The body of evidence about nuts and gut health continues to grow, with new local and international research papers regularly published.

Microbiome connections with host metabolism and habitual diet from 1,098 deeply phenotyped individuals. (2021).
Researchers performed metagenomic sequencing of 1,203 gut microbiomes from 1,098 people enrolled in the Personalised Responses to Dietary Composition Trial (PREDICT 1) study, where dietary information and cardiometabolic blood marker measurements were also available. They found that people who ate a diet rich in healthy, plant-based foods were more likely to have high levels of ‘good’ gut microbes. Among the findings, Prevotella copri, a species of bacteria, was associated with favourable post-prandial blood sugar control. These bacteria were more common when people ate a diet high in polyunsaturated fat, found in fish, nuts, and seeds.

Nuts and their effect on gut microbiota, gut function and symptoms in adults: A systematic review and meta-analysis of randomised controlled trials (2020)
This study assessed the impact of nuts on gut microbiota, gut function and gut symptoms via a systematic review and meta-analysis of randomised controlled trials (RCTs) in healthy adults. Eight studies reporting nine RCTs were included, investigating almonds (n = 5), walnuts (n = 3) and pistachios (n = 1). Nut consumption significantly increased Clostridium, Dialister, Lachnospira and Roseburia, and significantly decreased Parabacteroides. There was no effect of nuts on bacterial phyla, diversity or stool output.

Does ‘activating’ nuts affect nutrient bioavailability? (2020)
This study assessed the effects of different soaking regimes on phytate and mineral concentrations of whole and chopped almonds, hazelnuts, peanuts, and walnuts. The treatments were: 1. Raw; 2. soaked for 12 h in salt solution; 3. soaked for 4 h in salt solution; 4. soaked for 12 h in water. Although there were some statistically significant differences in phytate concentrations between treatments, no soaking treatment reduced phytate concentrations to a level that would result in clinically meaningful improvements in the bioavailability of minerals. In summary, the authors found no evidence that soaking is an effective strategy to reduce phytate concentrations and improve the nutrient bioavailability of almonds, hazelnuts, peanuts and walnuts.

Mediterranean diet intervention alters the gut microbiome in older people reducing frailty and improving health status: the NU-AGE 1-year dietary intervention across five European countries. (2020).
The Mediterranean diet is positively associated with health. The results of this study show that a greater adherence to the MedDiet modulates specific components of the gut microbiota that were associated with reductions in risk of frailty, improved cognitive function and reduced inflammatory status.

Walnuts and vegetable oils containing oleic acid differentially affect the gut microbiota and associations with cardiovascular risk factors: Follow-up of a randomized, controlled, feeding trial in adults at risk for cardiovascular disease. (2019).
Similarities between enrichment of SCFA-producing bacteria, including Roseburia and Eubacterium, following the walnut diet (WD) and walnut fatty acid matched diet (WFMD) illustrate the effect that the high unsaturated fat content, including ALA, may have on gut bacteria. The unique enrichment of Gordonibacter following the WD suggests that walnut-derived bioactive compounds and fibre modulate gut microbiota. The associations between Lachnospiraceae and improved cardiovascular risk factors suggest that the gastrointestinal microbiota may contribute to the underlying mechanisms of the beneficial health effects of walnut consumption.

Urolithin Metabotypes Can Determine the Modulation of Gut Microbiota in Healthy Individuals by Tracking Walnuts Consumption over Three Days. (2019).
Walnuts are rich in polyphenols ellagitannins, modulate gut microbiota (GM), and exert health benefits after long-term consumption. This study aimed to assess whether urolithin metabotypes (reported to predict host responsiveness to a polyphenol-rick intervention) were associated with differential GM modulation after short-term walnut consumption. In this study, 27 healthy individuals consumed 33 g of peeled raw walnuts over three days. The results show that walnuts consumption after only three days modulates GM in a urolithin metabotype-depending manner and increases the production of short-chain fatty acids (SCFA).

Walnut consumption alters the gastrointestinal microbiota, microbially derived secondary bile acids, and health markers in healthy adults: A randomized controlled trial. (2018).
Walnut consumption affected the gastrointestinal microbiota and microbially derived secondary bile acids and reduced serum total and LDL cholesterol in healthy adults. These results suggest that the gastrointestinal microbiota may contribute to the underlying mechanisms of the beneficial health effects of walnut consumption, including cardiometabolic and gastrointestinal health.

The effects of ‘activating’ almonds on consumer acceptance and gastrointestinal tolerance. (2018).
According to a study published in the European Journal of Nutrition, soaking (or activating) almonds did not reduce phytates, nor did it improve GI tolerance when compared to unsoaked nuts.

Prebiotic nut compounds and human microbiota. (2017).
Nuts contain non-bio-accessible material (mainly polysaccharides and polymerised polyphenols) and emerging evidence suggests that they appear to have a prebiotic effect, which may help to explain their many health benefits. However, data are very limited and more research is required, particularly from human intervention studies, as well as research on different types of nuts, doses, and over a sufficiently long period of time.

Health benefits of walnut polyphenols: An exploration beyond their lipid profile. (2017).
The main polyphenol in walnuts is pedunculagin, an ellagitannin. After consumption, ellagitannins are hydrolysed to release ellagic acid, which is converted by gut microflora to urolithin A and other derivatives such as urolithins B, C, and D. Ellagitannins possess well known antioxidant and anti-inflammatory bioactivity, and several studies have assessed the potential role of ellagitannins against disease initiation and progression, including cancer, cardiovascular, and neurodegenerative diseases.

Dietary pattern and colonic diverticulosis. (2017).
High-fibre diet does not prevent diverticulosis occurrence, and results about prevention/treatment of diverticular disease and acute diverticulitis are still conflicting. No association was seen between nut, corn or popcorn consumption and occurrence of diverticulosis, diverticular disease and acute diverticulitis.

Diverticular disease: reconsidering conventional wisdom. (2013).
Nuts and seeds do not increase the risk of diverticulitis or diverticular bleeding.

Lifestyle factors and the course of diverticular disease. (2012).
Contrary to a long-standing belief, a large prospective study found that nuts and corn did not increase the risk of diverticulitis or diverticular bleeding.

Low-residue diet in diverticular disease: putting an end to a myth. (2011)
Historically, low-residue diets have been recommended for diverticulosis because of a concern that indigestible nuts, seeds, corn, and popcorn could enter, block, or irritate a diverticulum and result in diverticulitis and possibly increase the risk of perforation. To date, there is no evidence supporting such a practice. In contrast, dietary fibre supplementation has been advocated to prevent diverticula formation and recurrence of symptomatic diverticulosis, although this is based mostly on low-quality observational studies.


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