Celery is a Green food. Green foods are safe to eat as a regular part of a diet.
Guideline related quotes related to Non-Starchy and Green throughout Geoff Bond's publications.
Eat at least 2 3/4 lbs of mixed salad and vegetables per day, consisting of "Green-Green” and “Green” foods. Of these, at least 3/4 lb should be mixed salad. Also include at least 5 cups of “Green-Green” leafy vegetables or 2 1/2 cups of other vegetables per week. ~Paleo in a Nutshell p.102
Specific references to Celery throughout Geoff Bond's publications.
The vegetables from above ground cover a huge range of plant parts: stems, such as asparagus from the Mediterranean and kohlrabi from Europe; buds, such as Brussels sprouts from Belgium; leafstalks, such as celery from the Mediterranean and rhubarb from Asia; leaves, such as Europe's cabbage, lettuce, and spinach; immature flowers, such as cauliflower from Europe, broccoli from Turkey, and artichoke from the western Mediterranean; immature fruits, such as eggplant from southern Asia and cucumber from northern India; mature "vegetable-fruits," such as tomato from Peru, avocado from Central America, and bell pepper from the Andes; edible bean pods, such as runner beans from tropical America; and edible fungi (mushrooms) from just about everywhere. Of course, today, these plants are grown all over the world, wherever farmers can produce them economically. ~Deadly Harvest p.56