Almonds help increase fibre intake without gut symptoms

Eating almonds provides no prebiotic effect on foecal bifidobacteria abundance and does not induce major changes in other gastrointestinal (GI) microbiota, GI transit, pH, pressure, stool output, or gut symptoms in adults, a study has shown.

Almonds, which contain lipid, fibre, and polyphenols, as well as physicochemical properties, “can [therefore] be incorporated into the diet to increase fibre consumption without gut symptoms,” according to the researchers.

This parallel, three-arm randomized controlled trial (RCT) included 87 healthy adults, who received whole almonds (56 g/d), ground almonds (56 g/d), or an isocaloric control in place of habitual snacks for 4 weeks. Of the participants, 79 were included in the modified intention-to-treat analysis.

The researchers measured gut microbiota composition and diversity using 16S rRNA gene sequencing, short-chain fatty acids (SCFA) using gas chromatography (GC), volatile compounds using GS mass spectrometry, gut transit time using wireless motility capsule, and stool output and gut symptoms using a 7-day diary at baseline and endpoint. They also measured the impact of almond form on particle size distribution (PSD) and predicted lipid release in 31 participants.

No significant differences were observed in mean abundance of foecal bifidobacteria after consumption of whole almonds (8.7 percent), ground almonds (7.8 percent), or control (13.0 percent; q=0.613). Pooled almond consumption also resulted in higher mean butyrate compared with control (24.1 vs 18.2 μmol/g; p=0.046). [Am J Clin Nutr 2022;116:1790-1804]

Notably, almonds showed no effect on gut microbiota at the phylum level or diversity, gut transit time, stool consistency, or gut symptoms. Likewise, almond form (whether whole or ground) had no impact on study outcomes. However, ground almond intake resulted in markedly smaller PSD and higher mean predicted lipid release compared with whole almonds (10.4 percent vs 9.3 percent; p=0.017).

These findings are consistent with those of earlier RCTs, which found no effect of almond consumption on bifidobacteria, except for one study that reported a significant reduction in bifidobacteria after a pooled analysis of four processed almond forms (ie, whole natural, whole roasted, chopped, and butter) compared with control. [Nutrients 2018;10:126; Nutr Res 2016;36:80-89; Curr Dev Nutr 2019;3:nzz079]

“As outlined, previous RCTs had significant limitations, which were overcome in the current trial and therefore our results can be considered robust,” the researchers said.

Short-chain fatty acids

In the present RCT, almond consumption led to changes in several members of the family Lachnospiraceae. However, these effects were attenuated after correction for multiple testing.

Lachnospiraceae are one of the main produces of colonic SCFAs. A meta-analysis of almond interventions showed that almond consumption influences members of this family. [Microorganisms 2020;8:573]

Additionally, researchers of the current study saw significant increases in the SCFA butyrate and several volatile organic compounds after almond consumption compared with control in the first RCT to assess the impact of almonds on bacterial metabolites.

This study was limited by sex distribution, which was predominantly female (86.2 percent) and young (mean age 27.5 years). Therefore, the results were not representative of male and older populations.

“These outcomes warrant further investigation in future RCTs, which should focus on confirming these findings in cohorts of older adults with an even sex distribution,” the researchers said. “Commercial processing of almonds increases predicted lipid bioaccessibility to a limited degree but did not appreciably influence gut health.”