Partly thanks to its popularization by Dr. Oz, white kidney bean extract is now a common weight loss aid. This supplement purportedly acts as a carbohydrate blocker and reduces the levels of sugar and fatty molecules in the blood. Read on to learn more about the health benefits and side effects of white kidney bean extract.
What Is White Kidney Bean Extract?
White kidney bean is a variety of the common bean (Phaseolus vulgaris), which contains a protein (α-amylase blocker) that purportedly blocks the breakdown and digestion of starch [1, 2, 3].
In humans, this protein has been claimed to:
- Act as a carbohydrate absorption blocker [4]
- Help burn fat reserves [5]
- Suppress appetite [6]
- Reduce blood sugar and insulin spikes after meals [7]
Additionally, white kidney beans contain the lectin phytohemagglutinin. While high amounts of phytohemagglutinin are toxic to humans, lower concentrations can have appetite-suppressing effects [8, 9, 10, 11].
For these reasons, white kidney bean extract is sold under different brands as a weight loss supplement. The main white kidney bean extract supplements are [12]:
- Phase 2 (also known as Phaseolamin 2250, Phase 2 Starch Neutralizer, and Starch Lite), an α-amylase blocker [13, 12]
- Beanblock, a combination of an α-amylase blocker and phytohemagglutinin [11]
Components
The main active compounds of white kidney bean extract are:
- α-Amylase blocker: also referred to as phaseolamin, this lectin acts as a carbohydrate blocker by preventing the binding of starch to the enzyme that breaks it down (α-amylase). This means that fewer carbohydrates are absorbed into the body [14, 15].
- Phytohemagglutinin: this lectin binds to receptors on the intestinal lining and suppresses appetite by influencing the release of certain hormones (decreases ghrelin) [11].
Other white kidney bean compounds that might be present in small amounts are:
- Trypsin and chymotrypsin blockers: they block the protein-digesting enzymes trypsin and chymotrypsin. High-temperatures and pressure can destroy these blockers, preventing the digestive problems experienced when eating beans or taking in the extract [16, 17, 18].
- Phaseolin: although it is a very nutritious amino acid source, this protein can cause allergies [19, 20].
- Saponins: these substances can have both positive (acting as antioxidants and protecting against fungi and viruses) and negative (reducing protein digestion and mineral uptake) effects [21].
- Phytic acid: it reduces the absorption of mineral nutrients and the digestion of proteins but enhances the immune system and may protect against some cancers [22].
- Arcelins: these lectins bind to a membrane in the gut of insects and prevent them from absorbing nutrients. No effects have been described in humans [23].
How It Works
Carbohydrates are digested by enzymes (α-amylases) found in the saliva and pancreas. Plants have developed several α-amylase blockers as defense mechanisms against insects and mammals feeding on them [24, 25].
The α-amylase blocker found in white kidney beans, α-AI1, is active against human α-amylases. This carbohydrate blocker binds to the α-amylase enzyme and prevents the access of starch. As a result, starch cannot be degraded and fewer simple sugars are absorbed by the intestines [14].
The factors that influence the activity of this blocker are [26, 15]:
- pH level: its activity is highest under slightly acid conditions.
- Time: optimal blocking activity is normally achieved after 10-40 minutes. However, up to 120 minutes can be required if the pH is not optimal.
The other active compound present in white kidney beans, phytohemagglutinin, binds to the inner surface of the small intestine. This triggers the release of the hormones that promote satiety (cholecystokinin and glucagon) and prevents the production of the hormone causing hunger (ghrelin), thus suppressing appetite [27, 11].
Health Benefits of White Kidney Bean Extract
Proponents of white kidney bean extract claim that it may help not only lose weight, but also lower blood sugar and fat levels, or reduce the risk of colon cancer, cavities, and blood clots.
However, white kidney bean extract is not approved by the FDA for any conditions. Supplements generally lack solid clinical research. Regulations set manufacturing standards for supplements but don’t guarantee that they are safe or effective. Talk to your doctor before using white kidney bean extract to avoid unexpected interactions.
