Phoebe Maltz has a suggestion for the fashion industry: accomodate the fact that weight fluctuations are a normal part of life:
If fashion is to blame for waste, blame the industry's insistance, season after season, of making us buy clothing with a particular fit, such that any gain or loss of five pounds makes much of a wardrobe unwearable. A more eco- and wallet-friendly approach would be outfits that allow for changes in shape. Leggings and sweatpants, saris and togas, wrap dresses and t-shirt dresses, turtleneck dresses and pants held up by a belt that comes with the pants... need I go on? Some such options might be either too revealing or too casual, but it's possible to find appropriate outfits for just about any setting that do not cause severe discomfort if weight is gained or turn into tents if any is lost.
This seems like the kind of thing that has to be consumer driven more than industry driven.