Legumes are a botanical family of plants that include dozens of varieties of beans, lentils, garbanzos, peas, soybeans, and peanuts. (Note, the coffee, cocoa, and vanilla “beans” are not, botanically speaking, legumes, and thus are excluded from this particular discussion.) While eating plants would generally be thought of as healthy, the part of the legume that we eat is actually the seed of the legume plant. As with grains, the seeds of legumes store a large amount of energy in the form of carbohydrate, which may or may not support healthy metabolic function (pending your individual context and health history).
Legumes are often recommended as a healthy dietary choice, based on their fiber, vitamins and minerals, and “high” protein content. But legumes aren’t really a dense protein source (most contain two to three times as much carbohydrate as protein), and they’re nowhere near as dense (or complete) as the protein found in meat, seafood, or eggs. In addition, when compared to vegetables and fruit, legumes pale in comparison in both micronutrient density and fiber.
Some legumes also contain considerable amounts of phytates — anti-nutrients which bind to minerals in the legumes, rendering them unavailable to our bodies. (This means some of the minerals technically present in the legumes aren’t able to be accessed by our bodies — and means that legumes aren’t as micronutrient-dense as nutrition data might suggest.*)
*Ancient cultures figured out that rinsing, prolonged soaking, cooking, and fermenting legumes reduces the anti-nutrient content. If you choose to eat legumes, we highly recommend you also take these steps to mitigate some of the potential downsides.
In addition, because some of the short-chain carbohydrates (sugars) found in legumes aren’t properly digested and absorbed in the digestive tract, they can act as food for bacteria living in the intestines. These bacteria then “ferment” these carbohydrates, which can create unpleasant symptoms like gas and bloating, and potentially contribute to gut dysbiosis – an inherently inflammatory condition.
Soybeans contain compounds called isoflavones, which are types of phytoestrogens (phyto meaning “plant,” estrogen as in that female sex hormone). These phytoestrogens are recognized in our bodies — male and female — as a female reproductive hormone. While phytoestrogens may be beneficial for a very specific population (such as perimenopausal women), the effects on other populations are largely unknown and, in our opinion, unduly risky.
Peanuts contain a unique, disruptive protein called a lectin. While lectins in other legumes are largely destroyed in the cooking process, the peanut lectins are not destroyed by heat, and are resistant to digestion. This means they arrive in your gut largely intact, and can fool your gut lining into letting them through, and into the bloodstream. Once inside the body, these peanut lectins provoke an immune response, promoting systemic inflammation.