You never really quite appreciate just what a cornucopia of food alternatives exists — just how many culinary directions you can set off in — until a few are cut off and you’re forced to re-route yourself. That’s a lesson that people with celiac disease and with diabetes have learned. It’s what vegetarians have long asserted. And it’s what gout is teaching me. In diet books, the word “substitution” comes across as some pathetic euphemism for “sacrifice” and “compromise,” a positive-spin noun born of negative circumstances. But substitution is indeed a plausible course, and not necessarily a punitive one. At breakfast, oatmeal thickened with a heaping tablespoon of peanut butter can provide the same wicked indulgence that pork sausage does. At dinnertime, chicken prepared with care and ingenuity can go a long way toward replacing lamb, and the right kind of omelet can be wholly satisfying.