White Kidney Bean Extract: How It Works, Evidence and Side Effects

White kidney bean extract is a supplement made from Phaseolus vulgaris beans that contains a natural alpha-amylase inhibitor, a protein that slows the enzyme your body uses to break down starch. Pooled trials report roughly 1 to 2 kilograms more weight loss than placebo over a few weeks to three months, but an independent 2011 review found the weight difference was not statistically significant, and many trials were small, short or linked to the maker of a branded extract. Side effects are usually digestive, such as gas and soft stools. The extract is not the same as eating raw beans, which contain a lectin that causes food poisoning. Here is how it works, what the studies show and how to read the labels.

Peptide Labs sells supplements that list white kidney bean extract, but this article does not recommend any of them. It is general information, not medical advice.

What is white kidney bean extract?

The white kidney bean, Phaseolus vulgaris, is a legume native to Mexico, Central America and South America, according to the NIH Office of Dietary Supplements (ODS). Extracts of the dried beans are sold as carbohydrate or starch blockers. The active protein is sometimes called phaseolamin.

Phase 2 is a branded white kidney bean extract made by the ingredient company Ashland and studied in several of the trials below. On labels it often appears as Phase 2 Carb Controller, used under license, as entries in the NIH Dietary Supplement Label Database show. Other products list generic white kidney bean extract without naming its source or strength.

How an alpha-amylase inhibitor works

Alpha-amylase, made in saliva and the pancreas, splits starch from foods like bread, pasta, rice and potatoes into smaller sugars that can be absorbed. An alpha-amylase inhibitor slows this step, so in theory some starch passes through undigested and supplies fewer calories. Starch that escapes digestion reaches the large intestine, where gut bacteria ferment it, which may explain the gas some people notice. Amylase acts on starch, so these extracts are not designed to affect table sugar, fruit sugar or sweet drinks. This is a different approach from orlistat, the drug in alli, which reduces fat absorption instead.

The 1980s starch blockers: a cautionary history

Bean-based starch blockers were a craze in the early 1980s. In 1982 a study in the New England Journal of Medicine measured what happened to calories from a high-starch spaghetti meal and found that the tablets of that era did not block starch digestion at all. On July 1, 1982, the FDA classified starch blockers as drugs and asked that they be removed from the market; by August it had received 75 reports of side effects such as bloating, nausea, abdominal pain, constipation and vomiting. A federal appeals court upheld the drug classification in 1983. A 1984 analysis of 10 brands found wildly varying levels of amylase inhibitor, lectin and other bean proteins.

Today’s branded extracts are standardized by their amylase-inhibiting activity, according to the researchers who test them, and they are sold as dietary supplements. Whether they work is a separate question, covered next.

Does white kidney bean extract work? What the trials show

Study	Who took part	Result	Limits
2007 trial, Italy	60 adults with slight overweight, 30 days	About 2.9 kg lost versus 0.35 kg on placebo	Very short; one product
2004 trial, US	39 adults with obesity started, 27 finished, 8 weeks	No significant difference from placebo	Small, high dropout
2014 trial	123 adults with overweight, 12 weeks, mild calorie cut	2.9 kg lost versus 0.9 kg on placebo	One branded extract
2024 trial	81 adults finished, 12 weeks, calorie-restricted diet	Weight and fat loss rose with the amount taken	Authors include consultants to the maker
2011 meta-analysis	6 trials, 247 people	Weight difference not significant; 1.86 kg less body fat	All trials had serious flaws
2018 meta-analysis	11 studies, 573 people	1.08 kg more weight loss than placebo	Lead author consulted for the maker; unpublished company data
2026 meta-analysis	8 trials, 543 people	1.62 kg more weight loss; smaller waist	Authors call for larger, longer, better trials

The picture is a possible modest effect, which is how the ODS rates it. A 2011 independent review from the University of Exeter included six trials and found that all of them had serious design flaws; the difference in weight loss was not statistically significant, although body fat fell by 1.86 kg more than with placebo. A 2018 meta-analysis of 11 studies found 1.08 kg more weight loss, but its lead author had been paid as a consultant by the extract’s maker and it included unpublished company data. A 2026 meta-analysis by researchers who declared no conflicts pooled 8 trials with 543 people and found 1.62 kg more weight loss and slightly smaller waists, while calling for larger, longer and higher quality studies.

