Have a niece who’s probably 250lbs and “vegan.” Likely much processed food including bread, crackers, chips, etc.
I have a couple as well. But to help them avoid this conundrum I taught them how to cook. I mean basic cooking with vegetables to make things taste good (think mirepoix). Before I intervened they were headed down a path of eating extreme amounts of processed foods. I convinced them that meat substitution wasn't "pure" veganism (gotcha girls!). I convinced them that eating plant only food is way different than the regular American diet. Trying to make things that are comparative to the foods non-vegans eat was a waste of time (see how I played on their visions of superiority?).
The point is that now they stop at the farmer's market rather than the grocery for their food. Yes they still eat a lot of carbs (mostly for texture), but they don't eat processed soy and copious amounts of sugar and carbs any more.
PS I am a meatasaurus and not a vegan.
I think my SIL is a heavy drinker. She also eats a lot of processed food, like oreos. Apparently those are vegan.