Supplement analysis backed by scientific evidence · PT

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Moderate evidenceWeight management

Carb Blocker Formulas

White kidney bean extracts that inhibit the starch-digesting enzyme alpha-amylase. Meta-analysis of eight small trials shows an average loss of about 1.6 kg over the study periods, which is real but modest, and most of the trials were funded by ingredient manufacturers.

Evidence last reviewed: August 2026

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What the science says

  • Modest weight and fat loss Moderate evidence

    A 2026 systematic review and meta-analysis of eight randomized trials (543 adults with overweight or obesity) found white kidney bean extract reduced body weight by 1.62 kg, BMI by 0.58 kg/m², fat mass by 1.17 kg and waist circumference by 1.58 cm versus placebo. Trials were small and short, and larger long-term studies are still needed.

  • No metabolic benefit beyond the weight change Moderate evidence

    The same meta-analysis found no significant differences in fasting glucose, triglycerides or insulin. The effect appears to be a mild reduction in absorbed starch calories rather than a metabolic improvement.

  • Individual trials are manufacturer-linked Limited evidence

    A 12-week double-blind randomized trial of a proprietary alpha-amylase inhibitor formulation reported weight and fat loss, but was conducted and authored in collaboration with the ingredient supplier, as is the case for most trials in this literature.

Dosage & safety

Studied doseTrials typically use 500–1500 mg of standardized Phaseolus vulgaris extract (commonly branded Phase 2) taken shortly before starch-containing meals, once to three times daily. It only makes sense taken with a meal that actually contains starch.
SafetyThe main effects are gastrointestinal: gas, bloating, cramping and loose stools from undigested starch reaching the colon. No serious adverse events were reported in the meta-analysis. Raw or under-processed kidney bean material contains toxic lectins, so use properly manufactured extracts only. Caution in people on diabetes medication, since carbohydrate absorption is altered, and avoid in pregnancy and breastfeeding for lack of data.

Scientific references

Where to buy

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