During WWII the U.S. government wanted to learn more about starvation so that they could better feed and care for the millions of starving people in Europe.
Flyers and advertisements were posted around the country, asking for volunteers in this noble experiment. Those that responded and were ultimately picked, were 36 conscientious objectors (from religious groups like the quakers who cannot commit violence). These 36 men were fit and healthy before hand, used to hard work and hardy meals to compliment their lifestyle. For the first three months the men were fed as they normally would with around 3200 kcal (same as calories we know today) provided, so that a baseline of data could be gathered. The head of the experiment was Professor Ancel Keyes, who then had the mens diets reduced to an intake of 1800 kcal for six months. This was a diet like millions of individuals in war-torn Europe heavily based on potatoes, turnips, rutabagas, dark bread and macaroni noodles. The last three months were a rehabilitation period where the men were then assigned 1 of 4 different groups of different energy intakes to find the best method to offer the starving in europe a healthy rehabilitation back to healthy levels.
During the semi-starvation period the men were expected to walk 22 miles a week, which would result in them burning 3009 kcal daily. As the semi-starvation process progressed the morale of the men and their enthusiasm for the project waned. The men became increasingly irritable and impatient and began to suffer the overwhelming mental and physical effects of limited food intake. These men were very kind and gentle people but after the experiment started they began to bicker and become angry with each other constantly (think of what the effects will be on someone who is already a hot head and dangerous). Common symptoms experienced were dizziness, extreme fatigue, hair loss, muscle soreness, reduced coordination and ringing in the ears.
Food became an obsession with every one of them, rituals replaced normal eating habits, and they diluted the food with water to “increase” the amount. Some of the men collected cookbooks and recipes as an obsession and one of them had over a 100 by the end of the experiment. All the men lost interest in women and their sex drive was replaced by food as their driving need. Many would see another person walking home from the campus (The experiment took place on campus at the University of Minnesota) and the men would think that he looked healthy and was moving quick so he must be going home for dinner. The men then would become extremely angry and develop a hatred for a complete stranger.
I give you this because it's a case in point for knowing the dangers of your fellow-man, and what happens when something as common (in a survival collapse scenario) as nutritional decrease occurs. In a collapse scenario food will be the driving force in everyone's lives, especially those who are not prepared. Many of them may be neighbors you've known for years or even unprepared friends and family, and you may want to help but can't because you can't spare any without endangering your own family. Think of how a religiously dedicated conscientious objector felt hatred towards a complete stranger he “THOUGHT” might be going to dinner, and how others who are less scrupulous may act in the same scenario.