Possibly Effective for:
1) Weight Loss
Because the first commercial bean extracts had low α-amylase blocker activity, a concentrate (6 to 8x more carbohydrate-blocker content) was developed. It broke down the α-amylases from the mouth and small intestine and reduced intestinal α-amylase activity and starch digestion in 2 small trials on 11 people [28, 29, 30].
Daily intake of Phase 2 extract before a carbohydrate-rich meal for 30 days reduced body weight, body mass index, fat mass, fatty tissue thickness, and waist, hip, and thigh sizes while maintaining lean body mass in a trial on 60 overweight people [31].
Phase 2 combined with a low-calorie diet (1,800 cal) and exercise had no effect on weight loss in a small trial on 25 overweight people. However, the Phase 2 individuals who had the most carbohydrates lost more weight and waist circumference [32].
In a study of over 100 overweight people, another commercial extract (IQP-PV-101)before meals combined with a low-calorie diet for 12 weeks reduced weight (weight-loss phase). 73% of the 49 people that continued taking IQP-PV-101 for 12 additional weeks with a non-restrictive diet maintained their weight (weight maintenance phase) [33].
In two studies with healthy and obese rats, the α-amylase blocker (either purified or raw beans) reduced body fat without reducing lean body weight [34, 35].
The benefits of white kidney bean extract for weight loss are only supported by limited, low-quality evidence. All the clinical trials were small and those testing commercial extracts were funded by the companies selling them (Pharmachem Laboratories Inc. and InQpharm Europe Ltd.). The studies suggest that Phase 2 and IQP-PV-101 help lose weight, but perhaps not to the extent that these companies claim.
2) Curbing Appetite
Beanblock, taken with a meal after a 12 hour fast, reduced appetite, production of the hunger hormone ghrelin, and glucose and insulin rises in the blood in a small trial on 12 healthy people [11].
Taken for 12 weeks, Beanblock reduced appetite, body weight, waist size, and oxidative damage in a clinical trial on 60 overweight people [36].
Similarly, a combination of bean and artichoke extracts taken for 2 months reduced appetite and blood sugar levels after meals in a clinical trial on 39 overweight people [37].
Beanblock also reduced food consumption in three studies in rats and mice [27, 38, 39].
Once again, the evidence is limited and based on a few, small human and animal studies. Additionally, those using Beanblock were all funded by the manufacturer (Indena SpA).
Insufficient Evidence for:
1) Blood Sugar and Insulin Reduction
In a small clinical trial on 18 people, those who took 1,500 mg and 750 mg of Phase 2 with their meal absorbed 1/3 and 2/3 of the carbohydrates, respectively, compared to the control group [40].
However, in another trial on 13 people, only a high dose (3,000 mg) of Phase 2 reduced blood sugar levels following a meal [41].
Purified white kidney bean α-amylase blocker reduced blood sugar and insulin level rises after meals in a small trial on 8 non-insulin-dependent diabetics [42].
In three rat studies, white kidney bean α-amylase blocker (purified or raw beans) significantly reduced blood sugar levels [43, 35, 34].
The quality of the evidence to claim that white kidney bean extract lowers blood sugar and insulin is insufficient. The clinical studies were very small and those using Phase2 were funded by the manufacturer (Pharmachem Laboratories, Inc.).
2) Reducing Blood Levels of Fats
In a trial on 27 obese people, Phase 2 had no effect on weight loss but reduced blood triglyceride levels after 8 weeks [44].
A supplement combining white kidney bean and carob extracts increased the elimination of fats (triglycerides) in feces and reduced the levels of cholesterol (both free and bound to LDL) in the blood in a clinical trial on 62 overweight and obese people [45].
Although the results are promising, the evidence to support the use of white kidney bean extract to lower blood fat levels is insufficient.
Animal and Cell Research (Lack of Evidence)
Researchers are studying other potential benefits of white kidney bean extract and its components in animals and cells. Note, however, that these are preliminary results that have not been tested in humans.
Colon Cancer
Non-digested starch may act similarly to fiber in the large intestine and thus help prevent colon cancer [46].
