This, folks, is ""longevity cookery"" produced, logically enough, by the California-based Longevity Foundation which has made a jogger out of an 87-year-old great-grandma. Their hook is that all fats, including the polyunsaturates, are bad for you--so much for safflower oil, peanut oil, and other health food store staples. Cholesterol is the chief villain of the various ""food-gremlins,"" but coffee, tea, sugar, and salt will also muck up your system. Hence this recipe book, geared mainly to ""purists"" though dabblers looking for the occasional ""shot of health"" (is that like a shot of penicillin?) are also invited to partake of this stringent diet which features recipes for ersatz sour cream, cheesecake, pizza, and ratatouille--all made without a drop of oil--and other gustatory wonders. This diet is designed not only to prevent but to reverse such degenerative diseases as atherosclerosis, hypertension, and diabetes. Any respectable M.D. would claim that's an impossibility, but that doesn't bother the authors a whit. Meantime, other food gurus--Carlton Fredericks and Dr. Reuben, for example--say that cholesterol won't hurt you: eat plenty of roughage and avoid chemical additives. So what's a poor fella longing for a banana fudge sundae to do?