What Are Carb Blockers and Do They Really Work?
carb blocker

What Are Carb Blockers and Do They Work?

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Ever since research came out stating that carbs are bad and fat is not, people have been doing what they can to reduce their intake of the starchy substance (1).

If you follow the ketogenic diet, then your carbohydrate intake is already low. However, some ketogenic dieters and people on regular diets are taking their carbohydrate restriction one step further by supplementing with carb blockers.

But if you’re already on a low-carb diet, do you really need a carb blocker or could taking one be doing more harm than good?

In this article, we will talk about what carb blockers are, how they work, and whether or not you should take them on the ketogenic diet and other diets.

What is a Carb Blocker?

Carb blockers, otherwise known as starch blockers, are substances or a combination of substances that help block the absorption of carbohydrates in your digestive tract. They usually consist of natural, plant-based chemicals that you can take in capsule supplement form. However, some brands of prescription carb blockers are also available to help treat type 2 diabetes.

In case you were wondering why someone would want to prevent their body from absorbing carbohydrates, keep in mind that excess refined carbohydrates have been linked to obesity, type 2 diabetes, metabolic disease, and more (2, 3, 4).


When you have too much glucose in your diet, it stimulates the production of insulin, which delivers any excess glucose in your blood to your fat, muscle, and liver cells to use for energy. Overeating carbohydrates and sweetened drinks can also contribute to brain fog, migraines, depression, and skin problems (5).

If you’re on the ketogenic diet, then you probably already know that eating too many carbohydrates will kick you out of ketosis, which is the fat-burning metabolic process responsible for all the health benefits of the diet. For this reason, some ketogenic dieters use carb blockers to reduce the effect of overeating carbs (we’ll discuss more about this below).

A carb blocker is designed to “block” the breakdown of starches in your body so that they aren’t absorbed into your bloodstream. Carb blockers prevent certain enzymes from breaking down and digesting carbohydrates and instead discrete them via the digestive process without taking up any of the nutrients. This means that your body doesn’t absorb any of the calories, nutrients, or glucose from the carbohydrate molecule.

What Are The Ingredients?

There are two primary forms of carb blockers that you can take. The first is known as alpha-amylase inhibitors and they are usually sold as weight loss supplements. You can find these at any supplement store. The main ingredient in these types of carb blockers is white kidney bean extract, which is also known as Phaseolus vulgaris extract.

Research shows that white kidney bean extract has a low glycemic index and slows the absorption of carbohydrates by inhibiting enzymes responsible for their digestion (6).

Specifically, white kidney bean extract helps induce weight loss when taken in the amount of 500 to 3000 mg per day and reduces the postprandial spike in blood sugar levels.

Additional research shows that white kidney bean extract significantly decreases fat mass and helps preserve lean body mass (7).

Another study found that people who took 1000 mg of white kidney bean extract before meals for four weeks lost more weight and had a more significant reduction in waist size than the placebo group who ate the same number of carbohydrates (8).

The second type of carb blocker comes in prescription form and is referred to as an alpha-glucosidase inhibitor or an AGI. Most AGI’s are used to treat type 2 diabetes or people with impaired glucose tolerance (9).  

Research shows that they are derived from bacteria and delay the absorption of carbohydrates in the small intestine, which lowers postprandial blood glucose and insulin levels to help control and prevent diabetes (10, 11).

The most common types of AGIs that are available for prescription use include acarbose, voglibose, and miglitol (12).

How Does it Work?

One of the enzymes in your body that is responsible for breaking down carbohydrates is called amylase. It is produced in your pancreas and works by breaking down longer carbohydrate chains into simple sugars where they are easily digested and absorbed in the body.

Alpha-amylase inhibitors work by preventing this enzyme from doing its job. Specifically, it prevents your pancreas from creating this digestive enzyme.

There is another type of enzyme responsible for breaking down glycogen molecules called alpha-glucosidase. AGI’s work by preventing alpha-glucosidase from doing its job. When alpha-glucosidase is inhibited, carbohydrates cannot be broken down as easily and this delays glucose absorption, which helps keep your blood sugar levels stable.

As you can see, both types of carb blockers work by preventing enzymes from breaking down carbohydrates so that your body doesn’t absorb them. They just target different enzymes.

Although you can’t get ahold of an AGI without a prescription, you can easily find white kidney bean extract at any health food store. You can also look into taking Salacia, which is a plant extract sold in supplement form that works just like an AGI.

Research shows that Salacia extract significantly lowers glucose and insulin, which plays an important role in reducing postprandial hyperglycemia (13).

It’s important to keep in mind that carb blockers only prevent the breakdown of complex carbohydrates and not simple carbs. This is important because it means that you can’t indulge in your favorite sweet treats and expect a carb blocker to save you from the calories and sugar rush.

Carb blockers work by preventing the breakdown of complex carbs with longer sugar chains into smaller, simple sugar molecules. If you eat simple sugars that are already broken down and don’t need an enzyme to further assist with the breakdown process, then a carb blocker will do nothing for you.

What Are The Benefits?

