Weight loss supplements generally work in one of three ways: helping your body break down fat, suppressing your appetite or inhibiting your body from absorbing nutrients after you eat them. That's what carb and starch blockers claim to do, and the same claim is made by fat blockers on the market. The consensus seems to be that carb blockers have a theoretically sound mechanism for working, but practically they don't. One of the major fat blockers, chitosan, is almost categorically deemed ineffective, while another one, orlistat, works but potentially comes with embarrassing side effects. In either case, supplements are simply helpers and don't replace the tried-and-true advice of eating less and moving more. Moreover, carb blockers don't work if you eat excessive fat, and fat blockers don't work if you overeat protein and carbohydrates. Calories are what counts. See your healthcare provider for advice if you want to use a fat or carb blocker.
Carb Blockers
Recognizing the role of refined carbohydrates in being overweight and obesity, makers of carb blockers claim their products helps to prevent or delay the absorption of carbohydrates in your digestive system. They claim to work by inhibiting the enzymes needed to break down carbs, including amylase and alpha-glucosidases (JACN). Most use a protein extract of the white kidney bean as the active ingredient. A Georgetown Medical School physiology study reported in the "Journal of the American College of Nutrition" that studied people and animals "clearly show that this agent works" and has "clinical utility."
But other health authorities, like the Mayo Clinic and the U.S. Food and Drug Administration, beg to differ. A report by the Health & Human Performance Center at San Juan College reviewed the claims of carb and starch blockers, which included that undigested starch would be eliminated in feces. In a review of quite outdated research, the center said that's not true, and that the amount of amylase people produce greatly exceeds the capacity of carb blockers on the market. The authors declare emphatically that starch blockers don't work and that you should save your money. In 2004, the FDA sent a warning letter to the makers of TrimSpa Carb Blocker, which has been discontinued, saying that the agency concluded the claims made by the company were not supported by reliable scientific evidence and were false or misleading.
Resurgence With Low-Carb Craze
In the mid-to-late 2000s, carb blockers reappeared on the market after a near-30 year absence, thanks in part to the resurgence of interest in low-carb diets and the need for an occasional cheat. The "Washington Post" reported that a nutrition foods industry group agreed that the first generation of carb blockers from the 1980s did not work. The paper quoted a Harvard Medical School researcher as saying that the blockers "are unproven, unscientific and unsafe." Fewer brands of carb blockers were on the market in the 2010s.
Fat Blockers: Chitosan
One version of popular fat blockers contains chitosan, which is made from chitin and forms in the shells of crustaceans. Chitosan is a polysaccharide, or long chain of sugar molecules, and acts similar to fiber by passing through your digestive tract without being absorbed. A report by Harvard's Medical School states that chitosan forms a gel around fat droplets in the intestine, protecting them from an enzyme that helps break down fat so that it can enter the bloodstream and be used by your body. Like carb blockers, chitosan-containing products claim that the substance increases the amount of fat eliminated in your stools. However, in their review, the authors found that chitosan didn't do that.
Fat Blockers: Orlistat
Orlistat also works by attaching to and deactivating lipase, an enzyme responsible for fat absorption. Orlistat is sold as a prescription drug under the name Xenical at 120 mg. An over-the-counter version of orlistat, Alli, comes in a 60 mg dose. Unlike chitosan, the Harvard authors' literature review demonstrated that orlistat indeed increases the amount of fat excreted out in feces and demonstrated significant weight loss. However, orlistat can cause severe, and possibly unacceptable, gastrointestinal problems including loose stools and a possible inability to control them. Moreover, San Juan College reported that orlistat works best if your fat intake is between 20 and 30 percent of the total calories of your meals. It doesn't work if you follow a low-fat diet. Harvard also questions whether the OTC version of orlistat works as well as the prescription version.
References
- Mayo Clinic: Over-the-Counter Weight-Loss Pills: Do They Work?
- "Journal of the American College of Nutrition"; Bean Amylase Inhibitor and Other Carbohydrate Absorption Blockers: Effects on Diabesity and General Health; Harry G. Preuss; June 2009
- "Washington Post"; Lean Plate Club: Block That Starch Blocker; Sally Squires; Oct. 28, 2003
- San Juan College HHPC: Are Weight-Loss Supplements Helpful?
- Harvard Medical School Science in the News; Bulking Up and Slimming Down: The Science of Supplements, Fat-Blockers & Fat-Burners; Oded Shaham
- Columbia University Go Ask Alice!; Do Fat Burners Really Work; Feb. 5, 2009
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