Simply put, not eating healthy makes me feel terrible. I'm sure it's the same with everyone but not everyone is willing/able to change the way they eat. At this time in my life, I have the resources and energy to eat different.
Also, a lot of why I do what I do is because I believe we are to be faithful stewards of what God has given us, including our bodies. As a believer, I know that this world, and everything in it, is not my home. My goal is not to live longer or have a happier life; my days are numbered and eating a certain way will not change that. But, God has given us these things and we should be good stewards of it.
What does the Bible say about food?
"And God said, 'Behold, I have given you every plant yielding seed that is on the face of all the earth, and every tree with seed in its fruit. You shall have them for food. And to every beast of the earth and to every bird of the heavens and to everything that creeps on the earth, everything that has the breath of life, I have given every green plant for food.' And it was so."
"Hear, my son, and be wise, and direct your heart in the way. Be not among drunkards or among gluttonous eaters of meat, for the drunkard and the glutton will come to poverty, and slumber will clothe them with rags."
"If you have found honey, eat only enough for you, lest you have your fill of it and vomit it."
1 Corinthians 6:19-20
"Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, for you were bought with a price.So glorify God in your body."
1 Corinthians 10:31
"So, whether you eat or drink, or whatever you do, do all to the glory of God."