But should you? Absolutely not.
KCCI, a local news station, reported that Iowan John Cisna lost 37 pounds after eating three meals a day at McDonald's for 90 days straight. In the 2004 documentary Super Size Me, a similar stunt left Morgan Spurlock sick and overweight, so fast-food enthusiasts were quick to point to Cisna as a counterexample.
Cisna himself told KCCI that he wanted people to know "it's our choices that make us fat, not McDonald's." He described a typical meal plan as "two egg white delights, a bowl of their maple oatmeal and a 1 percent milk" for breakfast, a salad for lunch, and a value meal for dinner.
But - while we don't recommend it - you could also lose weight eating nothing but jellybeans. The real story is about portion size and exercise: Cisna went from not exercising or watching his food intake to walking for 45 minutes each day and carefully restricting himself to 2,000 calories and recommended dietary allowances for carbohydrates, cholesterol, etc. (Compare that to Spurlock's 5,000 daily calories and many sodas during Super Size Me.)
Consuming nothing but McDonald's may have seemed like a way to add a fun twist to boring old diet advice (eat less + exercise more = lose weight), but it's also a terrible idea.
A Big Mac has half of your daily allowance for saturated fat. A fruit-and-maple oatmeal has as much sugar as a bag of M&Ms. Even a McWrap, McDonald's crucial play to capture the attention of health-conscious millennials, has 1280 milligrams of sodium - more than half of what an adult should take in during an entire day.
While Cisna demonstrated that staying within healthy calorie, fat, and sugar limits is possible at McDonald's (if not easy or encouraged), it's no way to get healthy. Health is about more than weight.
McDonald's offers a menu of food that is - for the most part - highly processed (the McWrap contains 121 ingredients). Everyone has different dietary needs, but most people interested in improving their health would do well to follow Michael Pollan's famous advice: "Eat food. Not too much. Mostly plants." By "food," Pollan explains, he means "whole fresh foods [rather] than processed food products."
At the most basic level, you should be eating plenty of fresh fruits and vegetables, which, as summarized by the Harvard School of Public Health, "can help you ward off heart disease and stroke, control blood pressure, prevent some types of cancer... and guard against cataract and macular degeneration, two common causes of vision loss."
Fruits and vegetables are also a primary source of many key nutrients including potassium, dietary fiber, folate, vitamin A, and vitamin C. Your body needs these to function properly, and deficiencies can impair your vision, your bone health, and your immunity.
Are there nutrients in McDonald's apple slices and side salads? Of course. But navigating a fast food menu so that you get the nutrients you need without completely overloading on calories, sugar, carbohydrates, and saturated fat would be a difficult and perhaps futile endeavor. If your end goal is to improve your health, it would also be ill-advised.
As McDonald's McResources site advised its own employees: "Although not impossible, it is more of a challenge to eat healthy when going to a fast food place."