“Do you have faith? Have it to yourself before God. Happy is he who does not condemn himself in what he approves. But he who doubts is condemned if he eats, because he does not eat from faith; for whatever is not from faith is sin.” Romans 14:19-23(NKJV)
When you stand in person before God, how your faith looks like. Are you really believing whatever the things you chose to do in your life, or do you know that you are wrong yet you continue to do so? If you go through the whole chapter 14 of Romans a lot of things are explained to be careful about our habits in front of others. On your own you can choose something more free when it is between God and you. But we should all be careful not to bring unnecessary misunderstandings when we are with other believers or nonbelievers.
Vegetarians and non-vegetarians: Those days many were strict vegetarians and are not tolerant to non-vegetarians. But these days it has gone down to restrictions on some meat yet we should be very careful not to eat meat or drink alcohol, if your brother is not comfortable with what you eat or drink. This way we should not hinder anyone from coming to the Lord.
Observing a fast or not: Most of us observe one day a week to fast and pray but if anyone is not doing that but instead they feast on that one day they get in a week; then we should not make fun of each other but should give respect. The one who fast and the one who feast they do it for the Lord. And it is between God and them.
Eating and drinking in faith: When you eat your food do not go on having doubts thinking, whether you are eating the right nutrients, or whether you are eating more or less fat, or whether you are adding too much salt or sugar, so on and so forth in your mind; and if you do, then you are not eating in faith. Do not waste your time on searching for the food you think is best, but buy what is available easily for you. When food is in front of you, you bless that and believe everything is perfected by the Lord at that moment for you and eat with thanksgiving to God. This is faith, which will balance your diet supernaturally.
“For none of us lives to himself, and no one dies to himself. For if we live, we live to the Lord; and if we die, we die to the Lord. Therefore, whether we live or die, we are the Lord’s.” Romans 14:7-13(NKJV)