Unhealthy but not hard...I'm 32 now and when I was 22, I was measured at 2.5% bodyfat at 5'9 145lbs and was very muscular....The trainer who measured me wanted to charge me on how to increase my bf%...I looked at him like he was a damn fool....I was perfectly healthy though had to eat all the time or else I would feel fatigue really quickly. Didn't try to get that way on purpose but was given that genetically. I faught hard to gain bf (taco bell and BK) and now measure at 8% and will probably drop to about 6% after my AAS cycle....I think no one should ever drop below 5% to be honest...Well at least not grown men anyway unless you are competing!!! Kids are a different story....For my son at 7 years of age is about 5% bf, but hey he has my genetics...