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 a 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.
They come in a variety of colors and patterns; white, cream, black, red, purple, spotted, striped, and mottled.
Kidney beans are mainly composed of carbs and fiber, but are also a good source of protein.
The table below contains detailed information on all the nutrients in kidney beans.
Proteins in Kidney Beans
Kidney beans are rich in protein.
One cup of boiled kidney beans (177 g) contains approximately 15 grams of protein, accounting for 27% of the total caloric content ().
Although the nutritional quality of bean proteins is lower than animal proteins, beans are an affordable alternative for many people in developing countries.
In fact, beans are one the richest plant-based sources of protein, sometimes referred to as "poor man's meat" ().
The most widely studied protein in kidney beans is phaseolin, which may cause allergic reactions in susceptible individuals (, ).
Kidney beans also contain proteins, such as lectins and protease inhibitors ().
Bottom Line: Kidney beans are among the richest sources of plant-based protein.
Kidney beans are mainly composed of carbs.
Carbs in kidney beans are known as starch, which accounts for approximately 72% of the total calorie content ().
Starch is predominantly made up of long chains of glucose, called amylose and amylopectin ().
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 (, ).
For this reason, bean starch is a so-called slow-release carbohydrate. Its digestion takes longer and it causes lower and more gradual rise in blood sugar than other types of starch, making kidney beans particularly beneficial for people with diabetes.
Kidney beans rank very low on the glycemic index (), which is a measure of how foods affect the rise in blood sugar after a meal.
In fact, bean starch has a more beneficial effect on blood sugar balance than many other high-carb foods (, ).
Bottom Line: Starchy carbs are the main nutritional component of kidney beans. They do not cause large spikes in blood sugar, making them suitable for diabetics.
Kidney beans are high in fiber.
They contain substantial amounts of resistant starch, which may play a role in weight management ().
Kidney beans also contain insoluble fibers known as alpha-galactosides, which may cause diarrhea and flatulence in some people (, ).
Both resistant starch and alpha-galactosides function as prebiotics. They move through the digestive tract until they reach the colon where they are fermented by beneficial bacteria, stimulating their growth (, ).
The fermentation of these healthy fibers also results in the formation of short-chain fatty acids, such as butyrate, acetate, and propionate (), which may improve colon health and reduce the risk of colon cancer (, ).
Bottom Line: Kidney beans are rich in healthy fibers, which moderate blood sugar levels and promote colon health. They may cause flatulence and diarrhea in some people.
Vitamins and Minerals
Kidney beans are rich in various vitamins and minerals.
- 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: An essential mineral that has many important functions in the body. Iron may be poorly absorbed from beans due to their phytate content ().
- Copper: An antioxidant trace element that is often low in the Western diet. Aside from beans, the best dietary sources of copper are organ meats, seafood, and nuts.
- Manganese: Found in most foods and drinks, especially in whole grains, legumes, fruits, and vegetables.
- Potassium: An essential nutrient that may have beneficial effects on heart health ().
- Vitamin K1: Also known as phylloquinone, vitamin K1 is important for blood coagulation.
- Phosphorus: Found in almost all foods, phosphorus is high in the Western diet.
Bottom Line: Kidney beans are a good source of several vitamins and minerals, such as molybdenum, folate, iron, copper, manganese, potassium, vitamin K1 and phosphorus.
Other Plant Compounds
Kidney beans contain all sorts of bioactive plant compounds that may have various effects on health, both good and bad.
- Isoflavones: A class of antioxidants found in high amounts in soybeans. They have all sorts of health effects and are categorized as phytoestrogens due to their similarity to the female sex hormone, estrogen ().
- Anthocyanins: A family of colorful antioxidants found in the skin of kidney beans. The color of red kidney beans is mainly due to an anthocyanin known as pelargonidin (, ).
- Phytohaemagglutinin: A toxic lectin (protein) found in high amounts in raw kidney beans, especially red kidney beans. It can be eliminated with cooking ().
- Phytic acid: Found in all edible seeds, phytic acid (phytate) impairs the absorption of various minerals, such as iron and zinc. It can be reduced by soaking, sprouting and fermenting the beans ().
- Starch blockers: A class of lectins, also known as alpha-amylase inhibitors. They impair or delay the absorption of carbs from the digestive tract, but are inactivated with cooking ().
Bottom Line: Kidney beans contain a variety of bioactive plant compounds, both good and bad. Phytohaemagglutinin is a toxic lectin only found in raw or improperly cooked kidney beans.
Overweight and obesity are major health problems, associated with increased risk for various chronic diseases.
Several observational studies have linked bean consumption with lower risk of overweight and obesity (, ).
One trial in 30 obese men and women on a weight loss diet, found that eating beans (and other legumes) 4 times per week for 2 months led to greater weight loss than a diet that excluded beans ().
A recent meta-analysis of 11 randomized controlled trials also found some evidence supporting this, but was not able to draw a firm conclusion due to the poor quality of the included trials ().
Various mechanisms have been discussed as an explanation for the beneficial effects of beans on weight loss. These include various fibers, proteins, and antinutrients.
