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Research Nut: Walnuts

Effect of nuts on gastrointestinal health. 

Mandalari, G., T. Gervasi, D.W. Rosenberg, K.G. Lapsley, D.J. Baer, 2023. Effect of nuts on gastrointestinal health. Nutrients. 15(7):1733. https://doi.org/10.3390/nu15071733

Nuts are high nutrient-dense foods containing healthy lipids, dietary fiber, and bioactive phytochemicals, including vitamins and minerals. Although the beneficial effect of nut consumption on different chronic diseases has been well documented, especially in relation to their cardiometabolic benefits, less scientific evidence is available on their possible beneficial effects on gastrointestinal health. In this narrative review, we summarize the most important findings and new research perspectives in relation to the importance of nut consumption on gastrointestinal health. The integrity of the cell wall structure, cell size and particle size after mastication are known to play a crucial role in energy, nutrient and bioactive release from nuts during digestion, therefore affecting bioaccessibility. Other mechanisms, such as cell wall composition, thickness and porosity, as well as stability of the membranes surrounding the oil bodies within the cell, are also important for energy extraction. As the undigested nutrients and phytochemicals are delivered to the colon, effects on gut microbiota composition are predicted. Although the overall effect of nut consumption on microbial alpha- and beta-diversity has been inconsistent, some scientific evidence suggests an increase in fecal butyrate after almond consumption, and a beneficial role of walnuts on the prevention of ulcerative colitis and protection against the development of gastric mucosal lesions.

Dietary walnuts preserve aspects of health span and alter the hippocampal lipidome in aged high-fat diet-fed mice.

Novaj, A., M.G. Engel, R. Wang, K. Mao, X. Xue, Y. Amir, G. Atzmon, D.M. Huffman, 2023. Dietary walnuts preserve aspects of health span and alter the hippocampal lipidome in aged high-fat diet-fed mice. Int. J. Mol. Sci. 24(3), 2314. https://doi.org/10.3390/ijms24032314

Evidence continues to accrue that aging and its diseases can be delayed by pharmacologic and dietary strategies that target the underlying hallmarks of the aging process. However, identifying simple, safe, and effective dietary strategies involving the incorporation of whole foods that may confer some protection against the aging process is also needed. Recent observational studies have suggested that nut consumption can reduce mortality risk in humans. Among these, walnuts are particularly intriguing, given their high content of n-3 fatty acids, fiber, and antioxidant and anti-inflammatory compounds. To this end, 12-month-old male CB6F1 mice were provided either a defined control low-fat diet (LFD), a control high-fat diet (HFD), or an isocaloric HFD containing 7.67% walnuts by weight (HFD + W), and measures of health span and related biochemical markers (n = 10-19 per group) as well as survival (n = 20 per group) were monitored. Mice provided the HFD or HFD + W demonstrated marked weight gain, but walnuts lowered baseline glucose (p < 0.05) and tended to temper the effects of HFD on liver weight gain (p < 0.05) and insulin tolerance (p = 0.1). Additional assays suggested a beneficial effect on some indicators of health with walnut supplementation, including preservation of exercise capacity and improved short-term working memory, as determined by Y maze (p = 0.02). However, no effect was observed via any diet on inflammatory markers, antioxidant capacity, or survival (p = 0.2). Ingenuity Pathway Analysis of the hippocampal transcriptome identified two processes predicted to be affected by walnuts and potentially linked to cognitive function, including estrogen signaling and lipid metabolism, with changes in the latter confirmed by lipidomic analysis. In summary, while walnuts did not significantly improve survival on a HFD, they tended to preserve features of health span in the context of a metabolic stressor with aging.

Effect of walnut consumption on neuropsychological development in healthy adolescents: a multi-school randomised controlled trial. 

Pinar-Martí, A., F. Gignac, S. Fernández-Barrés, D. Romaguera, A. Sala-Vila, I. Lázaro, O.T. Ranzani, C. Persavento, A. Delgado, A. Carol, J. Torrent, J. Gonzalez, E. Roso, J. Barrera-Gómez, M. López-Vicente, O. Boucher, M. Nieuwenhuijsen, M.C. Turner, M. Burgaleta, J. Canals,  V. Arija, X. Basagaña , E. Ros, J. Salas-Salvadó , J. Sunyer, J. Julvez, 2023. Effect of walnut consumption on neuropsychological development in healthy adolescents: a multi-school randomised controlled trial. EClinicalMedicine. 59, 101954. https://doi.org/10.1016/j.eclinm.2023.101954

