Also known as: Phaseolus vulgaris, Carb blocker, Phaseolamin, Alpha-amylase inhibitor
Fat MetabolismEmerging evidence
The carb blocker, and the mechanism is real. What it blocks in practice is a good deal less than the marketing implies, and the undigested starch has to go somewhere.
Typical dose
445.0–1500.0 mg per day
Immediately before starch-containing meals
What it is
White kidney bean extract comes from Phaseolus vulgaris, standardised for its content of a protein that inhibits alpha-amylase, the enzyme that digests starch.
That inhibitor is one reason raw beans are indigestible, and the extract concentrates it deliberately.
Standardisation varies enormously and is often expressed in inhibitory units rather than milligrams, which makes comparing products difficult. Potency is also lost with heat, so processing matters.
How it works
Alpha-amylase breaks starch into absorbable sugars. Inhibiting it means a portion of the starch in a meal passes through undigested rather than being absorbed as glucose.
That reduces both the calories absorbed from that starch and the blood glucose rise after the meal.
Two things follow. It affects starch only, so it does nothing about fat, sugar or alcohol. And the undigested starch continues into the large intestine where bacteria ferment it, which explains the gas and bloating people report.
What the evidence shows
The enzyme inhibition is well demonstrated, and trials have confirmed reduced blood glucose rise after starchy meals, which is the clearest finding.
Weight loss trials have reported modest reductions over 8 to 12 weeks, though results are inconsistent and several trials found no significant difference from placebo.
Estimates of how much starch is actually blocked in a real meal are considerably lower than laboratory conditions suggest, in the region of a modest fraction rather than the majority. A meta-analysis concluded the weight effect is small and not consistently significant.
Dosing
Trials have used 445 to 1,500 mg of standardised extract, taken immediately before starchy meals. Timing is tight: it needs to be present in the stomach when the starch arrives.
It does nothing for a meal that is mainly fat, sugar or protein, so taking it before every meal wastes it.
Expect digestive effects. The starch you prevent digesting gets fermented further down, and gas and bloating are the predictable result. Set expectations accordingly: this modestly reduces starch absorption from a starchy meal rather than cancelling it, and the calorie deficit still has to come from somewhere.
White kidney bean extract is generally well tolerated. Gas, bloating and loose stools are common and follow directly from the mechanism rather than indicating anything wrong.
Because it reduces starch digestion, it may affect the absorption of nutrients taken with the same meal, so separating it from supplements is sensible.
Speak to your doctor before use if your blood sugar is being managed, since reducing carbohydrate absorption can lower it further than expected, or if you take regular medication.
Who should avoid it
Speak to your doctor before use if your blood sugar is being managed, since it can lower it further than expected, or if you take regular medication. Expect gas and bloating. Separate from other supplements, since it may reduce absorption from the same meal. Not established in pregnancy or breastfeeding.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