Cutting carbs has many benefits on the body. Low-carb diets have been linked to weight loss, type 2 diabetes control and prevention, and a reduced risk of metabolic syndrome among other conditions. People who switch from a high-carbohydrate, low-fat diet to a high-fat, low-carbohydrate diet often report feeling better immediately (14).

Carb blockers act similarly to resistant starch in the body because they cannot be broken down by the digestive enzymes in your GI tract. This means they go through the digestive system undigested and aid in gut health, similar to fiber.

Research shows that the carb blocker bean extract can assist with weight loss and decrease triglycerides. You can also use white bean extract to help lower the glycemic index of high GI foods, such as white bread (15, 16).

Additional research shows that white bean extract reduces food intake, including calories from highly palatable foods, body weight, lipid deposit, and glycemia in rats. This is because carb blockers control some of the hormones that affect your hunger, especially the hunger hormone ghrelin (17).

Are There Any Side Effects?

Although carb blockers in the form of white kidney bean extract are generally considered safe, you won’t want to take too much of it. Doing so might lead to digestive upset such as bloating, cramping, stomach pain, gas, and diarrhea or constipation. Common side effects of prescription AGIs include an upset stomach, gas, diarrhea, and cramp.

As we mentioned before, carb blockers may also cause you to develop bad habits when it comes to carbohydrate intake such as including more “cheat” meals in your diet.

Do They Really Work?

Although carb blockers sound like they could be your savior if you decide to indulge in a large pizza, you may want to think again. Research shows that carb blockers only prevent about 53 percent of amylase and 66 percent of α-glucosidase (18).

In other words, just because carb blockers prevented the pancreas from producing 53 percent of amylase doesn’t mean that you will be protected against 53 percent of the carbs in your meal.

For example, one study found that although an amylase inhibitor prevented 96 percent of the enzyme from being formed, it still only prevented a small percentage of the carbohydrate meal from being absorbed (19).

So while carb blockers might do a good job at preventing certain enzymes from being formed in the pancreas, there is no guarantee that you will be protected against carbohydrate absorption from a meal high in carbs.

On the other hand, the ketogenic diet has proven to be effective for weight loss and other positive health outcomes. It’s an easy way to block carbs from your diet without having to take a supplement that interferes with your enzyme production or the role of your pancreas, which is an important part of the digestive process and would be better off not tampered with.

Should Keto Dieters Take Carb Blockers?

The best and most efficient way to reduce your carbohydrate absorption is to cut back on eating them. The ketogenic diet reduces your overall carbohydrate intake to less than five percent of your daily calories. Doing so puts your body into a state of ketosis, which has numerous benefits including better blood sugar control, weight loss, and improved neurological function. There are no shortcuts when you use the ketogenic diet, and it has been proven as a useful weight loss tool.

On the other hand, carb blockers could be risky and they allow for bad habits. Instead of giving up carbohydrates altogether, carb blockers give you the sensation that you can “cheat” or eat more carbohydrates than you’re allowed on the ketogenic diet. We recommend avoiding carb blockers whenever possible and focusing your attention on making smart ketogenic choices.

Get your carbs from low-carb vegetables such as spinach, broccoli, cauliflower, kale, and zucchini. It’s OK to enjoy berries in moderation, but this should be the extent of your sugar intake. Plus, berries and vegetables are loaded with nutrients such as vitamins, minerals, antioxidants, and fiber that benefit your health; therefore, you won’t want to block these carbs from being absorbed anyway.

Carb blockers set you up for a mindset that allows you to eat foods that you shouldn’t as long as you take a carb blocker first. When you avoid carb blockers and focus on eating a well-balanced ketogenic diet instead, you automatically cash in on the health benefits of a low-carb diet without having to take a carb blocker to get there.

Of course, carb blockers are not off limits, some people still take them on their normal diets. Many of the proven benefits of carb blockers, such as weight loss and blood sugar control, can be achieved by following the ketogenic diet alone. There’s no need to use carb blocker on the keto diet.

Also don’t confuse carb blocker with exogenous ketones, they are not the same thing. You can read our exogenous ketones review here to learn more about this keto supplement.


Carb blockers can be a useful tool if you’d like to cut down on the effects that carbohydrates have on your weight and blood sugar levels. There are two primary types of carb blockers. The first is white kidney bean extract, and you can purchase it at just about any health food store. The second type is known as an AGI, and it’s available via prescription only.

Both kinds of carb blockers work by preventing the pancreas from producing enzymes that are needed to break down carbs. Without this enzyme, complex carbohydrates cannot be broken down into smaller molecules where they are easily absorbed by the small intestine, which means that they pass through your digestive tract without any effect on your calorie intake or blood sugar levels.

However, carb blockers only work on complex carbohydrates. They won’t do a thing for you if you eat simple sugars, such as ice cream or candy. Because of this, we recommend staying away from carb blockers and focusing your attention on maintaining a healthy ketogenic diet instead. You’ll achieve even more health benefits as you would if you were to take a carb blocker.

Plus, you will be less likely to develop bad habits when it comes to cheating on keto by eating too many carbs. We recommend focusing on low-carb vegetables and berries as your only source of carbs and staying away from the carb blockers entirely.

If you need help with getting started on keto, don’t forget to check our keto food list and free meal plans!

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