Extent of Self-Preservation Rights

According to Tom Regan, every subject of a life has the same inherent value.  Even if we revise his theory to include different degrees of value (based off of sentience, life expectancy, and other factors), it appears that every sentient creature's life has a considerable value.  This supports the idea that one should not eat meat when it is possible to avoid doing so.  However, it seems that every organism similarly has a right to attempt to preserve its own life, so if meat is the only possible food source then it is acceptable to consume.  How far, though, does this principle extend?  If in order to preserve one's life one has to sacrifice many other lives, does one still have a right to do this?

A particular example I have in mind is that of someone who, due to a medical condition (such as certain varieties of anemia), must consume meat consistently in order to survive.  In order to preserve their own life, this person must therefore cause (directly or indirectly) the deaths of many non-human animals.  Are they justified in so doing?

I think that they are, because self-preservation rights do extend extremely far.  The question is more complicated than that, though; while the individual may have a right to preserve their own life at almost any cost if it is necessary, do we have a moral duty to interfere in the interest of preserving the greater quantity of lives, the combined value of which exceeds that of the one human life?  If we change the example to one human killing and devouring many other humans because (due to an admittedly fictional medical condition) they must consume human flesh in order to survive, I think that most would agree that we do indeed have such an obligation.

I do not think this extends to the human/non-animal example, however.  I think that the obligation present latter example (a human eating humans) is evolutionary in nature rather than moral.  If we create a third example, in which a dog must consume multiple other dogs in order to survive, I do not think that we have a moral obligation to interfere, because the dog is merely exercising its right to preserve its own life.  As we are not dogs, we do not have a duty to interfere unless the dog is killing more dogs than are necessary to continue living.  Similarly, we do not interfere in a wolf's killing deer and elk.

This subject gave me quite a lot of trouble, and I am still not certain that the line of reasoning I have followed is entirely valid.  If anyone has any ideas on this subject, I would very much appreciate reading them!