The three major divisions of eating lifestyle, omnivorous, vegetarian, and vegan, have motivations in both health and ethics.

My husband and I eat quasi-vegan two nights a week and I often eat vegan during the day because we think it's healthful. For us, a strained and defatted chicken broth wouldn't be out of place in a "vegan" meal, nor a cube of dehydrated beef bouillon, nor a dollop of honey. But to an ethical vegan, a vegan whose practice rests on beliefs about animal rights and harmony with nature, those foodstuffs are wrong and repellant. Ethical vegans don't eat flesh of any kind, and they don't eat animal products … honey … gelatin … If you're cooking for an ethical vegan, stick to fruits, vegetables, grains, and beans. (Some vegans eat yeast, some don't.)

Vegetarians too can have health or ethics or both as a basis for their lifestyle. Butter, cream, milk, eggs, and honey are fine with ethical vegetarians, but cheese, gelatin, and caviar are usually not, because they require killing the animals from which they come. (Most cheeses are coagulated with rennet, which comes from ruminants' stomachs. Rennetless cheese is available and OK with ethical vegetarians.) … vegan "gelatin" …Vegetarians for health reasons tend these days to go light on the butter and cream for the same reason all the rest of us do – a little is OK, a lot is not.

Vegetarians and vegans might perceive omnivores as wicked and unhealthful, but we too have our beliefs. I'm happy to serve my fellow omnivores roast beef, but I want it to come from a nearby farm and to have been treated decently, and I try to serve it in small portions. As with butter and cream for vegetarians, a little is fine, a lot will clog the arteries. … mad cow disease, high intensity farming, travel costs …

Natural food enthusiasts usually locate themselves somewhere along the vegetarian-vegan spectrum, but they have additional ideas about both health and ethics. I was startled to read in Heidi Swanson's Super Natural Cooking (Celestial Arts, 2007, page 16) that she doesn't approve of canola oil for health reasons. I myself (a laggard among health nuts) avoid corn oil and corn syrup in my cooking because of what I guess amount to ethical beliefs about monoculture and the planet – but I'd be happy to use small-batch corn oil from a family farm that grows corn in rotation with other crops.

Because healthnuts' beliefs are so idiosyncratic, there's no way somebody who's inviting one to supper can guess what foods are currently on the forbidden list, which can change from one issue of Vegetarian Times to the next. And sadly, most healthnuts are messianic. Asked what foods we're currently avoiding, we tend to launch into meandering diatribes on agribusiness, lycopene, and free radicals formed in grilling. If I weren't something of one myself, I'd suggest you never invite a known health nut to supper. When asked about my current beliefs, I try – I do try – to control myself.

Folks with allergies and other physiological restrictions are in a different boat from those who voluntarily eschew some foods. Vegetarianism and veganism are lifestyle choices. Allergic restrictions are not. If my vegan friend Martin eats an egg, he feels bad about himself; if my allergic friend Priscilla eats an egg, she goes to the emergency room Prime suspects for allergies are eggs, nuts, seeds, and peanuts, and it's important to understand that oils from the nuts, seeds, and peanuts are likely to be as harmful as the whole version. Two other biggies are wheat (celiac disease) and dairy (casein allergy or lactose intolerance). … drug interactions, grapefruit juice and statins …

Diabetics usually have to avoid sugar and starch. Meat is good, meatloaf is bad. Many people have adverse reactions to caffeine; think twice before serving a mocha mousse. People with a strong risk of heart disease need to watch their saturated fat intake; try dressing cooked vegetables with olive oil instead of butter. Certain kinds of arthritis flare up from eating tomatoes, potatoes, or eggplant.

At the milder end of the gamut of physiological restrictions, some people get upset stomachs from onions and garlic, and beans and whole grains make lots of people fart who don't eat them often enough to build up the right internal cultures. Savory dishes with no alliums (onions, garlic, leeks, chives, etc.) are surprisingly rare; try to find a recipe in which they play only a small role and leave them out, or go Japanese, or … Dutch? A side dish of wheat berries and lentils will probably cause little distress; a main with only a small side salad might well. People who avoid spicy foods may dislike the spiciness or may have adverse reactions to spices, and they may not themselves know which. Somebody who can drink root beer or eat catsup can probably tolerate most spices in small doses. It's not courteous to test the limits.

Two kinds of guests with physiological restrictions need special tact, alcoholics and the overweight. Many alcoholics find it difficult to watch other people drink; serve a delicious non-alcoholic fruit punch to everyone. Most alcoholics have trouble with a taste they associate with alcohol even if all the alcohol itself cooks off; no brandy cake or red-wine sauce. The overweight have comparable problems. Serve small portions to everybody, and consider plating instead of serving family-style, with bowls and platters lolling about the table, begging to provide seconds. And thirds. Never, never, say, "Oh my heavens, you didn't eat all of your three-cheese macaroni with butter crumbs. Would you like to take some home?"

Religious beliefs sometimes influence food choices. Strict Jews don't eat pork, of course, but they also don't eat shrimp or clams or oysters, and they don't eat meat and dairy at the same meal. Very strict Jews don't eat meat from a plate that has ever had dairy on it in its entire life history. (Paper plates to the rescue.) Strict Buddhists (something of a contradiction in terms) are often vegetarian, but clams and oysters don't count as animals. Jains are very vegetarian and don't eat vegetables that grow underground lest in digging them up one inadvertently kills an earthworm or a nematode.

And then, as if all these restrictions weren't enough, there are preferences and prejudices. My friends who don't eat sweet potatoes are unusual, but lots of folks don't like any vegetables but broccoli and lettuce. Fish used to be completely unsafe to serve to strangers, but lately (although you still hear people inveighing against "fishy fish") most people are willing to consume salmon and tuna. Some people are just not crazy about certain flavors or textures. I number among my nearest and dearest people who don't much like dill, cantaloupe, tomatoes, and mushrooms. Bizarre (I think).

And finally, there are the squeamish, people who don't like the idea of certain foods. I'm not going to use this book to campaign for offal and strong vegetables because campaigning doesn't seem to work, but golly, I feel sorry for people who don't try them.

So if you're having company over, you can inquire and hope your prospective guest will be forthcoming but not voluble. But what can you take to a potluck that has a chance of being acceptable to as many people as possible?

I'll tell you my solution, but I warn you if we're invited to the same potluck I'm bringing it. Bell pepper salad. Cut a bunch or red and yellow and orange bell peppers all the same way, slivers or matchsticks or slices or chunks short enough to fit on a fork. Salt them heavily with kosher salt. Let them sit for 10 minutes to draw off some of their moisture, and then rinse them off. Dress them with a little lemon juice and cold-pressed olive oil, plus maybe a whisper more of salt if you think it's needed to make the flavor pop. Carry it in a brand‑new, pretty covered bowl or, failing that, in a brand‑new foil turkey roasting pan from the supermarket.

Bell pepper salad is vegan. It's not fattening. It contains no alcohol. It's kosher, and neither milkish nor fleshly; the container is brand‑new, so it hasn't been used for serving anything else. Peppers are botanically fruits, and so are lemons and olives, so all the ingredients are fine for every kind of Hindu and fruitarian. Nothing is cooked, so you're in with the raw‑food people. It's delicious and healthful and beautiful. It would be even prettier if you used green bell peppers too, but lots of people don't like them.