Background: Omega-3 fatty acids are critical for neuropsychological functioning. Adolescence is increasingly believed to entail brain vulnerability to dietary intake. The potential benefit on adolescent neurodevelopment of consuming walnuts, a source of omega-3 alpha-linolenic acid (ALA), remains unclear. Methods: We conducted a 6-month multi-school-based randomized controlled nutrition intervention trial to assess whether walnut consumption has beneficial effects on the neuropsychological and behavioral development of adolescents. The study took place between 04/01/2016 and 06/30/2017 in twelve different high schools in Barcelona, Spain (ClinicalTrials.gov Identifier: NCT02590848). A total of 771 healthy teenagers aged 11–16 years were randomized into two equal groups (intervention or control). The intervention group received 30 g/day of raw walnut kernels to be incorporated into their diet for 6 months. Multiple primary endpoints concerning neuropsychological (working memory, attention, fluid intelligence, and executive function) and behavioral (socioemotional and attention deficit hyperactivity disorder [ADHD] symptoms) development were assessed at baseline and after intervention. Red blood cell (RBC) ALA status was determined at baseline and 6 months as a measure of compliance. Main analyses were based on intention-to-treat using a linear mixed-effects model. A per-protocol effect of the intervention was analysed using inverse-probability weighting to account for post-randomization prognostic factors (including adherence) using generalized estimating equations. Findings: In intention-to-treat analyses, at 6 months there were no statistically significant changes between the intervention and control groups for all primary endpoints. RBC ALA (%) significantly increased only in the intervention group, coefficient = 0.04 (95% Confidence Interval (CI) = 0.03, 0.06; p < 0.0001). The per-protocol (adherence-adjusted) effect on improvement in attention score (hit reaction time variability) was −11.26 ms (95% CI = −19.92, −2.60; p = 0.011) for the intervention group as compared to the control group, improvement in fluid intelligence score was 1.78 (95% CI = 0.90, 2.67; p < 0.0001), and reduction of ADHD symptom score was −2.18 (95% CI = −3.70, −0.67; p = 0.0050). Interpretation Our study suggested that being prescribed eating walnuts for 6 months did not improve the neuropsychological function of healthy adolescents. However, improved sustained attention, fluid intelligence, and ADHD symptoms were observed in participants who better complied with the walnut intervention. This study provides a foundation for further clinical and epidemiological research on the effect of walnuts and ALA on neurodevelopment in adolescents.

Adding walnuts to the usual diet can improve diet quality in the United States: diet modeling study based on NHANES 2015-2018. 

Spence, L.A., B. Henschel, R. Li, C.D. Tekwe, K. Thiagarajah, 2023. Adding walnuts to the usual diet can improve diet quality in the United States: diet modeling study based on NHANES 2015-2018. Nutrients. 15(2):258. https://doi.org/10.3390/nu15020258

Background: The under-consumption of calcium, potassium, fiber, and vitamin D is considered a U.S. public health concern. Shifts in eating patterns that increase the consumption of vegetables, fruits, whole grains, nuts/seeds, and dairy products can help achieve the recommended intakes of these nutrients, leading to healthier diets. Objective: We assessed the impact of adding 1 ounce (28.35 g) of walnuts to usual diets on diet quality and nutrients of concern, including magnesium, fiber, and potassium. Methods: We utilized 24 h dietary recalls obtained from the What We Eat in America, National Health and Nutrition Examination Survey (NHANES) and modeled the addition of 1 ounce (28.35 g) of walnuts to the usual diets of no-nut consumers. No-nut consumers aged _4 years (n = 7757) from the 2015–2018 NHANES study were included. Population percentages with intakes below the estimated average requirement (EAR) values for calcium, magnesium, folate, and vitamin E and above the adequate intake (AI) values for potassium and fiber were examined. Diet quality was assessed using the Healthy Eating Index-2015 (HEI-2015). The National Cancer Institute method was used to estimate the usual and modeled intakes. Significant differences between usual (current) and modeled intakes were determined using non-overlapping 95% confidence intervals. All analyses included sample weights to account for the NHANES survey design. Results: Adding 1 ounce (28.35 g) of walnuts to the usual diet resulted in significant reductions in the percentages of adults with intakes below the EAR for magnesium and folate (69.6% vs. 52.0%; 49.2% vs. 40.6%, respectively), and increased the percentage of adults above the AI for potassium (22.8% vs. 26.5%). A similar trend was observed among children (4–18 years). HEI scores improved significantly from 49.1 (95% CI: 48.0–50.4) to 58.5 (95% CI: 57.5–59.6) in children and from 52.4 (95% CI: 51.0–53.8) to 59.2 (95% CI: 58.0–60.5) in adults. Conclusions: Adding 1 ounce (28.35 g) of walnuts to the usual diet of no-nut consumers improved the diet quality and adequacy of some under-consumed nutrients.