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Almond Consumption May Benefit Some Gut Microbiota Functionality, Study Finds

Enjoying almonds increased butyrate concentrations in healthy adults


Modesto, CA – Scientific progress in understanding the human gut microbiome thrills experts in nutrition and gastrointestinal health. Researchers know that diet affects the gut microbiome in ways that benefit health and disease prevention, but they are still discovering the mechanisms of how this happens. New almond research may add another piece to the puzzle. A clinical study investigated how gut microbes break down almonds to produce butyrate, a specific microbiota product associated with several health benefits.  

New research1 found that consuming almonds significantly increases butyrate, a type of beneficial short-chain fatty acid (SCFA), in the colon. Butyrate, which is produced by microbes in the gut when they digest fiber, is the primary fuel source for colonocytes, the cells that line the colon, and may play a role in multiple processes related to human health, including improving sleep quality and fighting inflammation, and has been associated with a lower risk of colon cancer 2,3. Almond consumption also significantly increases stool output. Regular stool output is associated with a well-functioning gastrointestinal system. 

A team of researchers led by Professor Kevin Whelan from King’s College London, set out to determine the impact whole almonds and ground almonds have on the composition of gut microbiota, gut microbiota diversity and gut transit time. The study was funded by the Almond Board of California. 

“Part of the way in which the gut microbiota impact human health is through the production of short-chain fatty acids, such as butyrate. These molecules act as a fuel source for cells in the colon, they regulate absorption of other nutrients in the gut, and they help balance the immune system,” explained Kevin Whelan, PhD, RD, Professor of Dietetics, King’s College London. 

In this trial, researchers recruited 87 healthy adult participants, males and females, aged 18 to 45 years, who described themselves as regular snackers enjoying 2 or more snacks daily. Participants were consuming a typical diet that was lower in fiber than recommended and screened extensively for exclusion criteria. Each group comprised 29 participants; group one received 56 g/day (about 2 oz./day) of whole almonds, group two 56 g/day (about 2 oz./day) of ground almonds (almond flour), and the control group ate energy-matched snack muffins (2/day). Participants were required to take their study snacks instead of customary snacks, and they did this twice daily for 4 weeks. They drank at least 100 mL water with each snack. 

Measured outcomes included relative abundance of fecal bifidobacteria, fecal microbiota composition and diversity, fecal SCFAs, whole-gut transit time, gut pH, stool output (both frequency and consistency), and gut symptoms. 

A subgroup of 47 undertook measurement of gut transit time, pH, and pressure with a wireless motility capsule for baseline; 41 completed the endpoint. Another group of 31 participants were in the mastication analysis, designed to assess the impact of almond form (i.e., whole versus ground) on particle size distribution and lipid release following mastication. The fecal microbiota composition was analyzed, and there were no significant differences in phyla or genera between bacteria groups at baseline. Moreover, almonds in either whole or ground state did not increase the abundance of fecal bifidobacteria when compared to the control snack. However, a previous research study reported that almonds increased microbiome diversity, while decreasing relative levels of potentially harmful bacteria.4 

For the gut microbiota metabolites, researchers found no significant differences between groups for total or individual SCFAs. In the statistical analysis performed, butyrate was significantly higher among all almond consumers compared to those who consumed the snack muffin. There was no significant difference in whole-gut transit time, neither was a difference observed in small bowel pH or colonic pH. The whole-almond consumers experienced a significant difference in stool frequency with an additional 1.5 bowel movements per week. There were no differences in any of the groups for incidence or severity of common gastrointestinal symptoms.  

In summary, Professor Whelan and his colleagues found that study participants who consumed almonds experienced significant increases in butyrate as well as increased stool frequency. Almonds were well tolerated and did not lead to gastrointestinal symptoms, which indicates almond consumption may be a way to increase fiber without causing any adverse effects. This is suggestive of positive alterations to microbiota functionality.  

“We think these findings suggest almond consumption may benefit bacterial metabolism in a way that has the potential to influence human health,” said Professor Whelan. 

