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Type 2 diabetics could significantly improve their bodies' responses to stress simply by eating two servings of pistachios per day, according to a recent study conducted by researchers from Penn State University and published in the Journal of the American Heart Association.
"In adults with diabetes, two servings of pistachios per day lowered vascular constriction during stress and improved neural control of the heart," researcher Sheila G. West, PhD, said. "Although nuts are high in fat, they contain good fats, fiber, potassium and antioxidants. Given the high risk of heart disease in people with diabetes, nuts are an important component of a heart healthy diet in this population."
Healthier reactions under stress
The study was conducted on adults with well controlled type 2 diabetes and no other health problems. For six weeks, all participants ate only the meals provided by the researchers. The first two weeks consisted of a standard U.S. diet, containing 36 percent of its calories from fat and 12 percent of total calories from saturated fat. After this, participants were randomly assigned to consume one of two diets for another four weeks.
One group consumed a typical heart-healthy diet, with 27 percent of its calories from fat and 7 percent of calories from saturated fat. The other group consumed a diet that got 20 percent of its calories from pistachio nuts (3 ounces, corresponding to two servings or about 150 nuts per day). Participants on this diet got 33 percent of their calories from fat, but still only 7 percent from saturated fat.
After four weeks on the experimental diets, participants had their blood pressure and total peripheral vascular resistance measured while performing one of two stress tests. The first test (physical) consisted of placing a hand in icy water for two minutes. The researchers found that participants on the pistachio diet showed less vascular constriction (a sign of stress) than participants on the control diet.
"This cold stressor produces a large vascular constriction response in most people," West said. "In comparison with a low fat diet, the pistachio diet blunted that vascular response to stress."
Participants in the pistachio group showed the same effect during the second test, which consisted of solving a confusing mental math problem.
"After the pistachio diet, blood vessels remained more relaxed and open during the stress tests," West said.
West noted that it was the physiological stress response that pistachios blunted, not the emotional one.
"Our participants still felt frustrated and angry during the math test," West noted. "The pistachio diet reduced their bodies' responses to stress, but nuts are not a cure for the emotional distress that we feel in our daily lives."
Longer-term benefits
While there was no difference between the blood pressure of the two groups during the stress test, the researchers found that participants in the pistachio group did have lower blood pressure overall throughout the course of the day.
"We found that systolic blood pressure during sleep was particularly affected by pistachios," researcher Katherine A. Sauder said. "Average sleep blood pressure was reduced by about 4 points and this would be expected to lower workload on the heart."
The researchers also found that participants on the pistachio diet had improved heart rate variability, suggesting better nervous system control of the heart. This, in turn, suggests increased activity of the vagus nerve, which is associated with the parasympathetic nervous system ("the relaxation response").
"If sustained with longer term treatment, these improvements in sleep blood pressure, vascular response to stress and vagal control of the heart could reduce risk of heart disease in this high risk group," West said.
The study was funded by the American Pistachio Growers and the National Institutes of Health.
"In adults with diabetes, two servings of pistachios per day lowered vascular constriction during stress and improved neural control of the heart," researcher Sheila G. West, PhD, said. "Although nuts are high in fat, they contain good fats, fiber, potassium and antioxidants. Given the high risk of heart disease in people with diabetes, nuts are an important component of a heart healthy diet in this population."
Healthier reactions under stress
The study was conducted on adults with well controlled type 2 diabetes and no other health problems. For six weeks, all participants ate only the meals provided by the researchers. The first two weeks consisted of a standard U.S. diet, containing 36 percent of its calories from fat and 12 percent of total calories from saturated fat. After this, participants were randomly assigned to consume one of two diets for another four weeks.
One group consumed a typical heart-healthy diet, with 27 percent of its calories from fat and 7 percent of calories from saturated fat. The other group consumed a diet that got 20 percent of its calories from pistachio nuts (3 ounces, corresponding to two servings or about 150 nuts per day). Participants on this diet got 33 percent of their calories from fat, but still only 7 percent from saturated fat.
After four weeks on the experimental diets, participants had their blood pressure and total peripheral vascular resistance measured while performing one of two stress tests. The first test (physical) consisted of placing a hand in icy water for two minutes. The researchers found that participants on the pistachio diet showed less vascular constriction (a sign of stress) than participants on the control diet.
"This cold stressor produces a large vascular constriction response in most people," West said. "In comparison with a low fat diet, the pistachio diet blunted that vascular response to stress."
Participants in the pistachio group showed the same effect during the second test, which consisted of solving a confusing mental math problem.
"After the pistachio diet, blood vessels remained more relaxed and open during the stress tests," West said.
West noted that it was the physiological stress response that pistachios blunted, not the emotional one.
"Our participants still felt frustrated and angry during the math test," West noted. "The pistachio diet reduced their bodies' responses to stress, but nuts are not a cure for the emotional distress that we feel in our daily lives."
Longer-term benefits
While there was no difference between the blood pressure of the two groups during the stress test, the researchers found that participants in the pistachio group did have lower blood pressure overall throughout the course of the day.
"We found that systolic blood pressure during sleep was particularly affected by pistachios," researcher Katherine A. Sauder said. "Average sleep blood pressure was reduced by about 4 points and this would be expected to lower workload on the heart."
The researchers also found that participants on the pistachio diet had improved heart rate variability, suggesting better nervous system control of the heart. This, in turn, suggests increased activity of the vagus nerve, which is associated with the parasympathetic nervous system ("the relaxation response").
"If sustained with longer term treatment, these improvements in sleep blood pressure, vascular response to stress and vagal control of the heart could reduce risk of heart disease in this high risk group," West said.
The study was funded by the American Pistachio Growers and the National Institutes of Health.
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