In a recent narrative review published in the Nutrients Journal, researchers retrieved articles from multiple sources, including PubMed, MedLine, and Web of Science, discussing the effects of dried fruits on overall gastrointestinal (GI) health, including gut microbiota, cardiovascular disease (CVD) risk, type two diabetes (T2D), bone health, and diet quality.
More importantly, the researchers discussed the mechanisms possibly involved in these processes and highlighted dried fruits' phytochemical composition and their bioavailability and accessibility.
Study: Dried Fruits: Bioactives, Effects on Gut Microbiota, and Possible Health Benefits—An Update. Image Credit:5PH/Shutterstock.com
Background
Due to their high fiber content and antioxidant properties, dried fruits have multiple health benefits. In addition, they are shelf-stable, which makes them a convenient substitute for fresh fruits. Dried fruits contain several bioactive compounds broadly classified as phytochemicals, including phenolics, carotenoids, stilbenes, chalcones/dihydrochalcones, phytoestrogens, and flavonoids.
More recently, studies have found associations between dried fruit consumption on gut microbiota composition and functionality. Gut microbiota contributes to metabolic health; thus, identifying dietary strategies promoting metabolic health through modification of the gut microbial population should be a priority.
In addition, there is a need for an in-depth evaluation of the biological activity of the bioactive compounds in dried fruits and their bioaccessibility and bioavailability.
About the study
In the present narrative review, researchers restricted their literature search to articles published from 2000 onward to improve contemporary relevance. They covered articles on primarily seven topics, for instance, the phytochemical composition of frequently consumed dried fruits.
However, they examined selected articles in detail to compile evidence from in vivo and in vitro studies on the effects of commonly consumed dried fruits on cardiometabolic and GI health.
This helped the researchers provide updates on the phytochemical composition of dried fruits and mechanisms possibly involved in their biological effects. Finally, they made dried fruit consumption recommendations based on the reviewed evidence.
Effect of dried fruits composition
Alasalvar et al. showed that dried fruits have diverse phenolic profiles. However, the exact phenolic profiles of dried apples, peaches, and pears are unknown. They documented that nine dried fruits, viz., apples, cranberries, apricots, dates, peaches, pears, figs, prunes, and raisins, comprised phenolic compounds, such as anthocyanins, flavonols, flavones, phenolic acids, etc.
For instance, carotenoids (such as β-carotene) are plant pigments responsible for bright yellow, red, and orange hues in many vegetables and fruits and are abundant in all dried fruits except seedless raisins, though in variable quantities.
Apricots are the richest source of β-carotene, followed by peaches and prunes, with 2,163, 1,074, and 394μg/100 g of β-carotene in these dried fruits, respectively. Apricots, dates, prunes, and raisins also contain phytoestrogens, which are absent in dried apples, figs, peaches, and cranberries.
Studies should aim to comprehensively analyze different phenolic compound classes, viz., carotenoids and phytoestrogens in various dried fruits. In addition, consumption of 20 to 30 grams of dried fruits per/day could provide 10 to 16% of the recommended daily fiber intake, depending on the chosen dried fruit.
The oxygen radical absorbance capacity (ORAC) of dried fruits is relatively high, varying with type and variety. For example, golden seedless raisins have the highest ORAC value of 10,450 µmol Trolox equivalents (TE)/100 g.
Bioaccessibility and bioavailability of compounds in dried fruits
Several models mimicking human in vitro GI digestion processes (e.g., oral or salivary digestion and gastric digestion) have investigated the bioaccessibility and bioavailability of compounds in dried fruits cost-effectively.
When phytochemicals and micronutrients in food are released in the GI tract, then they become bioavailable for absorption to exert health effects.
The researchers observed the highest bioaccessibility of phenolics in prunes and the lowest in dates and cranberries in a recent study by Scrob et al. Total sugar content increased after in vitro digestion of coconuts, raisins, and dates but decreased for cranberries, prunes, and bananas. However, in vitro digestion increased the antioxidant activity of most dried fruits.
