Eating tree nuts appears to help reduce two of the five markers for metabolic syndrome, a group of factors that raise the risk for heart disease and other health problems such as diabetes and strokes, a new research paper says.
The paper found a "modest decrease" in blood fats known as triglycerides and blood sugars among people who added tree nuts to their diets compared to those who ate a control diet.
The paper, by Dr. John Sievenpiper, a physician and researcher in the Clinical Nutrition and Risk Factor Modification Centre of St. Michael's Hospital, was published today in the journal BMJ Open.
Dr. Sievenpiper said he believes this is the first systematic review and meta-analysis examining all of the collective evidence of randomized clinical trials on the effect of tree nuts on metabolic syndrome. After screening 2,000 articles published in peer-reviewed journals, he found 49 randomized control trials with 2,000 participants.
A person is considered to have metabolic syndrome if he or she has three of the following risk factors: low levels of "good" cholesterol; high triglycerides; high blood pressure; high blood sugar; extra weight around the waist.
Dr. Sievenpiper said the biggest reductions in triglycerides and blood glucose were seen when tree nuts replaced refined carbohydrates rather than saturated fats. He said there was no adverse impact on the other risk factors for metabolic syndrome or weight gain, even though nuts are high in calories. Nuts also have a high fat content, but it's good, or unsaturated, fat.
Tree nuts are such things as almonds, Brazil nuts, cashews, chestnuts, coconuts, hazelnuts, pecans, macadamia nuts, walnuts, pine nuts and pistachios. They do not include peanuts, which are legumes.
In the randomized control studies, patients ate about 50 grams of nuts a day or about 1-1/2 servings. One serving of tree nuts is about ¼ cup or 30 grams. He said that people in North America consume on average less than one serving a day, so this is one way they can adapt their diets to take advantage of the metabolic benefits.
"Fifty grams of nuts can be easily integrated into a diet as a snack or as a substitute for animal fats or refined carbohydrates," Dr. Sievenpiper said.
The U.S. Food and Drug Administration has granted tree nuts a qualified health claim for cardiovascular disease risk reduction. Tree nuts are also recommended as part of the Mediterranean, Portfolio and DASH (Dietary Approaches to Stop Hypertension) diets for cardiovascular disease prevention and management based on their ability to reduce bad cholesterol.