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 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.

[4] 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,[5][6] much of the same criticism leveled against the tobacco companies applies to fast food franchises whose product is both physiologically addictive and physically harmful.

He is seen by three physicians (cardiologist Stephen Siegel, gastroenterologist/hepatologist Lisa Ganjhu, and general practitioner Daryl Isaacs), as well as a nutritionist and a personal trainer.

It was not clear at the time whether or not Spurlock would be able to complete the entire month of the high-fat, high-carbohydrate diet, and family and friends began to express concern.

He compares Spurlock with the protagonist played by Nicolas Cage in the movie Leaving Las Vegas, who intentionally drinks himself to death in a matter of weeks.

This is accompanied by a cartoon tombstone, which reads "Ronald McDonald (1954–2012)", which originally appeared in The Economist in an article addressing the ethics of marketing to children.

[14] A short epilogue showed that the salads can contain even more calories than burgers if the customer adds liberal amounts of cheese and dressing before consumption.

It also described McDonald's discontinuation of the Super Size option six weeks after the movie's premiere, as well as its recent emphasis on healthier menu items such as salads, and the release of the new adult Happy Meal.

"[22] Robert Davis of Paste said the film accomplished some of its goals and addressed an important topic, but, at the same time, sometimes looked more like a publicity stunt than a documentary.

Davis explained he would have been more interested had the documentary been about trying to eat as healthy as possible at McDonald's: "You could choose low-fat options, but it would be impossible to get enough vegetables and fiber, and the low-fat meal would be incredibly bland, the product of a system that has worked to optimize food delivery and consistency and, in doing so, has invented foods so devoid of flavor that they require dressings, oils, beef tallow and goopy coatings to make them more than just textured blobs.

The industry has worked hard to convince consumers that these odd, sweet flavors are not only good but also unique, recognizable parts of a brand.

"[23] McDonald's UK responded that the author intentionally consumed an average of 5,000 calories per day and did not exercise, and that the results would have been the same regardless of the source of overeating.

The Houston Chronicle reports: "Unlike Spurlock, Naughton has a page on his Web site that lists every item (including nutritional information) he ate during his fast-food month.

"[25] After eating exclusively at McDonald's for one month, Soso Whaley said, "The first time I did the diet in April 2004, I lost 10 pounds (going from 175 to 165) and lowered my cholesterol from 237 to 197, a drop of 40 points."

I'm pushing taking accountability and making the right choice for you individually... As a science teacher, I would never show Super Size Me because when I watched that, I never saw the educational value in that...

This suggested that the extreme reaction must have had another cause,[28][29] and in 2017, Spurlock – who previously told his doctors he did not drink – admitted to copious amounts of alcohol consumption during the making of the film, which some critics, such as documentary filmmaker Phelim McAleer, have argued may better account for his liver issues and other health problems, since he had only changed his diet and not his alcohol intake during the experiment.

[33] The film was the inspiration for the BBC television series The Supersizers... in which the presenters dine on historical meals and take medical tests to ascertain the impact on their health.

The premise of the 2011 documentary Forks Over Knives was to create the "reverse" of Super Size Me, where the film's director "goes on this diet and gets better, instead of getting fatter and sicker".