Olestra (also known by its brand name Olean) is a fat substitute food additive that adds no metabolizable calories to products. It has been used in the preparation of otherwise high-fat foods, thereby lowering or eliminating their fat content.

The Food and Drug Administration (FDA) approved olestra for use in the US as a replacement for fats and oils in prepackaged ready-to-eat snacks in 1996,[2] concluding that such use "meets the safety standard for food additives, reasonable certainty of no harm".[3]: 46399  In the early 2000s, olestra lost popularity due to supposed side effects and is largely phased out, but products containing the ingredient are available in some countries.