Is it rude to ask if the food contains pork or alcohol?

Not rude here in the UK, or anywhere in the western world so far as I'm aware.

It is polite, though, to tell your host at an early enough opportunity that they haven't already bought the ingredients and cooked the meal!

Really you don't have to just ask them what's in the meal so much as tell them your dietary requirements - it would be inconsiderate of your host not to take into account your medical and religious dietary needs and cook something suitable.

It's not at all unusual for people here in London to have particular dietary needs - eg halal, kosher, vegetarian, vegan, non-dairy, non-gluten, etc etc. If I'm organising the food for a social or work event then I'd normally ask people about their dietary requirements beforehand.

I can not answer for the average USA person, but I can answer for the Dutch and likely also for those of Dutch descent who still hold most of their Dutch habits.

For us the worst question is the one that is not asked but should have been asked. If you can ask before the cooking is done, like a few days ahead of time when you are invited, your question will be taken as matter of fact and will be considered in making the menu and cooking, maybe by making extra dishes besides those that contain the items you do not eat.
If the dinner is already cooked when you are invited or when you think about reminding them you do not eat certain foods, you might be told to not have something and in the worst case, some cans will be opened to serve you an alternative dinner.
(But if they know you keep to certain food rules you may be catered for already.)

A friend of mine has a like list of items she cannot eat, in her case because of allergies, and nobody has ever been offended by her asking.
While your reason to ask may not be seen as as strong, many people will take it as very serious and rather tell you than have you finding out by the taste.

Added: This Chrismas my mother served the sweet course at the end of dinner and only then one of the guests (who has been to the house and joining dinner at least once a year for years) mentioned not having eaten dairy for a few years. If she had mentioned it before, even only a few minutes before, an alternative could have been served or at least offered and my mother would not have felt the embarreshment of serving 'non allowed' food.

The polite way to handle it, if possible, is to say 'thanks for the invitation, did you know I do not eat ...?' at which point the host can either confirm it will not be a problem or he will tell you that the food has already been prepared or the whole of the meal as planned will not suit you, sorry but alas and not go on with the invitation.

Last year, I was in the Middle East (in one of the countries where pork and alcohol are available, at least in major hotels) and I invited a colleague to dinner at the hotel restaurant one evening. This person happened to be deeply religious. Before accepting my invitation, he asked me, very apologetically, if I had any plans to consume alcohol at the table, because in that case, he would respectfully decline my invitation. I assured him that even if I was inclined to drink alcohol (which I almost never do in restaurants these days) out of respect for him it would not even cross my mind to do so while we are sitting at the same table. Thus assured, he joined me for dinner and we had a very pleasant evening and a good conversation. I certainly did not feel the least bit offended by his request.

So please, if someone invites you to dinner, do not hesitate to let them know your preferences. There is absolutely nothing rude about this. Whether you explain your reasons or not should be entirely up to you: You most certainly should not feel embarrassed about your religious reasons, but if you are not comfortable discussing it with others, simply state that you are not able to consume food that contains pork or alcohol and leave it at that. Others may have similar preferences (e.g., vegetarians, people with medical allergies, etc.) and any thoughtful host would take these preferences into account when deciding what to serve for dinner, as their goal is to make you feel comfortable as a guest. They may, in turn, ask you if it bothers you if others at the table consume food you would rather not (e.g., a pork dish, a glass of wine); it is up to you to decide if it is something that you can accept and tolerate.

I am a Christian born and living in Lebanon which is a country populated with an almost 1:1 ratio of Christians to Muslims. I have as much Muslim friends and as I have Christians and we invite each other for meals all the time, and almost always my Muslim friends ask if the food contain any alcohol or pork. This is very normal to a point that I don't actually notice it, and I've only thought about it now after reading your question.

Sometimes if we're having a certain food that usually contains pork (pepperoni pizza for example) but on this occasion was prepared with non-pork ingredients (say beef pepperoni) I would tell them myself that this is not pork.

In fact, while I was living in the US (went to school there for 3 years) some of the friends I made over there and who had invited me over had thought I was a muslim, and on a few occasions when they were offering drinks had asked me if I'm "allowed" to drink alcohol. They were pretty casual about it as well.

Respecting your guests comes naturally and respecting their religious beliefs is part of that.

So long-story-short, your question is not offending at all; and if I were in the place of your hosts and I hadn't thought of the possibility that not everyone eats pork and alcohol, I would be pleased to have learned this so I can be a better host in the future.

