Yeah, uh, that expression means that people can't be content just eating and existing. We need art, adventure, exploration of the world, our minds, etc, to be content. Bread just refers to food in general.
We have 3rd generation vegans now. So if vegans deteriorate, they probably weren't doing something right. I will admit it's harder to eat a nutritionally adequate vegan diet than a nutritionally adequate omnivorous diet. That said, I firmly believe based on the best available science that the optimal diet is vegan. Vegans live the longest and have the lowest incidences of various chronic diseases.
So the saying is basically saying, "We sell a product here, so you should buy it." Cool, dude.
I went whole food plant based just over 1 year ago. It was a gradual process - first I cut red meat years ago, then we cut chicken and fish, and eventually cheese and eggs. I read How Not to Die by Dr. Michael Greger. I watched Cowspiracy, Forks over Knives, and What the Health. I also watched a lot of videos from people like Joe Rogan, Chris Kresser, Lierre Keith, etc, to try to get a balanced perspective. Overall I found that the so called issues with veganism weren't based in science - it was mostly speculation by people who didn't know the facts. Plus, there is this longstanding belief that to reach optimal athleticism one must eat meat. This belief is trumpeted out daily on Lets Run....
So I loaded all my food into Cronometer to make sure I wasn't missing any micronutrients. I incorporated more things like seeds and legumes into my diet. I am probably more hardcore at it than Sage (I saw sage eating non-whole grain pasta in his camping video... wtf Sage!).
I lost a few pounds (I was already relatively skinny), and my recovery accelerated. What I noticed the most was that I felt amazing, and still do. After a big meal I used to feel tired and sleepy, but now I just feel full. I get sick less often. I seem to be less sore. I sleep better. My skin looks healthier - acne was rare before, but is now non-existent. My skin has more colour now.
That said, I don't believe diet is as huge a factor in running as many think. I did this mostly for my health and the environment. The side benefits of better recovery, and better welfare for animals is just a bonus.
Not all vegans are psycho. If I was stranded on an island and all there was to eat was pigs, dude, I'm eating a pig.