You may have seen that carb blocker supplements have had a surge in popularity as of late. If you're thinking about buying and taking a supplement I believe it's important to understand how and why something works so you can make an informed decision before putting a substance into your body.
I'll admit, first time I heard of carb blockers my first thought was that they have to be a complete scam. Turns out, I was wrong. There is some legitimacy to the claims made about these supplements. But, while they do block some of the carbs we eat, the question really becomes "How much?"
First, let's do a quick and dirty on carb blockers. The most commonly used ingredient is White Kidney Bean extract. There are several other types, but since this is the one I see most commonly I'll stick to it. White Kidney Bean extract works by inhibiting the digestion of long chain carbohydrates, preventing them from being broken down by the amylase enzymes.(1) Instead, the undigested carbohydrates remain in the intestinal system as resistant carbohydrate, which cannot be digested by the small intestine.(2) Resistant carbohydrates are transported to the colon where they can be fermented by the bacteria there to create short-chain fatty acids.
We can all agree that weight loss is a result of an imbalance of calories taken in and calories expended. So, by preventing the enzymes in our digestive systems from breaking down these long chain carbohydrates carb blockers can decrease the number of calories we eat in a meal. But is it significant?
One study showed that amylase inhibitor (dosed at 3.8g) decreased amylase production by 97%. But don't get too excited. Malabsorbed carbohydrate in the group with no supplementation was 4.7% (+/- 1.9%) only increased to 7%(+/- 1.4%). What this means is, if you're eating 200 calories of carbohydrate you're actually absorbing 186 calories. While this can add up over a long period of time it's not an awe inspiring number.
A number of studies completed on a product called Phase 2 (an amylase inhibitor) showed increased weight loss in groups taking Phase 2 over the placebo groups.(3) Before you drop your phone and run to the store to grab some carb blockers there are some considerations. *Note* These studies were small sample sizes, and funded by the supplement company, so they should be taken with a grain of salt.
Carb blockers have some unintended, but positive benefits. They seem to decrease the speed at which food leaves the stomach. This can be majorly beneficial because it increases feelings of fullness and satiety, which can help stick to a calorie deficit.
One rodent study showed that rats who consumed carb blockers prior to a meal ate 25-90% less than normal. Unfortunately, after the supplementation stopped the rats actually at more in following days until they regained all of their lost weight.(2) This makes sense because decreased circulating leptin levels lead to increased hunger in mammals. The body typically will 'defend' a certain level of body fatness, and after periods of under eating decreased leptin signaling and increased ghrenlin result in over eating as the brain attempts to return to previous levels of body fat. This is something to be aware of if you plan on supplementing with a carb blocker, once you stop taking it the appetite blunting benefits will go away. This combined with the increased hunger and dis-inhibition after an extended period of dieting can lead to over eating and weight regain.
While carb blockers can blunt appetite this is not a guarantee that you will, in fact, eat less. Very often people choose to use supplements like this in the face of 'cheat meals' or other high calorie binge type episodes. These meals are not strictly carbohydrate meals, and often are a combination of carbohydrates, fats, sodium. Highly palatable foods are easy to over eat, despite feelings of fullness and even discomfort. Ever notice how you can be stuffed at a restaurant, but still manage to find room for dessert? We are much more likely to overeat high reward foods.
"Not surprisingly, research suggests that people eat larger quantities of foods they like. John de Castro, a professor or psychology at Sam Houston State University, and his research team demonstrated that people living their every day lives eat 44 percent more calories at meals they describe as highly palatable than at meals they describe as bland. The brain perceives these foods as so valuable that it motivates us to keep eating them even if we have no particular need for energy - in fact, even if we're already drowning in energy." (5)
So, pairing highly rewarding foods with carb blockers might help us put the fork down sooner, but it's just as likely that the food reward can over power our decreased appetite.
A secondary warning, if you're using carb blockers infrequently (in the case of before a 'cheat meal') they can cause stomach upset. If you remember from before, the carbohydrates that aren't broken down are taken into the colon where they can be fermented. This can result in gas, bloating and diarrhea. These side effects usually subside after several days of continued use.(1)
Another consideration is that when it comes to dietary supplements they are not regulated by the FDA. This means there is a wide variance in the quality and dose of any given supplement. Proprietary blends list ingredients used, but since they do not offer the exact amount so you could be paying for something that contains less than the effective dose. Furthermore, the FDA has found that, due to a lack of regulation, what is written on the label isn't always what's in the bottle.(4) Always try to find supplements that have been tested and verified by a 3rd party.
Conclusion: If you can withstand the stomach upset for the first few days adding a carb blocker to a calorie controlled, healthy diet can be beneficial for short term success in weight loss. As with all supplements, nothing is a magic pill. If it helps you control appetite and eat less, that's great. But don't let it become a license to eat anything and everything. It is still possible to over eat on calories despite a portion of the carbohydrates not being broken down. Furthermore, after your diet is over hunger levels will rise, and you need to insure that you've found a method of eating that you can maintain over the long haul. Crash diets and extreme deficits combined with supplementation will only produce short term results.
(5) The Hungry Brain, Stephan Guyenet, Ph.D. pg 58