NHD-EXTRA: FOOD & DRINK
DRIED FRUIT AND DENTAL HEALTH Michèle J Sadler Rank Nutrition Ltd Michèle is Director of Rank Nutrition Ltd, which provides nutrition consultancy services to the food industry. Michèle has a BSc in Nutrition (University of London), a PhD in Biochemistry and Nutritional Toxicology (University of Surrey) and is a Registered Nutritionist.
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Dietitians will be well aware that traditional dried fruits, such as apricots, prunes and raisins, are high in fibre and low in fat. Depending on the type, dried fruit can also make a valuable contribution to intake of micronutrients, including some that may be vulnerable in people’s diets such as iron, vitamin K, potassium and magnesium. Regular consumption of dried fruit can thus make a useful contribution to achieving dietary guidelines. DIETARY ADVICE ON DRIED FRUIT
The new Eatwell Guide booklet advises that a serving of 30g dried fruit counts as one of ‘five-a-day’; it also advises that consumption should be restricted to mealtimes.1 Similarly, NHS Choices proposes that dried fruit is best enjoyed as part of a meal, not as a between-meal snack, to reduce the risk of tooth decay.2 This raises the question how strong is the evidence that dried fruit may be harmful to teeth and whether such restrictive advice about the timing of consumption is warranted by the evidence? In view of this, the Californian Prune Board commissioned a comprehensive review of the research base that prompted this dental health advice,3 as it seemed to be historic. POTENTIAL MECHANISM FOR EFFECT ON TEETH
The two main concerns about dried fruit and dental health relate to the sugar content and that dried fruit may be ‘sticky’ and adhere to the teeth. Any detrimental effects on teeth would be initiated by the sugars present in dried fruit dissolving into saliva and diffusing into dental plaque, where it is available for fermentation by the acidproducing bacteria (mutans streptococci) that reside in plaque. If plaque pH falls below pH 5.5, tooth enamel is subject to demineralisation and if this persists over time, it can lead to a carious lesion, a late stage of dental caries.
A number of factors may influence this solubilisation process, including the texture of dried fruit, the location of the sugars in the dried fruit matrix, the length of time that dried fruit stays in the mouth, the frequency and force of chewing and characteristics of the dental plaque such as its thickness. TYPE OF SUGARS IN DRIED FRUIT
The type of sugars in dried fruit has been somewhat controversial. In 1989, the UK adopted a classification of sugars based on their location within foods. Intrinsic sugars are located within the cellular structure, while NMES are those sugars not located within cells, but excluding those present in milk. Fruit and vegetables contain intrinsic sugars and fresh fruit, as consumed in the normal diet, is not considered to contribute to dental caries. Since an animal study and an in vitro study had previously suggested a cariogenic potential of dried fruit, it was postulated that it is unclear if the sugars in dried fruit should be classed as intrinsic, as the cellular integrity of dried fruit may be disturbed during the drying process.4 As there is no method to distinguish between intrinsic sugars and NMES, the sugars in dried fruit were arbitrarily classified as 50% NMES and 50% intrinsic (noted in Moynihan, 20035), though this was not universally accepted.6 Hence the sugars in dried fruit were partly caught within the type to be restricted. www.NHDmag.com February 2017 - Issue 121
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