Super Size Me is a 2004 American documentary film directed by and starring Morgan Spurlock, an American independent filmmaker. Spurlock's film follows a 30-day period from February 1 to March 2, 2003, during which he claimed to consume only McDonald's food, although he later disclosed he was also drinking heavy amounts of alcohol. The film documents the drastic change on Spurlock's physical and psychological health and well-being. It also explores the fast food industry's corporate influence, including how it encourages poor nutrition for its own profit and gain.

The film prompted widespread debate about public eating habits and has since come under scrutiny for the accuracy of its science and the truthfulness of Spurlock's on-camera claims.

Spurlock ate at McDonald's restaurants three times a day, consuming every item on the chain's menu at least once. Spurlock claimed to have consumed an average of 20.9 megajoules or 5,000 kcal (the equivalent of 9.26 Big Macs) per day during the experiment. He also walked about 2 kilometers (1.5 miles) a day. An intake of around 2,500 kcal within a healthy balanced diet is more generally recommended for a man to maintain his weight. At the end of the experiment the then-32-year-old Spurlock had gained 24.5 pounds (11.1 kg), a 13% body mass increase, increased his cholesterol to 230 mg/dL (6.0 mmol/L), and experienced mood swings, sexual dysfunction, and fat accumulation in his liver.

The reason for Spurlock's investigation was the increasing spread of obesity throughout US society, which the Surgeon General has declared an "epidemic", and the corresponding lawsuit brought against McDonald's on behalf of two overweight girls, who, it was alleged, became obese as a result of eating McDonald's food (Pelman v. McDonald's Corp., 237 F. Supp. 2d 512). Spurlock argued that, although the lawsuit against McDonald's failed (and subsequently many state legislatures have legislated against product liability actions against producers and distributors of "fast food"), as well as the McLibel case, much of the same criticism leveled against the tobacco companies applies to fast food franchises whose product is both physiologically addictive and physically harmful.

The documentary was nominated for an Academy Award for Best Documentary Feature and won Best Documentary Screenplay from the Writers Guild of America. A comic book related to the movie has been made with Dark Horse Comics as the publisher containing stories based on numerous cases of fast food health scares.

Spurlock released a sequel, Super Size Me 2: Holy Chicken!, in 2017.