Unless you live in a fairy tale, magic pills don’t exist.
And yet, when you hear the words “carb blocker,” it’s easy to think your fantasies are coming true.
Unfortunately, it’s not quite as simple as taking a supplement and eating a dozen guilt-free bagels. Before considering carb blocking pills, there are some important things to know.
What Are Carb Blockers?
To understand carb blockers, it helps to understand carbs.
There are two types of carbohydrates: simple and complex (1).
Simple carbs are composed of basic sugars that are broken down quickly by the body. They naturally occur in fruits and milk, as well as processed foods such as soda, candy, and baked goods.
Complex carbs are found in whole grains, legumes, and starchy vegetables. They’re composed of longer chains of sugar molecules that the body breaks down more slowly, leading to a more steady supply of energy.
Although your body needs a certain amount of quality carbohydrates, they tend to be high in calories. What’s more, some carbs are thought to slow the metabolism; a 2018 study found that participants on a low-carb diet actually burned more calories per day than those on a high-carb diet (2).
Carb blockers, sometimes referred to as “starch blockers,” block enzymes needed to break down complex carbs, preventing the carbs from being digested by the body and providing calories. For this reason, they’re frequently used as weight loss aids.
Do Carb Blockers Work?
There are two main types of carb blockers: Prescription medication and over-the-counter supplements.
Prescription medications, known as alpha-glucosidase inhibitors (AGIs), are used to prevent blood sugar spikes in patients with type 2 diabetes. Derived from bacteria (3), they disable enzymes in the gut necessary for carbohydrate absorption.
Carb blocker supplements use natural compounds extracted from beans, most commonly white kidney beans, known as Phaseolus vulgaris. Research has shown that white kidney bean extract, like some bacteria, can also slow carbohydrate absorption by inhibiting digestive enzymes (4).
Which is all well and good. But do carb blockers work? Can blocking enzymes result in actual weight loss? According to some research, yes.
In a double-blind study of 60 overweight adults, researchers found that participants who consumed white kidney bean extract with a carbohydrate-rich diet lost significantly more body weight than those given a placebo (5). A similar study found that in addition to losing weight, participants were able to maintain the loss (6).
However, other studies were unable to draw any conclusions about the efficacy of carb blockers (7). Although they appear to aid in weight loss, more research is clearly needed, says Amanda Kostro Miller, a registered dietitian based in Chicago.
“Currently, there is limited evidence that carb blockers work,” says Miller. “We are unable to draw conclusions in the research as a whole. No supplement can replace an overall healthy lifestyle and exercise routine.”
Benefits of Carb Blockers
Although carb blockers are primarily used for weight loss, the supplements may offer other benefits, as well.
There is some evidence that carb blockers may prevent overeating.
Bean extracts contain phytohaemagglutinin, a compound that can increase the hormones that lead to feelings of fullness. In one experiment, rats who consumed white bean extract ate 25 percent to 90 percent less calories (8). However, the effect wore off in a few days.
Regulate Blood Sugar Levels
By slowing the digestion of complex carbs, carb blockers can reduce spikes in blood sugar levels. Studies have shown that supplements containing Phaseolus vulgaris can cause blood sugar levels to remain more consistent while consuming carbs, as well as help sugar levels return to normal more quickly after meals (9).
Provide Resistant Starch
In rendering some carbs indigestible, carb blockers can slow down digestion, which can be beneficial.
“Carb blockers may provide non-digestible carbohydrates, similar to fiber, to slow the absorption of calories and nutrients through the gut,” says Miller.
Known as resistant starches, these undigested carbs eventually arrive in the large intestine and are fermented by gut bacteria, a process that releases beneficial fatty acids. Studies have shown that resistant starches—which occur naturally in foods such as legumes, bananas, and whole grains—can lead to decreased body fat, better insulin control, and healthier gut bacteria (10).
The downside? By increasing the amount of resistant starch, carb blockers can lead to bloating, cramping, diarrhea, and gas, warns Miller.
How to Choose a Carb Blocker
If you decide to take a carb blocker, it’s important to carefully choose your supplement.
There are a number of over-the-counter supplements marketed as “carb blockers” or “starch blockers,” but formulas vary. The only ingredient shown to have an effect on weight loss and blood sugar is white kidney bean extract, so be sure to choose a supplement that lists white kidney bean or Phaseolus vulgaris as an active ingredient.
Dosage recommendations vary among formulas, but most recommend taking two capsules before a starchy meal. However, they should never be used more than twice a day, says Miller.
The FDA classifies dietary supplements as foods (11), meaning their safety and sale isn’t regulated as closely as prescription medications. As with any supplement, it’s important to buy carb blockers from a trusted source and consult with your doctor, says Miller.
Precautions When Taking Carb Blockers
Although generally considered safe when taken by healthy individuals, carb blockers aren’t appropriate for everyone, cautions Miller.
Because of their potential to affect blood sugar levels, carb blocker supplements can be dangerous for those with diabetes. Due to lack of research, women who are pregnant or breastfeeding should avoid carb blockers. Patients with digestive disorders and liver or kidney disease are also discouraged from using carb blockers.
Regardless of health concerns, it’s always best to check in with your doctor before adding a supplement to your diet.
How to Reduce Carb Intake
While carb blockers may offer a boost or kick-start for some, a nutritious diet is the true answer to maintaining a healthy weight and relationship with food.
“Instead of looking for a quick fix, try to get to the bottom of it—ask yourself, ‘Why am I doing this?’” says Emily Pierce, a registered dietitian at OnPoint Nutrition in Philadelphia. “Then you can begin to look for healthy, long-term solutions that fit your goals.”
For those who want to lose weight, Pierce does recommend cutting back on carbs. However, instead of simply taking away the mashed potatoes and dinner rolls, try replacing them with an extra vegetable you enjoy.
“When you decrease carbs, you can increase your fruits, vegetables, proteins, and healthy fats,” she says. “Losing weight isn’t always about giving things up.”