Even in our modern lives, we have certain rules governing what we should eat on what occasion. Some of them have to do with the traditions observed at Easter, Christmas, and New Year's Eve - these are the modern-day versions of the ancient talismans thought to bring luck and happiness to the bearer (eater, in this case).
There are, in turn, some food taboos that, although dressed up in religious gowns, have pretty practical, health-related reasons behind them, even if some of them seem outdated today.
Forbidden flesh
One of the best-known sets of food-related rules and taboos is the Kashrut, the Jewish religious dietary law. This regulates a great many aspects that have to do with the followers' diet - most famously, it forbids the consumption of pork.
The interdiction to eat pork-derived products is just the tip of the iceberg, though - the regulations go beyond the popular provider of bacon. Under the Kashrut's regulations, it is forbidden to consume animals that don't chew their cud and don't have cloven hooves. The law goes into specifics in the case of the hare, the hyrax (a small herbivore similar to the marmot, living in Africa and the Middle East), the camel, and the pig. The pig is often seen as an "unclean" animal because of its diet - it will eat pretty much everything, including carrion and garbage, and it is often seen bathing in mud.
Besides, its keeping was not ecological and economical in the Middle East, considering that it requires shady areas and a lot of water, which was hard to come by in the area at the time. Besides, pigs can transmit various parasitic worms to humans if their meat is not cooked sufficiently. Considering the time and the area where these laws were penned, not eating pork is a rule that's not only practical but can be vital.
Carnivores are off the menu
The Kashrut allows only the consumption of a very specific subset of animals - those that chew their cud and have cloven hooves - which restricts the dietary choices to pretty much only land-dwelling herbivorous vertebrates (including the giraffe) and forbids pretty much everything else.
It is also pretty specific when it comes to birds: flesh-eating, fish-eating birds, and bats are strictly forbidden. These birds can often carry various diseases - not to mention the bats, the carriers of many dangerous viral and bacterial infections. Seafood is most likely restricted because of similar reasons: under a warm climate, shellfish like crabs, oysters, and clams start to go bad pretty quickly.
Milk and blood
The milk of any non-kosher animal is non-kosher and thus forbidden, the Jewish regulation states. Also, if an otherwise kosher animal is found to be diseased, its meat and milk instantly become non-kosher. Considering the rules above, this has likely much more to do with common sense than religion. And so does the rule stating that dairy and meat should be completely separated from the production of the food to the consumption. Milk spoils quickly, and it can serve as a breeding ground for the bacteria found in and on the meat, which makes this rule another healthy one in many cases (especially in the Middle Eastern climate and in a time when refrigerators were pretty hard to come by).
Finally, there's the blood, the animal by-product that's strictly forbidden under the Jewish dietary regulations. The animals slaughtered in a traditional fashion are bled out completely, and their blood vessels are also discarded. Considering that the blood can carry various bacteria and viruses and that it spoils very quickly, this is also a food taboo based on common sense.
