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Research Nut: Walnuts

Walnuts consumed by healthy adults provide less available energy than predicted by the Atwater Factors.

Baer, D., S. Gebauer, J. Novotny, 2016. Walnuts consumed by healthy adults provide less available energy than predicted by the Atwater Factors. J Nutr. 146:1–5.

Background: Previous studies have shown that the metabolizable energy (ME) content (energy available to the body) of certain nuts is less than predicted by the Atwater factors. However, very few nuts have been investigated to date, and no information is available regarding the ME of walnuts. Objective: A study was conducted to determine the ME of walnuts when consumed as part of a typical American diet. Methods: Healthy adults (n = 18; mean age = 53.1 y; body mass index = 28.8 kg/m2) participated in a randomized crossover study with 2 treatment periods (3 wk each). The study was a fully controlled dietary feeding intervention in which the same base diet was consumed during each treatment period; the base diet was unsupplemented during one feeding period and supplemented with 42 g/d walnuts during the other feeding period. Base diet foods were reduced in equal proportions during the walnut period to achieve isocaloric food intake during the 2 periods. After a 9 d diet acclimation period, subjects collected all urine and feces for ;1 wk (as marked by a Brilliant Blue fecal collection marker) for analysis of energy content. Administered diets, walnuts, and fecal and urine samples were subjected to bomb calorimetry, and the resulting data were used to calculate the ME of the walnuts. Results: One 28-g serving of walnuts contained 146 kcal (5.22 kcal/g), 39 kcal/serving less than the value of 185 kcal/ serving (6.61 kcal/g) currently used for food labeling. The ME of the walnuts was 21% less than that predicted by the Atwater factors (P < 0.0001). Conclusion: Consistent with other tree nuts, Atwater factors overestimate the metabolizable energy value of walnuts. These results could help explain the observations that consumers of nuts do not gain excessive weight, and improve the accuracy for food labeling.

Dietary α-linolenic acid, marine ω-3 fatty acids, and mortality in a population with high fish consumption: findings from the PREvención con DIeta MEDiterránea (PREDIMED) study.

Sala-Vila, A., M. Guasch-Ferré, F.B. Hu, A. Sánchez-Tainta, M. Bulló, M. Serra-Mir, C. López-Sabater, J.V. Sorlí, F. Arós, M. Fiol, M.A. Muñoz, L. Serra-Majem, J.A. Martínez, D. Corella, M. Fitó, J. Salas-Salvadó, M.A. Martínez-González, R. Estruch, E. Ros; and PREDIMED Investigators, 2016. Dietary α-linolenic acid, marine ω-3 fatty acids, and mortality in a population with high fish consumption: findings from the PREvención con DIeta MEDiterránea (PREDIMED) study. J Am Heart Assoc. 26:5(1).

Background: Epidemiological evidence suggests a cardioprotective role of α-linolenic acid (ALA), a plant-derived ω-3 fatty acid. It is unclear whether ALA is beneficial in a background of high marine ω-3 fatty acids (long-chain n-3 polyunsaturated fatty acids) intake. In persons at high cardiovascular risk from Spain, a country in which fish consumption is customarily high, we investigated whether meeting the International Society for the Study of Fatty Acids and Lipids recommendation for dietary ALA (0.7% of total energy) at baseline was related to all-cause and cardiovascular disease mortality. We also examined the effect of meeting the society’s recommendation for long-chain n-3 polyunsaturated fatty acids (≥500 mg/day). Methods and Results: We longitudinally evaluated 7202 participants in the PREvención con DIeta MEDiterránea (PREDIMED) trial. Multivariable-adjusted Cox regression models were fitted to estimate hazard ratios. ALA intake correlated to walnut consumption (r=0.94). During a 5.9-y follow-up, 431 deaths occurred (104 cardiovascular disease, 55 coronary heart disease, 32 sudden cardiac death, 25 stroke). The hazard ratios for meeting ALA recommendation (n=1615, 22.4%) were 0.72 (95% CI 0.56-0.92) for all-cause mortality and 0.95 (95% CI 0.58-1.57) for fatal cardiovascular disease. The hazard ratios for meeting the recommendation for long-chain n-3 polyunsaturated fatty acids (n=5452, 75.7%) were 0.84 (95% CI 0.67-1.05) for all-cause mortality, 0.61 (95% CI 0.39-0.96) for fatal cardiovascular disease, 0.54 (95% CI 0.29-0.99) for fatal coronary heart disease, and 0.49 (95% CI 0.22-1.01) for sudden cardiac death. The highest reduction in all-cause mortality occurred in participants meeting both recommendations (hazard ratio 0.63 [95% CI 0.45-0.87]). Conclusions:  In participants without prior cardiovascular disease and high fish consumption, dietary ALA, supplied mainly by walnuts and olive oil, relates inversely to all-cause mortality, whereas protection from cardiac mortality is limited to fish-derived long-chain n-3 polyunsaturated fatty acids.

