Nuts in the diet and bodyweight: What's the relationship?

Walnut consumption and health outcomes with public health relevance-a systematic review of cohort studies and randomized controlled trials published from 2017 to present

CONTEXT

Considering the accumulation of recent studies investigating the health effects of walnut consumption, both including and beyond cardiovascular health effects, a systematic review of this literature to investigate the strength of the evidence is warranted.

OBJECTIVE

To investigate associations between walnut consumption and outcomes with public health relevance (specifically all-cause mortality, type 2 diabetes, CVD, metabolic syndrome, obesity, cancer, neurological and mental health, musculoskeletal, gastrointestinal, and maternal disorders) and the effect on associated disease risk markers, reported in studies published from 2017 to present.

DATA SOURCES

MEDLINE, FSTA, CENTRAL, and Scopus were searched from 1 January 2017 to 5 May 2021.

DATA EXTRACTION

Human studies (cohort studies and RCTs) ≥3 weeks in duration comparing consumption of walnuts (whole, pieces, or 100% butter) to a control and measuring associations with relevant public health outcomes and disease risk markers were assessed. Key study characteristics were extracted independently by 2 investigators using a standardized table. The quality of the studies was assessed using the Cochrane Risk-of-Bias tool 2.0 and the Newcastle-Ottawa Scale.

DATA ANALYSIS

Only 1 RCT was considered to be at low risk of bias for any of its outcomes. The cohort studies were considered to be of moderate or high quality. The results were synthesized using vote counting, based on the direction of effect. Thirty-three articles, 23 describing RCTs (walnut dose ∼10-99 g/day, 1,948 subjects) and 10 describing cohort studies (∼675,928 subjects), were included. Vote counting could be performed for the blood lipids, cardiovascular function, inflammation- and hemostatic-related factors, markers of glucose metabolism, and body weight and composition outcome groupings. The results are presented in effect direction plots. With respect to blood lipids, results from 8/8 RCTs favoured walnuts, in accordance with associations with a reduced risk of CVD suggested by cohort studies; results from 6/6 RCTs favoured control with respect to body weight and composition, although most of these effects were small. This was contrary to cohort study results suggesting small benefits of walnut consumption on body weight. There was no overall consistent direction of effect for cardiovascular function, markers of glucose metabolism, or inflammation- and hemostatic-related factors.

CONCLUSIONS

Evidence published since 2017 is consistent with previous research suggesting that walnut consumption improves lipid profiles and is associated with reduced CVD risk. Evidence is accumulating in other areas, such as cognitive health, although more research is needed to draw firm conclusions.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no. CRD4202122.

Effects of Pistachio Consumption in a Behavioral Weight Loss Intervention on Weight Change, Cardiometabolic Factors, and Dietary Intake

Epidemiological studies have linked regular nut consumption with lower body mass index and reduced likelihood of weight gain in adulthood. Nuts can displace other foods in the diet, and thus, promote a healthier dietary pattern. The purpose of this study was to examine the effect of pistachio nut consumption in overweight/obese adults. This randomized controlled study enrolled non-diabetic overweight/obese adults (n = 100) assigned to a 4-month behavioral weight loss intervention only group (controls) or also prescribed 1.5 oz/day (42 g/day) of pistachios (pistachio group). Outcomes were change in body weight, cardiometabolic factors, and dietary intake. Percent weight change was similar in the two groups (−5.1 [0.5] (mean [SE])% in the control group and −4.9 [0.6]% in the pistachio group, and body mass index (BMI) and waist circumference were reduced in both groups (time effect p ≤ 0.05). The pistachio group (but not the control group) exhibited a significant reduction in both systolic and diastolic blood pressure (time effect p = 0.01). Plasma alpha-carotene, beta-carotene, and lutein concentrations increased significantly in the pistachio group (time effect p < 0.05). Pistachio consumption was associated with increased dietary fiber intake and decreased consumption of sweets. Regular consumption of pistachios was associated with a comparable degree of weight loss, and similar reductions in BMI and waist circumference, in overweight/obese men and women compared to controls, and favorable changes in the diet, in the context of a behavioral weight loss intervention.