Among the most widely studied antinutrients in raw kidney beans are the so-called starch blockers, a class of proteins that impair or delay the digestion and absorption of carbs (starch) from the digestive tract ().
Starch blockers, extracted from white kidney beans, have shown some potential as a weight loss supplement (, , ).
However, boiling at 212°F (100°C) for 10 minutes completely inactivates starch blockers, eliminating their effect in fully cooked beans ().
Even so, cooked kidney beans contain a number of weight loss friendly components, making them an excellent addition to an effective weight loss diet.
Bottom Line: Kidney beans are high in protein and fiber, and contain proteins that can reduce the digestion of starches (carbs). They may be considered a weight loss friendly food.
Other Health Benefits of Kidney Beans
Aside from being weight loss friendly, kidney beans may have a number of health benefits when properly cooked and prepared.
Improved Blood Sugar Control
Over time, high blood sugar may increase the risk of many chronic diseases, such as heart disease.
For this reason, moderating the rise in blood sugar after meals is considered beneficial for health.
Being rich in protein, fiber, and so-called slow-release carbs, kidney beans are particularly effective at maintaining healthy levels of blood sugar when included with meals.
They rank very low on the glycemic index, which means that the rise in blood sugar after eating them is low and more gradual ().
In fact, beans are better at controlling blood sugar than most dietary sources of carbs (, , , , ).
Several observational studies indicate that eating beans, or other foods that are low on the glycemic index, may cut the risk of becoming diabetic (, , ).
Eating low-glycemic foods may also improve blood sugar control in people who are already diabetic ().
Diabetic or not, adding beans to your diet may improve blood sugar balance, protect your overall health, and reduce the risk of many chronic diseases.
Bottom Line: Kidney beans are an excellent dietary choice for diabetics and those who want to stabilize their blood sugar levels.
Colon Cancer Prevention
Colon cancer is one of the most common types of cancer worldwide.
Observational studies have linked legume consumption (including beans) with reduced risk of colon cancer (, ).
This is supported by animal studies and test tube experiments (, , , ).
Beans contain a variety of nutrients and fibers with potential anti-cancer effects.
Fibers, such as resistant starch and alpha-galactosides, pass undigested down to the colon where they are fermented by friendly bacteria, resulting in the formation of short-chain fatty acids ().
Short-chain fatty acids, like butyrate, may improve colon health and cut the risk of colon cancer (, ).
Bottom Line: As a rich source of fermentable fiber, kidney beans may promote colon health and reduce the risk of colon cancer.
Adverse Effects and Individual Concerns
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 (lectin) called phytohaemagglutinin ().
Phytohaemagglutinin is found in many types of beans, but is in particularly high amounts in red kidney beans.
Kidney bean poisoning has been reported in both animals and humans (, ).
In humans, the main symptoms of kidney bean poisoning include diarrhea and vomiting, sometimes requiring hospitalization ().
Soaking and cooking the beans eliminates most of the toxin, making kidney beans safe to eat, harmless and nutritious (, ).
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 ().
Bottom Line: Raw kidney beans are toxic and should be avoided. This also applies to improperly cooked beans.
Antinutrients in Kidney Beans
Raw and improperly cooked kidney beans contain all sorts of antinutrients, substances that reduce nutritional value by impairing nutrient absorption from the digestive tract.
Although their actions may sometimes be considered beneficial, they are a serious concern in developing countries where beans are a staple food, making up a large portion of the daily diet.
The main antinutrients in kidney beans include:
- Phytic acid (phytate), which impairs the absorption of minerals, such as iron and zinc ().
- Protease inhibitors (trypsin inhibitors), proteins that inhibit the function of various digestive enzymes, impairing protein digestion ().
- Starch blockers (alpha-amylase inhibitors), substances that impair the absorption of carbs from the digestive tract ().
Phytic acid, protease inhibitors, and starch blockers, are all completely or partially inactivated when beans are properly soaked and cooked (, , ).
Fermenting and sprouting the beans may reduce antinutrients, such as phytic acid, even further ().
Bottom Line: Kidney beans contain so-called "antinutrients", substances that impair the absorption of minerals, proteins, and carbs. They can be eliminated (at least partially) by soaking and cooking the beans.
Flatulence and Bloating
In some people, bean consumption may cause unpleasant effects, such as bloating, flatulence, and diarrhea ().
Responsible for these effecs are insoluble fibers called alpha-galactosides, the most common of which are stachyose, verbascose, and raffinose ().
They belong to a group of fibers known as FODMAPs, which may exacerbate the symptoms of irritable bowel syndrome (, ).
Alpha-galactosides can be partially removed by soaking and sprouting the beans ().
Bottom Line: Kidney beans may cause bloating, flatulence, and diarrhea in some people.
Kidney beans are an excellent plant-based source of protein.
They are also rich in various minerals, vitamins, fibers, antioxidants, and other unique plant compounds.
For this reason, they may be useful as a part of a weight loss diet, while also promoting colon health and moderating blood sugar levels.
However, kidney beans should always be eaten well cooked. Raw or improperly cooked beans are toxic.