Research and health effects11 Jul 2017 In July 2003, the United States' Food and Drug Administration (FDA) approved the first qualified health claim specific to seeds lowering the risk of heart disease: "Scientific evidence suggests but does not prove that eating 1.5 ounces (42.5 g) per day of most nuts, such as pistachios, as part of a diet low in saturated fat and cholesterol may reduce the risk of heart disease". Although pistachios contain many calories, epidemiologic studies have provided strong evidence that their consumption is not associated with weight gain or obesity. A 2015 systematic review and meta-analysis of randomized controlled trials concluded that pistachio consumption in persons without diabetes mellitus appears to modestly lower systolic and diastolic blood pressure. Several mechanisms for pistachios' antihypertensive properties have been proposed. These mechanisms include pistachios' high levels of the amino acidarginine (a precursor of the blood vessel dilating compound nitric oxide); high levels of phytosterols and monounsaturated fatty acids; and improvement of endothelial cell function through multiple mechanisms including reductions in circulating levels of oxidized low density lipoprotein cholesterol and pro-inflammatory chemical signals.