Sugars and substitutes: sugar-free does not mean it will not cause caries

Advice to cut down on sugar is what patients hear most often and follow least, partly because it is generic and partly because labels are hard to read.

The useful distinction is between free and intrinsic sugars. The former are added to foods or present in honey and juices; the latter sit within the cellular structure of whole fruit.

Caries risk concerns almost only the former. A whole apple and a glass of apple juice have very different impacts despite containing sugars of the same nature.

The deciding factor is not total quantity but the number of exposures. Each intake lowers pH for a period, and saliva takes time to bring it back to safe values.

Six sweetened coffees spread across the day cause far more damage than a dessert eaten in one sitting, even though the total sugar may be lower.

This is the most useful message to give, because it is concrete and asks for no sacrifice: cluster rather than spread.

Sugar substitutes have differing potentials. Polyols such as xylitol, sorbitol and maltitol are not fermentable by cariogenic bacteria and do not lower pH.

Intense sweeteners such as aspartame, sucralose and stevia are used in minimal quantities and have no cariogenic potential.

What gets missed, however, is acidity. A sugar-free drink can have a very low pH from phosphoric or citric acid, and cause erosion even without caries.

Diet drinks are therefore not safe for teeth: they are safer for caries and equally dangerous for erosion. It is a distinction patients have never heard drawn.

On labels, sugars appear under many names: glucose syrup, fructose, dextrose, maltodextrins, concentrated juice. One product may contain several, each low in the list.

Sticky foods and those that are sucked prolong exposure more than those swallowed quickly, and a hard sweet counts for far more than a spoonful of sugar in terms of contact time.

In summary: free sugars matter and whole-fruit sugars far less, frequency outweighs quantity, polyols are not cariogenic but sugar-free drinks can be erosive, and on labels sugar goes by many names.