Some anti-Catholics try to use this verse to decry the Catholic practice of fasting. We as Catholics believe God's creation is good, just as the bible says. But we also know that "fasting" is used throughout the NT, even by Jesus, as the citations below will show. So something else must be going on in this passage.
Paul's conclusion makes clear what he is talking about throughout 1 Timothy. In the Greek, the word for "knowledge" is "gnosis." This was the term used for the secret knowledge taught by the Gnostic heresy of that time. They wrongly believed that matter was evil and only spirit was good. They had falsely concluded that marriage and eating were evil because they perpetuated our material lives. Paul is giving Timothy instruction on why and how to avoid the Gnostic heresy and their "false gnosis."