In a large Spanish study, participants who followed the Mediterranean diet supplemented with three nuts, primarily walnuts, showed a 13.7% decrease in Metabolic Syndrome -- as opposed to those following a Mediterranean diet supplemented with olive oil (6.7% decrease) and the control group consuming a standard low fat diet (2% decrease). According to The American Heart Association, 47 million Americans have metabolic syndrome and is a growing problem. metabolic syndrome is defined as having three or more of the following conditions: abdominal obesity, high triglycerides, low levels of good cholesterol (HDL), high blood sugar and high blood pressure was used as the outcome measurement.