Sixty days, give or take, is the rule of thumb, though results vary depending on the faster's body fat and striking strategy. Physiologists generally agree that no human being can survive losing more than 40 percent of his body mass—a threshold that McNabb, stunningly, may already have crossed, if reports of his starting (180 pounds to 185 pounds) and current (around 100 pounds) weights are to be believed.
Fasting becomes dangerous after just three to five days, at which point the body begins breaking down fat in order to produce energy. When the liver is reduced to breaking down fat (in lieu of the usual glucose), it produces ketone bodies, a toxic byproduct. These can be excreted through the urine, and a particular variety known as acetone can be expelled through the lungs. (Acetone makes a person's breath smell like pears.) Ketone bodies can also be oxidized by the brain in order to make the fuel it needs. But when ketone bodies become too numerous in the bloodstream, they can cause ketoacidosis, a potentially lethal condition that afflicts some diabetics.
It's all downhill after Week 3, or whenever weight loss exceeds 18 percent of the starting weight. The body tries to compensate by slowing down its metabolism, entering "starvation mode." Still, once fat stores are entirely depleted, the body has no choice but to mine the muscles and vital organs for energy. The striker simply wastes away as his body, quite literally, consumes itself.
The 60-day figure that is commonly quoted as the absolute limit assumes that the striker is a healthy adult with approximately 24 pounds of fat on his or her frame. Someone with a higher fat content might be able to last longer, since that person's body could delay turning to the vital organs for fuel.
Perhaps more important, there are certain tactics that hunger strikers can use to prolong their protests—and their agony. The Irish republicans who fasted near Belfast in 1981, including the famous Bobby Sands, supplemented their all-fluid diets with occasional spoonfuls of salt. If they hadn't, their bodies would have become too depleted of this essential nutrient, and their blood pressures would have become dangerously low at an early stage. (One of 10 prisoners who perished during the hunger strike, Sands lasted 66 days.)
The most innovative hunger strikers so far, however, have been Turkish Marxists protesting their country's shift from dormitory-style prisons to Western-style cells. Their fasts, which claimed an inmate's life this past February, are designed to keep the striker alive as long as possible; some of the strikers have lasted longer than 300 days. Their secret is to ingest salt, unrefined sugar, and vitamins, which limit weight loss to just a few ounces per day.
According to the Spokane Spokesman-Review, McNabb did briefly interrupt his hunger strike when he was sent to a hospital for a mental evaluation; there, for three days, he did eat some food. Still, by any objective measure, his 123-day fast is astonishingly long. Gandhi, perhaps history's most famous hunger striker, never fasted for more than 21 days.