Agreed with everyone else's comments here. What silliness to associate produce with "less stress". There's way too wide a range of lifestyle factors, as Calianna pointed out. That's almost exactly what I was going to say.

An analogy I often use: imagine if someone reported that wearing dress shoes to work is associated with more stress, or higher rate of heart attacks, or something like that. Do dress shoes cause heart attacks? Of course not. It just means that there are a lot of people who work stressful jobs that require office attire. A lot of people who wear casual shoes work less stressful jobs, but not all of them. Conversely, a lot of office-attire-wearing people love their jobs and don't feel stressed out. The silliness comes from there being no clear hypothesis of causation. The overly-stressed lawyer isn't going to prevent a heart attack by showing up in slippers.