Effects of diet composition and insulin resistance status on plasma lipid levels in a weight loss intervention in women.

Le, T., S.W. Flatt, L. Natarajan, B. Pakiz, E.L. Quintana, D.D. Heath, B.K. Rana, C.L. Rock, 2016. Effects of diet composition and insulin resistance status on plasma lipid levels in a weight loss intervention in women. J Am Heart Assoc. 5(1). doi: 10.1161/JAHA.115.002771.

Background: Optimal macronutrient distribution of weight loss diets has not been established. The distribution of energy from carbohydrate and fat has been observed to promote differential plasma lipid responses in previous weight loss studies, and insulin resistance status may interact with diet composition and affect weight loss and lipid responses. Methods and Results: Overweight and obese women (n=245) were enrolled in a 1‐year behavioral weight loss intervention and randomly assigned to 1 of 3 study groups: a lower fat (20% energy), higher carbohydrate (65% energy) diet; a lower carbohydrate (45% energy), higher fat (35% energy) diet; or a walnut‐rich, higher fat (35% energy), lower carbohydrate (45% energy) diet. Blood samples and data available from 213 women at baseline and at 6 months were the focus of this analysis. Triglycerides, total cholesterol, and high‐ and low‐density lipoprotein cholesterol were quantified and compared between and within groups. Triglycerides decreased in all study arms at 6 months (P<0.05). The walnut‐rich diet increased high‐density lipoprotein cholesterol more than either the lower fat or lower carbohydrate diet (P<0.05). The walnut‐rich diet also reduced low‐density lipoprotein cholesterol in insulin‐sensitive women, whereas the lower fat diet reduced both total cholesterol and high‐density lipoprotein cholesterol in insulin‐sensitive women (P<0.05). Insulin sensitivity and C‐reactive protein levels also improved. Conclusions: Weight loss was similar across the diet groups, although insulin‐sensitive women lost more weight with a lower fat, higher carbohydrate diet versus a higher fat, lower carbohydrate diet. The walnut‐rich, higher fat diet resulted in the most favorable changes in lipid levels.

Key area: insulin resistance, lipids, walnuts/ weight management/weight, satiety,

Effects of walnut consumption on endothelial function in people with type 2 diabetes: a randomized pilot trial.

Djoussé, L., B. Lu, M.J. Gaziano, 2016. Effects of walnut consumption on endothelial function in people with type 2 diabetes: a randomized pilot trial. Curr Nutr Rep. 5(1):1-8.

The aim of this study was to obtain preliminary data to test the hypothesis that (1) a 12-week intervention with 28 g/day of walnuts improves endothelial function in people with type 2 diabetes mellitus (DM) and (2) intake of walnuts improves plasma adipokines after 12 weeks of intervention. In this pilot randomized, single-blinded, controlled trial of 26 adult subjects with prevalent DM, each subject was randomized to a usual diet with 28 g of walnuts per day or usual diet without walnuts (control group). Reactive hyperemia index (RHI), a measure of endothelial function, was measured non-invasively at baseline and after 12 weeks using Endo-PAT2000. We used linear regression to examine the effects of the intervention on RHI. The mean age at baseline was 64.8 ± 11.6 years; 61.5 % of participants were female, and 15.4 % had coronary artery disease. The standard error of RHI was 0.19. The difference in change in RHI during the intervention between the two groups was −0.029 (95 % confidence interval (CI) −0.52, 0.46, p = 0.23). Walnut intervention led to a suggestive increase in adiponectin, albeit non-statistically significant (difference 0.50 μg/ml (95 % CI −0.10, 1.09), p = 0.65). We demonstrated the feasibility of the proposed randomized trial and obtained needed standard deviations to calculate the required sample size to test proposed hypotheses in an efficacy trial.