Rats given a cancer-causing compound had lower incidences of colon cancer and multiplying tumor cells when fed a diet containing beans compared to rats on a regular diet [47].
While promising, this animal-stage study is preliminary. Further studies have yet to determine if white kidney bean extract is a useful aid in colon cancer prevention.
A purified white kidney bean lectin prevented the growth and increased the death of skin and liver cancer cells [48].
However, many substances – including downright toxic chemicals like bleach – have anti-cancer effects in cells. This doesn’t mean that they have any medical value. On the contrary, most substances (natural or synthetic) that are researched in cancer cells fail to pass further animal studies or clinical trials due to a lack of safety or efficacy.
Preventing Cavities and Bleeding Gums
The α-amylases produced by the salivary glands have the following effects in the mouth [49, 50]:
- They begin the digestion of complex carbohydrates, thus increasing the availability of simple sugars.
- The α-amylases bind to mouth bacteria (such as Viridans streptococci) and help them break down carbohydrates into simple sugars that they use as a food source. Bacteria produce acids, which dissolve tooth enamel and form cavities.
- They bind to enamel and promote the formation of teeth plaque by bacteria. Plaque buildup can lead to bleeding gums and cavities.
By blocking α-amylases, white kidney bean extract may help prevent cavities and bleeding gums. However, this benefit is mere speculation based on this mechanism. No human or animal studies have tested if white kidney bean extract actually helps preserve teeth health.
Reducing the Risk of Blood Clots
Bean extract reduced the clumping of platelet cells. White kidney bean extract may thus reduce the formation of blood clots, although studies in humans and even in animals are needed to verify this finding [51].
Limitations and Caveats
Study Design
The studies often had small sample sizes, which can produce unreliable results [11, 52, 32, 40].
The long-term effects of white kidney bean extract were not studied [32, 53, 44, 37].
Several of the studies combined white kidney bean extract with the adoption of lifestyle modifications such as regular exercise or a low-calorie diet. The degree to which these modifications contributed to the bodyweight reduction observed is not clear [32, 33, 36].
A critical meta-analysis from 2011 concluded that the evidence in the studies published up to that time was insufficient to confirm that white kidney bean extract effectively helps lose weight. Longer, more rigorous trials were suggested [54].
The inhibitory effect of white kidney bean extract on cancer growth and blood clotting has only been tested in rats and platelet cells, respectively. In turn, its effect on teeth health is speculative and based on the role of α-amylases in causing cavities and bleeding gums. Trials in humans are required to confirm these preliminary results [47, 51].
Study Funding and Conflicts of Interest
Several of the studies were funded by Pharmachem Laboratories, InQPharm Europe Ltd., andIndena S.p.A, the companies selling the white kidney bean extracts used [31, 32, 33, 40, 41, 11, 36].
Recently, another meta-analysis (funded by Pharmachem Laboratories) reviewed only studies performed with Phase 2 and concluded that, as opposed to other generic extracts included in the previous review, Phase 2 caused significant weight and fat loss [55].
Side Effects & Precautions
Keep in mind that the safety profile of white kidney bean extract is relatively unknown, given the lack of well-designed clinical trials. The list of side effects below is, therefore, not a definite one. You should consult your doctor about other potential side effects based on your health condition and possible drug or supplement interactions.
1) White Kidney Bean Lectins
Lectins are carbohydrate-binding proteins that recognize specific cells and proteins. Common bean varieties contain different types of lectins, which are responsible for many toxic symptoms [56, 57].
The carbohydrate-binding capacity of lectins is a likely cause of their toxicity. Lectins may bind to the gut lining and interfere with the function of digestive enzymes [58, 57].
Because approximately 15% of a bean’s proteins are lectins, they can cause several harmful effects in lectin-sensitive individuals, such as:
- “Leaky gut” [59]
- Increased sensitivity to some food components [60]
- Autoimmune diseases [61]
- Reduced nutrient digestion and absorption [62]
Among bean lectins, the most relevant one to human health is phytohemagglutinin. Red kidney beans contain the highest concentration of phytohemagglutinin and white kidney beans have approximately ⅓ of that amount [63, 57].
