I have dealt with the obesity prejudices personally, and have gone from morbidly obese
to normal to obese
, the last because of pain issues, not caused by the weight, as my back was in decent shape when I was at my lowest weight for several years.
Weight can cause problems, or add to them, but it is not the answer to everything that goes wrong with a person. If he just sees your weight, he won't look for any other underlying conditions that might be causing a "weak" spine.