All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
In principle, all kinds of food are lawful unless there is evidence to prove that they are forbidden. This is indeed from the tolerance and easiness of the Islamic Sharee'ah, as no one can restrict the foods that are lawful to eat to certain items.
With regard to the kinds of food containing pork fat or alcohol, they are forbidden to eat, unless the fat and alcohol have been transformed to another substance. Then, the preponderant opinion in this case is that they become pure thereby and lawful to be used [or consumed].
If it is not known whether or not such substances have been transformed before they are added to food, then it seems that they are lawful because of its being widespread among the people in a way that makes them impossible to avoid, and because most of these manufactured substances have been treated until they have been transformed from their original state, and because, in principle, all things are permissible.
Shaykh Ibn ‘Uthaymeen was asked: “We found some publications saying that some kind of soap is made of lard (pork fat), what do you think? He replied: "I think that, in principle, it is lawful because all that Allaah has created for us on earth is lawful. Allaah says (what means): {It is He who created for you all of that which is on the earth...} [Quran 2:29] So, if someone claims that this soap is forbidden due to its being impure, or other things, he must provide evidence. In fact, believing in all conceptions and all that is said is something that has no foundation (in Sharee'ah). So, if one says, this bar of soap is from lard, then we will say to him, provide your evidence. Then if it is proven that most of it is pork fat or lard, it becomes an obligation for us to avoid it.” [Extracted from ‘Al-Baab Al-Maftooh meeting’ (a recording)]
As regards trans-fats, then we have not come across the statements of the contemporary scholars or researchers about its ruling. The harm that is mentioned about it is not a definite harm that necessitates the prohibition of consuming it in all cases. As for the news that is spread about it that it is not ideal, in a point of view of health, in a way that increases the percentage of likelihood of being affected by certain diseases, and that it adversely affects some patients - then such matters do not necessitate absolute prohibition. Rather, the prohibition should be linked to the confirmation of its real harm to everyone who consumes it. The basic principle, however, is that they are permissible.
Allaah Knows best.