The last 4 verses in the 89th section of the Doctrine and Covenants it provide a set of promises to those who obey the principles contained in the Word of Wisdom.
18 And all saints who remember to keep and do these sayings, walking in obedience to the commandments, shall receive health in their navel and marrow to their bones;
19 And shall find wisdom and great treasures of knowledge, even hidden treasures;
20 And shall run and not be weary, and shall walk and not faint.
21 And I, the Lord, give unto them a promise, that the destroying angel shall pass by them, as the children of Israel, and not slay them. Amen.
I have always taken a very pragmatic approach to obedience and blessings. Using D&C 132:5 as my reference, I feel that you should be able to easily tie blessings that are specifically promised to the commandment you are obeying.
5 For all who will have a blessing at my hands shall abide the law which was appointed for that blessing, and the conditions thereof, as were instituted from before the foundation of the world. (D&C 132:5)
For example, look at the Law of Tithing. Those who obey that law will almost always testify of the specific blessings they have received because they obeyed. Typically, those "windows of heaven" blessings are received in both temporal and spiritual blessings. So, the same pragmatic view of the blessings of the Word of Wisdom would be that if I am not enjoying these blessings, then I must not be obeying the commandment. Let's look at some of the blessings of the Word of Wisdom and see if we can determine what these blessings mean to us in our day.
Health in the navel and marrow to their bones
We are all familiar with the navel as it relates to our body. The belly button marks the former lifeline between the mother and the baby. This lifeline supplied all that was necessary for the baby to grow until birth. Most see this promise as a physical blessing of good health, but there is also a symbolism of spiritual blessings. It is a reminder for our need to connect regularly with God. To commune with deity and receive the spiritual nourishment we need as well. This symbolism implies that God will not leave us alone if we do not cut the cord. When we obey the Word of Wisdom we receive the blessing of a stronger relationship with God.
Bone marrow is the spongy tissue inside some bones, such as the hip and thigh bones. This marrow contains stem cells. The stem cells can develop into the red blood cells that carry oxygen through your body, the white blood cells that fight infections, and the platelets that help with blood clotting. Having healthy marrow leads to healthy blood. Healthy blood gives us protection from disease. This promise is a specific promise of improved health.
Wisdom and great treasures of knowledge
Elder Spencer W. Kimball taught us:
"We preach and discuss the revelation known as the Word of Wisdom, and usually think of the temporal blessings that will come to us in increased health if we live in harmony with its teaching, that we might run and not be weary and walk and not faint, and the destroying angel should pass us by (D&C 89:20-21) but there is also a spiritual aspect which is more far-reaching and should stimulate us to high purpose. The promise I am thinking of is this:
And all saints who remember to keep and do these sayings, walking in obedience to the commandments . . . shall find wisdom and great treasures of knowledge, even hidden treasures (D&C 89:18-19)
"What could be so priceless as wisdom and knowledge, even hidden treasures? Surely the treasures here referred to are not those of scientific accomplishments. Such will come revealed as light from heaven discovered through the research of men, but these hidden treasures of knowledge in the revelation are those which can be had only by use of the keys given which are: "Walking in obedience" (D&C 89:18) And while the discoveries in the physical world are very important to us here in mortality, the spiritual discovery of a knowledge of God and his program reach into and through eternity." (Spencer W. Kimball, "Ye May Know the Truth" October 1944 LDS General Conference)
Run and not be weary and walk and not faint
As I read verse 20 I ask myself if this is a blessing, or if this is the test to see if we are being obedient. Again, from a purely pragmatic view, it makes little difference. If you are otherwise free from disease and are unable to run or even walk without becoming weary and faint, then it is possible that there are additional items in the Word of Wisdom that are not being observed. This is why it is difficult to imagine that someone who is significantly above the ideal weight is really applying the principles of the Word of Wisdom in their lives. As I see the obese struggle to even climb one flight of stairs, I try to feel some empathy for them, but I also know, that just like a person who is suffering from emphysema as a result of tobacco use (prohibited by verse 8) could have avoided that disease, the obese can find their solution in the Word of Wisdom (verses 10-17). This wonderful blessing of strength and stamina comes to those who obey both the "do", and the "don't" the the principles of the Word of Wisdom.
Protection from the destroying angel
Marion G. Romney said, "It appears from the Word of Wisdom and other scriptures that there are destroying angels who have a work to do among the peoples of the earth in this last dispensation. The Lord told the Prophet Joseph Smith in 1831 that because all flesh was corrupted before him, and because the powers of darkness prevailed upon the earth, these angels were “waiting the great command to reap down the earth, to gather the tares that they [might] be burned” (D&C 38:12)." (Marion G. Romney, "Trust in the Lord", April 1979 LDS General Conference)
Another way to look at this may be the symbolism of the destroying angel. Just as the destroying angel prematurely took away the posterity of the Egyptians by killing the first born in each home, the destroying angel in our day prematurely takes away life as well. The top causes of death are largely preventable by following the principles in verses 10-17. (See: https://nutritionfacts.org/video/uprooting-the-leading-causes-of-death/) A careful reading of those verses will lead you to understand that a lifestyle in alignment with the Word of Wisdom is the optimum diet for the best health.