ANSWER: In a way, we can eat whatever we choose. How about a salad laced with arsenic? Or maybe gobble down what you find behind the barn? The reality is, God won't stop us from eating anything, but he has given us a menu of what's good for us and what isn't.
You know the arsenic salad would knock you dead in short order. Certain green herbs, such as digitalis and deadly nightshade, will do the same thing. So we know not to eat them. In the same way there are moving things that live which are not good for us.
We have terrible illnesses with no apparent cause. But the flesh of certain animals slowly breaks down the human system bringing on disease. Ingestion of the genetic code of such animals may be the cause of genetic mutation in the human body. Yet, like the plants, there is much flesh we can eat with no adverse results.
God knows which animals are harmful to the human body and because he loves us he has revealed which ones they are. The animals are found in the books of Leviticus Deuteronomy 14. God's guidelines make it fairly easy to understand that while cattle is good to consume eating pigs or even alligators certainly are not!
Clean birds, which the Bible says are made for mankind's health, have six primary characteristics. They are not birds that prey on others for food. They eat any food caught on the ground. They possess a longer middle toe. They generally stand on a perch with 3 toes on one side and 1 on the opposite side. Clean birds also possess crops. Lastly, these animals possess a gizzard. Any bird that does not have all these traits is considered Biblically unclean and unfit for human consumption.
Clean seafood can be determined fairly easily, as they must have not only fins but also scales. So why are oysters not fit for consumption? God made them, and certain other creatures like shrimp, to clean the waters they live in of harmful substances. Their meat, therefore, contains chemicals harmful to man.
Using only certain parts or sections of animals designated as unclean is also not permitted in the Bible. This means humans should not eat food cooked in pork fat (lard) or drink beverages containing clam juice. God's word also warns against eating the fat or blood on ANY animal whether they are clean or not (see Leviticus 3, 7).
One common food eaten today, mushrooms, are not specifically listed in the word of God. Recall that God stated to Noah that he could use any herb that was green for food. Mushrooms are neither green in color nor are their herbs. They are a fungus. According to some experts, even the supposedly edible mushrooms can have poisons in them.
Some Bible verses certainly SEEM, on the surface, to state that we humans can ingest anything. Here is something to consider however. God's word states at Jesus's second coming, those found eating pigs and even mice will be punished (see Isaiah 66:15 - 17). If we can eat anything we want, meaning all animals have suddenly become "clean" to consume, then this warning serves no purpose.
Christians are to offer their physical bodies as a sacrifice to God (see Romans 12) and therefore are required to keep them from being polluted. The Bible states that the Eternal will destroy all those who pollute themselves (see verses 16 and 17 of 1Corinthians 3). By virtue of conversion, believers are owned by Christ. We, therefore, are to take care of what he owns as his wishes (6:19 - 20) and only eat what he made for our health.