This is a very interesting question+answer that was asked on GotQuestions.org.
“Question: “How should a Christian view weight loss? What does the Bible say about obesity and weight loss?”
Answer: While nothing in the Bible specifically addresses obesity and weight loss, there is much in God’s Word about the importance of taking care of our bodies and our health, as well as commandments against gluttony. In the Old Testament we read of God’s specific warnings and instructions about what His people, the Israelites, were to eat (Deuteronomy 14:1-21). Most of these were commands God gave them in order to keep them from eating harmful foods which would impact their overall health in a negative way. Some of the commands were given so they wouldn’t imitate the diet and habits of the idolatrous people around them.
Gluttony, overeating or drinking to excess, is mentioned in the Bible as being something to avoid (Proverbs 23:20-21). Gluttony can lead to health risks and become a drain on our finances, and the love of food and drink can all too easily become an idol in our lives. Anything that takes the place of God or becomes our number one focus is by definition an idol and thus a sin against God (Exodus 21:3-6). As far as obesity goes, the word “fat” is used in the Bible to describe people who were displeasing to God. Job 15:20-31 describes the wicked man who defies God. His “waist bulges with flesh,” a description of a very fat man, and one that pampers the flesh, and indulges himself in eating and drinking and who, figuratively, is one who abounds in the good things of this world. Jeremiah reiterates this same idea, that “wicked men” whose “houses are full of deceit; they have become rich and powerful and have grown fat and sleek” (Jeremiah 5:27-28). Clearly, obesity is not a sign of blessing or favor with God. In fact, two men characterized by their obesity—King Eglon of Moab and Eli the priest—died traumatic deaths (Judges 3:17-22; 1 Samuel 4:18). Proverbs 23:2 exhorts us to “put a knife to your throat if you are given to gluttony,” an admonition to restrain our appetites.
In the New Testament, Paul tells followers of Jesus Christ that our bodies are temples of the Holy Spirit (1 Corinthians 6:19-20), and as such we are to take care of our bodies and keep them as healthy as we can. Since being obese leads to multiple health risks, we need to realize that as much as it is up to us in our choice and amount of food, drink, and exercise, we should strive to avoid becoming overweight.
A down side of this subject of obesity and weight loss is when we take it to the opposite extreme and become obsessed with our body image. Again, when something becomes the major focus of life and it isn’t God, it is sin. So to constantly obsess about exercise, diet, and weight loss means we’ve allowed our bodies to become the center of our lives. While the effects can be better for our health than being gluttonous and overweight, the result is still the same—our bodies have become an idol in our lives. An obsession with weight loss can easily tip over into anorexia or bulimia which also has a negative impact on our health.
The bottom line is that the Lord wants His children to take excellent care of their bodies since they are the residence of the Holy Spirit. A strong healthy body helps us stay in shape so we can better serve God each day and thus bring glory and honor to Him, our principal reason for living. The Lord wants us to keep our focus on Him and not fall into obsessing about weight gain, weight loss, or food and drink, any of which can become an idol in our lives.
Recommended Resource: Faith and Fitness: Diet and Exercise for a Better World by Tom Hafer.