However, theory is one thing, reality another. Most studies of amylase inhibitors have generally failed to find them effective.^1-3

Several possible reasons for this discrepancy have been proposed, such as that the amylase inhibitor may be broken down in the stomach, the product may supply enough of its own amylase to counteract any benefit, and that another enzyme, glucoamylase, may be able to take over when amylase can’t do the job. Whatever the cause, the net results in these studies were poor. Use of amylase inhibitors did not in fact block the digestion of starch.

However, according to the manufacturer of a current product, more concentrated extracts of Phaseolus vulgaris, taken in higher doses, do work. Up until recently, the evidence for this claim rested entirely on unpublished studies that could not be independently verified..^4-6

In 2007, however, a relevant trial was at last published.⁸. In this double-blind, placebo-controlled study, 60 slightly overweight people were given either placebo or a phaseolus extract once daily 30 minutes prior to a main meal rich in carbohydrates. Over the thirty days of the study, the results indicated that phaseolus treatment led to a significantly greater reduction of body weight and and improvement of lean/fat ratio as compared to placebo. While this is promising, independent confirmation in larger trials will be necessary before phaseolus can be considered a proven weight-loss product.

One published study failed to find that use of a phaseolus product reduced the usual blood sugar rise that follows a meal.⁷