How do the Seventh Day Adventist approach Old Testament laws? I know the Seventh Day Adventist church is known for following certain Old Testament laws found in Leviticus such as the food/dietary laws. However I'm also under the impression that they don't follow all 600+ Levitical laws either. Is there a reason why they follow certain Levitical laws like food/dietary but don't follow others, such as wearing clothing made of two different materials (Lev 19:19) or cutting the hair at the sides (Lev 19:17)? To what extent do they keep the laws?
We Seventh Day Adventists distinguish between three different kinds of laws in the Bible:


Moral laws.
Ceremonial laws.
We also believe that there were laws in the OT specific to Israel as a nation. Something like their "civil code".


(Strictly speaking, there are also a few descriptions of other nations' laws in some books, like Persian laws in Daniel, or Roman laws in the NT; but these have nothing to do with theology or with laws given by God to His people.)

First, let me say that for us, the only laws that apply today are the Moral laws. But this poses at least two more questions:


How do we distinguish between the three types of laws?
Why, if the ceremonial laws do not apply anymore, are we still not eating some meals?


I will do my best to briefly answer these questions:

1. Distinction

The moral laws are the Ten Commandments (Exodus 20 and Deuteronomy 5). They are different from any other laws in the OT in at least the following aspects:


Although beautifully synthesized in the Ten Commandments, all of them are supported by the Bible as a whole. For example, Adventists believe that the Sabbath of the Fourth Commandment started with the Creation (Genesis 2:1-3), and thus it was given to mankind and not just to Israel. I mention the Sabbath because most Christians will probably agree on the other nine as perfectly valid today (probably with some different points of views, mainly from the Roman Catholic Church regarding the Second Commandment). There is a lot to write about the Sabbath and why it's still important today, but that's better for a different, new question.
They were written by God Himself in stone and given to Moses (Exodus 31:18 and 32:16).
Those were the only laws in the Ark of the Covenant (2 Chronicles 5:10, Hebrews 9:4). That's in relation with Adventists' unique fundamental belief of the Sanctuary, which is probably the most distinctive doctrine in Adventism.
They will apply after the Second Coming of Jesus, as they are the base of God's government (Revelation 22:14, Isaiah 66:22-23).
The Law of God is of such importance that it required Jesus to die for us, as the Only Means of Salvation. In other words, His law is absolutely immutable, so not even God will change it, giving his only Son instead (John 3:16).


On the other hand, the ceremonial laws were only of importance in the context of giving the OT people the best possible understanding of God's plan of salvation. This is also better understood (in an Adventist context) through the belief of the Sanctuary. These, and only these laws, according to Adventism, were abolished in the cross.

Finally, regarding the laws that were only regulating OT Israel's life as a nation under the theocracy (although were applied too under certain kings—not all—during the Monarchy), probably most Christians will agree that those were given only for that context and that they are easy to distinguish even from ceremonial laws. Jesus even mentioned that some of them were given to Israel "because of the hardness of your hearts" (Mathew 19:8). For most Adventists interpreters, these laws have a relation with our fundamental belief of the Present Truth (a topic that would  exceed this question).

2. Health and OT laws:

The idea that we extract our health practices (barely the only practices in relation with the OT laws that aren't part of the moral law) from the OT ceremonial or "civil" laws is a misunderstanding of Adventism. In fact, a lot of Adventists are vegetarians simply because our idea is that God created us (and the animals—yes, our view of Creation is a bit different too) as vegetarians (Genesis 1:29-30, 2:9). That's present in other portions of the Bible, in relation with health (see Daniel 1:8-20). For example, Ellen White wrote about the people living before the Flood:


  "They loved to destroy the lives of animals. They used them for food,
  and this increased their ferocity and violence, and caused them to
  look upon the blood of human beings with astonishing indifference." 
  (Spirit of Prophecy, p. 69)


There are plenty of other White's statements about food and health (see Ellen G. White's Message on Health)

So for us, God authorized at some point to eat some meats, but that does not mean that that was His original plan at all. And the "authorized" meat was, in our view, the "less unhealthy". Also, it's worth noting that the distinction between clean and unclean animals appears much earlier in the Bible than when Israel's laws were given, as the clean animals are in the Flood story, supernaturally selected by God in bigger quantity to enter the Ark, as stated in Genesis 7:2:


  Of every clean beast thou shalt take to thee by sevens, the male and his female: and of beasts that are not clean by two, the male and his female.


So for Adventists who are not vegetarians, the OT food laws act as the guide, although a lot of us do understand that our duty is to become vegetarians. But please note that this is not the understanding of all Adventists, so our consensus is to at least, follow OT rules regarding food.

Finally, this page may be of help describing our 6 Doctrines and our 28 Fundamental Beliefs, including taking care of our bodies as a Temple for the Holy Spirit (1 Corinthians 6:19-20): www.adventist.org -> Beliefs.