One meta-analysis of 21 studies said that there was not enough evidence to conclude that saturated fat increases the risk of heart disease, but that replacing saturated fat with polyunsaturated fat may indeed reduce risk of heart disease. The main fat in their diet, though, was not the saturated animal fat common in countries with higher rates of heart disease. However, besides peanuts, peanut butter contains also added components like salt and vegetable oils. The adverse health effects of salt and trans fatty acids could inhibit the protective effects of peanuts.
– Previous studies have documented that scarfing down peanuts or nuts every day can lead to better cardiovascular health. But now research is suggesting that eating peanuts and tree nuts like almonds, cashews, and walnuts are linked to lower mortality rates, per a Maastricht University press release. The study, published online today in the International Journal of Epidemiology, found that both men and women who ate at least 10 grams of peanuts or nuts daily saw a reduced risk of dying from not only heart disease, but also from respiratory illnesses, cancer, diabetes, and neurodegenerative diseases. The only disappointing result, expressed in the saddest sentence you may read all week: "[The study] finds no protective effect for peanut butter." The press release notes that the health benefits of peanuts and nuts are probably due to what they're harboring inside their shells: an amalgam of monounsaturated and polyunsaturated fats (the so-called "good" fats), fiber, antioxidants, vitamins, and other compounds. And it's not like you have to go overboard in your nut-eating habits: Researchers in the Maastricht University study found that eating more than an average 15 grams per day—or half a handful—didn't confer any lower mortality risk. So what gives with peanut butter, which ostensibly contains those same ingredients? Researchers speculate it's all the other stuff peanut butter has added, such as salt and vegetable oils, that may prevent the tasty spread from being more healthful. (Peanut butter may be able to help in the fight against Alzheimer's.)