diet of bread and water?

What exactly would happen to a normal-weight person, health-wise, who was forced to exist for a month on a old-time prison-type diet of bread and water. Assuming, say, a half-loaf of bread and unlimited water. Weight loss, obviously, but how much and at what health cost? Curious, since I just finished a book about a poor Irish family whose only food was bread and tea for months at a time…

Can man live by bread alone?

I am thinking that a person eating only bread and drinking only water would get scurvy.

White bleached Wonder bread… or stoneground whole wheat bread? It would make a difference.

Does the Navy still put guys on bread and water (“cake and wine”)? They did when I was in, but they could only do it for three days. We liked the idea, since most of the guys who received this punishment were violent assholes who needed to be mellowed-out. (Also, if you were in the brig, you couldn’t lie in your rack except during lights-out. If you were nice they’d let you sit on your toilet, but otherwise standing all day was also supposed to reduce your energy level.)

The burning question to me is whether humans can maintain sustenance without food, but merely on light and air. Some believe this is possible. For example,

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