The Science Behind Carb Blockers and Weight Loss

Weight loss pills come with claims like ‘Eat all you want and still be slim’.

It seems like a dream come true but you know it is just a hoax.

But then you come to know the science behind it and you are pretty convinced that it should work.

One such really popular weight loss supplement was Orlistat, which worked on the principle of fat blocking.

If your diet is rich in fats then taking this pill prior to meals can prevent absorption of fats by intestine which is good if fats make you fat.

But what about carbs? Can you block these too?

What are Carbohydrate Blockers?

40-80% of average calorie intake comes from carbohydrates.

Based on their structure, carbohydrates are classified as absorbable, digestible, fermented and non-fermentable forms.

Overall they are simple or complex carbohydrates.

The basic component of carbohydrates are monosaccharides which are single units like glucose and fructose.

These are directly absorbed by the intestine. Complex carbs contain two or more of these structures and hence need to be broken down for absorption.

Digestion of carbs begins in the mouth. The enzyme alpha-amylase present in the saliva breaks down the bonds present in starch.

This digestion continues in the small intestine where the pancreas provides alpha-amylase. Alpha-amylase only breaks down complex carbs mainly starch, not sugars.

Digestion of the carbohydrates is completed by disaccharidases - these enzymes are secreted by walls of the small intestine and further break it into simple components.

Like maltase enzyme breaks down maltose and sucrase breaks down sucrose. Thereafter these simple components are absorbed by the intestine.

Carbohydrate blockers work by inhibiting the activity of these enzymes.

This leads to decreased absorption of main carbohydrates from diet and that means lesser calories which promote weight loss.

Inhibition of these enzymes also promotes satiety reducing energy intake.

Role of Carbohydrate Blockers in Weight Loss

There are a number of compounds that have been identified as carbohydrate blockers. They either block alpha-amylase or disaccharidases.

1. White kidney bean extract causes weight loss

This is the most popular carbohydrate blocker. White kidney bean extract contains a protein that binds to the alpha-amylase enzyme and inhibits its activity.

The proprietary blend goes with the name Phase 2, earlier known as Phaseolamin 2250- 1g of the product can block 2250 calories of starch.

Animal studies show that white kidney bean extract reduces food intake and consequently body weight. Acute consumption of 1.5 g of white kidney bean extract absorbed 66% of the carbohydrate of the meal.

A clinical trial lasting for 8 weeks reported a loss of an average of 3.79 pounds with Phase 2 administration.

A review of clinical studies reveals that Phase 2 at a dose of 500-3000mg has the potential to cause weight loss.

Studies in diabetic population reveal that white kidney bean extract is good for blood sugar control and can treat or prevent diabetes-induced obesity.

White kidney bean extract does help with weight loss if you have a high carb diet and is good for short term weight loss.

But sadly if you stop consuming it you are likely to gain weight. (Read White kidney bean extract for weight loss)

What does this mean? White kidney extract is the best carbohydrate blocker but it prevents absorption of calories only from starch. However one can expect modest weight loss from this within short span.

2. L-arabinose- the non-calorie sugar that is a starch blocker

L-arabinose is a compound that is slowly gaining popularity in the weight loss industry. This carb blocker inhibits the activity of sucrase- enzyme that breaks down table sugar.

And it is this table sugar which taken in excess can turn out to be a really bad carb.

Animal study shows that l-arabinose strongly inhibits the activity of sucrase and prevents spikes in blood glucose and also causes weight loss.

In one animal study the carbohydrate blocking activity of l-arabinose was compared to that of bean extract and hibiscus extract.

These inhibitors were provided with sugar solution. Upon ingestion l-arabinose strongly inhibited the activity of sucrose in comparison to the other two.

Combination of all three compounds significantly decreased starch as well as sucrose absorption.

Human studies showed that inclusion of 4% l-arabinose in sugar-sweetened beverages reduced the rise in blood sugar levels and had a beneficial effect on insulin levels.

An investigational product containing L-arabinose and other natural carbohydrate blocker was tested for its effect on body weight.

This study involved 120 obese individuals and lasted for 12 weeks.

Average weight loss of 3.29 kg was reported and the product caused no significant side effect.

What does this mean? L-arabinose blocks calories from sugar as it inhibits activity of enzyme sucrase. Large clinical trials are required to warrant its role in weight loss.

Carb Blockers and Weight Loss

3. Acarbose blocks calories from carbohydrates

Acarbose (also known as GlucoBay, Precose, Prandase) is a compound that inhibits the activity of disaccharidases.

This prevents the breakdown of dissacharides into glucose and simpler units.

