Kidney beans are a variety of the common bean (Phaseolus vulgaris), a legume native to Central America and Mexico.

The common bean is an important food crop and major source of protein throughout the world.

Used in a variety of traditional dishes, kidney beans are usually eaten well cooked. Raw or improperly cooked kidney beans are toxic, but well-prepared beans can be a healthy component of a well-balanced diet (1).

They come in a variety of colors and patterns, including white, cream, black, red, purple, spotted, striped, and mottled.

This article tells you everything you need to know about kidney beans.

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Kidney beans are mainly composed of carbs and fiber but also serve as a good source of protein.

The nutrition facts for 3.5 ounces (100 grams) of boiled kidney beans are:

  • Calories: 127
  • Water: 67%
  • Protein: 8.7 grams
  • Carbs: 22.8 grams
  • Sugar: 0.3 grams
  • Fiber: 6.4 grams
  • Fat: 0.5 grams

Protein

Kidney beans are rich in protein.

Only 3.5 ounces (100 grams) of boiled kidney beans boast almost 9 grams of protein, accounting for 27% of the total calorie content (2).

Although the nutritional quality of bean protein is generally lower than that of animal protein, beans are an affordable alternative for many people.

In fact, beans are one the richest plant-based sources of protein, sometimes referred to as “poor man’s meat” (3).

The most widely studied protein in kidney beans is phaseolin, which may cause allergic reactions in some people (4, 5).

Kidney beans also contain other proteins like lectins and protease inhibitors (6).

Carbs

Kidney beans are mainly composed of starchy carbs, which account for approximately 72% of the total calorie content (2).

Starch is predominantly made up of long chains of glucose in the form of amylose and amylopectin (3).

Beans have a relatively high proportion of amylose (30–40%) compared to most other dietary sources of starch. Amylose is not as digestible as amylopectin (7, 8).

For this reason, bean starch is a slow-release carb. Its digestion takes longer, and it causes a lower and more gradual rise in blood sugar than other starches, making kidney beans particularly beneficial for people with type 2 diabetes.

Kidney beans rank very low on the glycemic index (GI), which is a measure of how foods affect your rise in blood sugar after a meal (9).

In fact, bean starch has a more beneficial effect on blood sugar balance than many other high-carb foods (10, 11).

Fibers

Kidney beans are high in fiber.

They contain substantial amounts of resistant starch, which may play a role in weight management (12).

Kidney beans also provide insoluble fibers known as alpha-galactosides, which may cause diarrhea and flatulence in some people (13, 14).

Both resistant starch and alpha-galactosides function as prebiotics. Prebiotics move through your digestive tract until they reach your colon, where they’re fermented by beneficial bacteria (7, 15).

The fermentation of these healthy fibers results in the formation of short-chain fatty acids (SCFAs), such as butyrate, acetate, and propionate, which may improve colon health and reduce your risk of colon cancer (16, 17, 18).

SUMMARY Kidney beans are among the best sources of plant-based protein. They’re also rich in healthy fibers, which moderate blood sugar levels and promote colon health.

Kidney beans are rich in various vitamins and minerals, including (19, 20, 21, 22, 23):

  • Molybdenum. Beans are high in molybdenum, a trace element mainly found in seeds, grains, and legumes.
  • Folate. Also known as folic acid or vitamin B9, folate is considered particularly important during pregnancy.
  • Iron. This essential mineral has many important functions in your body. Iron may be poorly absorbed from beans due to their phytate content.
  • Copper. This antioxidant trace element is often low in the Western diet. Aside from beans, the best dietary sources of copper are organ meats, seafood, and nuts.
  • Manganese. This compound is present in most foods, especially in whole grains, legumes, fruits, and vegetables.
  • Potassium. This essential nutrient may have beneficial effects on heart health.
  • Vitamin K1. Also known as phylloquinone, vitamin K1 is important for blood coagulation.
SUMMARY Kidney beans are a good source of several vitamins and minerals, such as molybdenum, folate, iron, copper, manganese, potassium, and vitamin K1.

Kidney beans contain many bioactive plant compounds, including (24, 25, 26, 27, 28, 29):

  • Isoflavones. A class of antioxidants present in high amounts in soybeans, isoflavones are categorized as phytoestrogens due to their similarity to the female sex hormone, estrogen.
  • Anthocyanins. This family of colorful antioxidants occurs in the skin of kidney beans. The color of red kidney beans is mainly due to an anthocyanin known as pelargonidin.
  • Phytohaemagglutinin. This toxic protein exists in high amounts in raw kidney beans, especially red varieties. It can be eliminated through cooking.
  • Phytic acid. Found in all edible seeds, phytic acid (phytate) impairs your absorption of various minerals, such as iron and zinc. It can be reduced by soaking, sprouting, or fermenting the beans.
  • Starch blockers. A class of lectins, also known as alpha-amylase inhibitors, starch blockers impair or delay the absorption of carbs from your digestive tract but are inactivated by cooking.
SUMMARY Kidney beans contain a variety of bioactive plant compounds. Phytohaemagglutinin is a toxic lectin only found in raw or improperly cooked kidney beans.

Excess weight gain and obesity are major health problems, associated with an increased risk of various chronic diseases.

Several observational studies link bean consumption to a lower risk of excess weight gain and obesity (30, 31).

