PERSPECTIVES WITH DR ALAN BARCLAY

DRIED FRUITS KEEP IT REGULAR
The World Health Organisation classifies traditional dried fruits like apples, apricots, dates, figs, prunes, pears, raisins and sultanas as “fruit”, and like fresh fruit, their natural sugars content is not defined as “free sugars”. In contrast, some dried fruits such as blueberries, cranberries, cherries, strawberries and mangoes are often infused with sugar syrup or fruit juices prior to drying – although these fruits can also be dried without any infusion, which adds to consumer confusion. Candied fruits such as pineapples and papaya have a high added sugar content, but this is generally not mentioned on food labels. Check the nutrition information panel.

There are a number of reasons why sugar and or/sugar syrups are added to dried fruit:

• It improves palatability to tart fruits (e.g. cranberries) by adding sweetness. 
• It helps a sweet fruit remain soft throughout its shelf life since sugar and sugar syrups act as natural humectants (a kind of food additive used to reduce moisture loss). 
• Sugar and or/sugar syrups also have a preservative function by helping to reduce the water activity within the fruit, decreasing microbial growth. 

THE NUTRIENT CONTENT of traditional dried fruits is similar to the fresh fruit equivalent, though more concentrated due to their lower water content. Traditional dried fruits are therefore good sources of dietary fibre and a number of micronutrients including vitamins A, certain B group vitamins, Vitamin K and potassium, but unlike most fresh fruits, they are not good sources of vitamin C which is lost in processing.

Dried fruits are high in a range of dietary fibres and other bioactive compounds with prebiotic effects (e.g. polyphenols), while some dried fruits (e.g., prunes and apricots) also contain high levels of the sugar alcohol sorbitol, which has laxative properties and also increases stool weight.

GUT HEALTH is of major public health importance around the world and low stool weight, delayed gut transit time and alterations in the gut microbiome along with their associated metabolites (e.g. short-chain fatty acids), are key risk factors for common gastrointestinal disorders (e.g. constipation, diverticular disease, colorectal cancers, etc.), all of which can be manipulated via the diet. For example, increased stool weight is one of the major mechanisms underlying the relationship between high intakes of dietary fibre and reduced risk of colorectal cancer.

There are currently a small number of high-quality human studies that show some benefits of traditional dried fruits (e.g. prunes) in some areas of gut health (e.g., stool weight/frequency). Like many areas of research, more studies are warranted to extend our knowledge of the potential beneficial impact for public health, particularly investigating the full range of dried fruits and investigating the relative contribution of dietary fibre and sorbitol to these effects.

DRIED FRUITS AND DENTAL HEALTH There is some concern about the potential impact of dried fruit on dental health, particularly dental caries – where bacteria in dental plaque ferment free sugars resulting in acid production. Free sugars can come from both sugary and starchy foods (certain starches are broken down into the sugar glucose in the mouth by salivary amylase). When the acid level (pH) falls below 5.5 in the mouth, tooth enamel can soften. After repeated insults it can result in the formation of tooth cavities, eventually resulting in dental caries.

For dried fruit to contribute to dental caries, the sugars present in the food matrix need to be solubilised and diffuse into dental plaque. The rate of solubilisation depends on the location of the sugars in the dried fruit matrix (inside or outside the cellular structure), the fruit texture, and the force and frequency of chewing. Other influential factors include plaque thickness, the length of time dried fruit stays in the mouth allowing the sugars to dissolve, and the buffering capacity of saliva (which affects acid levels in the mouth). The different categories of dried fruit may, therefore, behave differently in the mouth.

With a pH of 7, saliva is the tooth’s natural protective mechanism, buffering the effect of oral acids. Following each eating episode, there is a time lapse of approximately 40 minutes before resting oral pH is restored. Therefore, eating less sugary and starchy foods between main meals may help decrease the risk of dental caries.

A recent systematic review addressed the perception that dried fruit adheres to teeth and is detrimental to teeth because of its sugars content. No randomised controlled trials were identified that explored dental caries as an outcome per se, as this would be unethical. One observational study was identified but the intake of dried fruit was too low for any meaningful analysis. One study investigated the effect of whole and juiced fruits and vegetables and whole raisins individually on net demineralisation of enamel compared with positive and negative controls, and found statistically significant net demineralisation with all test foods compared with the negative control, suggesting that raisins were not more detrimental to teeth than fresh fruits or vegetables.

Studies of oral clearance have used different methods and endpoints, and improved techniques for assessment are needed. A recent systematic review found one study that compared subjective perceptions of the stickiness of 21 foods in 315 adults with an objective measure of retention of 9–30g portions of the same foods in 5 young adults. There was a low correlation between perceived stickiness and oral clearance rates (r=0.46) suggesting that most people cannot accurately assess the stickiness of foods. This study also showed low to intermediate retention (based on dry weight retained) for raisins and figs respectively, and intermediate clearance rates (weight retained with time). Another study also measured food retention of 48 snacks and found that dates were ranked 15/48 for carbohydrate retention at 5 minutes, and raisins were ranked 29. This study also suggested that dried fruits do not adhere to teeth more than alternative snacks, such as cookies (biscuits), crackers, apple pie and candies (sweets). A third study that measured the quantity of oral lactic acid production as a marker of oral clearance concluded that foods containing sugars, but no starch, clear the oral cavity more rapidly than starch-containing foods.

It would, therefore, seem prudent to re-evaluate the concept of “sticky” foods and the effect of dried fruits on dental health in general.

DIETARY GUIDELINES encourage us to consume more fruit, with most recommending we aim for a minimum of 2 serves each day including fresh, frozen, canned and traditionally dried fruit. However, few of us do get 2 serves a day; and dried fruit makes up only a small fraction of our total fruit intake. Here are the recommendations for the USA, the UK and Australia. 

• USA – all forms of fruits, including fresh, canned, dried, and frozen, are recommended as part of a healthy eating pattern and ½ a cup of dried fruit is considered equivalent to 1 cup of fresh fruit. 
• UK – dried fruit is also considered a healthy option equivalent to fresh, canned or frozen fruits and one serve is based on a portion size of approximately 30g (1oz). However, to reduce the risk of tooth decay, it is recommended that dried fruits are eaten with main meals and not as snacks. 
• Australia – unlike the USA and UK, dried fruits are not considered an everyday food due to their “stickiness”, and higher energy density. Like the UK, a 30g (1oz) portion is considered an appropriate serve size, but to be consumed only occasionally. High quality scientific evidence does not support current advice in Australia to limit dried fruit consumption. 

Read more:

• Dried Fruit and Public Health: What Does the Evidence Tell Us? 
• Eat well – NHS 
• DIETARY GUIDELINES FOR AMERICANS 2015-2020 
• The Australian Dietary Guidelines

Alan Barclay, PhD is a consultant dietitian and chef (Cert III). He worked for Diabetes Australia (NSW) from 1998–2014 . He is author/co-author of more than 30 scientific publications, and author/co-author of  The good Carbs Cookbook (Murdoch Books), Reversing Diabetes (Murdoch Books), The Low GI Diet: Managing Type 2 Diabetes (Hachette Australia) and The Ultimate Guide to Sugars and Sweeteners (The Experiment, New York).

Contact: You can follow him on Twitter or check out his website.