Another study by Ma et al. investigated the biological activities of kiwifruits, including dried slices under simulated GI in vitro digestion. Though dried kiwi slices and jams had the highest quantity of minerals per unit weight than other forms, dried slices showed the lowest biological activity compared to raw fruit, juice, yogurt, wine, and jelly.
Effect of dried fruits on gut health, and their dietary recommendations
Data are scarce on the effects of dried fruits on metabolite production in the gut and their functions. However, this is certain that the consumption of dried fruits modulates the gut microbiota to influence health.
Most likely, phytochemicals in dried fruits undergo substantial biotransformation by gut microbiota to produce metabolites that influence health. Future mechanistic studies should address these questions.
Suboptimal fruit intake is a key contributor to CVDs, T2D, and neoplasms. So a healthy diet comprising five portions of fruit and vegetables per day, excluding starchy fruits, is the basis for current dietary recommendations by the World Health Organization (WHO). The current dietary guidelines for Americans also recommend four servings of fruit per day, where one-fourth of a cup of dried fruits equals half a cup of fruit.
Unfortunately, fruit consumption in most countries, including some European countries and the United States of America, falls short of current dietary recommendations for fruit (20 to 30 grams per day) per the Global Burden of Disease Study 2017.
Mechanisms driving dried fruits-related health benefits
Human studies have found that dried fruits have a low-to-moderate glycemic index due to their high mineral content, especially potassium and magnesium, and increased fiber content, as well as high levels of antioxidants and phytochemicals.
Thus, frequent consumption of dried fruits benefits cardiovascular, gut microbiota, and bone health. Strikingly, their consumption might also offer therapeutic benefits. However, how dried fruits reduce the severity of chronic metabolic diseases warrants further in-depth exploration.
A recent study evidenced that prunes prevent and reverse bone loss in postmenopausal women and potentially in men. Phytochemicals, such as chlorogenic acid and catechin, have osteoprotective effects; however, the mechanisms governing these effects remain unknown.
Epidemiological and clinical evidence for health benefits of dried fruits
Few epidemiological studies reported favorable associations between dried fruit and CVDs, T2D, and body weight but did not fetch consistent results. Also, the overall diet quality of the participants confounded the observed associations.
More extensive adjustments for dietary and lifestyle factors might help future epidemiological studies investigating dried fruit consumption. Also, those studies should include populations that regularly consume greater dried fruits to fetch stronger evidence of associations between dried fruit intake and health benefits.
There is mixed evidence regarding the effect of dried fruit consumption on CVD risk factors. Several clinical studies have shown their consumption reduces cholesterol and blood pressure without harming glycemic control. Additional randomized controlled trials accounting for the potential confounding effect of body weight are needed to confirm the cardiovascular benefits of dried fruit consumption.
Five clinical trials performed in postmenopausal women have shown that an intake of 50 to 100 grams of prunes daily for three to 12 months has some osteoprotective effects. The other four clinical trials showed the potential anti-inflammatory effects of dried fruits and their beneficial effects on bone formation and resorption markers.
Another study by Hooshmand et al. showed eating 100g of prunes per day increased bone mineral density (BMD) of the ulna and spine in a year compared to 75g of dried apple.
Conclusions
Though an emerging area of research, current evidence on the effects of dried fruits on the human microbiome, bone health, diet quality, and CVD risk is scarce and warrants further investigation. Studies have adequately investigated the phytochemical profiles of different dried fruits; however, an understanding of their bioaccessibility and bioavailability is limited.
The encouraging results from the studies elucidating the benefits of dried fruits, fresh fruits, and juices justify further research. Additional research could also provide a better understanding of the biological effects of dried fruits on major chronic diseases and their underlying biological mechanisms to inform future dietary guidance for dried fruits.
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