Associations between nut consumption and inflammatory biomarkers

Yu, Z., V.S. Malik, N. Keum, F.B. Hu, E.L. Giovannucci, M.J. Stampfer, W.C. Willett, C.S. Fuchs, Y. Bao, 2016. Associations between nut consumption and inflammatory biomarkers. AJCN. First published ahead of print July 27, 2016 as doi: 10.3945/ajcn.116.134205.

Background: Increased nut consumption has been associated with reduced risk of cardiovascular disease and type 2 diabetes, as well as a healthy lipid profile. However, the associations between nut consumption and inflammatory biomarkers are unclear. Objective: We investigated habitual nut consumption in relation to inflammatory biomarkers in 2 large cohorts of US men and women. Design: We analyzed cross-sectional data from 5013 participants in the Nurses’ Health Study (NHS) and Health Professionals Follow-Up Study (HPFS) who were free of diabetes. Nut intake, defined as intake of peanuts and other nuts, was estimated from food frequency questionnaires, and cumulative averages from 1986 and 1990 in the NHS and from 1990 and 1994 in the HPFS were used. Plasma biomarkers were collected in 1989–1990 in the NHS and 1993–1995 in the HPFS. Multivariate linear regression was used to assess the associations of nut consumption with fasting plasma C-reactive protein (CRP, n = 4941), interleukin 6 (IL-6, n = 2859), and tumor necrosis factor receptor 2 (TNFR2, n = 2905). Results: A greater intake of nuts was associated with lower amounts of a subset of inflammatory biomarkers, after adjusting for demographic, medical, dietary, and lifestyle variables. The relative concentrations (ratios) and 95% CIs comparing subjects with nut intake of $5 times/wk and those in the categories of never or almost never were as follows: CRP: 0.80 (0.69, 0.90), P-trend = 0.0003; and IL-6: 0.86 (0.77, 0.97), P-trend = 0.006. These associations remained significant after further adjustment for body mass index. No significant association was observed with TNFR2. Substituting 3 servings of nuts/wk for 3 servings of red meat, processed meat, eggs, or refined grains/wk was associated with significantly lower CRP (all P , 0.0001) and IL-6 (P ranges from 0.001 to 0.017). Conclusion: Frequent nut consumption was associated with a healthy profile of inflammatory biomarkers.

Nut consumption and prostate cancer risk and mortality.

Wand, W., M. Yang, S.A. Kenfield, F.B. Hu, M.J. Stampfer, W.C. Willett, C.S. Fuchs, E.L. Giovannucci,  Y. Bao, 2016. Nut consumption and prostate cancer risk and mortality. British Journal of Cancer.doi:10.1038/bjc.2016.181

Background: Little is known of the association between nut consumption, and prostate cancer (PCa) incidence and survivorship. Methods: We conducted an incidence analysis and a case-only survival analysis in the Health Professionals Follow-up Study on the associations of nut consumption (updated every 4 years) with PCa diagnosis, and PCa-specific and overall mortality. Results: In 26 years, 6810 incident PCa cases were identified from 47 299 men. There was no association between nut consumption and being diagnosed with PCa or PCa-specific mortality. However, patients who consumed nuts five or more times per week after diagnosis had a significant 34% lower rate of overall mortality than those who consumed nuts less than once per month (HR=0.66, 95% CI: 0.52–0.83, P-trend=0.0005). Conclusions: There were no statistically significant associations between nut consumption, and PCa incidence or PCa-specific mortality. Frequent nut consumption after diagnosis was associated with significantly reduced overall mortality.

