Peanuts have been touted as a healthy snack, but you should know by now not to believe everything that conventional wisdom tells you. These little nuts are not nuts at all, they’re legumes, and legumes are not Paleo-friendly.
Although peanuts contain a fair amount of nutrients, they are also very high in an anti-nutreint called lectins. Lectins are designed to protect the plant by by making any foragers sick after they eat the lectin-containing plant. It’s not enough to be fatal, but just enough to impart a warning. Many foods contain lectins, but few are as rich in lectins as peanuts.
Lectins cause digestive issues by binding to the lining of the small intestine, resulting in intestinal damage that reduces the body’s ability to absorb other nutrients, like minerals and proteins. Lectins have also been shown to cause leaky gut, which allows the lectins (along with other particles, such as partially digested foods and toxins) to enter directly into the bloodstream. This creates an immune response in which the body attacks both the lectins, and the healthy tissue the lectins have latched onto, leading to inflammation and a host of possible autoimmune conditions.
Mark Sisson has a more comprehensive post on why we should beware of lectins here.
Peanuts are also susceptible to a particular mold which produces a carcinogen known as aflatoxin. The U.S. Department of Agriculture (USDA) tests every truckload of raw peanuts to make sure that none contain more than 15 parts per billion of aflatoxin. That level is enough to induce acute aflatoxicosis, but what about the cumulative effects of consuming small amounts of a carcinogen on a daily basis for years? The USDA seems unwilling to address that issue, probably because it is too difficult to measure, but why take the risk?
Mark Sisson has a post on the potential dangers of aflatoxins here.