One of the things that you need to keep in mind as a prepper is the fact that your diet can have a direct effect on your long term health, as with your hygiene habits. We need to realize that micronutrients like vitamin C are just as important, if not more important than the macronutrients such as fat and protein. Now keep in mind that you can use supplements and multivitamins to compensate for a lack of micronutrients, but you can also live solely on micronutrients for a while. The amount of time you can sustain yourself on this diet can greatly depend on the size of your fat stores.
As far as body fat is concerned, we must realize that our body prefers to work off of the stored body fat, over fresh supplies of fat from food you just ate. The average time it takes to digest food and process it is about 8-10 hours in general. After this time, your body will start using the fat stores for energy. This is a good thing, even though you may feel hungry.
One of the common trends in the fitness community, that I actually participate in myself, is fasting. Fasting is basically not eating for a period of time so that your system can get a "reset" and have an opportunity to cleanse itself of toxins. Research has shown that fasting is a great way to fight aging, prevent diabetes, and boost growth hormone production.
Take a minute to think about the fact that mankind did not start out with McDonalds around the corner. We had to hunt and gather everyday in order to survive. Sometimes we would go days without eating. Our bodies are designed to handle this. We get a temporary boost in growth hormone during the time of fasting, probably because the body is preparing us to go out and use all our possible stength to hunt and gather food so we can feed our bodies. Our bodies are laid out to survive, but at the same time, we are prone to glutiny. But that is mainly because we are instinctively programmed to prepare for famine. The most obvious evidence of this is stress eating.
Now the biggest benefit for me is giving my pancreas a break from having to produce insulin to bring my blood sugar levels down. Artificial sweeteners like aspirtame have shown to do just as much harm to the pancreas as high fructose corn syrup and sugar, but without providing the energy boost of sugar. Basically these sweeteners trick your pancreas into thinking you just had sugar, so it compensates by pumping your blood with insulin. This results in your body craving more sugar due to the sudden drop in blood sugar levels, which results in you consuming sweeter things to answer that craving. It is a compounding bombardment on the body that will take its toll throughout time. The worst thing that could happen for you is having your Pancreas fail when there is no medical facility that can give you the testing and medical supplies necessary to keep you alive.
Now as I was saying, your diet can play a huge part in your overall health throughout the time that you are trying to survive during a disaster. I recommend preparing your diet by working up to fasting 12-18 hours a day. This will help give you a chance to get used to the fact that just because it wants something, doesn't mean that it truly "needs" it. I also think you will feel much better, focused, and more energetic as you get used to this schedule of only eating once a day. To me, this schedule and diet plan is a win-win.