Sugar: It's Not the Amount. It's the Frequency.

Sep 6

4 min read

By Dr John Barclay | DRJB Smile Clinic, Ruabon, North Wales

Most people understand that sugar causes decay. Fewer understand why frequency matters more than quantity — and this misunderstanding is responsible for a lot of preventable dental disease.

Here's how it actually works.

What Happens in Your Mouth When You Eat Sugar

Every time you consume sugar — or any fermentable carbohydrate — the bacteria in dental plaque metabolise it and produce acid as a byproduct. That acid drops the pH in your mouth from its resting level of around 7 to as low as 4 within minutes. At pH 5.5 and below, enamel begins to dissolve. This is an acid attack.

The mouth recovers. Saliva buffers the acid and the pH gradually returns to normal over about 20 to 40 minutes. During the recovery phase, remineralisation occurs — minerals from saliva are redeposited into the enamel surface. The damage from a single acid attack, if the mouth is given time to recover fully, can be repaired.

The problem is what happens when the mouth never fully recovers.

Why Frequency Is the Critical Variable

If you eat a piece of cake at lunch, your mouth experiences one acid attack. It recovers. The enamel remineralises. Net damage: minimal.

If you eat five biscuits spread across the morning — one at 9, one at 10, one at 11, one at midday, one at 1 — your mouth experiences five acid attacks in rapid succession. Each one begins before the previous one has fully resolved. The pH never returns to a safe level. The remineralisation window never opens. Net damage: significant, cumulative, and compounding.

The total amount of sugar consumed in both scenarios might be the same. The dental consequence is completely different. This is the Stephan curve in practice — the relationship between sugar exposure events and enamel dissolution — and it's why dentists ask about snacking frequency, not just sugar intake.

The Specific Things That Cause the Most Damage

Slow-dissolving or sticky sugars. Boiled sweets, chewy sweets, cereal bars, dried fruit — foods that maintain sugar contact with the tooth surface for extended periods cause prolonged acid attacks rather than brief ones.

Sugary drinks sipped over time. A can of cola consumed in five minutes is one acid attack. The same can sipped over two hours is a continuous acid attack. Sports drinks, fruit juices, and flavoured waters present the same problem — particularly when consumed during exercise, when salivary flow is reduced.

Sugars between meals. An apple at lunch with a meal is one exposure folded into an existing acid event. An apple at 3pm is a separate acid attack on a mouth that had recovered. The timing is the variable.

Sugars last thing at night. Salivary flow drops significantly during sleep. A sugary drink or snack after brushing at night leaves sugar in contact with teeth without the buffering action of saliva. The acid environment persists for hours.

What This Means in Practice

Reducing the frequency of sugar exposure matters more than reducing the total amount. Practically: keep sweet foods and drinks to mealtimes where possible. Avoid grazing on sugary snacks throughout the day. Drink sugary drinks quickly rather than sipping them over extended periods. Don't eat or drink anything sugary after your last brush at night.

This isn't about eliminating sugar. It's about confining the acid attacks to times when the mouth can recover properly between them.

Where Toothpaste Fits In

Fluoride toothpaste — used at the right concentration and without rinsing afterwards — significantly improves the mouth's ability to remineralise after acid attacks. Spit, don't rinse. The fluoride film left on the tooth surface after brushing continues to work. Rinsing with water immediately after brushing removes it.

This is why the timing of brushing relative to eating matters too. Brush last thing at night, after the final meal or snack. Don't brush immediately after an acidic drink — wait 30 minutes for the enamel to reharden first.

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References & Further Reading

1. Sheiham A, James WPT. A reappraisal of the quantitative relationship between sugar intake and dental caries. Journal of Dental Research, 2014. → Key evidence base for frequency of sugar exposure as the primary determinant of caries risk.

2. Stephan RM. Changes in hydrogen-ion concentration on tooth surfaces and in carious lesions. Journal of the American Dental Association, 1940. → Original paper establishing the pH drop curve following sugar exposure — the Stephan curve.

3. Moynihan PJ, Kelly SAM. Effect on caries of restricting sugars intake: systematic review to inform WHO guidelines. Journal of Dental Research, 2014. → Supports the dietary questioning framework and the link between free sugar frequency and decay.

4. Zero DT. Sugars — the arch criminal? Caries Research, 2004. → Comprehensive review of the relationship between sugar type, frequency, form and cariogenic potential.

5. Public Health England / OHID. Delivering Better Oral Health: An Evidence-Based Toolkit for Prevention. 4th ed. OHID, 2021. → Underpins the dietary advice given in this post.