Probably depends on the individual and why they’re doing it.
Personally, I’m not much into fasting per se, but I find that a full stomach—and over-indulgence generally—makes me logy and slows down my metabolism so that clarity of focus suffers. My main meditation times are in the morning after coffee/tea and maybe some Tai Chi (but not breakfast), and later at night some hours after dinner; I tend to eat lightly during the day, with a full meal in the evening. I also “fast” from TV, and just “fasted” from the internet totally for three months, for example; others may not need to. (After spending most of my adult life in the hurley-burley of a high-contact, high-activity vocation, I now live quietly in the country and have little outside social contact—another kind of “fast,” again, that may not be the thing for others.)
What you want is clarity of attention/awareness without undue distraction from either bodily functions or mind-clutter (though you need to be aware of what’s going on in your body/mind—otherwise you’re asleep). Since the behavior of the mind is not divorced from neuro-biological activity (there really is no mind/spirit-body separation), how you eat, whether and how you exercise, your mental intake, etc., have impact. The spiritual is not anti-body (or anti-sensation, or anti-matter, or anti-pleasure): it’s all a matter of balance.
Reduce those things that drain your energy, clutter your mind, and trigger negative emotional responses—as much as you need to. And recognize that different people have different capacities.