Table 1.
Characteristics of the selected studies.
| Reference | Country | Study (RCT) Design |
Exposure Period |
Washout Period |
Participants (n), Health Status |
Age (Years), (SD)/(IQR) (Range) | Female (%) | Walnut Intervention (g/d) |
Control Intervention |
Outcome of Interest |
|---|---|---|---|---|---|---|---|---|---|---|
| Zambόn et al., 2000 [31] | Spain, USA | Crossover | 6 weeks | 0 | 49 polygenic hypercholesterolemia * | 56 (±11) | 47% | 41–56 g/d (18% of the energy need) | MedD (no walnut) |
BW, TC, LDL-C, HDL-C, TG |
| Ros et al., 2004 [32] |
Spain | Crossover | 4 weeks | 0 | 20 healthy, non-smokers (hypercholesterolemia) | 55 (±55.9) | 60% | 40–65 g/d (18% of energy need) | MedD (no walnut) |
BW, SBP, DBP, TC, LDL-C, HDL-C, CRP, |
| Tapsell et al., 2004 [33] | Australia | Parallel | 6 months | NA | 58 T2D * | 59.3 (±8.1) | 41.37% | 30 g/d—walnut-enriched modified low-fat diet | Modified low-fat diet (no walnuts) | BW, BMI, HbA1c, TC, LDL-C, HDL-C, TG |
| Olmedilla- Alonso et al., 2008 [34] |
Spain | Crossover | 5 weeks | 1 month | 25 CV risk, smokers | 54.4 (±8.1) | 40% | 19.4 g/d (20% walnut-enriched meat products) | Restructured meat products (no walnut) | TC, HDL-C, LDL-C, TG, BW, SBP, DBP |
| Spaccarotella et al., 2008 [35] | USA | Crossover | 8 weeks | 2 weeks | 21 healthy, non-smokers | 65.9 (55–75) | 0% | 75 g/d (24% of energy need) | Western-type diet (no walnut) | SBP, DBP, TC, HDL-C, LDL-C |
| Tapsell et al., 2009 [36] | Australia | Parallel | 1 year | NA | 50 T2D * | 54 (±8.7) | NI | 30 g/d (walnut-enriched 2000 kcal diet, 30% fat) | 2000 kcal diet, 30% fat (no walnut) | BW, FBG, TC, HDL-C, LDL-C, TG, HbA1c, insulin |
| Ma et al., 2010 [37] |
USA | Crossover | 8 weeks | 8 weeks | 21 T2D, non-smokers | 58.1 (±9.2) | 58.30% | 56 g/d | Habitual diet (no walnut) | TC, HDL-C, LDL-C, TG, FPG, insulin, HOMA-IR, BW, BMI, WC, SBP, DBP |
| Torabian et al., 2010 [38] | USA | Crossover | 6 months | 0 | 87 healthy, non-smokers | 54 (±10.2) | 56% | 28–64 g/d (12% of energy need) | Habitual diet (no walnut) | TC, LDL-C, HDL-C, TG |
| Canales et al., 2011 [39] | Spain | Crossover | 5 weeks | 4–6 weeks | 22 CV risk, smokers | 54.8 (±9.4) | 40% | 34–29 g/d (20% walnut-enriched meat) | Low-fat meat products (no walnut) | VCAM-1, ICAM-1, HDL-C |
| Katz et al., 2012 [40] |
USA | Crossover | 8 weeks | 4 weeks | 40 healthy, non-smokers (overweight, MetS risk) | 57.4 (±11.9) | 60.9% | 56 g/d | Habitual diet (no walnut) | TC, HDL-C, LDL-C, TG, FPG, insulin, HOMA-IR, BW, BMI, WC, SBP, DBP |
| Wu et al., 2014 [41] |
Germany, USA | Crossover | 8 weeks | 2 weeks | 40 healthy * | 60 (±6.32) | 75% | 43 g/d (replacing 30 g saturated fat in Western-type diet) | Western-type diet (no walnut) | TC, LDL-C, HDL-C, FBG, insulin, HOMA-IR, HbA1c, VCAM-1, ICAM-1 |
| Bamberger et al., 2017 [42] | Germany | Crossover | 8 weeks | 4 weeks | 194 healthy, non-smokers | 63 (±7) | 69% | 43 g/d | Western-type diet (no walnut) | TC, LDL-C, HDL-C, TG |
| Bitok et al., 2018 [43] | USA, Spain | Parallel | 2 years | NA | 307 healthy * | 69.4 (±3.9) | 67% | 28; 42; 56 g/d (15% of energy need) | Habitual diet (no walnut) | BW, WC |
| Domènech et al., 2019 [44] | USA, Spain | Parallel | 2 years | NA | 236 healthy * (60% mild hyper-tension) | 68.8 (±3.3) | 65% | 30–60 g/d, (15% of energy need) | Habitual diet (no walnut) | SBP, DBP |
| Sanchis et al., 2019 [45] | Spain | Crossover | 30 days | 30 days | 13 CKD * | 71 (±10.11) | 46.20% | 30 g/d (walnut-enriched CKD diet) | CKD patients’ diet (no walnut) | BMI, TC, HDL-C, LDL-C, TG, FBG, HbA1c, CRP |
| Abdrabalnabi et al., 2020 [46] | USA, Spain | Parallel | 2 years | NA | 625 healthy * | 69.1 (±3.6) | 67% | 30; 45; 60 g/d (15% of energy need) | Habitual diet (no walnut) | BMI, SBP, DBP, TG, HDL-C, FBG |
| Cofán et al., 2020 [47] | USA, Spain | Parallel | 2 years | NA | 634 healthy * | 69.1 (±3.6) | 66% | 30; 45; 60 g/d (15% of energy need) | Western-type diet (no walnut) | VCAM-1, ICAM-1, IL-6, IFN-γ, IL-1β, TNF-α, E-selectin, hs-CRP |
*—non-specified smoking status; RCT—randomized controlled trials; NA—not applicable; BMI—body mass index; BW—body weight; CKD—chronic kidney disease; CV—cardiovascular; CRP—C-reactive protein; hs-CRP—high-sensitivity C-reactive protein; DBP—diastolic blood pressure; FBG—fasting blood glucose; HbA1c—glycosylated hemoglobin A1c; HDL-C—high-density lipoprotein cholesterol; HOMA-IR—homeostatic model assessment for insulin resistance; ICAM—intercellular adhesion molecule; IFN-γ—interferon gamma; IL-1β—interleukin-1β; IL-6—interleukin-6; IQR—interquartile range; LDL-C—low-density lipoprotein cholesterol; MedD—Mediterranean diet; MetS—metabolic syndrome; NI—no information; SBP—systolic blood pressure; SD—standard deviation; T2D—type 2 diabetes; TC—total cholesterol; TG—triglycerides; TNF-α—tumor necrosis factor-alpha; VCAM—the vascular cell adhesion molecule; WC—waist circumference.