A 2-month study in 30 obese adults on a weight loss diet showed that eating beans and other legumes 4 times per week led to greater weight loss than a bean-free diet (32).

A recent review of 11 studies also found some supporting evidence but was unable to draw a firm conclusion (33).

Various mechanisms may contribute to the beneficial effects of beans on weight loss. These include fibers, proteins, and antinutrients.

Among the most widely studied antinutrients in raw kidney beans are starch blockers, a class of proteins that impair or delay the digestion and absorption of carbs (starch) from your digestive tract (29).

Starch blockers, extracted from white kidney beans, demonstrate some potential as a weight loss supplement (34, 35, 36).

However, boiling for 10 minutes completely inactivates starch blockers, eliminating their effect in fully cooked beans (29).

Even so, cooked kidney beans offer a number of weight-loss-friendly compounds, making them an excellent addition to an effective weight loss diet.

SUMMARY Kidney beans are high in protein and fiber and contain proteins that can reduce the digestion of starches (carbs), all of which may aid weight loss.

Aside from being weight loss friendly, kidney beans may have a number of benefits when properly cooked and prepared.

Improved blood sugar control

Over time, high blood sugar may increase your risk of many chronic illnesses, such as heart disease. Thus, moderating your rise in blood sugar after meals is considered beneficial for health.

Being rich in protein, fiber, and slow-release carbs, kidney beans are very effective at maintaining healthy levels of blood sugar.

They have a low GI score, which means that your rise in blood sugar after eating them is low and more gradual (9).

In fact, beans are better at controlling blood sugar than most dietary sources of carbs (10, 11, 37, 38, 39).

Several observational studies indicate that eating beans or other low-glycemic foods may reduce your risk of type 2 diabetes (40, 41, 42).

Eating low-glycemic foods may also improve blood sugar control in people who already have type 2 diabetes (43).

Even if you don’t have this condition, adding beans to your diet may improve blood sugar balance, protect your overall health, and reduce your risk of many chronic diseases.

Colon cancer prevention

Colon cancer is one of the most common types of cancer worldwide.

Observational studies link legume intake, including beans, with a reduced risk of colon cancer (44, 45).

This is supported by test-tube and animal studies (46, 47, 48, 49).

Beans contain a variety of nutrients and fibers with potential anticancer effects.

Fibers, such as resistant starch and alpha-galactosides, pass undigested down to your colon, where they’re fermented by friendly bacteria, resulting in the formation of SCFAs (50).

SCFAs like butyrate may improve colon health and lower your risk of colon cancer (18, 51).

SUMMARY Kidney beans are an excellent choice for people with type 2 diabetes and others who want to stabilize their blood sugar levels. They may also promote colon health and reduce your risk of colon cancer.

Even though kidney beans may have a number of health benefits, raw or inadequately cooked kidney beans are toxic.

In addition, some people may wish to limit their consumption of beans due to bloating and flatulence.

Raw kidney bean toxicity

Raw kidney beans contain high amounts of a toxic protein called phytohaemagglutinin (1).

Phytohaemagglutinin is found in many beans but is particularly high in red kidney beans.

Kidney bean poisoning has been reported in both animals and humans. In humans, the main symptoms include diarrhea and vomiting, sometimes requiring hospitalization (52, 53).

Soaking and cooking the beans eliminates most of this toxin, making properly prepared kidney beans safe, harmless, and nutritious (27, 52).

Before consumption, kidney beans should be soaked in water for at least 5 hours and boiled at 212°F (100°C) for at least 10 minutes (54).

Antinutrients in kidney beans

Raw and improperly cooked kidney beans harbor many antinutrients, which are substances that reduce nutritional value by impairing nutrient absorption from your digestive tract.

Although they may sometimes be beneficial, antinutrients are a serious concern in developing countries in which beans are a staple food.

The main antinutrients in kidney beans are (28, 29, 55):

  • Phytic acid. This compound, also known as phytate, impairs your absorption of minerals, such as iron and zinc.
  • Protease inhibitors. Also known as trypsin inhibitors, these proteins inhibit the function of various digestive enzymes, impairing protein digestion.
  • Starch blockers. These substances, sometimes called alpha-amylase inhibitors, impair the absorption of carbs from your digestive tract.

Phytic acid, protease inhibitors, and starch blockers are all completely or partially inactivated when beans are properly soaked and cooked (29, 56, 57).

Fermenting and sprouting the beans may reduce antinutrients, such as phytic acid, even further (58).

Flatulence and bloating

In some people, beans may cause unpleasant effects, such as bloating, flatulence, and diarrhea (13).

Insoluble fibers called alpha-galactosides are responsible for these effects. They belong to a group of fibers known as FODMAPs, which may exacerbate the symptoms of irritable bowel syndrome (IBS) (7, 59, 60).

Alpha-galactosides can be partially removed by soaking and sprouting the beans (7).

SUMMARY Raw or improperly cooked kidney beans are toxic and should be avoided. What’s more, these beans contain antinutrients and may cause bloating, flatulence, and diarrhea in some people.

Kidney beans are an excellent plant-based source of protein. They’re also rich in various minerals, vitamins, fibers, antioxidants, and other unique plant compounds.

Therefore, these beans may aid weight loss, promote colon health, and moderate blood sugar levels.

However, kidney beans should always be eaten well cooked. Raw or improperly cooked beans are toxic.