You really do get taken less seriously when you're fatter if you're not also super manly.
My dad is like 280 pounds, but he's very butch, if that's the right word, has a giant beard, wears flannel shirts, and sells doors, windows, and other hardware for a living. I didn't do any of those things, and I was 230 pounds, and I was constantly just laughed at in a metaphorical sense when people first met me. I had to cut through a membrane before I was taken seriously. Now I'm 170 pounds, and I'm taken seriously automatically.
Doesn't help that I'm a 5'8" manlet, I suppose. Maybe if you're fat and tall, like my dad (he's not like this obese monster, but he is 280 pounds, muscle density helps cut down how fat he looks) you're taken seriously.