Mark 7:15-23
15 There is nothing from without a man, that entering into him can defile him: but the things which come out of him, those are they that defile the man.
16 If any man have ears to hear, let him hear.
17 And when he was entered into the house from the people, his disciples asked him concerning the parable.
18 And he saith unto them, Are ye so without understanding also? Do ye not perceive, that whatsoever thing from without entereth into the man, it cannot defile him;
19 Because it entereth not into his heart, but into the belly, and goeth out into the draught, purging all meats?
20 And he said, That which cometh out of the man, that defileth the man.
21 For from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders,
22 Thefts, covetousness, wickedness, deceit, lasciviousness, an evil eye, blasphemy, pride, foolishness:
23 All these evil things come from within, and defile the man.
(KJV)

Nothing that you eat or drink can corrupt you; if you don't think it's a sin to eat a certain food then it isn't.   Your consumption and your surroundings don't make you a sinner.  Hanging around "sinners", or being in a "sinful place" isn't a sin.  What matters is what are your intentions for being there.  If you are in a nightclub with the hopes of possibly sinning, but you don't actually do it, you have sinned.  If a fireman goes to put out a fire in a whorehouse it doesn't make him a sinner.  Going into "sinful places" or having "sinners" for friends is not a sin; it depends on your thoughts and intentions.
 
 

Rom 14:1-14
1 Accept him whose faith is weak, without passing judgment on disputable matters.
2 One man's faith allows him to eat everything, but another man, whose faith is weak, eats only vegetables.
3 The man who eats everything must not look down on him who does not, and the man who does not eat everything must not condemn the man who does, for God has accepted him.
4 Who are you to judge someone else's servant? To his own master he stands or falls. And he will stand, for the Lord is able to make him stand.
5 One man considers one day more sacred than another; another man considers every day alike. Each one should be fully convinced in his own mind.
6 He who regards one day as special, does so to the Lord. He who eats meat, eats to the Lord, for he gives thanks to God; and he who abstains, does so to the Lord and gives thanks to God.
7 For none of us lives to himself alone and none of us dies to himself alone.
8 If we live, we live to the Lord; and if we die, we die to the Lord. So, whether we live or die, we belong to the Lord.
9 For this very reason, Christ died and returned to life so that he might be the Lord of both the dead and the living.
10 You, then, why do you judge your brother? Or why do you look down on your brother? For we will all stand before God's judgment seat.
11 It is written: "'As surely as I live,' says the Lord, 'every knee will bow before me; every tongue will confess to God.'"
12 So then, each of us will give an account of himself to God.
13 Therefore let us stop passing judgment on one another. Instead, make up your mind not to put any stumbling block or obstacle in your brother's way.
14 As one who is in the Lord Jesus, I am fully convinced that no food is unclean in itself. But if anyone regards something as unclean, then for him it is unclean.
(NIV)

It is not up to man (you) to judge what another person should eat.  Paul states in verse 14 that he believes that no food is unclean, but that if someone believes that it is unclean, it is unclean to them.  Meaning that if you think that it is a sin to eat pork, and you eat it, then you have sinned.  Even though God wouldn't have considered it a sin otherwise. 

This has huge implications.  This implies that your belief can determine what is sinful for you.  If God does not consider something a sin, but you do, then it is a sin for you to commit it because you thought you were sinning against God.  A much larger, and rarely discusses, implication of this is that your religion can impose extra burdens on you.  If your religion leads you to believe something is a sin and you commit it then you have sinned against God even though God may have never said (in the Bible) that it was a sin.   God has given you his holy word, the bible, to instruct you on many things including what is considered sin.  If you leave it to someone else's interpretation you could be imposing religious laws and traditions on yourself that God never intended for you to follow.

Titus 1:15
15 Unto the pure all things are pure: but unto them that are defiled and unbelieving is nothing pure; but even their mind and conscience is defiled.
(KJV)

1 Tim 4:1-5
1 The Spirit clearly says that in later times some will abandon the faith and follow deceiving spirits and things taught by demons.
2 Such teachings come through hypocritical liars, whose consciences have been seared as with a hot iron.
3 They forbid people to marry and order them to abstain from certain foods, which God created to be received with thanksgiving by those who believe and who know the truth.
4 For everything God created is good, and nothing is to be rejected if it is received with thanksgiving,
5 because it is consecrated by the word of God and prayer.
(NIV)

Although God's original list can be used to determine what foods are healthy to eat, Jesus has made it clear that nothing that you put into your body is a sin.