A systematic review and meta-analysis of randomized clinical trials on the effects of tree nuts for metabolic syndrome found a "modest decrease" in blood fats known as triglycerides and blood sugars compared to those who ate a control diet. 

 Tree nuts are such things as almonds, Brazil nuts, cashews, chestnuts, coconuts, hazelnuts, pecans, macadamia nuts, walnuts, pine nuts and pistachios and appear 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. 

Sorry Mr. Peanut, you are not on the list because you are a legume.

Credit and link: gloriouskyle

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. 
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. 

The authors screened 2,000 articles published in peer-reviewed journals and used 49 randomized control trials with 2,000 participants. 

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.

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," said Dr. John Sievenpiper, a physician and researcher in the Clinical Nutrition and Risk Factor Modification Centre of St. Michael's Hospital.

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.

Citation: Sonia Blanco Mejia, Cyril W C Kendall, Effie Viguiliouk, Livia S Augustin, Vanessa Ha, Adrian I Cozma, Arash Mirrahimi, Adriana Maroleanu, Laura Chiavaroli, Lawrence A Leiter, Russell J de Souza, David J A Jenkins, John L Sievenpiper, 'Effect of tree nuts on metabolic syndrome criteria: a systematic review and meta-analysis of randomised controlled trials', BMJ Open 2014;4:e004660 doi:10.1136/bmjopen-2013-004660. Source: St. Michael's Hospital