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Research Area: Cardiovascular Health

Effects of walnut consumption on blood lipids and other cardiovascular risk factors: an updated meta-analysis and systematic review of controlled trials.

Guasch-Ferré, M., J. Li, F.B. Hu, J. Salas-Salvadó, D.K. Tobias, 2018. Effects of walnut consumption on blood lipids and other cardiovascular risk factors: an updated meta-analysis and systematic review of controlled trials. Am J Clin Nutr. doi: 10.1093/ajcn/nqy091. [Epub ahead of print]

BACKGROUND: Intervention studies suggest that incorporating walnuts into the diet may improve blood lipids without promoting weight gain. OBJECTIVE: We conducted a systematic review and meta-analysis of controlled trials evaluating the effects of walnut consumption on blood lipids and other cardiovascular risk factors. Design: We conducted a comprehensive search of PubMed and EMBASE databases (from database inception to January 2018) of clinical trials comparing walnut-enriched diets with control diets. We performed random-effects meta-analyses comparing walnut-enriched and control diets for changes in pre-post intervention in blood lipids (mmol/L), apolipoproteins (mg/dL), body weight (kg), and blood pressure (mm Hg). RESULTS: Twenty-six clinical trials with a total of 1059 participants were included. The following weighted mean differences (WMDs) in reductions were obtained for walnut-enriched diets compared with control groups: -6.99 mg/dL (95% CI: -9.39, -4.58 mg/dL; P < 0.001) (3.25% greater reduction) for total blood cholesterol (TC) and -5.51 mg/dL (95% CI: -7.72, -3.29 mg/dL; P < 0.001) (3.73% greater reduction) for low-density lipoprotein (LDL) cholesterol. Triglyceride concentrations were also reduced in walnut-enriched diets compared with control [WMD = -4.69 (95% CI: -8.93, -0.45); P = 0.03; 5.52% greater reduction]. More pronounced reductions in blood lipids were observed when walnut interventions were compared with American and Western diets [WMD for TC = -12.30 (95% CI: -23.17, -1.43) and for LDL = -8.28 (95% CI: -13.04, -3.51); P < 0.001]. Apolipoprotein B (mg/dL) was also reduced significantly more on walnut-enriched diets compared with control groups [WMD = -3.74 (95% CI: -6.51, -0.97); P = 0.008] and a trend towards a reduction was observed for apolipoprotein A [WMD = -2.91 (95% CI: -5.98, 0.08); P = 0.057]. Walnut-enriched diets did not lead to significant differences in weight change (kg) compared with control diets [WMD = -0.12 (95% CI: -2.12, 1.88); P = 0.90], systolic blood pressure (mm Hg) [WMD = -0.72 (95% CI: -2.75, 1.30); P = 0.48], or diastolic blood pressure (mm Hg) [WMD = -0.10 (95% CI: -1.49, 1.30); P = 0.88]. Conclusions: Incorporating walnuts into the diet improved blood lipid profile without adversely affecting body weight or blood pressure.

Effect of distinct lifestyle interventions on mobilization of fat storage pools: The CENTRAL MRI randomized controlled trial.

Gepner, Y., I. Shelef, D. Schwarzfuchs, H. Zelicha, L. Tene, A. Yaskolka Meir, G. Tsaban, N. Cohen, N. Bril, M. Rein, D. Serfaty, S. Kenigsbuch, O. Komy, A. Wolak, Y. Chassidim, R. Golan, H. Avni-Hassid, A. Bilitzky, B. Sarusi, E. Goshen, E. Shemesh, Y. Henkin, M. Stumvoll, M. Blüher, J. Thiery, U. Ceglarek, A. Rudich, M.J. Stampfer, I. Shai, 2018. Effect of distinct lifestyle interventions on mobilization of fat storage pools: The CENTRAL MRI randomized controlled trial. Circulation. 137(11):1143-1157. doi: 10.1161/CirculationAHA.117.030501.

Background: We aimed to assess whether distinct lifestyle strategies can differentially affect specific body adipose depots. Methods: We performed an eighteen-month randomized controlled trial among 278 sedentary adults with abdominal obesity (75%) or dyslipidemia in an isolated workplace with a monitored provided lunch. Participants were randomized to iso-caloric low-fat (LF) or Mediterranean/low-carbohydrate (MED/LC) diet+28g walnuts/day with/without added moderate physical activity (PA;80% aerobic; supervised/free gym membership). Overall primary outcome was body fat re-distribution, and the main specific endpoint was visceral adipose tissue (VAT). We further followed the dynamics of different fat depots [deep/superficial subcutaneous (D/SSAT), liver, pericardial, muscle, pancreas and renal-sinus] by magnetic-resonance-imaging. Results: Of 278 participants (age=48y; 89%men, body-mass-index=30.8kg/m2), 86% completed the trial, with good adherence. The LF group preferentially decreased reported fat intake (-21.0% vs. -11.5% for the MED/LC; P<0.001), and the MED/LC group decreased reported carbohydrates intake (-39.5%vs. -21.3% for the LF;P<0.001). The PA+ groups significantly increased the metabolic-equivalents (METs)/week vs. the PA- groups (19.0 vs. 2.1;P=0.009). Whereas final moderate weight loss was indifferent, exercise attenuated the waist circumference rebound with the greatest effect in MED/LCPA+ group (P<0.05). VAT (-22%), intra-hepatic (-29%), and Intra-pericardial (-11%) fats declines were higher than pancreatic and femur intermuscular fats (1-2%) loss. Independent of weight loss, PA+ with either diet had a significantly greater effect on decreasing VAT [mean-of-difference=-6.67cm2;95%CI:(-14.8 to -0.45) compared with PA-]. The MED/LC diet was superior to LF in decreasing intra-hepatic, intra-pericardial and pancreatic fats (P<0.05 for all). In contrast, renal-sinus and femoral-intermuscular fats were not differentially altered by lifestyle interventions, but by weight loss per-se. In multivariate models, further adjusted for weight loss, losing VAT or intra-hepatic fat were independently associated with improved lipid profile, losing deep-SAT with improved insulin sensitivity and losing superficial-SAT remained neutral except of association with decreased leptin. Conclusions: Moderate weight loss alone inadequately reflects the significant lifestyle effects on atherogenic and diabetogenic fat depots. The MED/LC diet mobilizes specific ectopic fat depots, and exercise has an independent contribution to VAT loss. Fat depots exhibit diverse responsiveness and are differentially related to cardiometabolic markers. Distinct lifestyle protocols may uniquely induce fat mobilization from specific anatomical sites.

