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When you’re trying to shed pounds and the scale isn’t moving in the right direction, it can be tempting to want to try something else, like a no-prescription weight loss supplement.

Some of those supplements are called "starch blockers" or "carbohydrate blockers." They may seem like a good option because they claim to keep starches , and the calories found in them, from being digested.

But it's not quite that simple. If you're thinking about trying them for weight loss, you should know this first.

What Are Starch Blockers?

Starch blockers are made from white kidney beans, which have a natural chemical called amylase. Amylase helps digest starch or complex carbohydrates. When amylase is blocked, those carbs pass through the body undigested, so you don't absorb the calories.

Some starch blockers need a prescription. They are called acarbose (Precose), and miglitol (Glyset). These are used as treatments for blood sugar control in people with type 2 diabetes.

There are also starch blockers that are sold without a prescription as supplements.

What's the difference?

Prescription drugs have to prove to the FDA that they are safe and effective. Supplements don't. You also can't be sure of what's in a supplement.

Some supplements may have unlisted ingredients, maybe stimulants, that could be dangerous for people with diabetes, says Kathleen Dungan, MD, an endocrinologist at Ohio State University.

Prescription versions won’t have those extra ingredients, so they tend to be safer.

The FDA has sent warning letters to makers of no-prescription starch blockers in the past, saying their marketing claims are misleading.

If you're considering using any product marketed for weight loss, talk to your doctor or a dietitian first. Ask yourself if it sounds too good to be true, and be skeptical.

Do They Work?

When it comes to shedding pounds, the evidence is not clear. There’s little data to support the use of herbal supplements as carb blockers, Dungan says.

As for side effects, you could get gas, bloating, stomach cramping, and diarrhea, she says.

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