Carbs may seem like the enemy on the Keto diet. After all, it’s about increasing your healthy fats and decreasing your carb consumption.

Carb blockers are sometimes referenced in this process, but what exactly are they and how can they be helpful?

Read on to find out!

Carb Blockers and How They Work

Carb blockers, also known as starch blockers, are a type of dietary supplement. They often come in prescription medication/pill form.

As you may already know, the body uses carbohydrates as an energy source after converting them to glucose. The body also converts them into fat, and the keto diet relies on ketones for energy instead of glucose.

The real threats to a healthy diet are refined carbohydrates and added sugars. Refined carbs, also referred to as ‘simple’ carbs, are in foods like white bread, pasta, rice, etc.

These carbs are basically empty calories and cause spikes in blood sugar that lead to an eventual ‘crash’ of fatigue—like sugar itself or caffeine.

Added sugars are often found in processed foods and take the form of cane sugar, high fructose corn syrup, raw sugar, corn syrup, and so on.

These ingredients are often added to carbohydrate and processed foods that can result in negative health consequences.

How They Help

In any case, one of the fundamentals of the keto diet is keeping your carb intake low.

Carb blockers are made from a compound known as alpha-amylase inhibitors and are usually extracted from white kidney beans.

What does the research say?

Research has shown that this type of alpha-amylase inhibitor can aid in weight loss or glycemic control.

These inhibitors prevent the enzymes from separating the complex carbs, which means that these carbs go onto the intestine without being absorbed into the circulatory system.

In other words:

Carb blockers only keep a part of the carbs you eat from being processed. Specifically, they appear to block anywhere from 50% to 65% of carb-digesting enzymes.

As a result, these undigested carbs do not contribute to calories or raise blood sugar [1].

One study showed that kidney bean extract had a positive effect in reducing food intake, body weight gain, fat deposits, and glycemia (sugar in the blood).

Groups of lab rats were fed a starch-enriched diet. One group consumed a fixed diet that contained the bean extract, and the control group ate the same fixed diet but without the bean extract.

Over several months, weight gain was largely lower in the experimental group than in the control group. In the experimental group, there was a significant reduction in the body content of fat as well.

Thirdly, in the experimental group, the food intake was approximately 90% lower than in the group that ate the food without the extract.

In an experiment on human beings, eating foods with the white kidney bean extract fed after a 2-month treatment increased the feeling of fullness in healthy overweight and obese subjects [2].

On the Market

Here’s an example…

It’s called Phase 2 Carb Controller. It has been proven to cause weight loss with single or divided doses. Another proven effect is that it reduces the blood sugar spikes caused by carbohydrates.

Phase 2 can be integrated into various foods and beverages without changing the food’s appearance, texture, or taste. No serious side effects have been reported from Phase 2 consumption [3].

Additionally, some studies show that carb blockers can decrease appetite. One reason is that the carb blockers’ bean extracts contain a compound called phytohaemagglutinin, which can boost the levels of some of the hormones involved in fullness.

In another study using lab rats, after taking in a form of carb blockers, the rats reduced the amount they ate by 15%-25% over a period of time. One suggestion was that the bean extract in the carb blocker possibly suppressed levels of ghrelin, a hunger hormone.

Risks of Carb Blockers and How to Use Them

Carb blockers are typically found in over-the-counter pill form, though some types require a prescription.

If you are interested in purchasing carb blocking supplements, try to look for brands that have the beneficial white kidney bean extract ingredient we discussed before.

Phase 2 is one of the most popular brands. Other renowned brands can be found at your local GNC or Vitamin Shoppe, and include:

  • Ancient Nutrition Keto Fire
  • Genetic Solutions White Kidney Bean Extract
  • NOW Foods Phase 2 (all-natural and vegetarian)
  • Irwin Naturals Maximum Strength 3-in-1 Carb Blocker
  • Nature’s Design Pure White Kidney Bean Extract by Nature’s Design

Most carb blocker manufacturers recommend no more than two doses, or two capsules, daily. These capsules should ideally be taken 10 minutes before the starch-containing meal, or right at the beginning of eating the meal.

Carb blockers are by and large thought to be pretty safe. However, it is strongly recommended that you consult with your medical practitioner before taking these supplements for safety purposes.

Why, you ask?…

Consuming these blockers can result in embarrassing or uncomfortable side effects, such as diarrhea, bloating, flatulence, and cramping.

There have also been concerns about the authenticity of carb blockers’ ingredients. While prescription drugs have to prove their efficacy through the FDA, over-the-counter supplements do not.

There have been significant reported discrepancies in the ingredients listed on supplement labels and the ingredients found in medicine.

Similar findings happened in dietary supplements. Therefore, there’s a good bet that many of the OTC carb blockers don’t actually contain the ingredients listed on the label, and may have other additives.

Be sure to stick with reputable manufacturers if you’re going to buy carb blockers.

Final Thoughts

Carb blockers have been scientifically proven useful in many cases and can be an asset in the keto diet.

However, like any dietary supplement, they shouldn’t be considered silver bullets or a critical part of the diet.

Again, we strongly encourage you to speak to your doctor or medical practitioner before consuming carb blocker supplements.


[1] Mojica L, de Mejía EG. Optimization of enzymatic production of anti-diabetic peptides from black bean (Phaseolus vulagirs L.) proteins, their characterization, and biological potential. Food Funct. 2016 Feb;7(2):713-27. doi: 10.1039/c5fo01204j.

[2] Mauro AM Carai, Noemi Fantini, Barbara Loi, Giancarlo Colombo, Antonella Riva, and Paolo Morazzoni. Potential efficacy of preparations derived from Phaseolus vulgaris in the control of appetite, energy intake, and carbohydrate metabolism. Diabetes Metab Syndr Obes. 2009; 2: 145–153.
Published online 2009 Sep 7.

[3] Barrett ML, Udani JK. A proprietary alpha amylase inhibitor from white bean (Phaseolus vulgaris): a review of clinical studies on weight loss and glycemic control. Nutr J. 2011 Mar 17;10:24. doi: 10.1186/1475-2891-10-24.