This is only one study, but there's some evidence that stress and the belief that stress is detrimental are correlated with detrimental health effects [1]. In other words, there may be a negative placebo effect at play where its less to do with the stress and more to do with how you respond to it.
Now, consider that fasting (and, really, consistent exercise as well) is correlated with high self-control and an internal belief that you're doing this to improve your physical health. The worst kind of Stress is stress from sources you can't control, but you have complete control over what you eat.
Now, consider that fasting (and, really, consistent exercise as well) is correlated with high self-control and an internal belief that you're doing this to improve your physical health. The worst kind of Stress is stress from sources you can't control, but you have complete control over what you eat.
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3374921/