When people in the study added 56 grams of walnuts (2 ounces, or about 14 walnuts) to their daily diet for six months, they had improvements in blood vessel function and reductions in “bad” LDL cholesterol, which builds up in blood vessels and can lead to blood clots and heart attacks.
Blood vessel dysfunction and high LDL cholesterol are both risk factors for type 2 diabetes, which is associated with obesity and aging and occurs when the body can’t make or process enough of the hormone insulin.
Walnuts, which are rich in fatty acids and other nutrients like folate and vitamin E, weren’t linked to weight gain in the study even though they are a high-calorie food.
“Adding walnuts to your diet will improve your diet quality and health – cardiometabolic health specifically – and you can add walnuts without fear of weight gain because they are very satiating and appear to bump out other calories quite reliably and make room for themselves,” said study author Dr. David L. Katz of the Yale University Prevention Research Center in Derby, Connecticut.
The nuts didn’t seem to improve high blood pressure and high blood sugar, two other risk factors for diabetes, Katz and colleagues reported in BMJ Open Diabetes Research and Care.
For the study, the researchers randomly assigned 31 men and 81 women at high risk for diabetes to follow a reduced calorie diet with or without nutrition counseling.
Within these groups, half of the participants were assigned at random to add walnuts to their diet for six months. After a three-month break from the experiment, researchers then switched the groups and assigned walnuts to the participants who were previously asked to abstain from eating them.
Participants ranged in age from 25 to 75. All had multiple risk factors for diabetes, such as being overweight, or having high blood sugar, blood pressure or cholesterol, or having excess fat around the midsection.
After taking into account factors such as age, exercise habits, calorie consumption and fatty acid intake, the study found walnuts were linked to improved diet quality regardless of whether people received nutrition counseling.
The California Walnut Commission funded the study and has compensated Katz for speaking engagements.
One limitation of the research is that participants weren’t given specific foods to consume and diets were assessed based on self-reported surveys asking people at several points to recall what they ate in the previous 24 hours, the authors acknowledge. The study also wasn’t designed to show whether walnuts could prevent diabetes, which makes the results less reliable.
Even though the data from the study suggest that adding walnuts to the diet can help maintain overall healthy eating habits, more research from larger and longer-term studies is still needed to fully understand the potential benefits of walnuts, said Roberta Holt, a nutrition researcher at the University of California, Davis, who wasn’t involved in the study.
Results from the periodic diet surveys aren’t enough to prove walnuts caused the changes in LDL cholesterol or blood vessel function, Holt added by email.
“While the intake of walnuts improved LDL cholesterol and vascular function from baseline, the control (no walnuts) also improved,” Holt noted.
Even so, there is plenty of previous research linking consumption of walnuts to improved markers of heart health and lower risks of diabetes and heart disease, noted Deirdre Tobias, an epidemiologist at Brigham and Women’s Hospital and Harvard Medical School in Boston.
“Walnuts and other tree nuts are a healthful source of plant-based protein and fat,” Tobias, who wasn’t involved in the study, said by email. “They are a food that (is) consistent with overall dietary recommendations and can easily be incorporated into a patient’s diet, if they like walnuts and are not allergic.”
SOURCE: bit.ly/1NG8vvI BMJ Open Diabetes Research and Care, online November 23, 2015.
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