How does weight loss impact pack fitting?

I am currently quite obese, roughly 100 pounds from the "ideal" weight for my height. I am making sweeping changes to my diet and exercising weekly, so far I have lost just under 20 pounds and am familiar with losing weight and all the fun that comes with it.

I've decided to, heavily, incorporate hiking on 'easy/moderate' trails this summer and have been putting together gear lists and trying to figure out how I am going to equip myself when I am out hiking. I currently have a 23 Liter Camelbak bag from Sportsman's Warehouse. I don't think this is probably very good for the kind of hiking I am hoping to do in the long-term.

I believe I 'need' or should get an actual daypack from a place like REI with proper support. I believe I will eventually want a 21-35L daypack as I currently don't plan to do any overnight stays (but may want to later).

My question is whether or not I should wait until I lose substantially more weight before going out and getting a more suitable/nicer daypack. I know that daypack fittings are based on torso height/width. I don't see the height changing over my weight loss journey, but am not sure if the width will significantly change enough to make it worth the weight.

Any information anyone could provide would be greatly appreciated.

So two things:

1. You are right, the fit is what matters, and if your body changes a lot, that will change how pack fits.

2. The standard advice is to buy all the gear that goes in your pack first...as that will then tell how big a pack you need.

You don't say what you're going to be carrying in this pack, but we've day-hiked for years and years with a small daypack. The bigger the pack, the more likely you are to fill it with stuff you won't use.

Hope that helps.

Appreciate the response. I don't intend to carry much outside the "Ten Essentials". My main extra's will be some form of rain protection, maybe dry socks and that's about it. I would like to carry my DSLR camera, but have not found a way to do it comfortably yet.

Yeah, a big camera can be a pain in the neck, literally. And if you take it in your pack, it's never ready when you want to take a photo.

I've settled on a little pocket point and shoot...and leave the pro photography to those with stronger neck muscles.

Get what works for you now. For a daypack, fit is not that critical. Sure changes in body affect fit, but you will have a lot more increase in comfort from the weight loss than any increase in discomfort from an ill-fitting daypack.