Effects of tree nuts on blood lipids, apolipoproteins, and blood pressure: systematic review, meta-analysis, and dose-response of 61 controlled intervention trials.

Del Gobbo, L.C., M.C. Falk, R. Feldman, K. Lewis, D. Mozaffarian, 2015. Effects of tree nuts on blood lipids, apolipoproteins, and blood pressure: systematic review, meta-analysis, and dose-response of 61 controlled intervention trials. AJCN. First published ahead of print November 11, 2015 as doi: 10.3945/ajcn.115.110965.

Background: The effects of nuts on major cardiovascular disease (CVD) risk factors, including dose-responses and potential heterogeneity by nut type or phytosterol content, are not well established. Objectives: We examined the effects of tree nuts (walnuts, pistachios, macadamia nuts, pecans, cashews, almonds, hazelnuts, and Brazil nuts) on blood lipids [total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein, and triglycerides], lipoproteins [apolipoprotein A1, apolipoprotein B (ApoB), and apolipoprotein B100], blood pressure, and inflammation (C-reactive protein) in adults aged $18 y without prevalent CVD. Design: We conducted a systematic review and meta-analysis following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Two investigators screened 1301 potentially eligible PubMed articles in duplicate. We calculated mean differences between nut intervention and control arms, dose-standardized to one 1-oz (28.4 g) serving/d, by using inverse-variance fixed-effects meta-analysis. Dose-response for nut intake was examined by using linear regression and fractional polynomial modeling. Heterogeneity by age, sex, background diet, baseline risk factors, nut type, disease condition, duration, and quality score was assessed with meta-regression. Publication bias was evaluated by using funnel plots and Egger’s and Begg’s tests. Results: Sixty-one trials met eligibility criteria (n = 2582). Interventions ranged from 3 to 26 wk. Nut intake (per serving/d) lowered total cholesterol (24.7 mg/dL; 95% CI: 25.3, 24.0 mg/dL), LDL cholesterol (24.8 mg/dL; 95% CI: 25.5, 24.2 mg/dL), ApoB (23.7 mg/dL; 95% CI: 25.2, 22.3 mg/dL), and triglycerides (22.2 mg/dL; 95% CI: 23.8, 20.5 mg/dL) with no statistically significant effects on other outcomes. The dose-response between nut intake and total cholesterol and LDL cholesterol was nonlinear (P-nonlinearity , 0.001 each); stronger effects were observed for $60 g nuts/d. Significant heterogeneity was not observed by nut type or other factors. For ApoB, stronger effects were observed in populations with type 2 diabetes (211.5 mg/dL; 95% CI: 216.2, 26.8 mg/dL) than in healthy populations (22.5 mg/dL; 95% CI: 24.7, 20.3 mg/dL) (P-heterogeneity = 0.015). Little evidence of publication bias was found. Conclusions: Tree nut intake lowers total cholesterol, LDL cholesterol, ApoB, and triglycerides. The major determinant of cholesterol lowering appears to be nut dose rather than nut type. Our findings also highlight the need for investigation of possible stronger effects at high nut doses and among diabetic populations.

A cross sectional study of the association between walnut consumption and cognitive function among adult us populations represented in NHANES.

Arab, L., A. Ang, 2015. A cross sectional study of the association between walnut consumption and cognitive function among adult us populations represented in NHANES. J Nutr Health Aging. 19(3):284-290.