A study shows that acarbose inhibits the activity of alpha-amylase, sucrase, and maltase.

Acarbose is found to aid in weight maintenance and prevent weight regain. One study in diabetic patients reports insignificant weight loss with acarbose.

A study in PCOS patients reported a significant decrease in BMI in 6 months with acarbose.

What does this mean? Acarbose is a popular anti-diabetic medication which blocks calories from sugars and proven to cause modest weight loss but in limited studies.

4. Gymnema sylvestre- the anti-sweet herb

Gymnema Sylvestre is a herb whose active compound is gymnemic acid.

This has unique carbohydrate absorption blocking properties.

The structure of gymnemic acid is similar to that of sugar and if taken before meals, it goes and blocks the absorption sites for sugar in the intestine.

Since sugar is not absorbed the calories associated with are excreted.

Another unique property of this herb it suppresses sweetness.

If you chew a tablet of Gymnema extract such that it coats the tongue, then it will reduce your ability to taste the sweetness in the food.

As a result you are deprived of the rewarding feeling and you lose the desire to eat sweet foods.

Review of clinical studies suggests that gymnema sylvestre has anti-obesity and anti-diabetic effect as it reduces body weight and decreases glucose absorption.

Animal studies suggest that gymnema sylvestre extract prevents weight gain due to the high fat diet.

What does this mean? Gymnema sylvestre is a unique herb that not only prevents carbohydrate absorption but also reduces appetite for sweet treats.

5. Other natural carbohydrate blockers

A few compounds found naturally in plants also exhibit inhibitory activity against enzymes involved in carbohydrate digestion.

Green tea catechins

Green tea is touted for its weight loss benefits primarily for its fat burning capabilities and thermogenic property.

Interestingly a few studies show that active ingredients of green tea can inhibit the activity of enzymes involved in carbohydrate digestion.

A study in humans proved that a single dose (4g) of green tea extract taken prior to a starchy meal decreases starch digestion and absorption. (Read Green tea for weight loss)

Mulberry extract

Deoxynojirimycin is a compound isolated from mulberry trees that inhibits the activity of an enzyme involved in carbohydrate digestion, alpha glucosidase. Derivatives of this compound have also been developed.

Animal studies show that this compound and its derivatives can inhibit the activity of enzymes, prevent weight gain and pose an anti-diabetic effect.

A clinical trial with deoxynojirimycin derivative reported a decrease in sucrose (table sugar) absorption and reduced spikes in blood sugar.

However gastric discomfort was a common side effect in the study population.

Hibiscus extract

Hibiscus tea is a herbal tea prepared from calices of hibiscus.

It has a tart flavour and is said to be very useful for treating obesity.

Among the different pharmacological properties of hibiscus tea that aid in reducing body weight, hibiscus tea inhibits the activity of enzymes involved in carbohydrate digestion and absorption.


Wheat flour also contains a few proteins that inhibit the activity of alpha amylase. Pure preparations of this protein have been found to inhibit 90% of the enzyme activity.

What does this mean? A number of natural compounds mimic the carbohydrate blocking activity of commercial starch blockers and few to name are green tea, mulberry extract, hibiscus tea etc.

However, a few scientists have a different view on carb blockers

One research study specifically investigated the effect of consuming starch blockers on calorie excretion and how many calories were excreted.

Individuals were given high starch meal and starch blocker tablets prior to the meals.

It was hypothesized that if the starch blockers worked then about 400 kcal should be excreted but test results should no such calorie excretion.

Scientists concluded that starch blockers do not inhibit carbohydrate digestion.

Similar results were also reported by other studies on humans.

What does this mean? A few researchers have shown that calorie excretion after taking starch blockers is insignificant enough to cause weight loss.


Dosage for carb blockers depends on the extract that you are taking.

For example, one study reports that 2.9g of amylase inhibitor is a safe dose as it would not cause gastric discomfort.

For white kidney bean extract it is 500mg thrice a day.

The key is to take these supplements 15-30 minutes prior meals.


The only bothersome side effects that could occur due to blockage of carbohydrate digestion is a gastrointestinal problem such as bloating, flatulence, diarrhea.

So it is not advisable for long term.

Also, these supplements are generally given to diabetic individuals so if you are taking anti-diabetic medications, you might want to take these with care.

Consult a health physician before taking any supplement.


Carbohydrate blockers scientifically have a great mode of action for protection against weight gain.

However, they are useful only, if you consume a high carb diet or if you are suffering from diabetes.

They are good for short term weight loss but the weight loss outcome is pretty modest. If you stop taking them you are likely to regain the weight.

If you have tried any of these carb blockers, please share your experience with us.

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