Can man live by bread alone?
Can man live by bread alone? If so, how long?
Long enough to wish it were shorter, Irv. What we are about to discuss here is the massive breakdown of the human body. It will be a slow death and a messy one, but before we proceed let me say that science hopes you will step forward. Not until some selfless volunteer such as yourself eats bread and dies will your question receive the precise answer it deserves.
First the good news. You may assume that you would die of thirst. That's not necessarily true--if you take certain precautions. Bread is about 35 percent water, but most breads also contain so much salt that a greater amount of water than is contained in a loaf is needed to rinse that loaf's sodium out of your body. If you were to try to live on ordinary bread, you would become hypernatremic (too much sodium in the blood--for a fine word like that you should pay me), you would vanish into a coma and in about ten days you would vanish forever out of it.
So ... if drinking water is out, as I assume from your question it is ... find yourself a low-salt bread that doesn't resort to potassium chloride or some other hazardous (in your case) ingredient as a substitute (salt keeps bread from rising too quickly and then collapsing, in case you were wondering). Then find yourself a nice room somewhere with a steady temperature of 65 degrees and relative humidity of 60 percent (optimal conditions for avoiding the disastrous loss of precious bodily fluids by sweating) and start to eat. And eat. Yes, a lot of eating is ahead of you, Irving, because to extract the two pounds of water you need each day you will have to eat nearly six one-pound loaves a day. Easy does it--you can't afford to upchuck.
So in theory at least, we've licked the thirst problem. The next one's tougher. Bread is great for carbohydrates but it isn't exactly a teeming hotbed of proteins and vitamins. If you were a rat you'd be sitting pretty, because rats manufacture their own vitamin C. But humans must consume vitamin C in their diets, and bread, alas, doesn't have any. (Not even raisin bread, and I am not going to sully this discussion by considering wacky, hypothetical "breads" like lemon-peel loaf.) So there doesn't seem to be any way you can avoid getting scurvy.
Scurvy is the reason many of the seamen of old didn't live to become old seamen. After about six weeks on a bread-only diet the level of ascorbic acid, or vitamin C, in your body will drop to zero. The early signs of scurvy are fatigue, loss of appetite (you're going to have to force those six loaves down) and aching bones and joints. Then your gums will begin to bleed and your teeth start to wiggle. Without ascorbic acid, a protein called collagen that holds the body together will stop doing its job. Look for hemorrhaging under the skin, with anemia resulting. Your hair will begin to split and coil and bury itself in its follicles. The nice thing about scurvy is that vitamin C can reverse it at any point, but we're not going to allow any backsliding here. The preterminal signs are vomiting and swooning blood pressure. You will be weak by now, collapsing on so many fronts and so open to infection that it might be hard to pinpoint the exact cause of death.
Breads in general also won't give you enough of vitamins A and D and some of the B vitamins. This deprivation will contribute to your general deterioration, but not as swiftly or as critically as the lack of vitamin C. Doing without vitamin A, for example, will eventually cause you to go blind, and your corneas will fall out, but you have a two-year supply of vitamin A stored up in your liver, and before it's gone you'll probably already have croaked of other causes.
So how long would you last? Judging from the experiences of old sea dogs and pilgrims with scurvy, it's possible you could live two years, especially if you allow yourself to drink water. (Purists such as myself regard this as cheating, but I know how it is with you kids these days.) With water you can eat less bread and not worry about your sodium intake--either the perilous excess or, conversely, a deficiency of sodium, which would also mean a hastier death. But if you don't drink water, and consequently try to shove six loaves down your throat day in and day out--and that means consuming about 8,000 calories a day, four times what a 160-pound man needs when he's moderately active (and you won't be)--you'll be lacing your urine with glucose and wildly overtaxing your kidneys. Which means you should be happy to be alive six months later--that is, if you don't wish you were dead.