Elsevier

Anaerobe

Volume 26, April 2014, Pages 1-6
Anaerobe

Clinical microbiology
Prebiotic effects of almonds and almond skins on intestinal microbiota in healthy adult humans

https://doi.org/10.1016/j.anaerobe.2013.11.007Get rights and content

Highlights

  • The change of intestinal microbiota in the healthy population.

  • Almond and almond skin intake provoke fecal bifidobacteria & lactobacilli populations.

  • Almond and almond skin intake modify the intestinal bacterial activities.

  • Almond and almond skin possess potential prebiotic effect.

Abstract

Almonds and almond skins are rich in fiber and other components that have potential prebiotic properties. In this study we investigated the prebiotic effects of almond and almond skin intake in healthy humans. A total of 48 healthy adult volunteers consumed a daily dose of roasted almonds (56 g), almond skins (10 g), or commercial fructooligosaccharides (8 g) (as positive control) for 6 weeks. Fecal samples were collected at defined time points and analyzed for microbiota composition and selected indicators of microbial activity. Different strains of intestinal bacteria had varying degrees of growth sensitivity to almonds or almond skins. Significant increases in the populations of Bifidobacterium spp. and Lactobacillus spp. were observed in fecal samples as a consequence of almond or almond skin supplementation. However, the populations of Escherichia coli did not change significantly, while the growth of the pathogen Clostridum perfringens was significantly repressed. Modification of the intestinal microbiota composition induced changes in bacterial enzyme activities, specifically a significant increase in fecal β-galactosidase activity and decreases in fecal β-glucuronidase, nitroreductase and azoreductase activities. Our observations suggest that almond and almond skin ingestion may lead to an improvement in the intestinal microbiota profile and a modification of the intestinal bacterial activities, which would induce the promotion of health beneficial factors and the inhibition of harmful factors. Thus we believe that almonds and almond skins possess potential prebiotic properties.

Introduction

It is well established that the colonic microbiota have a profound influence on health. The human gut contains a large variety of bacterial genera, species, and strains, which are either beneficial (e.g., Bifidobacterium spp. and Lactobacillus spp.) or harmful (e.g., Clostridium spp., Shigella spp., and Veillonella spp.) to host health. The intestinal microbiota play an essential role in influencing the health of the host. They can greatly influence the intestinal environment [1], contributing to the host's health through a variety of mechanisms such as activation of the immune response, production of bacteriocins, nutritional and physical competition with pathogens, and maintenance of an acid environment.

Currently there is great interest in the use of prebiotics as functional food ingredients to manipulate the composition of colonic microbiota in order to improve health [2]. Many food oligosaccharides and polysaccharides (including dietary fiber), such as fructooligosaccharides, inulin, galactooligosaccharides, and other related carbohydrates, are reported to have prebiotic properties. In contrast to a probiotic that introduces exogenous bacteria into the colonic microbiota, a prebiotic aims to stimulate the growth of one or a limited number of the potentially health-promoting indigenous microorganisms, thus modulating the composition of the natural ecosystem [3]. It is not the prebiotic by itself, but rather the changes induced in the microbiota composition that are responsible for its effects. Besides, dietary prebiotics have the potential advantage over some probiotics of not being susceptible to antibiotics [4].

Almonds (Prunus amygdalus L.) are a good source of nutrients such as vitamin E, monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA), arginine, and magnesium [5]. Almonds also contain considerable amounts of potential prebiotic indigestible carbohydrates. Almond skins, which are removed from the almond kernel by hot water blanching, constitute 4% of the total almond weight and are generally treated as a waste product [6]. However, an array of flavonoids, including catechins, flavonols, and flavanones in their aglycone and glycoside forms, have been identified in almond skin. These compounds may contribute to the health benefits associated with almond consumption. Many researchers have studied the functions of almonds in the diet, including lipid regulation [7], [8], antioxidant activity [9], [10], [11], weight control [8], [12], and Yin-Yang balance [13]. It is also reported that, almond or almond skin can serve as a candidate food for potential prebiotic effects [14], [15], [16]. Mandalari et al. [15], [16] investigated the prebiotic effects of almond seeds and almond skins in vitro by using mixed fecal bacterial cultures, and found that after digested by simulative in vitro gastric and duodenal digestion, almond seeds and almond skins significantly increased the populations of bifidobacteria and Eubacterium rectale. The results were consistent with our previous findings. Male SPF Wistar rats were subjected to daily oral treatment with raw almond or roasted almond for 4 weeks to assess the influence of almond intake on the composition of gut bacteria populations. After 4 weeks of treatment, the populations of Bifidobacterium spp. and Lactobacillus spp. in feces and ceca of the rats increased significantly, while the populations of Escherichia coli and Enterococus spp. in feces and ceca of the rats decreased significantly (Zhibin Liu, unpublished results).

Unfortunately, to the extension of our knowledge, there are no available data from clinical studies concerning the prebiotic properties of almonds or almond skins consumption in healthy subjects. The aim of present study was to investigate the effects of daily consumption of either almonds or almond skins on the composition of the fecal microbiota and on selected indicators of microbial activity (fecal pH and water content, activities of β-galactosidase, β-glucuronidase, nitroreductase and azoreductase) in healthy adult volunteers.

Section snippets

Subjects

A total of 48 subjects (24 males and 24 females), 18–22 years of age, were recruited from Fuzhou University. All subjects lived in school dormitories with a similar environment throughout the study period. The eligibility criteria for candidates included being of good health; a nonsmoker; stable weight (deviation of <2.5 kg over the previous 3 months); daily defecation; using no antibiotics, laxatives or other gastrointestinal medications in the 3 months prior to the beginning of the study; and

Characteristics of the study subjects

Throughout the whole experimental period, there were no serious adverse reactions to the diets reported by the subjects, except for 4 subjects in the FOS control group reported mild diarrhea on the first week of FOS ingestion, however they recovered naturally a few days later. All of the 16 subjects in each group were in good health, except for two subjects, one in control group and the other in the almond group who failed to finish the study for personal reasons. The weight, BMI, body fat

Discussion

Healthy adult humans were used as the subjects in this study to evaluate the impact of the consumption of almonds and almond skins on human intestinal microbiota. A total of 48 healthy college students were involved in an intervention trial including a 2-week run-in period, a 6-week treatment period, and a 2-week wash-out period. The 48 subjects were not selected randomly. A screening procedure was carried out first. The criteria were the stability of intestinal bacteria of subjects. In the

Acknowledgments

We are grateful to the Almond Board of California for the financial support of this research. We value the leadership of Dr. Karen Lapsley, Chief Scientific Officer of the Almond Board of California, and Sam Cunningham, chair of the Nutrition committee at the Almond Board of California. The authors thank all volunteers from Fuzhou University for assisting in this project.

References (28)

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