The red blood cell proportion of arachidonic acid relates to shorter leukocyte telomeres in Mediterranean elders: A secondary analysis of a randomized controlled trial.

Freitas-Simoes, T.M., M. Cofán, M.A. Blasco, N. Soberón, M. Foronda, D. Corella, E.M. Asensio, M. Serra-Mir, I. Roth, C. Calvo, C. Valls-Pedret, R.P. Casaroli-Marano, M. Doménech, S. Rajaram, J. Sabaté, E. Ros, A. Sala-Vila, 2018. The red blood cell proportion of arachidonic acid relates to shorter leukocyte telomeres in Mediterranean elders: A secondary analysis of a randomized controlled trial. Clin Nutr. pii: S0261-5614(18)30074-8. doi: 10.1016/j.clnu.2018.02.011. [Epub ahead of print]

BACKGROUND & AIMS: Shortening of leukocyte telomere length (LTL) is a biomarker of aging. Epidemiologic studies of LTL in relation to dietary fatty acids have reported conflicting results. The red blood cell (RBC) fatty acid status is a valid objective biomarker of long-term dietary intake of C18:2n-6, C18:3n-3 and long-chain n-3 polyunsaturated fatty acids (C20:5n-3 and C22:6n-3). In healthy older individuals, we investigated whether LTL relates to the RBC proportions of the main dietary polyunsaturated fatty acids (PUFA), and to the RBC proportion of arachidonic acid (C20:4n-6), a fatty acid that can generate pro-inflammatory lipid mediators once released from cell membranes. DESIGN: Cross-sectional study in 344 subjects (mean age 68.8 y, 68.6% women) who participated in a randomized controlled trial testing whether a diet enriched in walnuts can delay the onset of age-related diseases (https://clinicaltrials.gov/ct2/show/NCT01634841). At baseline, we assessed LTL by high-throughput quantitative fluorescence and determined fatty acids in RBCs by gas chromatography. RESULTS: In multivariate models adjusted for age and gender, the RBC proportions of dietary PUFA were unrelated to LTL. In contrast, the RBC proportion of arachidonic acid inversely related to LTL (regression coefficient [95% confidence interval], -0.10 (-0.19 to -0.01), P = 0.023). CONCLUSION: An increasing proportion of C20:4n-6 in RBCs is associated with shorter telomeres. Further research is needed to investigate the role of this fatty acid and its derived lipid mediators in the aging process.

A walnut-enriched diet affects gut microbiome in healthy Caucasian subjects: A randomized, controlled trial.

Bamberger, C., A. Rossmeier, K. Lechner, L. Wu, E. Waldmann, S. Fischer, R.G. Stark, J. Altenhofer, K. Henze, K.G. Parhofer, 2018. A walnut-enriched diet affects gut microbiome in healthy Caucasian subjects: A randomized, controlled trial. Nutrients. 10(2). pii: E244. doi: 10.3390/nu10020244.

Regular walnut consumption is associated with better health. We have previously shown that eight weeks of walnut consumption (43 g/day) significantly improves lipids in healthy subjects. In the same study, gut microbiome was evaluated. We included 194 healthy subjects (134 females, 63 ± 7 years, BMI 25.1 ± 4.0 kg/m²) in a randomized, controlled, prospective, cross-over study. Following a nut-free run-in period, subjects were randomized to two diet phases (eight weeks each); 96 subjects first followed a walnut-enriched diet (43 g/day) and then switched to a nut-free diet, while 98 subjects followed the diets in reverse order. While consuming the walnut-enriched diet, subjects were advised to either reduce fat or carbohydrates or both to account for the additional calories. Fecal samples were collected from 135 subjects at the end of the walnut-diet and the control-diet period for microbiome analyses. The 16S rRNA gene sequencing data was clustered with a 97% similarity into Operational Taxonomic Units (OTUs). UniFrac distances were used to determine diversity between groups. Differential abundance was evaluated using the Kruskal-Wallis rank sum test. All analyses were performed using Rhea. Generalized UniFrac distance shows that walnut consumption significantly affects microbiome composition and diversity. Multidimensional scaling (metric and non-metric) indicates dissimilarities of approximately 5% between walnut and control (p = 0.02). The abundance of Ruminococcaceae and Bifidobacteria increased significantly (p < 0.02) while Clostridium sp. cluster XIVa species (Blautia; Anaerostipes) decreased significantly (p < 0.05) during walnut consumption. The effect of walnut consumption on the microbiome only marginally depended on whether subjects replaced fat, carbohydrates or both while on walnuts. Daily intake of 43 g walnuts over eight weeks significantly affects the gut microbiome by enhancing probiotic- and butyric acid-producing species in healthy individuals. Further evaluation is required to establish whether these changes are preserved during longer walnut consumption and how these are linked to the observed changes in lipid metabolism.