Red 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:
Protein: 8.7 grams
Carbs: 22.8 grams
Sugar: 0.3 grams
Fiber: 6.4 grams
Fat: 0.5 grams
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).
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).
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 among the best sources of plant-based protein. They’re also rich in healthy fibers, which moderate blood sugar levels and promote colon health.
Vitamins and minerals
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 are a good source of several vitamins and minerals, such as molybdenum, folate, iron, copper, manganese, potassium, and vitamin K1.
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Other plant compounds
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.
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 (30Trusted Source, 31Trusted Source).
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 (32Trusted Source).
A recent review of 11 studies also found some supporting evidence but was unable to draw a firm conclusion (33Trusted Source).
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 (29Trusted Source).
Starch blockers, extracted from white kidney beans, demonstrate some potential as a weight loss supplement (34Trusted Source, 35Trusted Source, 36Trusted Source).
However, boiling for 10 minutes completely inactivates starch blockers, eliminating their effect in fully cooked beans (29Trusted Source).
Even so, cooked kidney beans offer a number of weight-loss-friendly compounds, making them an excellent addition to an effective weight loss diet.
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.
Other health benefits of kidney beans
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 (9Trusted Source).
In fact, beans are better at controlling blood sugar than most dietary sources of carbs (10Trusted Source, 11Trusted Source, 37Trusted Source, 38Trusted Source, 39Trusted Source).
Several observational studies indicate that eating beans or other low-glycemic foods may reduce your risk of type 2 diabetes (40Trusted Source, 41Trusted Source, 42Trusted Source).
Eating low-glycemic foods may also improve blood sugar control in people who already have type 2 diabetes (43Trusted Source).
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 (44Trusted Source, 45Trusted Source).
This is supported by test-tube and animal studies (46Trusted Source, 47Trusted Source, 48Trusted Source, 49Trusted Source).
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 (50Trusted Source).
SCFAs like butyrate may improve colon health and lower your risk of colon cancer (18Trusted Source, 51Trusted Source).
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 (1Trusted Source).
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 (52Trusted Source, 53Trusted Source).
Soaking and cooking the beans eliminates most of this toxin, making properly prepared kidney beans safe, harmless, and nutritious (27Trusted Source, 52Trusted Source).
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 (54Trusted Source).
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 (28Trusted Source, 29Trusted Source, 55Trusted Source):
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 (29Trusted Source, 56, 57).
Fermenting and sprouting the beans may reduce antinutrients, such as phytic acid, even further (58Trusted Source).
Flatulence and bloating
In some people, beans may cause unpleasant effects, such as bloating, flatulence, and diarrhea (13Trusted Source).
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) (7Trusted Source, 59Trusted Source, 60Trusted Source).
Alpha-galactosides can be partially removed by soaking and sprouting the beans (7Trusted Source).
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.
The bottom line
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.
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Written by Atli Arnarson BSc, PhD on May 14, 2019