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 (1Trusted Source).

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.

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 (2Trusted Source).

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 (4Trusted Source, 5Trusted Source).

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

Dark Red Kidney Beans

Carbs

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

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 (7Trusted Source, 8Trusted Source).

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 (9Trusted Source).

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

Fibers

Kidney beans are high in fiber.

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

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

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 (7Trusted Source, 15Trusted Source).

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 (16Trusted Source, 17Trusted Source, 18Trusted Source).

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

• 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.

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

• 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.