I don't believe that a tarantula's health rests on how fat or skinny it is - - like human's do. The biggest danger lies in an increased risk of injury if the spider falls at all. As long as you have a "safe" tank setup with plenty of soft substrate and don't handle the spider, then I don't see a problem with fat spiders.
That being said, I know that it's commonly believed that powerfeeding your spider (overfeeding with warmer temperatures as well) will cause the spider to grow faster and possibly shorten it's lifespan as well. But again, it's not the same type of health risks that you would encounter with an overfed human.
it can cause health problems. they will becme slow and sluggish to begin with. but if its to fat jsut feed it less or none for a short time and it will skinny down a bit. i have sling thats fattens up easily.. so i give it a short fast occasinally and its back to normal
It definatly doesnt cause calesterol problems and heart attacks in tarantulas it just increases the chanse of abdomen injury since the abdomen is able to stretch to twice or three times its size or so Slings can consume lots and by lots i mean atleast 10 times its abdomen size worth of pray food, tarantulas are opportunistic eaters so they will eat as much as they can as often as they can even when they look like they cannot move and about to burst they will accept pray hunt it and kill it or wait for feeders to wonder to them. I do honestly believe that young slings have a critical mass trigger mechanism where upon consuming their absolute fill(if such exists) they trigger a molt to increase their abdomen size. i have triggered molts in some of my slings a week or two after they have previously molted by super feeding them and keeping the temperatures high
At least for many nw terrestrials that reach, say, 6-8 inches in legspan, there should not be a problem caused by powerfeeding until it reaches 3+"- as long as the temps are not too low. I have noted with A geniculata and N tripepii that the abdomen can begin to look somewhat mishappen when fed too frequently after they're large juvies or subadults- losing the natural, firm roundness and bulging slightly in other areas- overall looking very unnatural. Smaller "balloon-butted" slings do not seem to have any trouble with this but could rupture much more easily during a fall. They often become lethargic and go into premolt when this happens. I do not currently powerfeed AS MUCH as I used to but still do with the little tikes, at least in comparison to some other keepers.