Adventists take the ministry of Health seriously. The Bible tells us that our bodies are the temple of the Holy Spirit (1 Corinthians 6:19).
We believe that the Bible laid out the principles for a healthy lifestyle, and that we should strive to practice what we preach by living that life style.
Fruits, nuts & grains were the foods given to Adam and Eve while they were in the Garden of Eden. This "Original Diet" is thought to be the most healthful for our bodies because it was given by God before sin.
Because of this, many Adventists will be vegetarian (No meat) or even vegan (No meat or dairy). Not because they think it is a sin (Jesus ate meat), but because it is thought to be the healthiest diet possible.