When you first start low carb you tend to lose a lot of water really fast. Carbs make your body hang on to a lot of water, so drink plenty to replace the fluids you will be losing. But also realize that you may lose potassium along with the water, I suggest you supplement potassium at first. Calcium, magnesium, potassium and a good multivitamin (one that includes most of the B complex) are good choices.

I specifically mention potassium though because the side effects from losing potassium can be uncomfortable and you don't want to worry your wife. You lose too much potassium and you can get leg cramps (charley horses) while sleeping or heart palpitations while awake. It affects your muscles and the heart is a muscle. So make sure you take some potassium pills. Most of the ones on the market are at really small amounts, which is good, because excessive potassium can be dangerous, but not enough isn't good either.