Is White Kidney Bean Extract Safe?

Phaseolamine is an extract of the white kidney bean. Phaseolamine is marketed under several brand names as a "starch blocker," a supplement intended to cause weight loss by inhibiting -amylase (alpha-amylase), a digestive enzyme that breaks complex carbohydrates into simple sugars. Many plants produce -amylase inhibitors in their seeds where they function as insecticides or repellents. For example, wheat presents albumin fractions with multiple proteins adapted to inhibit several types of -amylase. For this reason, the safety of starch blocking extracts as a dietary supplement was controversial.

Bad Reputation

The white kidney bean or cannellini shares a bad reputation for toxicity with light and dark red kidney beans. These beans cause episodes of nausea, vomiting and diarrhea if they are not cooked at high temperature for 10 or 15 minutes and then drained and washed before simmering till done. The bean toxin is a protein that binds to starches in cell membranes and blocks digestion, but it does not persist after high temperature cooking.

Amala Cancer Research Center, India

In 2005, Dr. Kuzhuvelil Harikumar, et al, of the Amala Cancer Research Centre, India, administered phaseolamine brand name "Phase 2" at 2 grams per kg of body weight for 90 days to male and female young adult rats. Writing in the International Journal of Toxicology, Dr. Kuzhevelil stated that phaseolamine had not produced any loss of body weight in the rats, nor did it damage kidney or liver function or change blood or lipid profiles. He concluded that phaseolamine was not a dangerous toxin or cancer risk.

Pharmachem Laboratories, Kearny, New Jersey

In 2006, Dr. Dilip Chokshi of Pharmachem Laboratories, Inc., Kearny, New Jersey, administered phaseolamine brand name Blockal at 2 grams per kg of body weight for four weeks to rats and reported the same results as Dr. Harikumar. Writing in the same journal, Dr. Chokshi concluded that the "Phase 2" active ingredient in Blockal was a safe dietary supplement. The International Journal of Toxicology is published in association with the American College of Toxicology headquartered in Bethesda, Maryland.

Weight Loss Claim

Phaseolamine marketing targets body builders and the obese with promises of weight loss. The premise of starch-blockers is that starch that passes undigested through the small intestine will then be eliminated through the colon with no absorption into the body. Thus, a reduction in digested calories will lead to weight loss the same as a reduced calorie diet.

Test of Weight Loss Claim

To test this claim, Dr. George W. Bo-Linn, et al, examined the feces of test subjects after high carbohydrate meals. Some test subjects were given a starch blocker and some were given a placebo. If the starch blocker had functioned as claimed, the carbohydrate content feces of subjects given the starch blocker should have increased by 400 kilocalories. Analysis of the feces showed no increase in carbohydrates being eliminated from the colon. Dr. Bo-Linn's conclusions were published in the December 2, 1982 issue of the New England Journal of Medicine.

Rebuttal of Weight Loss Claim

Dr. Gabe Mirkin, M.D. reported for CBS Radio News that starch blockers are unlikely to function as described in weight loss claims. He pointed out that if starch passes undigested through the small intestine and into the colon, the starch is then exposed to the colon's bacteria, which will ferment the starches, causing an episode of painful gas and diarrhea. Dr. Mirkin concluded that if supplements taken as starch blockers did not cause gas and diarrhea, then most certainly they had not blocked starches.