Doesn't matter what my BMI is, I won't be on this earth one day longer than the Lord wants me to. Is this fatalism, no, our decisions do matter in this life, but I don't think constantly worrying about fitting society's mold of perfect health is what God would have us to do.
From a study Iconoclast posted in another thread:
http://www.baptistboard.com/showthread.php?t=70446
God Ordains the Days of Our Lives Again, the sovereign Lord of heaven and earth completely controls worlds, nations, calamities, individuals, even sinful actions. Does it surprise us that all the days of our lives "were ordained" (Psa 139:16)? God wrote the script to our lives, from birth to death. Though we do not know what the future will hold, we should reflect on this in reverence and obey His revealed will, His law. Ultimately, God has decreed what will come to pass, even to the minutest detail. Because of this, the Word tells us that our plans should be guided by this truth, "If the Lord wills..." (Jam 4:15). This is illustrated when Paul left Ephesus. He said, "I will return to you again if God wills" (Act 18:21). The Latin phrase which translates "if God wills" is Deo volente. So, it is right to plan and we can hardly avoid it, but we must remember all we intend is Deo volente.
Psa 22:9 Yet Thou art He who didst bring me forth from the womb; Thou didst make me trust when upon my mother's breasts. 10 Upon Thee I was cast from birth; Thou hast been my God from my mother's womb.
Psa 71:6 By Thee I have been sustained from my birth; Thou art He who took me from my mother's womb; my praise is continually of Thee.
Psa 139:16 Thine eyes have seen my unformed substance; and in Thy book they were all written, the days that were ordained for me, When as yet there was not one of them.
Num 24:23 And he took up his discourse and said, "Alas, who can live except God has ordained it?"
Pro 20:24 Man's steps are ordained by the LORD, how then can man understand his way?
Job 14:1 Man, who is born of woman, Is short-lived and full of turmoil. 2 Like a flower he comes forth and withers. He also flees like a shadow and does not remain. 3 Thou also dost open Thine eyes on him, and bring him into judgment with Thyself. 4 Who can make the clean out of the unclean? No one! 5 since his days are determined, the number of his months is with Thee, and his limits Thou hast set so that he cannot pass.
Jam 4:13 Come now, you who say, "Today or tomorrow, we shall go to such and such a city, and spend a year there and engage in business and make a profit." 14 Yet you do not know what your life will be like tomorrow. You are just a vapor that appears for a little while and then vanishes away. 15 Instead, you ought to say, "If the Lord wills, we shall live and also do this or that."