Yeah I understand that, but the body was not designed to be kept that low. At 4% you've got virtually no insulation over your body which could affect your core temperature. Also, your body's natural energy reserves, i.e. fat, are non-existant, so if you miss a meal, or your metabolism/heart rate gets elevated for any length of time, you're too depleted for your body to cope.
I'm not trying to be difficult here, but I don't see the point of getting into that condition for any longer than is necessary.