Phytohemagglutinin poisoning is relatively common and can have the following symptoms [64, 65, 66]:
- Nausea
- Vomiting
- Diarrhea
- Stomach pain
- Bowel inflammation
- Reduced nutrient absorption in the bowel
- Defective liver function
In rats, phytohemagglutinin caused the excessive growth of small intestine bacteria, which may contribute to gut disorders [63].
Phytohemagglutinin is broken down when the beans are soaked and properly cooked. Therefore, avoid consuming raw beans and improperly processed white kidney extract to prevent poisoning [67].
2) White Kidney Bean Antinutritional Substances
Common bean varieties contain several antinutritional substances such as [57]:
- α-Amylase blockers
- Protein-digesting enzyme blockers (trypsin and chymotrypsin blockers)
- Saponins
- Phytic acid
α-Amylase blockers prevent bean starches from being digested by pest insects and mammals. When used for weight loss and blood sugar control, white kidney bean extract has been reported to cause the following symptoms due to the increased fermentation of undigested carbohydrates in the large intestine [68, 69]:
- Gas
- Diarrhea
- Bloating
- Constipation
The symptoms are normally mild and resolve after a few days of continued treatment [70].
Trypsin and chymotrypsin blockers prevent these enzymes from digesting proteins in the bowel. Additionally, they may cause [71, 72, 73]:
- Reduced nutrient absorption (in mice)
- Indigestion
- Stomach pain
White kidney beans also contain different saponins. The main potential harmful effects of saponins include [74, 21]:
- Reduced cholesterol absorption
- Breaking down red blood cells
- Reduced mineral uptake
- Reduced protein digestion
- Weight loss and reduced food intake due to inefficient digestion
Phytic acid cannot be properly digested by humans and may thus cause [75, 22, 76]:
- Reduced availability of essential minerals like calcium, magnesium, iron, and zinc (phytic acid binds to them)
- Reduced absorption of proteins and fats (phytic acid binds to and blocks protein- and fat-digesting enzymes like trypsin and lipases)
Because these antinutritional substances are generally not found in the seed coat, bean dehulling does not reduce their levels [77].
4) White Kidney Bean Allergens
White kidney bean extract contains several proteins that cannot be digested by pepsin in the stomach. This is a characteristic feature of food allergens since pepsin-resistant proteins are then more likely to reach the small intestine and trigger the intestinal immune system [78, 79].
Kidney bean proteins identified as allergens include:
- Phaseolin [20]
- Phytohemagglutinin [80]
- α-Amylase blocker precursor [57]
- Late embryogenesis abundant proteins [57]
Kidney bean extract caused a higher frequency of allergic reactions than any other extracts from the most common legumes in an observational study on 355 people with allergies and asthma [81].
A 23-year-old woman suffered a potentially life-threatening allergic reaction (anaphylactic shock) after eating cooked white kidney beans. Phytohemagglutinin and phaseolin were identified as the compounds that most likely triggered it [82].
In a study in mice, kidney bean proteins increased the blood levels of antibodies, histamine, white blood cells (mast and eosinophil cells), protein-degrading enzymes, and cytokines [83].
Drugs Interactions
Because the α-amylase blocker present in white kidney bean extract may lower blood sugar levels, its effect can add to that of antidiabetic drugs and cause blood sugar levels to drop too low [40, 52, 42].
Diabetic patients taking white kidney bean extract should frequently monitor blood sugar levels and may need to speak to their doctor about dosages of medications such as [84]:
- Insulin
- Glimepiride
- Glyburide
- Pioglitazone
- Rosiglitazone
- Chlorpropamide
- Glipizide
- Tolbutamide
Traces of phytic acid may be present in white kidney bean extract. Because it may slow down blood clotting, white kidney bean extract may increase the risk of bleeding and bruising when combined with medications that also reduce blood clotting such as [85, 86]:
Small amounts of trypsin and chymotrypsin blockers may be present in white kidney bean extract and block these protein-degrading enzymes (trypsin and chymotrypsin). Patients taking protein drugs, such as some vaccines (e.g., hepatitis B virus vaccine), interferons (e.g., IFN-α2b), hormones (e.g., human growth hormone), and enzymes (e.g., prolactazyme) may have to lower the dosage, since the blocking of trypsin and chymotrypsin can increase the time it takes the body to eliminate them [87].
