Obviously, foods that contain any sort of dairy products are not suitable for vegans to eat. For vegetarians, though, the lines become a little more blurred. The stricter of us recognize that there are ingredients such as rennet (often referred to as enzymes) and whey that cannot be identified as vegetarian or not unless it is specified on the package.
There is a rule in Kosher that prohibits those who adhere to the diet from consuming meat and dairy at the same time.
“Meat and dairy cannot be prepared or eaten together and their consumption must be separated by a prescribed waiting period, generally established to be six hours,” explains Eve Lichtgarn in her article about Kosher Food Labeling.
This specific law is very beneficial to vegetarians. Rennet is not always vegetarian–it is an enzyme that is extracted from calves’ stomachs and used (very basically) to separate milk into whey and the substances that form cheese.
We can therefore assume that whey, too, is not always really vegetarian. If it was created with non-vegetarian rennet, it is technically unsuitable for consumption by strict vegetarians.
Vegetarian rennet does exist, though. It can be either vegetable sourced or microbial rennet. Most food packages fail to label the source of their rennet, though, which makes eating anything with either rennet or whey as an ingredient a chore for non-vegan strict vegetarians.
This is when we get really grateful for having so many Kosher friends! Basically, if something is labeled Kosher and it has dairy in it, it should not have meat. Thus, it is safe to assume that, at least from the stricter Kosher labeling organizations, if you see a dairy product (ice cream, for example, or cheese) that is labeled as Kosher, it’s okay to eat for strict vegetarians.
The most prevalent Kosher labels are OU (a U encompassed by a circle) and OK (a K encompassed by a circle). Many labeling organizations exist, though, and may vary in how strictly they label their products. For this reason, it may be advisable to stick to the major two.
Note, too, that fish may be consumed with dairy, so things with fish and dairy in them may still be labeled Kosher. If you’re vegetarian, then, make sure there are no fish ingredients.
Kosher does not mean vegetarian, but it certain combinations, it can. Kosher gelatin, for example, is fish gelatin, which means that both Kosher and non-Kosher marshmallows are not suitable for vegetarians, for example. However, since there is not likely going to be fish in, say, ice cream, if you find ice cream marked with a Kosher symbol, the product can likely be consumed by strict vegetarians.
The main formula for deciphering vegetarian food using the Kosher symbol is to find a product you want, verify that it has major dairy ingredients, and then check for a Kosher symbol. Once again, you may want to verify that there are no fish ingredients.
Lichtgarn Eve Understanding Kosher Food Labeling AssociatedContent.com