Diet and Tooth Decay: Why Frequency Matters as Well as Quantity
How often you have sugar matters as well as how much. Plaque turns acidic within a minute of sugar and takes 20 to 40 minutes to recover, so sugar spread across the day means more acid attacks than the same sugar at one meal. This guide covers how sugar and acid damage teeth: the acid attack cycle, hidden sugars, acidic foods and drinks, erosion, swaps and brushing, from UK guidance.
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Clinically reviewed by Dr Ibraheem Ijaz, dentist · GDC 301711
Medical disclaimer: This page is for general information only. It does not replace an examination or treatment by a dentist.
Dr Ibraheem Ijaz, GDC 301711, principal dentist at Deepcar Dental Care, reviewed this page. He is a General Dental Practitioner with a BDS, BSc (Hons), MSc (Leeds) and postgraduate qualifications in implant, restorative and aesthetic dentistry.
Why does how often you have sugar matter?
How often you have sugar matters because every sugar intake starts a new acid attack on your teeth. Delivering Better Oral Health (DBOH), England's prevention toolkit for dental teams, explains why.
Take six sweets. Eaten together at the end of a meal, they count as one sugar intake, so one acid attack. Eaten one at a time through the day, they make six intakes, so six acid attacks. DBOH advises having sugary food and drink as part of a meal, not as a between-meal snack.
Amount still counts. Drawing on the Scientific Advisory Committee on Nutrition (SACN), DBOH says studies in children and teenagers link more sugar with more decay, with less evidence in adults. More frequent intake of foods and drinks with free sugars, though not of total sugars, is linked with more decay too. To lower dietary caries risk, its advice is to cut both.
What happens during an acid attack?
An acid attack is the drop in plaque pH after sugar, when bacteria turn the sugar into acid and minerals start to leave the enamel.
DBOH uses the Stephan curve, a graph of plaque pH after sugar, to show the cycle. Plaque pH falls within one minute of eating sugar, then slowly recovers over 20 to 40 minutes as saliva washes and buffers the acid and the sugar is used up. When sugar intakes are spaced some hours apart, minerals have a good chance to return, which works better with fluoride. Repeated sugar keeps the pH low for long periods, leaving too little time for effective repair.
The pH at which enamel starts to dissolve is the critical pH. It is often quoted as 5.5, but a peer-reviewed 2003 paper by Dawes explains it is not fixed. It depends on the calcium and phosphate in saliva and plaque fluid, and in plaque fluid it may be as low as 5.1.
Saliva is stimulated at mealtimes and much reduced during sleep, DBOH notes, so it advises avoiding sugary food and drink at bedtime. Our page on how cavities form explains what happens once enamel breaks down.
How are tooth decay and dental erosion different?
Tooth decay (dental caries) comes from acid that plaque bacteria make from sugar. Dental erosion comes from acid in food, drink, some medicines or the stomach, with no plaque involved.
DBOH counts erosion as one cause of tooth wear, alongside attrition and abrasion. Erosion has no clear-cut critical pH, because a drink's minerals, such as calcium, may lessen its effect. Once tooth tissue is lost to wear, it cannot be reversed, DBOH says.
Acidic drinks are generally accepted as the most common unhealthy drinks for erosion, DBOH says. For high-risk people with signs of wear, its list of possible acid sources includes fizzy drinks other than unflavoured sparkling water, fruit juices such as orange, smoothies, fruit teas, sports and energy drinks, wine, acidic sweets and vinegar-based foods such as pickles, though the list rests on expert opinion and low-quality evidence. Swishing or holding drinks in the mouth may prolong the effect.
Our page on dental erosion covers acid wear in depth, and the tooth wear page explains worn teeth and their causes. Tooth wear can progress over time, though not inevitably, DBOH says.
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What are some practical swaps for your teeth?
Practical swaps reduce how much and how often your teeth meet sugar or acid, and DBOH and NHS guidance suggest several:
- Water or milk between meals, and tea or coffee without sugar. DBOH says unflavoured water, milk, tea and coffee have the lowest erosive potential.
- Whole fresh fruit, or fruit frozen or canned in juice, as a between-meal snack. DBOH says honey, smoothies, fruit juice, dried fruit and fruit in sugary syrup belong with meals.
- Sugar-free versions of medicines, which the NHS recommends.
DBOH says the general population should not be advised to eat less fruit, and snacking on fruit should not be discouraged unless it is identified as a risk factor.
When should you brush around meals and drinks?
Brush at least twice a day, last thing at night and at one other time, with fluoride toothpaste, DBOH advises. Spit out rather than rinsing, the NHS adds. Our page on how fluoride protects teeth covers toothpaste strengths.
Concerns have been raised about brushing soon after acidic food. DBOH says there is no strong evidence that brushing timing is of great importance in preventing tooth wear, or that everyone should delay brushing after erosive meals. After vomiting, it advises rinsing with water rather than brushing, and medical advice where reflux or an eating disorder is a source of acid.
When should you speak to your dentist?
Speak to your dentist if you notice possible signs of decay or wear. Signs include:
- White, brown or black spots on a tooth. The NHS lists these among the signs once decay makes a hole, and advises seeing a dentist as soon as possible if you think you or your child has tooth decay.
- Changes in the shape of your teeth, such as flattened or shorter-looking front teeth. DBOH says visible changes to tooth shape can appear as tooth wear progresses.
Frequently asked questions
Are fruit juices bad for teeth?
Fruit juice can harm teeth in two ways. Its sugars are free sugars, even when unsweetened, and many juices are acidic. The NHS advises keeping fruit juice and smoothies to 150ml a day in total, drunk with a meal. Sugars in whole fruit are less likely to cause decay, because they stay inside the fruit's structure, the NHS explains.
Do sugar-free drinks damage teeth?
Sugar-free drinks avoid the sugar that feeds decay, but being sugar-free does not stop a drink being acidic. DBOH says sparkling water flavoured with fruit or lemon has high erosive potential, while unflavoured sparkling water is fine for teeth. Its expert-opinion list for worn teeth also names certain sugar-free sweets.
Can alcohol affect your teeth?
Alcohol can affect teeth in two ways. DBOH counts all the sugars in alcoholic drinks as free sugars, and its expert-opinion list for worn teeth names wine, alcopops and fortified wines with fruity flavours as possible sources of acid wear. The NHS includes not regularly drinking more than 14 units a week in its advice on preventing tooth decay.
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Diet is one part of preventing tooth decay, and the options in this section cover other parts.
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