Supplementation
Phase 2 is used as a dietary supplement in several forms, including [69]:
- Powder
- Tablets
- Capsules
- Chewables
- Powdered drinks
Phase 2 has been introduced into products such as chewing gum, bread and pizza dough, and mashed potatoes without loss of efficacy or altering the look, texture, and shape of the food [69].
Beanblock is sold as [36]:
- Capsules
- Tablets
Dosage and Toxicity
Because white kidney bean extract is not approved for any conditions, there is no official dose. Supplement manufacturers and users have established unofficial guidelines based on trial and error.
Phase 2
Phase 2 is standardized to an α-amylase activity of at least 3,300 units/mg. A typical dose of Phase 2 is 1-2 capsules (500 mg each) taken before each meal [69].
No serious adverse effects have been reported in the different clinical trials using up to 3,000 mg/day Phase 2 for periods ranging from 30 days to 24 weeks. A private safety panel approved a maximum Phase 2 intake of 10 g per day [69].
In rats, a single dose of Phase 2 up to 5 g/kg body weight or in doses of up to 1 g/kg body weight for 90 days did not cause any adverse reactions, changes in organ weight, or increased death rate [88].
Similarly, no adverse effects were observed in rats given up to 2.5 g/kg body weight Phase 2 for 28 days [18].
To reduce the side effects associated with these proteins, a specialized preparation process of white kidney bean extract substantially breaks down phytohemagglutinin and trypsin blockers [69].
Beanblock
Beanblock is standardized to at least 1,100 units/mg of α-amylase activity and between 10,000 and 30,000 of phytohemagglutinin activity/g. The recommended dose is 100 mg, 2x/day with meals. No serious adverse effects have been observed in trial subjects taking a standard dose for periods of up to 12 weeks [36, 11].
A food mixture containing white kidney bean extract did not cause mutations in Salmonella or hamster cells. Taken for 28 days, it had no effects on the behavior, total body weight, organ weight, and death of rats [89].
User Experiences
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Users who took white kidney bean extract as a carbohydrate blocker reported successful weight loss and appetite curbing, although some users complained that the weight loss was less than they had expected.
Bloating and gas were the most common side effects.
Some users stopped taking the supplement after not seeing any effects and a few even gained weight because they ate more carbohydrates.
Consumers who used white kidney bean extract to reduce their blood sugar levels (most of whom were diabetic) were happy with its effects.
Do Carbohydrate Blockers Work?
Limited evidence suggests that white kidney bean extract may help lose weight, reduce blood sugar and insulin spikes after meals, curb appetite, and lower blood fat levels. However, the results are inconclusive and more, better-designed studies are needed to confirm them.
Importantly, the α-amylase present in the supplement is only effective against starch. Therefore, people on a low-carbohydrate diet will see little results, while the most drastic effects will be observed in those whose diet frequently includes complex carbohydrates such as:
- Bread
- Pasta
- Rice
- Pizza
- Potatoes
The extract does not prevent the absorption of simple sugars that do not require α-amylase for their digestion, such as those found in:
- Fruit
- Milk
- Candy
- Cakes
- Snacks
Carbohydrate blockers work better in combination with a low-calorie diet and some exercise. This will not only help burn fat but also prevent the loss of lean body mass.
Although the extract is generally recognized as safe, its toxicity has only been evaluated for short-time periods. Long-term effects of white kidney bean extract are unknown. Likewise, information on its effects during pregnancy and breastfeeding, as well as in patients with liver and kidney damage, have not been studied.
White kidney bean extract (and other carbohydrate blockers) cannot substitute for a healthy diet combined with physical exercise in individuals wishing to lose weight. However, it may be used as an aid, especially by people who regularly eat complex carbohydrates.