Two details matter when reading these numbers. Participants followed a set meal plan or a reduced-calorie diet in these trials, so the extract was at most an add-on. And according to the ODS, no trial has lasted longer than 13 weeks, so long-term effects are unknown.

Blood sugar after meals

A small 2013 study gave 12 healthy volunteers a mixed meal with a purified extract or a placebo. With the extract, blood sugar and insulin rose less after the meal and people reported less desire to eat over the next three hours. That was a single meal in a dozen people. The 2026 meta-analysis found no difference in fasting blood sugar or triglycerides over longer trials. Ingredients marketed for blood sugar are compared in our berberine benefits guide, and our article on how to stop sugar cravings covers food-based steps for sweets, which a starch-focused extract does not target.

White kidney bean extract benefits: a realistic summary

Putting the research together, these are the white kidney bean extract benefits with some support, and their limits:

• Weight: a modest added loss, roughly 1 to 2 kg over up to three months, in trials of mixed quality that paired it with a meal plan or calorie-reduced diet.
• Body fat and waist size: small reductions in pooled analyses, measured in only a few trials.
• Post-meal blood sugar: a smaller rise after one starchy meal in a tiny study; no change in fasting blood sugar over weeks.
• Appetite: lower desire to eat in one small single-meal study; not well established.

Raw beans, lectins and why the extract is different

Kidney beans naturally contain phytohaemagglutinin, a lectin that causes food poisoning when beans are eaten raw or undercooked. The FDA’s Bad Bug Book says as few as four or five raw beans can trigger symptoms, starting with extreme nausea and vomiting within one to three hours, followed by diarrhea. Recovery is usually quick, but some people have been hospitalized. The FDA warns that slow cookers do not get hot enough to destroy the toxin, and cites British studies recommending soaking beans for at least five hours, discarding the water and boiling them in fresh water for at least 30 minutes.

The danger is not theoretical for dieters. In 2006 a Japanese TV program promoted eating powdered, lightly toasted white kidney beans with meals to block starch. More than 1,000 viewers developed acute stomach and intestinal symptoms and about 100 were hospitalized; testing showed the home heating had not inactivated the lectin, even though the amylase inhibitor survives heat. Commercial extracts are processed, but neither of the labels we carry states how much lectin activity remains. Never make your own bean powder or eat undercooked beans for this purpose.

Side effects and who should be careful

The ODS lists headache, soft stools, gas and constipation as reported side effects, with no serious adverse effects in trials of up to 13 weeks. Talk to a clinician or pharmacist first if any of these apply:

• Insulin or other glucose-lowering medicines: because the extract can blunt the rise in blood sugar after starchy meals, ask your prescriber before adding it.
• Bean or legume allergy: the extract comes from beans, and bean lectins are recognized allergens.
• Digestive conditions: extra starch reaching the colon can mean more gas and changes in stool.
• Pregnancy or breastfeeding: safety has not been established.

See a doctor for vomiting, severe abdominal pain, blood in the stool or unexplained weight loss rather than adjusting a supplement.

Products we carry that list white kidney bean extract

We carry two products that list white kidney bean extract, both multi-ingredient formulas:

• Natnect GLP-1 Supplement lists white kidney bean extract with hops extract, capsicum, garcinia, bitter melon, green tea extract, berberine, licorice root, ginger and aloe vera gel. The label does not state caffeine content. It is a dietary supplement, not a GLP-1 medication; our explainer on GLP-1 support supplements explains the difference.
• FOODOLOGY Coleology Cut PRO is built around green tea extract, rhodiola and banaba leaf; white kidney bean extract appears among the ingredients present at less than 2%. It contains milk and fish, and its green tea extract naturally contains caffeine.

Neither label names a branded extract or states its amylase-inhibiting strength, so the trial results above cannot be assumed to apply. Our carb blocker range groups related products, most of them built around other ingredients such as berberine.

Frequently Asked Questions

Questions about a label? Contact us or read our Buyer’s Guide. Follow the label and ask a healthcare provider before starting any supplement, especially if you take medicines. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

Last reviewed September 2026.

Related guides: Berberine Benefits: What the Research Shows and What It Does Not, alli (Orlistat 60 mg): How It Works, Results, Side Effects and alli vs Xenical, What Are “GLP-1 Support” Supplements? Reading the Label Honestly.