Suzanne -
Crisco will work well to coat cast iron and prevent oxidation, however, it can and does go rancid whereas coconut oil, does not.
Rancid fats are chock full of free-radicals that do all kinds of damage. The more free radicals you are exposed to the more damage occurs to our cells and tissues.
Another down-side that you may not be aware of is that hydrogenated fats (shortening, in this case) are trans fatty acids. There are health concerns about consumption of trans fatty acids. If this quote is correct from Walter Willett, M.D., professor of epidemiology and nutrition at Harvard School of Public Health, "These are probably the most toxic fats ever known... It looks like trans fatty acids are two to three times as bad as saturated fats in terms of what they do to blood lipids." (Information from Harman, D., et al. 1976. Free radical theory of aging: effect of dietary fat on central nervous system functions. Journal of the American geriatrics Society 24(7): 301 and Raloff, J., 1996. Unusual fats lose heart-friendly image. Science News 150(6):87.)
If you eat margarine, shortening, hydrogenated or partially hydrogenated oils (common food additives), then you are consuming trans fatty acids. If you consume vegetable oils, they can be rancid without giving off an odor. In one book I read recently, it said, "all processed vegetable oils are rancid by the time they reach the store". To add to the problem, they are kept at room temperature and then cooking accelerates the oxidizing process making the oil even more rancid and unhealthy. Cooking creates toxic trans fatty acids as well.
As a choice I've made for my health, I avoid all "fats from techonology" (hydrogenated and partially hydrogenated fats and oils), prefering to use butter, organic coconut oil, olive oil, and an occasional dip into the lard bucket. The key being choice. Before I knew more about this subject, I chose what I now consider "bad" fats.