No, it would never be considered rude to inquire after the contents of food being offered for your consumption, whether for religious or health reasons, as long as you yourself are not rude in your manner of inquiry.

"I'm personally deeply religious and my faith precludes me eating pork, or consuming any alcohol; may I ask if you were planning on using any of either in the ingredients of the meal?" ... nice, polite, non-confrontational.

"I'm a Muslim and we can't eat pork, you Christian wanker! What are you DOING?!" ... not so much. :)

I know this question has been covered pretty extensively, but I thought I would put in my two cents worth:

1. If a dish is prepared with alcohol, and there is just the taste of the alcohol left, sometimes just the taste of alcohol can be deadly to a person who is an alcoholic and is trying to stay away from abusing it. So whether or not it is burned off is not the issue. A good host would never endanger the health of his or her guest.

2. As advances in medical tests occur, it has been found that SOME foods are actually harmful to SOME people (for example, as in biopsy-diagnosed Celiac disease). Following this to its logical conclusion, we might be in a time when certain of our friends and family find out that they must stay away from certain foods to enhance their health. Again, a good host would never endanger the health of his or her guest. Maybe we are in a time when a dinner invitation should also include the tactful questioning of what foods to avoid in the dinner preparation.

3. Lastly, to reference the original question: I, as a 60-year-old white, western Christian, with many white, western Christian friends and family, have noticed this: everyone I know already asks this question, and is delighted to prepare special, new dishes to accommodate our friends and family. I now know many, many vegan, non-gluten, no-alcohol, no pine-nut dishes! All delicious, might I add!

Not rude at all! Even more : the substances you've mentioned are potential causes of an allergic reactions and conditions, so it's nothing bad in asking if there's such a substance in the food you're about to eat.

Are Allergies Rude?

Imagine you were allergic to, say, garlic. Would you feel rude to mention this to your host? In my opinion you should not. Similarly, should not feel rude when mentioning any other dietary restriction or preference, regardless of the reason behind it. It makes no sense to compare the importance of one dietary restriction over the other, nor does it make any sense to grade personal reasons on someone else's scale: my coriander allergy is not more important than your no-vegemite religious reason.

Plan and Inform Ahead

Personally, whenever I have dietary restrictions I mention them and people are usually most accommodating. In fact, what usually happens is that the host asks for dietary restrictions before I even mention them. In any case, be sure to mention your needs early enough to allow your host enough time to accommodate them by planning alternatives. Showing up to a dinner party, openly stating that you don't eat kiwis on Thursdays and spending the whole night fasting will definitely be perceived as rude.

If All Else Fails

If, upon stating your dietary preferences, you perceive unhappiness in your host then by all means change host. Why would you want to have dinner with someone with whom you are incompatible?

A a westerner who doesn't eat onions, it's fine to tell someone you can't eat something, but do it in a nice way, and ask far ahead of time.

(expanded from my comment above)

Background: I am an atheist and will-eat-all-that-stays-in-my-plate.

I can also understand that some people find some food disgusting and would prefer not to eat rather than witness that. This can be pork, alcohol, cheese, dogs, reptiles, humans - whatever.

My son has an almost-vomit reaction to cheese (and yes, we are French...) and we do not force him to watch us when we have some. There is a difference between "you are impure/an animal/[insert insult here] for eating [insert food here]" and "due to my upbringing/culture, looking at [insert food] being eaten is just too much, I will pass".

So, in addition to other answers, most civilized people will understand that being part of a dinner where the food is incompatible with you is not a great experience However:

• it must indeed be incompatible, that is: you are sick looking at that and not merely do not like it. I would be devastated to spend an hour looking at someone who eats kittens alive by biting their head off, but I do not care if someone eats andouillette even though I would not bring it close to my mouth (yuck!).
• the host must be warned in advance. If you do not warn him or her, then it becomes your problem and you suck it up. Now, if the host had an idea about you (and specifically about your religion or strong feelings about a food culture), he should have anticipated (if you have suspicions that someone is a pastafarian, you will be nice and not prepare noodles broyh-bramlack).

EDIT: Following David's comment I updated my answer with the only (made up by me) meal pastafarians must not eat or their beer turns stale.

If you feel too shy for even the suggestions already given, how about, “I appreciate the invitation, but I have too many dietary restrictions to bother you with.”

