Nutritional research now confirms that walnuts and nuts in general are one of the healthiest food-groups that we can consume for supporting cardiovascular health.
Studies have found that higher nut intake is associated with reduced risk of cardiovascular disease, total cancer and all-cause mortality, and mortality from respiratory disease, diabetes, and infections. 
All tree nuts are considered to be healthy, however walnuts may offer additional heart-health benefits due to their unique nutrient composition and rich content of polyunsaturated omega-3 fatty acids(alpha-linolenic acid).
Walnuts are so powerful that they have the ability to address multiple common risk factors for developing atherosclerosis such as endothelial dysfunction, inflammation, oxidative stress, obesity and dyslipidemia.
Let’s take a look at five evidence-based ways walnuts help to support cardiovascular health and to reduce risk of developing heart disease.
Walnuts Significantly Decrease Total & LDL-Cholesterol Levels
A meta-analysis and systematic review published in 2009 conducted a literature review and a meta-analysis to combine the results from several trials and to estimate the effect of walnuts on blood lipids.
Thirteen studies representing 365 participants were included in the analysis. Diets lasted 4–24 wk with walnuts providing 10–24% of total calories.
When compared with control diets, diets supplemented with walnuts resulted in a significantly greater decrease in total cholesterol and in LDL-cholesterol concentrations (total cholesterol: WMD = −10.3 mg/dL, P < 0.001; LDL cholesterol: WMD = −9.2 mg/dL, P < 0.001).
The meta-analysis and systematic review concluded:
Overall, high-walnut-enriched diets significantly decreased total and LDL cholesterol for the duration of the short-term trials. 
Walnuts Improve Endothelial Function
Endothelial dysfunction is a systemic pathological state of the endothelium (the inner lining of blood vessels) and is considered to be a major pathophysiological mechanism in the development of cardiovascular disease.
Nuts and Walnuts in particular have been shown to improve endothelial function in many studies.
A meta-analysis of randomized controlled trials (RCTs) aimed to quantitatively assess the effect of nuts on vascular endothelial function.
A total of nine papers (10 trials) involving 374 participants were included. The pooled estimates found that nut consumption significantly improved FMD.
Subgroup analyses indicated that walnuts significantly improved FMD (WMD: 0.39%; 95% CI: 0.16%, 0.63%; P = 0.001).
The systematic review and meta-analysis concluded:
Nut consumption significantly improved endothelial function. However, the beneficial effect was limited to walnuts. 
Another study published 2012 in the Journal Of The American College Of Nutrition performed a randomized controlled crossover trial to investigate the effects of daily walnut consumption on endothelial function and other biomarkers of cardiac risk in a population of overweight individuals with visceral adiposity.
FMD improved significantly from baseline when subjects consumed a walnut-enriched diet as compared with the control diet (1.4% ± 2.4% versus 0.3% ± 1.5%; p = 0.019). Beneficial trends in systolic blood pressure reduction were seen, and maintenance of the baseline anthropometric values was also observed. Other measures were unaltered.
Daily ingestion of 56 g of walnuts improves endothelial function in overweight adults with visceral adiposity. The addition of walnuts to the diet does not lead to weight gain. 
Walnut Enriched Diets Promote Weight Loss
One of the biggest myths surrounding nuts is the fear that they may increase weight gain, due to the moderately high calorie and fat content.
However, the research has consistently found the complete opposite to be true, which is that nut enriched diets actually promote weight loss, have an anti-obesity effect and don’t cause any significant weight gain. Nuts have also been shown to reduce abdominal adiposity(belly fat).
The fats that nuts contain are predominantly the heart-healthy monunsaturated fatty acids and in walnuts case, the rich content of Omega-3 fatty acids also, which are thought to confer to additional cardio-protective benefits.
A study published 2017 in the BioMed Central Nutrition Journal compared the effects of a walnut-enriched reduced-energy diet to a standard reduced-energy-density diet on weight, cardiovascular disease risk factors, and satiety.
The study concluded:
These findings provide further evidence that a walnut-enriched reduced-energy diet can promote weight loss that is comparable to a standard reduced-energy-density diet in the context of a behavioral weight loss intervention.
Although weight loss in response to both dietary strategies was associated with improvements in cardiovascular disease risk factors, the walnut-enriched diet promoted more favorable effects on LDL-C and systolic blood pressure.
Another study published in 2017 examined the impact of including walnuts in diets for weight loss.
The study concluded:
Including 30 grams walnuts/day in an individualized diet produced weight loss and positive changes in food choice. 
Walnuts Reduce Some Markers Of Inflammation
The inflammatory hypothesis of atherosclerosis is now well-accepted at this point. with a massive body of scientific literature supporting the role of inflammation in the development of cardiovascular disease.
A study published 2009 in the American Journal Of Clinical Nutrition stated:
Some inflammatory markers also improved with walnut consumption compared with other diets. Evidence for C-reactive protein reduction was inconsistent, although decreases in VCAM-1 were apparent among subjects during walnut-rich diets. 
Walnuts Reduce Some Markers Of Oxidative Stress
Much like inflammation, oxidative stress is another common factor in the development of heart disease and many other serious health problems.
Walnut polyphenols had the best efficacy among the nuts and also the highest lipoprotein-bound antioxidant activity. 
General antioxidant capacity was evaluated in 2 studies, both of which found significant decreases in oxidized glutathione during the walnut diet phase compared with the control phase.
The other common marker between the 2 studies was glutathione, but only 1 study found significantly decreased concentrations. Other markers of antioxidant capacity were improved with a walnut diet in individual studies, but have yet to be evaluated in other trials. 
 Nut consumption and risk of cardiovascular disease, total cancer, all-cause and cause-specific mortality: a systematic review and dose-response meta-analysis of prospective studies
 Effects of walnut consumption on blood lipids and other cardiovascular risk factors: a meta-analysis and systematic review
 Effect of nut consumption on vascular endothelial function: A systematic review and meta-analysis of randomized controlled trials.
 Effects of Walnuts on Endothelial Function in Overweight Adults with Visceral Obesity: A Randomized, Controlled, Crossover Trial
 Walnut consumption in a weight reduction intervention: effects on body weight, biological measures, blood pressure and satiety
 Impact of providing walnut samples in a lifestyle intervention for weight loss: a secondary analysis of the HealthTrack trial
 Nuts, especially walnuts, have both antioxidant quantity and efficacy and exhibit significant potential health benefits.
The information in this article has not been evaluated by the FDA and should not be used to diagnose, cure or treat any disease, implied or otherwise.