Fat carried on the body is the most weight and bulk efficient way of carrying calories for later use. It has been suggested, fairly seriously, that astronauts being twenty pounds over normal weight would save many pounds in food. Considering that even boosting a single pound into low-earth-orbit might cost ten thousand dollars because every pound lofted requires fuel, which also requires lifting. On longer trips saving a pound is a high priority.

Fat astronauts make a lot of sense.

Body fat represents a valuable store of calories and insulation. That said it is also weight that slows you down and wears on joints. Unlike astronauts in zero-gravity where weight is largely meaningless, and wear on joints less an issue, earthbound humans may find themselves hard against cargo limits and a disaster is a hell of a time to blow out a knee. Put in terms of recent events; you have ten minutes warning of an tsunami, you have two miles to safety. Would you, or would you rather not, be twenty pounds over your ideal weight and be running on bad knees and wobbly ankles?

There is also the matter of fitness. It has been learned in the last decades that weight can be, but is often not, unrelated to overall health and fitness. While there are indeed some people who are overweight but strong and healthy the majority of overweight people have other issues. Strength, endurance, heart health and joint issues are all common for people who are overweight.