At the most, you can survive without food for a couple of weeks, occasionally a bit longer but for most people starvation will kill you. But the limits on how long people can go without eating are actually very complicated and are more of a case by case basis. Without water, people can only really survive a week, but without food, things can change very dramatically.
Take for example the tale of Angus Barbieri who was able to go 382 days without food or eating anything at all. And this was all followed by doctors at the time, with documentation being published in the Postgraduate Medical Journal in 1973. Apparently, he walked into the Royal Infirmary of Dundee Scotland looking for help as he was grossly obese at the time.
Barbieri weighed 456 pounds so the doctors put him on a short fast, thinking it would let him lost some weight quickly. What they did not expect was Barbieri’s resolve and determination to keep it up. As a couple of days turned into a couple of weeks, Barbieri expressed his interest in keeping with the program.
Fast over more than 40 days are considered extremely dangerous, but he was resolved to reach his ideal weight which he had targeted at 180 pounds. Luckily for Barbieri, he was able to live his daily life from home and just come into the hospital for checkups, though he did require a couple of overnight stays.
At first, the doctors were skeptical so they took regular blood tests, which did indeed prove that he was not eating. He did drink coffee, tea, and sparkling water through these liquids are all naturally calorie-free. He did mention that nearer the end of his fast he started to have a bit of milk or sugar in his tea, but after 382 days he did reach his ideal weight!
And the best part was even five years later, he was still able to keep off the weight, tipping the scales at 196 pounds. His fast is maybe the most extreme starvation diet to ever be recorded. Make no mistake it is a dangerous way to lose weight, after the 1970s it was largely abandoned by doctors as a strategy to lose weight due to the likelihood of the patient dying.