Fat Blockers

For most people struggling with weight loss, the first rule of their diet is to cut back on fatty foods.  Fats are a major source of calories with about 9 calories per gram – more than twice found in a gram of protein or carbohydrates.  Since unhealthy, high-fat foods dominate cuisine in western culture, it can be a very daunting task for dieters to avoid consuming too much fat.

Fat blockers seem like a dieter’s dream come true: they promise that you can eat all the fatty foods you want and not have to worry about gaining weight.  One fat blocker supplement even put the name “Cheater” in its name to suggest how easy dieting can be with the product.  For people who truly love fatty foods, fat blockers can be a great tool to help weight loss.  However, as one would expect from anything which seems too good to be true, there are some downsides to these fat blocker supplements.

How Fat Blockers Work

Fat blockers claim to work in one of two ways: they disrupt the enzymes which break down fat or change the composition of dietary fats so they become indigestible.  In either of these scenarios, the end result is the same.  Instead of the fats being absorbed by the body for fuel, they get expelled as bowel movements.

Currently, the only prescription fat blocker available is Xenical, which contains the active ingredient orlistat. A few years after Xenical gained approval for treating obesity, orlistat was approved for over-the-counter sale in smaller dosages.  The popularity of orlistat spurred an industry of “natural” fat binders.  There are now hundreds of different over-the-counter supplements available which supposedly block absorption of dietary fats.

Most over-the-counter fat binder supplements contain chitosan, a compound made from crustacean shells.  Unlike orlistat which affects gastrointestinal enzymes and lipases, chitosan purports to affect dietary fats. When it comes in contact with the dietary fats, it causes the fat molecules to ball up and they become indigestible.  There are also several fat binders made from cacti extracts which supposedly work in the same manner.  Despite the popularity of these natural fat binders, there is little scientific evidence backing up their effectiveness.

Side Effects of Fat Blockers

Because fat blockers prevent dietary fats from being absorbed by the body, the fats instead are excreted out of the body in bowel movements.  While this probably isn’t harmful, it does cause some very unpleasant side effects.  Fat blockers are known to cause gas, oily stools, oily discharge from the anus, fecal incontinence, and diarrhea.  These symptoms are related to the amount of fat in the meal consumed.  If the meal only has a small amount of fat, then the symptoms will be mild because there is less fat being blocked and excreted.  Fat blockers usually come with warnings that only low-fat meals should be eaten in order to avoid side effects.  Some evidence shows that fat blockers may even be effective in promoting long-term weight loss through aversion therapy: the user will soon associate the side effects with fatty foods and thus make healthier food choices.

The only evident risk of fat blockers is that they could lead to deficiencies in fat-soluble vitamins and nutrients.  People using fat blockers should take a multi-vitamin that contains fat soluble nutrients like vitamins A, D, E, K and beta-carotene.  This vitamin should be taken at least a few hours apart from the fat blocker. There is some evidence that orlistat may in rare cases lead to liver damage but this has not yet been confirmed.

Do Fat Blockers Really Help Weight Loss?

If weight loss is going to occur, then the person must consume fewer calories than he/she is burning.  Fat blockers can help weight loss because they block fat absorption, thus also blocking many calories.  However, fat blockers will not block calories from other sources like carbohydrates nor will they have any effect on stored fats.  So, if a person is still consuming more calories than burned (even when negating the calories from fat), weight gain will still occur.

Fat blockers are best for people whose weight problems are from eating too many fatty foods.  An effective fat blocker can help fatty food lovers endure diet plans without feeling too guilty about indulging in high-fat foods like ice cream every once in a while – but they should be prepared to put up with the side effects!


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Schiller RN, Barrager E, Schauss AG, Nichols EJ. “A Randomized, Double-Blind, Placebo-Controlled Study Examining the Effects of a Rapidly Soluble Chitosan Dietary Supplement on Weight Loss and Body Composition in Overweight and Mildly Obese Individuals”. Journal of the American Nutraceutical Association 4.1 (2001): 42-49.


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