treacle.
It's important to note that the 'sugar' percentage listed on the nutrition label of a food doesn't differentiate between naturally occurring sugar and added sugar.
For example, natural yoghurt contains ~5g per 100g of naturally occurring sugar in the form of lactose, while flavoured yoghurt contains ~15g per 100g of sugar (5g of naturally occurring sugar + 10g of added sugar).
You don't need to worry about sugar from lactose, particularly in yoghurt, as bacteria often digest a lot of the lactose before you eat it.
So, our recommendation to choose foods with less than 5g of sugar per 100g refers to the naturally occurring sugars found in some foods, not added sugar.
Here are the steps we recommend taking when choosing a food product:
Check for any added sugar listed in the ingredients list
If there's no added sugar listed there (in any form), the next step is to check the food label and aim to choose a product with less than 5% naturally occurring sugar (i.e. less than 5g of sugar per 100g of food).