Orlistat (Xenical)

The idea behind orlistat (Xenical) is beautifully simple: if you want to cut calories and you can't stop consuming fatty foods, then stop absorbing fat from your gut. Indeed, that's what orlistat helps you with. Fat from food can only be absorbed if it is broken down into its components: fatty acids and glycerin. This is accomplished by lipase, the enzyme that pancreas releases into the gut after a meal. Orlistat inhibits lipase, which reduces the absorption of fat, thereby cutting intake of calories and promoting weight loss.

As is often the case in medicine, the reality is more complicated than a simple neat idea. Indeed, orlistat reduces the amount of fat you absorb and does induce some weight loss. However, the weight loss is less than one would expect. Studies show that after two year only about 20% of overweight people on orlistat lose 10% or more of body weight. This is a relatively modest effect considering that 10% of overweight people will lose 10% or more of body weight if give placebo (sugar pill). The fact that orlistat produces a smaller than expected weight loss may be due to incomplete inhibition of lipase, increased appetite as a result of reduced fat absorption, reactive increase in secretion of lipase by the pancreas or all of the above.

Still, why not take orlistat anyway - modest weight loss is better than none, right? Don't rush to the pharmacy just yet. Like most drugs, orlistat is associated with risks and side effects. The most common ones include diarrhea, oily spotting and flatulence - all consequences fat malabsorption. There is also some risk of reduced absorption of fat-soluble vitamins (such as A, E and D), which can be remedied by the corresponding vitamin supplements. More alarming are reports of orlistat causing an increase in precancerous colon polyps in experimental animals. However, there is no clear evidence that orlistat at commonly used doses increases colon cancer risk in humans.

One should weigh carefully whether a real but modest weight loss produced by orlistat is worth the side effects, expense and uncertainties ragarding health risks.

See also the index of related studies and drug label information for orlistat (Xenical).