Why is it easier to neglect one's self than others? If I am hungry, I often ignore my hunger because I'm more interested in continuing what I'm currently working on than getting myself food. However, if someone else (my girlfriend, a friend, a sibling, etc) expresses that they are hungry (even unintentionally, perhaps by their stomach growling), I am much more likely to get them something to eat.

In both situations, I need to stop what I am currently doing. In one situation, I receive food. In the other situation, someone else receives food. Why is someone else receiving food (or some other benefit) a stronger motivator than receiving that benefit myself?
It seems that what you are describing is Empathy-Altruism.

Debate over whether other-helping behavior is motivated by self- or other interest has raged over the last 20 or so years. The prime people involved in this debate are Daniel Batson arguing for empathy-altruism, Robert Cialdini arguing for self-interest and the works of John Thibaut, Harold Kelley, Caryl Rusbult, and George Homans on Social Exchange Theory

Social Exchange Theory states that human relationships are formed by the use of a subjective cost-benefit analysis and the comparison of alternatives.  The basis is that that altruism does not exist unless benefits to the helper outweigh the costs.

By contrast, C. Daniel Batson holds that people help others in need out of genuine concern for the well-being of the other person.


  The key ingredient to helping is "empathic concern". According to [Batson's] 'empathy-altruism hypothesis', if someone feels empathy towards another person, they will help them, regardless of what they can gain from it.