A person with a weight issue is showing to a degree their personal, emotional issues as well. Most of the time extra weight is the direct result of certain middos that could use some serious fine tuning. Therefore, beyond the aesthetics which may or may not be an issue, the extra weight on a potential spouse should be a serious red flag regarding the persons middos.
Also, having extra weight could very well have a direct impact on a persons ongoing mood and ability to exercise calmness and other nice, quality middos so the bottom line is, extra weight and good / bad middos are not really 2 separate things to consider when going out.