JOEL - In the absence of a temple, the first School of the Prophets was held in a small room in the home of Bishop Newel K. Whitney. Brigham Young was one of the early participants in this school, and he described a scene which frequently presented itself during meetings:

"The brethren came to that place for hundreds of miles to attend school in a little room probably no larger than eleven by fourteen. When they assembled together in this room after breakfast, the first they did was to light their pipes, and, while smoking, talk about the great things of the kingdom, … and as soon as the pipe was out of their mouths a large chew of tobacco would then be taken. Often when the Prophet entered the room to give the school instructions he would find himself in a cloud of tobacco smoke. This, and the complaints of his wife at having to clean [the] floor, made the Prophet think upon the matter, and he inquired of the Lord relating to the conduct of the Elders in using tobacco." (Journal of Discourses, 12:158.)

This of course led to the revelation we call the "Word of Wisdom" in Section 89 of the D&C.
Concerning meats this revelation states:

"“Yea, flesh also of beasts and of the fowls of the air, I, the Lord, have ordained for the use of man with thanksgiving; nevertheless they are to be used sparingly;
And it is pleasing unto me that they should not be used, only in times of winter, or of cold, or famine." (D&C 89:12-13)

The Word of Wisdom does not advocate total vegetarianism as evidenced in the following scriptures:

"And whoso forbiddeth to abstain from meats, that man should not eat the same, is not ordained of God;
For, behold, the beasts of the field and the fowls of the air, and that which cometh of the earth, is ordained for the use of man for food and for raiment, and that he might have in abundance." (D&C 49:18-19; see also 1 Tim. 4:1-3.)

In fact the original 1835 edition of the Book of Commandments, leaves out a very important comma in verse 13, causing it to read:
"And it is pleasing unto me that they should not be used only in times of winter, or of cold, or famine."

With the comma gone after the word "used" it now reads that eating of meats should not be restricted to times of winter or famine. No one knows for sure who put the comma in there for subsequent editions , only that it was inserted by an editor (possibly James E. Talmadge in 1921)who was preparing the text for a new printing. Researchers are unaware of any direction from Church authorities to make the change. Regardless of this, the previous verse does say we should eat meat "sparingly".

There are a few reasons why God might want us to limit our consumption of meats. For example, we now know that certain cancers have been implicated in the excessive use of meat, namely cancer of the colon and rectum, which are two of the major cancers in the United States. It has also been suggested by research that intake of a high fiber diet will reduce the risk of colorectal cancer. (Charles R. Smart, Observing the Word of Wisdom Can Aid Cancer Prevention, Tambuli, Oct. 1983, 18)
At the time this revelation was given people relied heavily on meat as a staple in their diet because it was available and plentiful and could be easily stored in the cold weather, while crops might be in limited supply, especially during the winter months. People sometimes followed harmful dietary extremes, eating too much meat, because they had no accurate idea what they should eat. Thus, the Word of Wisdom gave them guidelines in what would be proper nutrition We have more balanced diets in our day and through modern science are now more aware of some problems when the meat intake is very high.
When meat makes up the main part of our food intake, we crowd out other foods and, consequently, their nutrients. In a recent extreme example, a widower had milk for breakfast, a hamburger for lunch, and steak for dinner. He disliked onions and other vegetables, thought potatoes were "fattening," and was not interested in fruit. He developed scurvy! (Harold H. Sandstead, James P. Carter, and William J. Darby, How to Diagnose Nutritional Deficiencies, Nutrition Today, Nutrition Today Teaching Aid Number 8, Washington, D.C., 1969, p. 3.)

Another problem more clearly associated with a high meat (or a high protein) diet is the extra work placed on the kidneys. Protein not needed for building or repairing body tissue is broken down; part of the molecule is used for energy or stored as fat while the other part of the molecule is excreted as waste in urine.
Protein in the diet also influences calcium retention. Our teeth and bones need calcium throughout life, but the body doesn’t retain it well when the protein intake is considerably higher than necessary. Reducing meat intake might actually benefit those with limited calcium intake, although of course they’d need to be sure that their protein intake is still adequate. (Lora Beth Larson, "The Do’s in the Word of Wisdom," Ensign, Apr. 1977, 46)

So these are some reasons why we should limit our meat consumption, that Joseph Smith probably didn't even know about in 1833.
I think it's pretty obvious the things that can happen to people who become addicted to tobacco, drugs, and alcohol.
A Dr. George Van Komen who is an internist in Salt Lake City works with patients addicted to chewing tobacco. He says,
"There is no habit uglier from the doctor’s standpoint than chewing tobacco. The mouth is caked with green grime from the tobacco. The tongue, the pharynx, the teeth are all stained from it. A squamous cell cancer can develop and spread to the lymph nodes and to the bony structures and tissues within the head and neck. Those who do not die from it undergo a very deforming surgical attempt to rid themselves of the cancer. The most amazing thing to me is how rapidly these cancers can develop." (See Janet Thomas, Hooked! New Era, Sept. 1995, 40)

Verse 17 of Section 89 mentions feeding rye to swine. I once heard an interesting story of a church member who had a pig farm and decided to follow this advice to the letter. He began feeding his pigs on a rye diet, and grew some pigs that had the best meat in the entire state. People came from miles around to buy his rye-fed pigs.