Limitations of this study are seen in both the sex distribution of volunteers, where more than 86% were female, as well as in age. Average age of participants was 27.5 years. The researchers recognize their findings are not necessarily generalizable to males or to older populations. 

Almonds provide fiber (12.5 / 3.5 g per 100g / 30g serving) and 15 essential nutrients including (per 100g / 30g serving): magnesium (270 / 81 mg), potassium (733 / 220 mg), and vitamin E (25.6 / 7.7 mg), making them a perfect nutrient-rich snack to promote gut health. 

Study at-a-Glance: 

The Study  

  • Researchers explored the prebiotic effect of almonds and the potential impact almond processing had on this effect in a free-living, 4-week, 3-arm, parallel-design randomized controlled trial.   

  • Eighty-seven healthy adults participated and received either 56 g/d whole almonds, 56 g/d ground almonds, or an isocaloric snack muffin as the control. 

  • Baseline and endpoint measures included gut microbiota composition and diversity, short-chain fatty acids, volatile organic compounds (VOCs), gut transit time, stool output, and gut symptoms (n=87). A subgroup (n=31) was measured for the impact of almond form, ground or whole, on particle size distribution (PSD) along with predicted lipid release. 


  • Researchers observed no significant differences in the abundance of fecal bifidobacteria following consumption of either form of almond or the control snack. Almond consumers (both ground and whole almonds), had higher butyrate (24.1 µmol/g; SD 15.0 µmol/g) compared to the control (18.2 µmol/g, SD 9.1 µmol/g; p=0.046). 

  • There was no effect of almonds on gut microbiota at the phylum level or diversity, gut transit time, stool consistency, or gut symptoms. Three VOCs increased following almond consumption compared to control muffins, but this change was not statistically significant.  

  • Ground almonds resulted in significantly smaller PSD and higher predicted lipid release (10.4%, SD 1.8%) in comparison to whole almonds (9.3%, SD 2.0%; p=0.017). 

  • Of the subgroup participating in the mastication study, analysis of PSD demonstrated a significant interaction between whole almonds and the particle size on PSD; however, commercially ground almonds did not differ meaningfully in their nutrient bioaccessibility from whole almonds. 

  • Post-hoc testing showed whole almond participants had higher intakes of monounsaturated fatty acids, total fiber, potassium, along with other nutrients when compared to the control participants. Similarly, ground almond consumers had higher intakes of monounsaturated fatty acids, total fiber, and other micronutrients. 


  • Participants who consumed almonds experienced small but significant differences in stool frequency as well as significant increases in butyrate in the colon. Researchers indicate that these findings suggest positive alterations to gut microbiota functionality. The impact of almond consumption on bacterial metabolism has the potential to influence human health. 

  • These results have inspired thinking regarding how almonds may benefit older adults as well as those with constipation, as these populations are known to have lower levels of bifidobacteria than healthy, young adults as well as those without constipation.  

Creedon, A. C., Dimidi, E., Hung, E. S., Rossi, M., Probert, C., Grassby, T., Miguens-Blanco, J., Marchesi, J. R., Scott, S. M., Berry, S. E., & Whelan, K. (2022). The impact of almonds and almond processing on gastrointestinal physiology, luminal microbiology and gastrointestinal symptoms: a randomized controlled trial and mastication study. American Journal of Clinical Nutrition, nqac265.


Koh, A., De Vadder, F., Kovatcheva-Datchary, P., & Backhed, F. (2016). From dietary fiber to host physiology: short-chain fatty acids as key bacterial metabolites. Cell, 165(6), 1332-1345. doi: 10.1016/j.cell.2016.05.041


Szentirmai, E., Millican, N. S., Massie, A. R., & Kapas, L. (2019). Butyrate, a metabolite of intestinal bacteria, enhances sleep. Scientific Reports, 9:7035, 1-9.


Dhillon, J., Li, Z., & Ortiz, R. M. (2019). Almond snacking for 8 wk increases alpha-diversity of the gastrointestinal microbiome and decreases Bacteroides fragilis abundance compared with an isocaloric snack in college freshmen. Current Developments in Nutrition, 3(8), 1-9.