The most critical element for survival with any diet - particularly with low calorie intake - is protein. Eggs just happen to be the easiest form factor. Personally when I'm on a weight loss regimen, I take in more canned Wild Pacific Salmon than eggs. Salmon, containing less mercury than many other fish, is a fairly safe bet for frequent consumption.

I'm curious how someone with a constant diet of something like eggs and biscuits for 5+ years fares regarding severe deficiencies in truly necessary vitamins and minerals. I do think the body is a miraculous machine that will successfully adapt to many diets that experts would otherwise claim as being dangerously deficient.