Studies (and personal experiences) have shown that physical fitness (exercise and proper diet) contributes to increased discipline, mental alertness, better sleep, better memory retention, higher energy levels, lower rates of depression, decreased illness, increased production and many other general health benefits that can favorably affect our spiritual training. Likewise, a healthy spiritual life leads to a clear conscience (less stress) that generally benefits our physical lives.
Stress can negatively affect both our physical and spiritual well-being. In the physical realm, it can be caused by such things as financial problems, marital issues, job demands, illness, or numerous other situations. In the spiritual realm, stress is almost always caused by guilt, brought on initially by unconfessed sin. At times, guilt can even hang on long after we've repented and been forgiven, but we must learn to trust God and let it go.
This is not to say that all guilt is necessarily bad. Good guilt serves as an early warning system spiritually, just as does pain or discomfort to us physically. When we experience pain (or other abnormal symptoms) in our physical body, it alerts us that something is wrong. Depending on the severity, we may need to seek professional medical help to remedy the problem. If we continue to ignore them, much more serious problems would likely occur. Similarly, when we experience spiritual problems, the Holy Spirit convicts us of our sin (makes us feel guilty over our sin) so that we can turn to the Great Physician, confess our sin, and remedy our spiritual problem. If we continually ignore the conviction of the Spirit, our conscience can become seared and much bigger spiritual problems will develop.
Preferably however, we should not wait for a symptom to manifest itself. For this reason, many people have regular examinations by their doctor to discover and address any concealed physical issues before they develop into real problems. Spiritually, we should take the attitude of King David the Psalmist who wrote “Search me, O God, and know my heart; test me and know my anxious thoughts. Point out anything in me that offends you, and lead me along the path of everlasting life” (Ps 139:23-24 - NLT). When the Spirit’s “examination” turns up any spiritual problems, we should immediately confess and repent. Failure to do so will lead to diminished fellowship with God and even hinder our prayers (Ps 66:18). In almost all physical or spiritual cases, the earlier we detect any abnormalities, the easier the treatment and recovery.
In the end, whether physically or spiritually, we should do everything for the glory of God.
Then I acknowledged my sin to you and did not cover up my iniquity. I said, “I will confess my transgressions to the LORD.” And you forgave the guilt of my sin (Ps 32:5). If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness (1Jn 1:9). So whether you eat or drink or whatever you do, do it all for the glory of God (1Cor 10:31).