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White Kidney Bean Extract

White Kidney Bean extract, or Phase 2, is a dietary carbohydrate blocker similar to chlorogenic acid and is sometimes used alongside carb containing meals to reduce the absorption of carbohydrates. It does appear to work, but its potency is quite unreliable and relatively subpar.

Our evidence-based analysis on white kidney bean extract features 13 unique references to scientific papers.

Research analysis led by and reviewed by the Examine team.
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Research Breakdown on White Kidney Bean Extract

1Overview and Pharmacology

White kidney bean extract is specifically known as alpha-amylase inhibitor isoform 1. It is extracted from any legume source although it is known as white kidney bean extract due to it's high prevalence in that specific bean.

Alpha-amylase inhibitor isoform 1 (henceforth Alpha-AI1) is one of the main starch inhibitors alongside Alpha-AI2 and Alpha-AIL. The starch inhibitors are bean lectins, alongside arcelins and phytohaemagglutinin (PHA), although they do not confer the same harms that PHA does since, despite a very similar structure, they have a differently structured 'binding loop' which does not allow carbohydrate binding.[1] PHA, arcelins, and Alpha-AIL fail to inhibit amylase to a large degree due to steric hindrance from their looped structures, and only Alpha-AI1 shows effective amylase binding abilities in vivo in mammals.[2]

Alpha-AI1 seems to have highly unpredictable effects on in vivo carbohydrate metabolism as the activity of the binding process is influenced highly by pH, temperature (when away from optimum pH) and coingestion with particular ions as Nitrate, chloride, bromide, iodide, thiocyanate, and calcium ions all increase the ability for Alpha-AI1 to bind to amylase, whereas potassium, magnesium, sulfate and sodium showed no effect.[3] As well as other indirect effects like an increased secretion of amylase from the pancreas in response to slower intestinal transit time.

2Phase 2

Phase 2 is a brand name for a specific processed extract of Phaseolus Vulgaris.

Subpar extracts of Phaseolus vulgaris can result in a very high phytohaemagglutinin (PHA) content[4], which would reduce the high safety threshold of white kidney bean extract significantly. They also have been reported to have much lower intestinal action on the amylase enzyme.[5][6]

Phase 2 undergoes a process that inactivates the PHA content and increases the activity of Alpha-AI1 and is used in the majority of human studies.[7]

3Colonic Activity

Via inhibition of Alpha-amylase, Alpha-AI1 prevents long chain carbohydrates from being taken up in the small intestine for nutritional value to the human. This causes said starches to pass through to the colon where they have the potential to be fermented by bacteria. In this manner, Alpha-AI1 can make ingested carbohydrates act like a probiotic.

When fermented, these carbohydrates can release short-chain fatty acids including propionic acid, butyric acid, and acetic acid. These short chain fatty acids are thought to be involved in reducing the risk of colon cancer (as has been shown in experimentally induced animal models[8]) as well as having other benefits, such as modulating insulin/glucagon release and acting as a low grade systemic Histone deacetylase(HDAC) inhibitor.

4Human Studies

It has been noted in humans to effectively decrease amylase activity.[5]

Initially, studies in animals noted that raw bean consumption was able to ameliorate weight gain[9] and later studies found that it could wholly be accounted for by a combination of reduced food intake and increased starch excretion[8], suggesting that the mechanism of action in vivo is due to malabsorption and that in vitro studies carry over.

Human studies measuring weight loss typically report a small, variable, but always present effect on nutrients absorbed during a meal[10][11] and fat loss over time[12][13]

5Safety Profile

The acute toxicity of Phase 2 has been established as greater than 5g per kg of body weight in rats, a dose well above recommended human consumption, leading white kidney bean extract to have an excellent safety profile.

Chronic intake over the span of 28 days in doses up to 2500mg/kg bodyweight have been concluded as safe in lab animals additionally.[7]


Alpha-AI1, specifically in the patented form of Phase 2, seems to be effective in inducing starch malabsorption and thus induce weight loss by ways of mimicking a caloric deficit. Human studies all show benefit in supplementation with the highest starch containing meal, although the degree of benefit seems highly variable.

It is not recommended as a first-line fat burner due to it's inability to induce fat loss, but can be used as a band-aid supplement to a subpar diet like most calorie blockers.


  1. ^ Purification and Properties of Phaseolamin, an inhibitor of alpha-amylase, from the Kidney Bean Phaseolus vulgaris.
  2. ^ Ishimoto M, Yamada T, Kaga A. Insecticidal activity of an alpha-amylase inhibitor-like protein resembling a putative precursor of alpha-amylase inhibitor in the common bean, Phaseolus vulgaris L. Biochim Biophys Acta. (1999)
  3. ^ Characterization of a purified α-amylase inhibitor from white kidney beans (Phaseolus vulgaris).
  4. ^ Liener IE, Donatucci DA, Tarcza JC. Starch blockers: a potential source of trypsin inhibitors and lectins. Am J Clin Nutr. (1984)
  5. ^ a b Layer P, Carlson GL, DiMagno EP. Partially purified white bean amylase inhibitor reduces starch digestion in vitro and inactivates intraduodenal amylase in humans. Gastroenterology. (1985)
  6. ^ Layer P, Zinsmeister AR, DiMagno EP. Effects of decreasing intraluminal amylase activity on starch digestion and postprandial gastrointestinal function in humans. Gastroenterology. (1986)
  7. ^ a b Subchronic oral toxicity of a standardized white kidney bean (Phaseolus vulgaris) extract in rats.
  8. ^ a b Hangen L, Bennink MR. Consumption of black beans and navy beans (Phaseolus vulgaris) reduced azoxymethane-induced colon cancer in rats. Nutr Cancer. (2002)
  9. ^ Pusztai A, et al. Lipid accumulation in obese Zucker rats is reduced by inclusion of raw kidney bean (Phaseolus vulgaris) in the diet. Br J Nutr. (1998)
  10. ^ Layer P, et al. Effect of a purified amylase inhibitor on carbohydrate tolerance in normal subjects and patients with diabetes mellitus. Mayo Clin Proc. (1986)
  11. ^ Boivin M, et al. Gastrointestinal and metabolic effects of amylase inhibition in diabetics. Gastroenterology. (1988)
  12. ^ Udani J, Hardy M, Madsen DC. Blocking carbohydrate absorption and weight loss: a clinical trial using Phase 2 brand proprietary fractionated white bean extract. Altern Med Rev. (2004)
  13. ^ A Dietary Supplement Containing Standardized Phaseolus vulgaris Extract Influences Body Composition of Overweight Men and Women.