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Legumes: Good or Bad?

Woman Holding a Bowl of PeasLegumes are quite controversial these days.

Depending on who you ask, they are either incredibly nutritious or uniquely harmful.

Some people even choose to eliminate legumes from their diet altogether.

Should legumes be avoided, or can they play a part in a healthy diet?

This article takes a close look at the evidence.

What Are Legumes?

The legume family consists of plants that produce a pod with seeds inside.

In this article, we use the term “legumes” to describe the seeds of these plants.

Common edible legumes include lentils, peas, chickpeas, beans, soybeans and peanuts.

The different types vary greatly in nutrition, appearance, taste and use (1).

Bottom Line: Legumes is a general term used to describe the seeds of plants from the legume family, which includes beans, peas, lentils and peanuts.

Legumes Are Uniquely Rich in Both Protein and Fiber

Bowl of Lentils

Legumes have quite a remarkable nutrition profile (2), and are a rich source of healthy fibers and protein.

One cup of cooked lentils provides (3):

  • 18 grams of protein.
  • 16 grams of fiber.
  • 40 grams of carbohydrate.
  • 37% of the RDA for iron.
  • 90% of the RDA for folate.
  • 18% of the RDA for magnesium.
  • 21% of the RDA for potassium.
  • Over 10% of the RDA for Vitamins B1, B3, B5 and B6, phosphorus, zinc, copper and manganese.

This is coming with a calorie ticket of 230, which makes legumes highly nutritious, calorie for calorie.

Legumes have an ability to fix nitrogen from the atmosphere. Nitrogen is an essential component of amino acids, the building blocks of proteins.

This is why legumes are among the best plant-based sources of dietary protein.

Not only are legumes highly nutritious, they are also very cheap, which makes them an important food staple in many developing countries (4).

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Bottom Line: Legumes are highly nutritious and very high in both protein and fiber. They are also cheap and widely available.

Legumes Contain Anti-Nutrients

Unfortunately, there is a downside to the nutritional quality of legumes.

They also contain so-called anti-nutrients, which are substances that can interfere with digestion and the absorption of other nutrients.

Different Lentils

Phytic Acid

Phytic acid, or phytate, is found in all edible plant seeds, including legumes.

It impairs the absorption of iron, zinc and calcium from the meal (5, 6), and may increase the risk of mineral deficiencies over time.

However, this is only relevant when meat intake is low and high-phytate foods regularly make up a large part of meals.

Meat eaters are not at risk of mineral deficiencies caused by phytic acid. Iron and zinc absorption from meat is efficient, even in the presence of phytic acid (7, 8, 9).

Conversely, phytic acid is a serious concern when the diet is largely based on grains and legumes, which is often the case in developing countries. Vegetarians may also be at risk (10, 11).

In these situations, several strategies can be used to reduce the phytic acid content and increase the nutritional value. These include soaking (12), sprouting (13), and fermentation (14).

Lectins

Legume lectins are a family of proteins found in legumes, where they may constitute up to 10% of the total protein content (15).

They resist digestion and some of them may affect the cells lining the intestinal tract.

There are many different types of legume lectins. One well-studied lectin is phytohemagglutinin, found in many types of beans, especially red kidney beans.

Phytohemagglutinin is toxic in high amounts, and several incidents of poisoning have been reported after consumption of raw or improperly cooked kidney beans (16).

In most other edible legumes, the amount of lectins is not high enough to cause symptoms in humans.

However, as a general rule, beans should never be eaten unless fully cooked and prepared.

Soaking overnight and boiling at 212°F (100°C) for at least 10 minutes, degrades phytohemagglutinin and other legume lectins (17, 18).

Saponins

Saponins are a diverse group of nutrients found in a variety of plants. They are resistant to digestion but may affect the cells lining the gut.

Some believe that they may increase intestinal permeability, also called leaky gut, leading to a range of health problems.

Currently, this remains purely speculative and there is no good evidence that saponins in legumes cause harm in humans.

Bottom Line: Raw legumes contain substances called “anti-nutrients,” which may cause harm. Proper preparation methods get rid of most of them.

Legumes are Rich in Healthy Fibers

Legumes are particularly rich in healthy fibers, such as resistant starch and soluble fibers (1, 4, 19).

Young Girl Eating Peas

Resistant starch and soluble fibers have a few things in common.

They pass undigested through the stomach and small intestine until they reach the colon, where they feed the friendly bacteria residing there.

Unpleasant side effects often include gas and bloating, but it also leads to the formation of short-chain fatty acids, such as butyrate, which may improve colon health and reduce the risk of colon cancer (20, 21, 22).

Both resistant starch and soluble fibers are also very satiating and may reduce food intake (23, 24, 25, 26), which in the long run can lead to weight loss.

Additionally, they are very effective at moderating blood sugar levels after meals (27, 28, 29) and may improve insulin sensitivity (30, 31).

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Bottom Line: Legumes are a rich source of fibers that may have various beneficial health effects.

Other Health Benefits of Legumes

Variation of Legumes

Legumes have been linked with various other health benefits.

According to observational studies, legumes are associated with reduced risk of heart disease (32) and lower cholesterol levels (33).

Randomized controlled trials also suggest that regular consumption of legumes may reduce blood pressure and have favorable effects on cholesterol and triglycerides (34, 35).

Due to their high fiber and protein content, legumes are very fulfilling. This may reduce food intake and lead to weight loss in the long term (36, 37).

Bottom Line: Consumption of legumes may improve blood pressure, reduce cholesterol, lower heart disease risk and promote weight loss in the long term.

Take Home Message

Legumes are linked with various health benefits.

They have an impressive nutritional profile, and are one of the best plant-based sources of protein.

However, like many other plant foods, they also contain so-called anti-nutrients, which may impair their nutritional value. Kidney beans may even be toxic when raw.

Various strategies can be used to neutralize these anti-nutrients. Throughout the ages, traditional methods like soaking, sprouting, and boiling, have been used to good effect.

At the end of the day, properly prepared legumes are very healthy when consumed as part of a balanced, real food based diet.