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?
In humans, this protein may:
- Act as a carbohydrate absorption blocker 
- Help burn fat reserves 
- Suppress appetite 
- Reduce blood sugar and insulin spikes after meals 
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 :
- 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 
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) .
Other white kidney bean compounds that might be present in small amounts are:
- Trypsin and chymotrypsin blockers: 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 (acts as an antioxidant and protection against fungi and viruses) and negative (reduced protein digestion and mineral uptake) effects .
- Phytic acid: its intake reduces the absorption of mineral nutrients and the digestion of proteins but enhances the immune system and can protect against some cancers .
- 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 .
Mechanism of Action
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 [R, R].
- 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) and thus, suppressing appetite [27, 11].
Health Benefits of White Kidney Bean Extract
1) White Kidney Bean Extract Helps 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 (Infusion of 2-5 mg/ml at 5 ml/min and 5-10 g, RCT with 7 and 4 subjects) [28, 29, 30].
Daily intake of Phase 2 extract before a carbohydrate-rich meal reduced body weight, body mass index, fat mass, fatty tissue thickness, and waist, hip, and thigh sizes while maintaining lean body mass (445 mg for 30 days, DB-RCT of 60 overweight subjects) .
Phase 2 with a low-calorie diet (1,800 cals) and exercise had no effect on weight loss. However, the Phase 2 individuals who had the most carbohydrates lost more weight and waist circumference (1 g 2x/day for 4 weeks, DB-RCT of 25 healthy overweight individuals) .
In a study of 123 overweight subjects, 2 x 500 mg Phase 2 tablets 3x/day before meals on a low-calorie diet for 12 weeks reduced weight compared to the control group (weight-loss phase). 73% of the 49 subjects that continued taking Phase 2 for 12 additional weeks with a non-restrictive diet maintained their weight (weight maintenance phase) .
2) White Kidney Bean Extract Reduces Blood Sugar and Insulin
In two experiments, subjects 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 (DB-RCT of 11 and 7 subjects) .
However, in another study, only a high dose of 3,000 mg of Phase 2 reduced blood sugar levels following a meal (crossover study of 13 healthy individuals) .
Intake of 50 g of starch and 4-10 g of purified white kidney bean α-amylase blocker reduced blood sugar and insulin level rises after meals (DB-RCT of 8 non-insulin-dependent diabetics) .
3) White Kidney Bean Extract Curbs Appetite
Beanblock (100 mg), 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 (DB-RCT of 12 healthy individuals) .
Beanblock supplementation reduced appetite, body weight, waist size, and oxidative damage (50 mg 2x/day for 12 weeks, DB-RCT of 60 overweight individuals) .
4) White Kidney Bean Extract Reduces Fatty Molecule Levels in the Blood
Phase 2 (two 150 mg capsules, a 3x/day for 9 months) increased the elimination of fats (triglycerides) in feces and reduced the levels of cholesterol and the protein that carries it to the blood vessels (LDL) in the blood (DB-RCT of 62 overweight and obese individuals) .
Phase 2 (1,500 mg, 2x/day for 8 weeks) had no effect on weight loss but reduced blood triglyceride levels (DB-RCT of 27 obese subjects) .
5) White Kidney Bean Extract Helps Prevent Cavities and Bleeding Gums
- 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.
6) White Kidney Bean Extract May Help Prevent Colon Cancer
Non-digested starch may act similarly to fiber in the large intestine and thus help prevent colon cancer .
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 .
A purified white kidney bean lectin prevented cancer cell growth and increased cell death (skin and liver cancer cell lines) .
7) White Kidney Bean Extract May Reduce 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 are needed to verify these findings .
1) Side Effects of White Kidney Bean Lectins
Because approximately 15% of a bean’s proteins are lectins, they can cause several harmful effects in lectin-sensitive individuals, such as:
- Leaky gut 
- Increased sensitivity to some food components 
- Autoimmune diseases 
- Reduced nutrient digestion and absorption 
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 [59, 53].
- Stomach pain
- Bowel inflammation
- Reduced nutrient absorption in the bowel
- Defective liver function
In rats, phytohemagglutinin intake caused the excessive growth of small intestine bacteria, which may contribute to gut disorders .
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 .
2) Side Effects of White Kidney Bean Antinutritional Substances
Common bean varieties contain several antinutritional substances such as :
- α-Amylase blockers
- Protein-digesting enzyme blockers (trypsin and chymotrypsin blockers)
- 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 may cause the following symptoms due to the increased fermentation of the non-digested carbohydrates in the large intestine [14, 13]:
The symptoms are normally mild and resolve after a few days of continued treatment .
- Reduced nutrient absorption (in mice)
- Stomach pain
- Reduced cholesterol absorption
- Breaking down red blood cells
- Reduced mineral uptake
- Reduced protein digestion
- Weight loss and reduced food intake due to inefficient digestion
- 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 .
3) Side Effects of 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 [71, 72].
Kidney bean proteins identified as allergens include:
- Phaseolin 
- Phytohemagglutinin 
- α-Amylase blocker precursor 
- Late embryogenesis abundant proteins 
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 .
Limitations and Caveats
Several of the studies combined the intake of 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 body weight reduction observed is not clear [32, 33, 41].
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 .
The inhibitory effect of white kidney bean extract on cancer growth and blood clotting has only been tested in rats and platelet cells, respectively. Trials in humans are required to confirm these preliminary results [49, 51].
Study Funding and Conflicts of Interest
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 .
Because the α-amylase blocker present in white kidney bean extract lowers blood sugar levels, its effect can add to that of antidiabetic drugs and cause blood sugar levels to drop too low [36, 37, 38].
Traces of phytic acid may be present in white kidney bean extract. Because it slows down blood clotting, its intake may increase the risk of bleeding and be bruising when combined with medications that also reduce blood clotting such as [80, 81]:
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 .
Forms of supplementation
Phase 2 is used as a dietary supplement in several forms, including :
- 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 .
Beanblock is sold as :
Dosage and Toxicity
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 .
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 .
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 .
Similarly, no adverse effects were observed in rats given up to 2.5 g/kg body weight Phase 2 for 28 days .
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 .
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 [41, 11].
A food mixture containing white kidney bean extract did not cause mutations in Salmonella or hamster cells. Its intake for 28 days had no effects on the behavior, total body weight, organ weight, and death of rats .
Users who took it 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?
According to the evidence obtained through clinical trials, white kidney bean extract seems to help weight loss, reduce blood sugar and insulin spikes after meals, curb appetite, and reduce blood fatty molecule levels.
However, 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 individuals whose diet frequently includes complex carbohydrates such as:
The extract does not prevent the absorption of simple sugars that do not require α-amylase for their digestion, such as those found in:
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.