The one who observes that day does so to the Lord. The one who eats, eats to the Lord, for he gives thanks to God; and the one who abstains, abstains to the Lord, and he gives thanks to God.
Romans 14:6 TLV

The only days that can be observed and honored or not as a matter of opinion in relation to eating or not eating are man-made days of fasting and Yom Kippur, and Yom Kippur seems very unlikely to be the topic here. This is about fasting days and eating meat of animals that might have been sacrificed to idols. See 1 Corinthians 8-10.

People see anything about an ambiguous "day" in Paul's letters and they automatically assume he's telling people they don't need to keep God's Law. That's just the rebellious nature of their flesh. Even in Colossians when he actually uses the word "sabbath", he is clearly talking about man-made traditions--he even says so--not God's commandments.