The Effects of Almonds on Gut Microbiota, Glycometabolism, and Inflammatory Markers in Patients with Type 2 Diabetes: A Systematic Review and Meta-Analysis of Randomised Controlled Trials

Abstract

The use of nutritional interventions for managing diabetes is one of the effective strategies aimed at reducing the global prevalence of the condition, which is on the rise. Almonds are the most consumed tree nut and they are known to be rich sources of protein, monounsaturated fatty acids, essential minerals, and dietary fibre. Therefore, the aim of this review was to evaluate the effects of almonds on gut microbiota, glycometabolism, and inflammatory parameters in patients with type 2 diabetes. Methods: This systematic review and meta-analysis was carried out according to the preferred reporting items for systematic review and meta-analysis (PRISMA). EBSCOhost, which encompasses the Health Sciences Research Databases; Google Scholar; EMBASE; and the reference lists of articles were searched based on population, intervention, control, outcome, and study (PICOS) framework. Searches were carried out from database inception until 1 August 2021 based on medical subject headings (MesH) and synonyms. The meta-analysis was carried out with the Review Manager (RevMan) 5.3 software. Results: Nine randomised studies were included in the systematic review and eight were used for the meta-analysis. The results would suggest that almond-based diets have significant effects in promoting the growth of short-chain fatty acid (SCFA)-producing gut microbiota. Furthermore, the meta-analysis showed that almond-based diets were effective in significantly lowering (p < 0.05) glycated haemoglobin (HbA1c) levels and body mass index (BMI) in patients with type 2 diabetes. However, it was also found that the effects of almonds were not significant (p > 0.05) in relation to fasting blood glucose, 2 h postprandial blood glucose, inflammatory markers (C-reactive protein and Tumour necrosis factor α, TNF-α), glucagon-like peptide-1 (GLP-1), homeostatic model assessment of insulin resistance (HOMA–IR), and fasting insulin. The biological mechanisms responsible for the outcomes observed in this review in relation to reduction in HbA1c and BMI may be based on the nutrient composition of almonds and the biological effects, including the high fibre content and the low glycaemic index profile. Conclusion: The findings of this systematic review and meta-analysis have shown that almond-based diets may be effective in promoting short-chain fatty acid-producing bacteria and lowering glycated haemoglobin and body mass index in patients with type 2 diabetes compared with control. However, the effects of almonds were not significant (p > 0.05) with respect to fasting blood glucose, 2 h postprandial blood glucose, inflammatory markers (C-reactive protein and TNF-α), GLP-1, HOMA–IR, and fasting insulin.

Gut microbiota: A new target for T2DM prevention and treatment

“…A previous study has also shown that an almond-based low carbohydrate diet may improve glucose metabolism in patients with T2DM by increasing SCFA-producing bacteria, including Roseburia, Ruminococcus and Eubacterium, to elevate SCFA production and activate GPR43 to sustain GLP-1 secretion (48). Consistently, another study has suggested that almondbased diets may promote SCFA-producing bacteria while decreasing hemoglobin and body mass index (BMI) in T2DM individuals (241). The Green-Mediterranean diet with a gradual increase in plant components induces specific alterations in the intestinal flora and BCAA metabolism, including an elevation in Prevotella abundance and BCAA degradation as well as a decrease in Bifidobacterium abundance and BCAA biosynthesis, leading to increased insulin sensitivity (242).…”

Almond intake alters the acute plasma dihydroxy-octadecenoic acid (DiHOME) response to eccentric exercise

“…Almond (poly)phenolics possess anti-inflammatory, vasodilatory and antioxidant activities ( 15 – 19 ). Four-weeks intake of almonds has been linked to reduced oxidized LDL and fatty acid peroxidation malondialdehyde (MDA) and creatinine-adjusted urinary isoprostane output ( 17 , 18 ). Limited data suggest reduced levels of depression with increased almond intake that may in part be due to almond-related anti-inflammatory and antioxidant effects ( 20 ).…”

Nuts in the Prevention and Management of Type 2 Diabetes

“…Between 2020 and 2022 (present day), several other SRMAs of RCTs have been conducted assessing the effect of a specific nut type on markers of glycemic control in people with T2D. Two SRMA’s assessed the effect of almond intake; the first SRMA (8 RCTs) showed a significant lowering in HbA1c but no impact on fasting glucose, insulin, or HOMA-IR [ 36 ], whereas the second SRMA (9 RCTs) showed no impact on markers of glycemic control, including HbA1c, fasting glucose, and insulin [ 37 ]. Another SRMA assessed the effect of pistachio intake in individuals with T2D, prediabetes, and metabolic syndrome (6 RCTs), which showed a significant lowering in fasting glucose and HOMA-IR, but not HbA1c or fasting insulin [ 34 ].…”