Objective: To examine the association between walnut consumption and measures of cognitive function in the US population. Design: Nationally representative cross-sectional study using 24-hour dietary recalls of intakes to assess walnut and other nut consumption as compared to the group reporting no nut consumption. Setting: 1988–1994 and 1999–2002 rounds of the National Health and Nutrition Examination Survey (NHANES). Population Representative weighted sample of US adults 20 to 90 years of age. Main Outcome Measure: The Neurobehavioral Evaluation System 2 (NES2), consisting of simple reaction time (SRTT), symbol digit substitution (SDST), the single digit learning (SDLT), Story Recall (SRT) and digit-symbol substitution (DSST) tests. Results: Adults 20–59 years old reporting walnut consumption of an average of 10.3 g/d required 16.4ms less time to respond on the SRTT, P=0.03, and 0.39s less for the SDST, P=0.01. SDLT scores were also significantly lower by 2.38s (P=0.05). Similar results were obtained when tertiles of walnut consumption were examined in trend analyses. Significantly better outcomes were noted in all cognitive test scores among those with higher walnut consumption (P < 0.01). Among adults 60 years and older, walnut consumers averaged 13.1 g/d, scored 7.1 percentile points higher, P=0.03 on the SRT and 7.3 percentile points higher on the DSST, P=0.05. Here also trend analyses indicate significant improvements in all cognitive test scores (P < 0.01) except for SRTT (P = 0.06) in the fully adjusted models. Conclusion: These significant, positive associations between walnut consumption and cognitive functions among all adults, regardless of age, gender or ethnicity suggest that daily walnut intake may be a simple beneficial dietary behavior.

 

Dietary walnut suppression of colorectal cancer in mice: Mediation by miRNA patterns and fatty acid incorporation.

Tsoukas, M.A., B.J. Ko, T.R. Witte, F. Dincer, W.E. Hardman, C.S. Mantzoros, 2015. Dietary walnut suppression of colorectal cancer in mice: Mediation by miRNA patterns and fatty acid incorporation. J Nutr Biochem. 26(7):776-83.

Abstract: Colorectal cancer, unlike many other malignancies, may be preventable. Recent studies have demonstrated an inverse association between nut consumption and incidence of colon cancer; however, the underlying mechanisms are not fully understood. An emerging concept suggests that microribonucleic acids (miRNAs) may help explain the relationship between walnut consumption and decreased colorectal neoplasia risk. Seven days after HT-29 colon cancer cell injection, mice were randomized to either control or walnut diets for 25days of diet treatment. Thirty samples of tumor and of omental adipose were analyzed to determine changes in lipid composition in each dietary group. In the tumors of the walnut-containing diet, we found significant increases in α-linolenic, eicosapentaenoic, docosahexaenoic and total omega-3 acids, and a decrease in arachidonic acid, as compared to the control diet. Final tumor size measured at sacrifice was negatively associated with percentage of total omega-3 fatty acid composition (r=-0.641, P=.001). MicroRNA expression analysis of colorectal tumor tissue revealed decreased expression of miRNAs 1903, 467c and 3068 (P<.05) and increased expression of miRNA 297a* (P=.0059) in the walnut-treated group as compared to control diet. Our results indicate that changes in the miRNA expression profiles likely affect target gene transcripts involved in pathways of anti-inflammation, antivascularization, antiproliferation and apoptosis. We also demonstrate the incorporation of protective fatty acids into colonic epithelium of walnut-fed mice, which may independently alter miRNA expression profiles itself. Future studies of the mechanism of widespread miRNA regulation by walnut consumption are needed to offer potential prognostic and therapeutic targets.

 

Health benefits of walnut polyphenols: an exploration beyond their lipid profile.

Sánchez-González, C., C.J. Ciudad, V. Noé, M. Izquierdo-Pulido, 2015. Health benefits of walnut polyphenols: an exploration beyond their lipid profile. Crit Rev Food Sci Nutr. 57(16):3373-3383.

Walnuts are commonly found in our diet and have been recognized for their nutritious properties for a long time. Traditionally, walnuts have been known for their lipid profile which has been linked to a wide array of biological properties and health-promoting effects. In addition to essential fatty acids, walnuts contain a variety of other bioactive compounds such as, vitamin E and polyphenols. Among common foods and beverages, walnuts represent one of the most important sources of polyphenols, hence, their effect over human health warrants attention. The main polyphenol in walnuts is pedunculagin, an ellagitannin. After consumption, ellagitannins are hydrolyzed 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 ETs against disease initiation and progression, including cancer, cardiovascular and neurodegenerative diseases. The purpose of this review is to summarize current available information relating to the potential effect of walnut polyphenols in health maintenance and disease prevention.