There have been a lot of excellent answers, and I agree with all/many/most of them.

However, to simplify matters: it is as rude as informing people of dietary allergies.

You can't/won't eat something for whatever reason.

Personally, I cannot tolerate mushrooms, simply for their texture. Sometimes I lie and tell people that I am allergic. More often, I simply say that I won't eat mushrooms.

I have lived/worked 30+ years in countries/cultures other than the one into which I was born. Until now, no one has ever been offended if I asked "does this contain <mushrooms>", and I am sure that you can substitute <mushrooms> with pork/alcohol. I strongly doubt that anyone is not aware that some people will not consume these.

If it happens once, refuse. If it happens twice, leave and don't go back.

As others have said if there are items that you must, or wish to, avoid then politely stating so as soon as possible, possibly including giving the host a chance to withdraw the invitation if the restrictions are severe or contrary to point of the invitation, e.g. Shellfish allergy at a clam bake or pork at a hog roast.

Do be prepared to need to clarify the level or degree of restriction - for example I have heard that some strictly kosher practices insist that food cannot be prepared, nor consumed with, equipment and tableware that has been in contact with non-kosher material and some people not only do not consume alcohol they are uncomfortable with others doing so in their presence.

If your restrictions extend to others it is probably better to use the form of "I would love to come but I cannot because...." as in many of the places that I have been placing restrictions on yourself and asking others if they can accommodate them is considered fine, with the proviso of politely stated restrictions and plenty of notice, but attempting to force your restrictions on others is not considered acceptable.

Also it is sometimes necessary to ask for clarification - I had one friend ask what a stew being served at a mass catering even was and on being told it was pork he explained that he had dietary restrictions that forbade pork and said he would go and find something else. The caterer asked if he was OK with beef and offered to see if the beef stew was ready. On checking she stated that it was not ready and offered a ham salad as a "suitable" alternative.

Many people are not aware of what is in the food that we eat ourselves, I am remided of a well known brand of Vegitarian foods that it was revealed the "secret ingredient" that made them taste so good was pork fat, and this can lead to confusion.

Do be aware that you may encounter a certain amount of wry humour if your restrictions seem contradictory, e.g.: I know a number of claimed "vegetarians" who do eat sea food, poultry and bacon - I accommodate them but I may also tease them about it.

No, it is not rude (unless the inquiry itself is made in an obnoxious way). People have all sorts of dietary restrictions for any number of reasons (religious/cultural, allergies, interaction with medications, other medical conditions, etc.) After all consuming food is an intimate act and no one should expect anyone to ignore what they are putting into their body and respect their guest's boundaries in this matter.

Of course out of courtesy one should make these restrictions known at the earliest possible time to give the host the chance to accommodate those restrictions.

Mentioning this at the time of the invitation is indeed ok. The problem might be in mentioning this while eating and causing an awkward situation. The hosts might feel bad if they cooked and then you simply do not eat.

The alcohol one and the pork one are, in my mind, different questions.

Most dishes cooked with alcohol do not have alcohol in them. Alcohol is only part of the cooking process, but the alcohol itself boils away extremely quickly and 100% thoroughly. You usually can eat a big dish of whatever cooked with tons of booze and never blow numbers. So they aren't an issue. You are no more consuming alcohol in those dishes than eating sea salt means you're drinking sea water...the water (and the alcohol) are long gone.

Food items prepared where alcohol is actually present in the end product you should already know about. Nobody should be slipping you morsels that are boozed up without telling you. That would be extremely rude on THEIR part, and even have borderline legality in some places. You get to choose whether you want to be intoxicated at a given moment, and if they're gonna make booze food they darn well better tell you what you're eating. What happens if they just fed the designated driver 4 shots worth of whatever without telling him? No...alcoholic stuff is practically always well explained or labeled, and there are plenty of people that choose not to drink at any given moment for many reasons.

The pork question, on the other hand, is a different matter. If it's an apple pie then you'd look a bit foolish...but meat dishes where the meat is not clearly known it's absolutely reasonable to just say "Is pork in it? I just ask because I don't eat pork, I'll just eat the other dishes if there is."

One addition: I'm a bit skeptical of one of your commentors suggesting you state this at the time of invitation. This might be fine in some settings...but in many settings you giving your list of acceptable food at the time of invite would be quite rude. For small stuff this might be ok, but for large stuff the implication that they should make a menu for 30 people around your preferences would not go so well. So use a little judgement there.