Effects of Supplementing the Usual Diet with a Daily Dose of Walnuts for Two Years on Metabolic Syndrome and Its Components in an Elderly Cohort

Abstract

Accumulating evidence links nut consumption with an improved risk of metabolic syndrome (MetS); however, long-term trials are lacking. We examined the effects of a daily dose of walnuts for two years on MetS in a large elderly cohort. A total of 698 healthy elderly participants were randomly assigned to either a walnut supplemented or a control diet. The participants in the walnut group were provided with packaged walnuts (1, 1.5, or 2 oz. or ~15% of energy) and asked to incorporate them into their daily habitual diet. The participants in the control group were asked to continue with their habitual diet and abstain from eating walnuts and other tree nuts. Intake of n-3 fatty acid supplements was not permitted in either group. Fasting blood chemistries, blood pressure, and anthropometric measurements were obtained at baseline and at the end of intervention. A total of 625 participants (67% women, mean age 69.1 y) completed this two-year study (90% retention rate). Triglycerides decreased in both walnut (−0.94 mg/dl) and control (−0.96 mg/dl) groups, with no significant between-group differences. There was a non-significant decrease in systolic and diastolic blood pressure in the walnut group (−1.30 and −0.71 mm Hg, respectively) and no change in the control group. Fasting blood glucose decreased by ~1 point in both the walnut and control groups. There were no significant between-group differences in the development or reversion of MetS. In conclusion, supplementing the diet of older adults with a daily dose of walnuts had no effect on MetS status or any of its components, although the walnut group tended to have lower blood pressure.

Effects of walnut intake on blood pressure: A systematic review and meta‐analysis of randomized controlled trials

“…In general, studies before 2004 did not provide adequate data for our analyses. Studies were conducted in the United States (Al Abdrabalnabi et al, 2020; Katz et al, 2012; Ma et al, 2010; Njike, Ayettey, Petraro, Treu, & Katz, 2015; Rock, Flatt, Barkai, Pakiz, & Heath, 2017; Spaccarotella et al, 2008; Tindall et al, 2019), Republic of Korea (Hwang et al, 2019), Australia (Ndanuko, Tapsell, Charlton, Neale, & Batterham, 2018), Iran (Fatahi, Haghighatdoost, Larijani, & Azadbakht, 2019; Nezhad, Aghasadeghi, Hakimi, Yarmohammadi, & Nikaein, 2016), United Kingdom (Din et al, 2011), Spain (Olmedilla‐Alonso et al, 2008; Ros et al, 2004; Sanchis et al, 2019), Chine (Wu et al, 2010), and New Zealand (Mukuddem‐Petersen, Stonehouse Oosthuizen, Jerling, Hanekom, & White, 2007). The follow‐up period ranged from 4 weeks to 2 years.…”

“…Another limitation is the follow‐up period, which ranged from 4 weeks to 2 years and, therefore, long‐term effects (i.e., years) of walnut consumption on BP cannot be estimated. Only two included studies were carried out on a ≥1 year follow‐up (Al Abdrabalnabi et al, 2020; Sanchis et al, 2019).…”

Dose-dependent effect of nuts on blood pressure: a systematic review and meta-analysis of randomized controlled trials

“…Eventually, 108 full texts were fully reviewed for eligibility. Of those, 31 randomised trials with 2784 participants were eligible for inclusion in dose-response meta-analysis (27-57). Detailed screening and data extraction processes are depicted in Supplementary Figure 1 , and list of studies excluded based on reviewing the full texts are presented in Supplementary Table 2 .…”

“…Eligible trials were published between 2007 and 2020. Twelve trials were conducted in individuals at high risk of CVD (with at least one cardiometabolic risk factor) (36, 37, 40, 42, 45-47, 49-51, 53, 55), six trials each in patients with type 2 diabetes (30, 38, 41, 43, 48, 56) and healthy individuals (27, 32-34, 50, 52), four in patients with the metabolic syndrome (29, 44, 54, 57), and three in those with a history of CVD (28, 31, 39). Fourteen trials were conducted exclusively in individuals with overweight/obesity (30-33, 35, 36, 40, 42, 45, 47, 49, 50, 52, 53), and the remainders in mixed populations (27-29, 34, 37-39, 41, 43, 44, 46, 48, 51, 54-57).…”

“…The dose of nut consumption ranged between 15 to 85 g/d. Three trials compared the effect of two doses of a specific type of nut against a nut free diet (52, 54, 55), and the remainder compared the effects of a nut-supplemented diet against a nut free diet (27-51, 53, 56, 57). One study compared the effect of two different types of nuts against a nut free diet and thus, was included as two study arms in the analysis (44).…”